merge multiple repositories into an existing monorepo

- merged using: 'monorepo_add.sh services-track-changes:services/track-changes'
- see https://github.com/shopsys/monorepo-tools

services/track-changes/.dockerignore

@@ -0,0 +1,7 @@
+node_modules/*
+gitrev
+.git
+.gitignore
+.npm
+.nvmrc
+nodemon.json

services/track-changes/.eslintignore

@@ -0,0 +1 @@
+app/lib/diff_match_patch.js

services/track-changes/.eslintrc

@@ -0,0 +1,86 @@
+// this file was auto-generated, do not edit it directly.
+// instead run bin/update_build_scripts from
+// https://github.com/sharelatex/sharelatex-dev-environment
+{
+  "extends": [
+    "eslint:recommended",
+    "standard",
+    "prettier"
+  ],
+  "parserOptions": {
+    "ecmaVersion": 2018
+  },
+  "plugins": [
+    "mocha",
+    "chai-expect",
+    "chai-friendly"
+  ],
+  "env": {
+    "node": true,
+    "mocha": true
+  },
+  "rules": {
+    // TODO(das7pad): remove overrides after fixing all the violations manually (https://github.com/overleaf/issues/issues/3882#issuecomment-878999671)
+    // START of temporary overrides
+    "array-callback-return": "off",
+    "no-dupe-else-if": "off",
+    "no-var": "off",
+    "no-empty": "off",
+    "node/handle-callback-err": "off",
+    "no-loss-of-precision": "off",
+    "node/no-callback-literal": "off",
+    "node/no-path-concat": "off",
+    "prefer-regex-literals": "off",
+    // END of temporary overrides
+
+    // Swap the no-unused-expressions rule with a more chai-friendly one
+    "no-unused-expressions": 0,
+    "chai-friendly/no-unused-expressions": "error",
+
+    // Do not allow importing of implicit dependencies.
+    "import/no-extraneous-dependencies": "error"
+  },
+  "overrides": [
+    {
+      // Test specific rules
+      "files": ["test/**/*.js"],
+      "globals": {
+        "expect": true
+      },
+      "rules": {
+        // mocha-specific rules
+        "mocha/handle-done-callback": "error",
+        "mocha/no-exclusive-tests": "error",
+        "mocha/no-global-tests": "error",
+        "mocha/no-identical-title": "error",
+        "mocha/no-nested-tests": "error",
+        "mocha/no-pending-tests": "error",
+        "mocha/no-skipped-tests": "error",
+        "mocha/no-mocha-arrows": "error",
+
+        // chai-specific rules
+        "chai-expect/missing-assertion": "error",
+        "chai-expect/terminating-properties": "error",
+
+        // prefer-arrow-callback applies to all callbacks, not just ones in mocha tests.
+        // we don't enforce this at the top-level - just in tests to manage `this` scope
+        // based on mocha's context mechanism
+        "mocha/prefer-arrow-callback": "error"
+      }
+    },
+    {
+      // Backend specific rules
+      "files": ["app/**/*.js", "app.js", "index.js"],
+      "rules": {
+        // don't allow console.log in backend code
+        "no-console": "error",
+
+        // Do not allow importing of implicit dependencies.
+        "import/no-extraneous-dependencies": ["error", {
+          // Do not allow importing of devDependencies.
+          "devDependencies": false
+        }]
+      }
+    }
+  ]
+}

services/track-changes/.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,38 @@
+<!-- BUG REPORT TEMPLATE -->
+
+## Steps to Reproduce
+<!-- Describe the steps leading up to when / where you found the bug. -->
+<!-- Screenshots may be helpful here. -->
+
+1.
+2.
+3.
+
+## Expected Behaviour
+<!-- What should have happened when you completed the steps above? -->
+
+## Observed Behaviour
+<!-- What actually happened when you completed the steps above? -->
+<!-- Screenshots may be helpful here. -->
+
+## Context
+<!-- How has this issue affected you? What were you trying to accomplish? -->
+
+## Technical Info
+<!-- Provide any technical details that may be applicable (or N/A if not applicable). -->
+
+* URL:
+* Browser Name and version:
+* Operating System and version (desktop or mobile):
+* Signed in as:
+* Project and/or file:
+
+## Analysis
+<!--- Optionally, document investigation of / suggest a fix for the bug, e.g. 'comes from this line / commit' -->
+
+## Who Needs to Know?
+<!-- If you want to bring this to the attention of particular people, @-mention them below. -->
+<!-- If a user reported this bug and should be notified when it is fixed, provide the Front conversation link. -->
+
+-
+-

services/track-changes/.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,48 @@
+
+<!-- ** This is an Overleaf public repository ** -->
+
+<!-- Please review https://github.com/overleaf/overleaf/blob/master/CONTRIBUTING.md for guidance on what is expected of a contribution. -->
+
+### Description
+
+
+
+#### Screenshots
+
+
+
+#### Related Issues / PRs
+
+
+
+### Review
+
+
+
+#### Potential Impact
+
+
+
+#### Manual Testing Performed
+
+- [ ]
+- [ ]
+
+#### Accessibility
+
+
+
+### Deployment
+
+
+
+#### Deployment Checklist
+
+- [ ] Update documentation not included in the PR (if any)
+- [ ]
+
+#### Metrics and Monitoring
+
+
+
+#### Who Needs to Know?

services/track-changes/.github/dependabot.yml

@@ -0,0 +1,23 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "daily"
+
+    pull-request-branch-name:
+      # Separate sections of the branch name with a hyphen
+      # Docker images use the branch name and do not support slashes in tags
+      # https://github.com/overleaf/google-ops/issues/822
+      # https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates#pull-request-branch-nameseparator
+      separator: "-"
+
+    # Block informal upgrades -- security upgrades use a separate queue.
+    # https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates#open-pull-requests-limit
+    open-pull-requests-limit: 0
+
+    # currently assign team-magma to all dependabot PRs - this may change in
+    # future if we reorganise teams
+    labels:
+      - "dependencies"
+      - "type:maintenance"

services/track-changes/.gitignore

@@ -0,0 +1,7 @@
+**.swp
+node_modules/
+forever/
+*.js.map
+
+# managed by dev-environment$ bin/update_build_scripts
+.npmrc

services/track-changes/.mocharc.json

@@ -0,0 +1,3 @@
+{
+  "require": "test/setup.js"
+}

services/track-changes/.nvmrc

@@ -0,0 +1 @@
+12.22.3

services/track-changes/.prettierrc

@@ -0,0 +1,11 @@
+# This file was auto-generated, do not edit it directly.
+# Instead run bin/update_build_scripts from
+# https://github.com/sharelatex/sharelatex-dev-environment
+{
+  "arrowParens": "avoid",
+  "semi": false,
+  "singleQuote": true,
+  "trailingComma": "es5",
+  "tabWidth": 2,
+  "useTabs": false
+}

services/track-changes/Dockerfile

@@ -0,0 +1,23 @@
+# This file was auto-generated, do not edit it directly.
+# Instead run bin/update_build_scripts from
+# https://github.com/sharelatex/sharelatex-dev-environment
+
+FROM node:12.22.3 as base
+
+WORKDIR /app
+
+FROM base as app
+
+#wildcard as some files may not be in all repos
+COPY package*.json npm-shrink*.json /app/
+
+RUN npm ci --quiet
+
+COPY . /app
+
+FROM base
+
+COPY --from=app /app /app
+USER node
+
+CMD ["node", "--expose-gc", "app.js"]

services/track-changes/LICENSE

@@ -0,0 +1,662 @@
+
+                    GNU AFFERO GENERAL PUBLIC LICENSE
+                       Version 3, 19 November 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The GNU Affero General Public License is a free, copyleft license for
+software and other kinds of works, specifically designed to ensure
+cooperation with the community in the case of network server software.
+
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+our General Public Licenses are intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change the software or use pieces of it in new
+free programs, and that you know you can do these things.
+
+  Developers that use our General Public Licenses protect your rights
+with two steps: (1) assert copyright on the software, and (2) offer
+you this License which gives you legal permission to copy, distribute
+and/or modify the software.
+
+  A secondary benefit of defending all users' freedom is that
+improvements made in alternate versions of the program, if they
+receive widespread use, become available for other developers to
+incorporate.  Many developers of free software are heartened and
+encouraged by the resulting cooperation.  However, in the case of
+software used on network servers, this result may fail to come about.
+The GNU General Public License permits making a modified version and
+letting the public access it on a server without ever releasing its
+source code to the public.
+
+  The GNU Affero General Public License is designed specifically to
+ensure that, in such cases, the modified source code becomes available
+to the community.  It requires the operator of a network server to
+provide the source code of the modified version running there to the
+users of that server.  Therefore, public use of a modified version, on
+a publicly accessible server, gives the public access to the source
+code of the modified version.
+
+  An older license, called the Affero General Public License and
+published by Affero, was designed to accomplish similar goals.  This is
+a different license, not a version of the Affero GPL, but Affero has
+released a new version of the Affero GPL which permits relicensing under
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+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+  Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License.  If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
+
+  9. Acceptance Not Required for Having Copies.
+
+  You are not required to accept this License in order to receive or
+run a copy of the Program.  Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance.  However,
+nothing other than this License grants you permission to propagate or
+modify any covered work.  These actions infringe copyright if you do
+not accept this License.  Therefore, by modifying or propagating a
+covered work, you indicate your acceptance of this License to do so.
+
+  10. Automatic Licensing of Downstream Recipients.
+
+  Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License.  You are not responsible
+for enforcing compliance by third parties with this License.
+
+  An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations.  If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+  You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License.  For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+  11. Patents.
+
+  A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based.  The
+work thus licensed is called the contributor's "contributor version".
+
+  A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version.  For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
+
+  Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+  In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement).  To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+  If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients.  "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+  If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+  A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License.  You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+  12. No Surrender of Others' Freedom.
+
+  If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Remote Network Interaction; Use with the GNU General Public License.
+
+  Notwithstanding any other provision of this License, if you modify the
+Program, your modified version must prominently offer all users
+interacting with it remotely through a computer network (if your version
+supports such interaction) an opportunity to receive the Corresponding
+Source of your version by providing access to the Corresponding Source
+from a network server at no charge, through some standard or customary
+means of facilitating copying of software.  This Corresponding Source
+shall include the Corresponding Source for any work covered by version 3
+of the GNU General Public License that is incorporated pursuant to the
+following paragraph.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the work with which it is combined will remain governed by version
+3 of the GNU General Public License.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU Affero General Public License from time to time.  Such new versions
+will be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU Affero General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU Affero General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU Affero General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If your software can interact with users remotely through a computer
+network, you should also make sure that it provides a way for users to
+get its source.  For example, if your program is a web application, its
+interface could display a "Source" link that leads users to an archive
+of the code.  There are many ways you could offer source, and different
+solutions will be better for different programs; see section 13 for the
+specific requirements.
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU AGPL, see
+<http://www.gnu.org/licenses/>.

services/track-changes/Makefile

@@ -0,0 +1,90 @@
+# This file was auto-generated, do not edit it directly.
+# Instead run bin/update_build_scripts from
+# https://github.com/sharelatex/sharelatex-dev-environment
+
+BUILD_NUMBER ?= local
+BRANCH_NAME ?= $(shell git rev-parse --abbrev-ref HEAD)
+PROJECT_NAME = track-changes
+BUILD_DIR_NAME = $(shell pwd | xargs basename | tr -cd '[a-zA-Z0-9_.\-]')
+
+DOCKER_COMPOSE_FLAGS ?= -f docker-compose.yml
+DOCKER_COMPOSE := BUILD_NUMBER=$(BUILD_NUMBER) \
+	BRANCH_NAME=$(BRANCH_NAME) \
+	PROJECT_NAME=$(PROJECT_NAME) \
+	MOCHA_GREP=${MOCHA_GREP} \
+	docker-compose ${DOCKER_COMPOSE_FLAGS}
+
+DOCKER_COMPOSE_TEST_ACCEPTANCE = \
+	COMPOSE_PROJECT_NAME=test_acceptance_$(BUILD_DIR_NAME) $(DOCKER_COMPOSE)
+
+DOCKER_COMPOSE_TEST_UNIT = \
+	COMPOSE_PROJECT_NAME=test_unit_$(BUILD_DIR_NAME) $(DOCKER_COMPOSE)
+
+clean:
+	-docker rmi ci/$(PROJECT_NAME):$(BRANCH_NAME)-$(BUILD_NUMBER)
+	-docker rmi gcr.io/overleaf-ops/$(PROJECT_NAME):$(BRANCH_NAME)-$(BUILD_NUMBER)
+	-$(DOCKER_COMPOSE_TEST_UNIT) down --rmi local
+	-$(DOCKER_COMPOSE_TEST_ACCEPTANCE) down --rmi local
+
+format:
+	$(DOCKER_COMPOSE) run --rm test_unit npm run --silent format
+
+format_fix:
+	$(DOCKER_COMPOSE) run --rm test_unit npm run --silent format:fix
+
+lint:
+	$(DOCKER_COMPOSE) run --rm test_unit npm run --silent lint
+
+test: format lint test_unit test_acceptance
+
+test_unit:
+ifneq (,$(wildcard test/unit))
+	$(DOCKER_COMPOSE_TEST_UNIT) run --rm test_unit
+	$(MAKE) test_unit_clean
+endif
+
+test_clean: test_unit_clean
+test_unit_clean:
+ifneq (,$(wildcard test/unit))
+	$(DOCKER_COMPOSE_TEST_UNIT) down -v -t 0
+endif
+
+test_acceptance: test_acceptance_clean test_acceptance_pre_run test_acceptance_run
+	$(MAKE) test_acceptance_clean
+
+test_acceptance_debug: test_acceptance_clean test_acceptance_pre_run test_acceptance_run_debug
+	$(MAKE) test_acceptance_clean
+
+test_acceptance_run:
+ifneq (,$(wildcard test/acceptance))
+	$(DOCKER_COMPOSE_TEST_ACCEPTANCE) run --rm test_acceptance
+endif
+
+test_acceptance_run_debug:
+ifneq (,$(wildcard test/acceptance))
+	$(DOCKER_COMPOSE_TEST_ACCEPTANCE) run -p 127.0.0.9:19999:19999 --rm test_acceptance npm run test:acceptance -- --inspect=0.0.0.0:19999 --inspect-brk
+endif
+
+test_clean: test_acceptance_clean
+test_acceptance_clean:
+	$(DOCKER_COMPOSE_TEST_ACCEPTANCE) down -v -t 0
+
+test_acceptance_pre_run:
+ifneq (,$(wildcard test/acceptance/js/scripts/pre-run))
+	$(DOCKER_COMPOSE_TEST_ACCEPTANCE) run --rm test_acceptance test/acceptance/js/scripts/pre-run
+endif
+
+build:
+	docker build --pull --tag ci/$(PROJECT_NAME):$(BRANCH_NAME)-$(BUILD_NUMBER) \
+		--tag gcr.io/overleaf-ops/$(PROJECT_NAME):$(BRANCH_NAME)-$(BUILD_NUMBER) \
+		.
+
+tar:
+	$(DOCKER_COMPOSE) up tar
+
+publish:
+
+	docker push $(DOCKER_REPO)/$(PROJECT_NAME):$(BRANCH_NAME)-$(BUILD_NUMBER)
+
+
+.PHONY: clean test test_unit test_acceptance test_clean build publish

services/track-changes/README.md

@@ -0,0 +1,20 @@
+overleaf/track-changes
+========================
+
+An API for converting raw editor updates into a compressed and browseable history.
+
+Acceptance tests can be run with the command
+```
+AWS_BUCKET=<bucket-name> AWS_ACCESS_KEY_ID=<aws-access-key> AWS_SECRET_ACCESS_KEY=<aws-secret-access-key> make test
+```
+where `bucket-name`, `aws-access-key` and `aws-secret-access-key` are the credentials for an AWS S3 bucket.
+
+
+
+
+License
+-------
+
+The code in this repository is released under the GNU AFFERO GENERAL PUBLIC LICENSE, version 3. A copy can be found in the `LICENSE` file.
+
+Copyright (c) Overleaf, 2014-2019.

services/track-changes/app.js

@@ -0,0 +1,161 @@
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS103: Rewrite code to no longer use __guard__
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const Metrics = require('@overleaf/metrics')
+Metrics.initialize('track-changes')
+const Settings = require('@overleaf/settings')
+const logger = require('logger-sharelatex')
+const TrackChangesLogger = logger.initialize('track-changes').logger
+
+if ((Settings.sentry != null ? Settings.sentry.dsn : undefined) != null) {
+  logger.initializeErrorReporting(Settings.sentry.dsn)
+}
+
+// log updates as truncated strings
+const truncateFn = updates =>
+  JSON.parse(
+    JSON.stringify(updates, function (key, value) {
+      let len
+      if (typeof value === 'string' && (len = value.length) > 80) {
+        return (
+          value.substr(0, 32) +
+          `...(message of length ${len} truncated)...` +
+          value.substr(-32)
+        )
+      } else {
+        return value
+      }
+    })
+  )
+TrackChangesLogger.addSerializers({
+  rawUpdate: truncateFn,
+  rawUpdates: truncateFn,
+  newUpdates: truncateFn,
+  lastUpdate: truncateFn,
+})
+
+const Path = require('path')
+
+Metrics.memory.monitor(logger)
+
+const childProcess = require('child_process')
+
+const mongodb = require('./app/js/mongodb')
+const HttpController = require('./app/js/HttpController')
+const express = require('express')
+const bodyParser = require('body-parser')
+
+const app = express()
+
+app.use(bodyParser.json())
+
+app.use(Metrics.http.monitor(logger))
+
+Metrics.injectMetricsRoute(app)
+
+app.post('/project/:project_id/doc/:doc_id/flush', HttpController.flushDoc)
+
+app.get('/project/:project_id/doc/:doc_id/diff', HttpController.getDiff)
+
+app.get('/project/:project_id/doc/:doc_id/check', HttpController.checkDoc)
+
+app.get('/project/:project_id/updates', HttpController.getUpdates)
+app.get('/project/:project_id/export', HttpController.exportProject)
+
+app.post('/project/:project_id/flush', HttpController.flushProject)
+
+app.post(
+  '/project/:project_id/doc/:doc_id/version/:version/restore',
+  HttpController.restore
+)
+
+app.post('/project/:project_id/doc/:doc_id/push', HttpController.pushDocHistory)
+app.post('/project/:project_id/doc/:doc_id/pull', HttpController.pullDocHistory)
+
+app.post('/flush/all', HttpController.flushAll)
+app.post('/check/dangling', HttpController.checkDanglingUpdates)
+
+let packWorker = null // use a single packing worker
+
+app.post('/pack', function (req, res, next) {
+  if (packWorker != null) {
+    return res.send('pack already running')
+  } else {
+    logger.log('running pack')
+    packWorker = childProcess.fork(
+      Path.join(__dirname, '/app/js/PackWorker.js'),
+      [
+        req.query.limit || 1000,
+        req.query.delay || 1000,
+        req.query.timeout || 30 * 60 * 1000,
+      ]
+    )
+    packWorker.on('exit', function (code, signal) {
+      logger.log({ code, signal }, 'history auto pack exited')
+      return (packWorker = null)
+    })
+    return res.send('pack started')
+  }
+})
+
+app.get('/status', (req, res, next) => res.send('track-changes is alive'))
+
+app.get('/oops', function (req, res, next) {
+  throw new Error('dummy test error')
+})
+
+app.get('/check_lock', HttpController.checkLock)
+
+app.get('/health_check', HttpController.healthCheck)
+
+app.use(function (error, req, res, next) {
+  logger.error({ err: error, req }, 'an internal error occured')
+  return res.sendStatus(500)
+})
+
+const port =
+  __guard__(
+    Settings.internal != null ? Settings.internal.trackchanges : undefined,
+    x => x.port
+  ) || 3015
+const host =
+  __guard__(
+    Settings.internal != null ? Settings.internal.trackchanges : undefined,
+    x1 => x1.host
+  ) || 'localhost'
+
+if (!module.parent) {
+  // Called directly
+  mongodb
+    .waitForDb()
+    .then(() => {
+      app.listen(port, host, function (error) {
+        if (error != null) {
+          return logger.error(
+            { err: error },
+            'could not start track-changes server'
+          )
+        } else {
+          return logger.info(
+            `trackchanges starting up, listening on ${host}:${port}`
+          )
+        }
+      })
+    })
+    .catch(err => {
+      logger.fatal({ err }, 'Cannot connect to mongo. Exiting.')
+      process.exit(1)
+    })
+}
+
+module.exports = app
+
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/app/js/DiffGenerator.js

@@ -0,0 +1,340 @@
+/* eslint-disable
+    camelcase,
+    no-proto,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let DiffGenerator
+var ConsistencyError = function (message) {
+  const error = new Error(message)
+  error.name = 'ConsistencyError'
+  error.__proto__ = ConsistencyError.prototype
+  return error
+}
+ConsistencyError.prototype.__proto__ = Error.prototype
+
+const logger = require('logger-sharelatex')
+
+module.exports = DiffGenerator = {
+  ConsistencyError,
+
+  rewindUpdate(content, update) {
+    for (let j = update.op.length - 1, i = j; j >= 0; j--, i = j) {
+      const op = update.op[i]
+      if (op.broken !== true) {
+        try {
+          content = DiffGenerator.rewindOp(content, op)
+        } catch (e) {
+          if (e instanceof ConsistencyError && (i = update.op.length - 1)) {
+            // catch known case where the last op in an array has been
+            // merged into a later op
+            logger.error(
+              { err: e, update, op: JSON.stringify(op) },
+              'marking op as broken'
+            )
+            op.broken = true
+          } else {
+            throw e // rethrow the execption
+          }
+        }
+      }
+    }
+    return content
+  },
+
+  rewindOp(content, op) {
+    let p
+    if (op.i != null) {
+      // ShareJS will accept an op where p > content.length when applied,
+      // and it applies as though p == content.length. However, the op is
+      // passed to us with the original p > content.length. Detect if that
+      // is the case with this op, and shift p back appropriately to match
+      // ShareJS if so.
+      ;({ p } = op)
+      const max_p = content.length - op.i.length
+      if (p > max_p) {
+        logger.warn({ max_p, p }, 'truncating position to content length')
+        p = max_p
+      }
+
+      const textToBeRemoved = content.slice(p, p + op.i.length)
+      if (op.i !== textToBeRemoved) {
+        throw new ConsistencyError(
+          `Inserted content, '${op.i}', does not match text to be removed, '${textToBeRemoved}'`
+        )
+      }
+
+      return content.slice(0, p) + content.slice(p + op.i.length)
+    } else if (op.d != null) {
+      return content.slice(0, op.p) + op.d + content.slice(op.p)
+    } else {
+      return content
+    }
+  },
+
+  rewindUpdates(content, updates) {
+    for (const update of Array.from(updates.reverse())) {
+      try {
+        content = DiffGenerator.rewindUpdate(content, update)
+      } catch (e) {
+        e.attempted_update = update // keep a record of the attempted update
+        throw e // rethrow the exception
+      }
+    }
+    return content
+  },
+
+  buildDiff(initialContent, updates) {
+    let diff = [{ u: initialContent }]
+    for (const update of Array.from(updates)) {
+      diff = DiffGenerator.applyUpdateToDiff(diff, update)
+    }
+    diff = DiffGenerator.compressDiff(diff)
+    return diff
+  },
+
+  compressDiff(diff) {
+    const newDiff = []
+    for (const part of Array.from(diff)) {
+      const lastPart = newDiff[newDiff.length - 1]
+      if (
+        lastPart != null &&
+        (lastPart.meta != null ? lastPart.meta.user : undefined) != null &&
+        (part.meta != null ? part.meta.user : undefined) != null
+      ) {
+        if (
+          lastPart.i != null &&
+          part.i != null &&
+          lastPart.meta.user.id === part.meta.user.id
+        ) {
+          lastPart.i += part.i
+          lastPart.meta.start_ts = Math.min(
+            lastPart.meta.start_ts,
+            part.meta.start_ts
+          )
+          lastPart.meta.end_ts = Math.max(
+            lastPart.meta.end_ts,
+            part.meta.end_ts
+          )
+        } else if (
+          lastPart.d != null &&
+          part.d != null &&
+          lastPart.meta.user.id === part.meta.user.id
+        ) {
+          lastPart.d += part.d
+          lastPart.meta.start_ts = Math.min(
+            lastPart.meta.start_ts,
+            part.meta.start_ts
+          )
+          lastPart.meta.end_ts = Math.max(
+            lastPart.meta.end_ts,
+            part.meta.end_ts
+          )
+        } else {
+          newDiff.push(part)
+        }
+      } else {
+        newDiff.push(part)
+      }
+    }
+    return newDiff
+  },
+
+  applyOpToDiff(diff, op, meta) {
+    let consumedDiff
+    const position = 0
+
+    let remainingDiff = diff.slice()
+    ;({ consumedDiff, remainingDiff } = DiffGenerator._consumeToOffset(
+      remainingDiff,
+      op.p
+    ))
+    const newDiff = consumedDiff
+
+    if (op.i != null) {
+      newDiff.push({
+        i: op.i,
+        meta,
+      })
+    } else if (op.d != null) {
+      ;({ consumedDiff, remainingDiff } =
+        DiffGenerator._consumeDiffAffectedByDeleteOp(remainingDiff, op, meta))
+      newDiff.push(...Array.from(consumedDiff || []))
+    }
+
+    newDiff.push(...Array.from(remainingDiff || []))
+
+    return newDiff
+  },
+
+  applyUpdateToDiff(diff, update) {
+    for (const op of Array.from(update.op)) {
+      if (op.broken !== true) {
+        diff = DiffGenerator.applyOpToDiff(diff, op, update.meta)
+      }
+    }
+    return diff
+  },
+
+  _consumeToOffset(remainingDiff, totalOffset) {
+    let part
+    const consumedDiff = []
+    let position = 0
+    while ((part = remainingDiff.shift())) {
+      const length = DiffGenerator._getLengthOfDiffPart(part)
+      if (part.d != null) {
+        consumedDiff.push(part)
+      } else if (position + length >= totalOffset) {
+        const partOffset = totalOffset - position
+        if (partOffset > 0) {
+          consumedDiff.push(DiffGenerator._slicePart(part, 0, partOffset))
+        }
+        if (partOffset < length) {
+          remainingDiff.unshift(DiffGenerator._slicePart(part, partOffset))
+        }
+        break
+      } else {
+        position += length
+        consumedDiff.push(part)
+      }
+    }
+
+    return {
+      consumedDiff,
+      remainingDiff,
+    }
+  },
+
+  _consumeDiffAffectedByDeleteOp(remainingDiff, deleteOp, meta) {
+    const consumedDiff = []
+    let remainingOp = deleteOp
+    while (remainingOp && remainingDiff.length > 0) {
+      let newPart
+      ;({ newPart, remainingDiff, remainingOp } =
+        DiffGenerator._consumeDeletedPart(remainingDiff, remainingOp, meta))
+      if (newPart != null) {
+        consumedDiff.push(newPart)
+      }
+    }
+    return {
+      consumedDiff,
+      remainingDiff,
+    }
+  },
+
+  _consumeDeletedPart(remainingDiff, op, meta) {
+    let deletedContent, newPart, remainingOp
+    const part = remainingDiff.shift()
+    const partLength = DiffGenerator._getLengthOfDiffPart(part)
+
+    if (part.d != null) {
+      // Skip existing deletes
+      remainingOp = op
+      newPart = part
+    } else if (partLength > op.d.length) {
+      // Only the first bit of the part has been deleted
+      const remainingPart = DiffGenerator._slicePart(part, op.d.length)
+      remainingDiff.unshift(remainingPart)
+
+      deletedContent = DiffGenerator._getContentOfPart(part).slice(
+        0,
+        op.d.length
+      )
+      if (deletedContent !== op.d) {
+        throw new ConsistencyError(
+          `deleted content, '${deletedContent}', does not match delete op, '${op.d}'`
+        )
+      }
+
+      if (part.u != null) {
+        newPart = {
+          d: op.d,
+          meta,
+        }
+      } else if (part.i != null) {
+        newPart = null
+      }
+
+      remainingOp = null
+    } else if (partLength === op.d.length) {
+      // The entire part has been deleted, but it is the last part
+
+      deletedContent = DiffGenerator._getContentOfPart(part)
+      if (deletedContent !== op.d) {
+        throw new ConsistencyError(
+          `deleted content, '${deletedContent}', does not match delete op, '${op.d}'`
+        )
+      }
+
+      if (part.u != null) {
+        newPart = {
+          d: op.d,
+          meta,
+        }
+      } else if (part.i != null) {
+        newPart = null
+      }
+
+      remainingOp = null
+    } else if (partLength < op.d.length) {
+      // The entire part has been deleted and there is more
+
+      deletedContent = DiffGenerator._getContentOfPart(part)
+      const opContent = op.d.slice(0, deletedContent.length)
+      if (deletedContent !== opContent) {
+        throw new ConsistencyError(
+          `deleted content, '${deletedContent}', does not match delete op, '${opContent}'`
+        )
+      }
+
+      if (part.u) {
+        newPart = {
+          d: part.u,
+          meta,
+        }
+      } else if (part.i != null) {
+        newPart = null
+      }
+
+      remainingOp = {
+        p: op.p,
+        d: op.d.slice(DiffGenerator._getLengthOfDiffPart(part)),
+      }
+    }
+
+    return {
+      newPart,
+      remainingDiff,
+      remainingOp,
+    }
+  },
+
+  _slicePart(basePart, from, to) {
+    let part
+    if (basePart.u != null) {
+      part = { u: basePart.u.slice(from, to) }
+    } else if (basePart.i != null) {
+      part = { i: basePart.i.slice(from, to) }
+    }
+    if (basePart.meta != null) {
+      part.meta = basePart.meta
+    }
+    return part
+  },
+
+  _getLengthOfDiffPart(part) {
+    return (part.u || part.d || part.i || '').length
+  },
+
+  _getContentOfPart(part) {
+    return part.u || part.d || part.i || ''
+  },
+}

services/track-changes/app/js/DiffManager.js

@@ -0,0 +1,188 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let DiffManager
+const UpdatesManager = require('./UpdatesManager')
+const DocumentUpdaterManager = require('./DocumentUpdaterManager')
+const DiffGenerator = require('./DiffGenerator')
+const logger = require('logger-sharelatex')
+
+module.exports = DiffManager = {
+  getLatestDocAndUpdates(project_id, doc_id, fromVersion, callback) {
+    // Get updates last, since then they must be ahead and it
+    // might be possible to rewind to the same version as the doc.
+    if (callback == null) {
+      callback = function (error, content, version, updates) {}
+    }
+    return DocumentUpdaterManager.getDocument(
+      project_id,
+      doc_id,
+      function (error, content, version) {
+        if (error != null) {
+          return callback(error)
+        }
+        if (fromVersion == null) {
+          // If we haven't been given a version, just return lastest doc and no updates
+          return callback(null, content, version, [])
+        }
+        return UpdatesManager.getDocUpdatesWithUserInfo(
+          project_id,
+          doc_id,
+          { from: fromVersion },
+          function (error, updates) {
+            if (error != null) {
+              return callback(error)
+            }
+            return callback(null, content, version, updates)
+          }
+        )
+      }
+    )
+  },
+
+  getDiff(project_id, doc_id, fromVersion, toVersion, callback) {
+    if (callback == null) {
+      callback = function (error, diff) {}
+    }
+    return DiffManager.getDocumentBeforeVersion(
+      project_id,
+      doc_id,
+      fromVersion,
+      function (error, startingContent, updates) {
+        let diff
+        if (error != null) {
+          if (error.message === 'broken-history') {
+            return callback(null, 'history unavailable')
+          } else {
+            return callback(error)
+          }
+        }
+
+        const updatesToApply = []
+        for (const update of Array.from(updates.slice().reverse())) {
+          if (update.v <= toVersion) {
+            updatesToApply.push(update)
+          }
+        }
+
+        try {
+          diff = DiffGenerator.buildDiff(startingContent, updatesToApply)
+        } catch (e) {
+          return callback(e)
+        }
+
+        return callback(null, diff)
+      }
+    )
+  },
+
+  getDocumentBeforeVersion(project_id, doc_id, version, _callback) {
+    // Whichever order we get the latest document and the latest updates,
+    // there is potential for updates to be applied between them so that
+    // they do not return the same 'latest' versions.
+    // If this happens, we just retry and hopefully get them at the compatible
+    // versions.
+    let retry
+    if (_callback == null) {
+      _callback = function (error, document, rewoundUpdates) {}
+    }
+    let retries = 3
+    const callback = function (error, ...args) {
+      if (error != null) {
+        if (error.retry && retries > 0) {
+          logger.warn(
+            { error, project_id, doc_id, version, retries },
+            'retrying getDocumentBeforeVersion'
+          )
+          return retry()
+        } else {
+          return _callback(error)
+        }
+      } else {
+        return _callback(null, ...Array.from(args))
+      }
+    }
+
+    return (retry = function () {
+      retries--
+      return DiffManager._tryGetDocumentBeforeVersion(
+        project_id,
+        doc_id,
+        version,
+        callback
+      )
+    })()
+  },
+
+  _tryGetDocumentBeforeVersion(project_id, doc_id, version, callback) {
+    if (callback == null) {
+      callback = function (error, document, rewoundUpdates) {}
+    }
+    logger.log(
+      { project_id, doc_id, version },
+      'getting document before version'
+    )
+    return DiffManager.getLatestDocAndUpdates(
+      project_id,
+      doc_id,
+      version,
+      function (error, content, version, updates) {
+        let startingContent
+        if (error != null) {
+          return callback(error)
+        }
+
+        // bail out if we hit a broken update
+        for (const u of Array.from(updates)) {
+          if (u.broken) {
+            return callback(new Error('broken-history'))
+          }
+        }
+
+        // discard any updates which are ahead of this document version
+        while ((updates[0] != null ? updates[0].v : undefined) >= version) {
+          updates.shift()
+        }
+
+        const lastUpdate = updates[0]
+        if (lastUpdate != null && lastUpdate.v !== version - 1) {
+          error = new Error(
+            `latest update version, ${lastUpdate.v}, does not match doc version, ${version}`
+          )
+          error.retry = true
+          return callback(error)
+        }
+
+        logger.log(
+          {
+            docVersion: version,
+            lastUpdateVersion: lastUpdate != null ? lastUpdate.v : undefined,
+            updateCount: updates.length,
+          },
+          'rewinding updates'
+        )
+
+        const tryUpdates = updates.slice().reverse()
+
+        try {
+          startingContent = DiffGenerator.rewindUpdates(content, tryUpdates)
+          // tryUpdates is reversed, and any unapplied ops are marked as broken
+        } catch (e) {
+          return callback(e)
+        }
+
+        return callback(null, startingContent, tryUpdates)
+      }
+    )
+  },
+}

services/track-changes/app/js/DocumentUpdaterManager.js

@@ -0,0 +1,90 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let DocumentUpdaterManager
+const request = require('request')
+const logger = require('logger-sharelatex')
+const Settings = require('@overleaf/settings')
+
+module.exports = DocumentUpdaterManager = {
+  getDocument(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error, content, version) {}
+    }
+    const url = `${Settings.apis.documentupdater.url}/project/${project_id}/doc/${doc_id}`
+    logger.log({ project_id, doc_id }, 'getting doc from document updater')
+    return request.get(url, function (error, res, body) {
+      if (error != null) {
+        return callback(error)
+      }
+      if (res.statusCode >= 200 && res.statusCode < 300) {
+        try {
+          body = JSON.parse(body)
+        } catch (error1) {
+          error = error1
+          return callback(error)
+        }
+        logger.log(
+          { project_id, doc_id, version: body.version },
+          'got doc from document updater'
+        )
+        return callback(null, body.lines.join('\n'), body.version)
+      } else {
+        error = new Error(
+          `doc updater returned a non-success status code: ${res.statusCode}`
+        )
+        logger.error(
+          { err: error, project_id, doc_id, url },
+          'error accessing doc updater'
+        )
+        return callback(error)
+      }
+    })
+  },
+
+  setDocument(project_id, doc_id, content, user_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    const url = `${Settings.apis.documentupdater.url}/project/${project_id}/doc/${doc_id}`
+    logger.log({ project_id, doc_id }, 'setting doc in document updater')
+    return request.post(
+      {
+        url,
+        json: {
+          lines: content.split('\n'),
+          source: 'restore',
+          user_id,
+          undoing: true,
+        },
+      },
+      function (error, res, body) {
+        if (error != null) {
+          return callback(error)
+        }
+        if (res.statusCode >= 200 && res.statusCode < 300) {
+          return callback(null)
+        } else {
+          error = new Error(
+            `doc updater returned a non-success status code: ${res.statusCode}`
+          )
+          logger.error(
+            { err: error, project_id, doc_id, url },
+            'error accessing doc updater'
+          )
+          return callback(error)
+        }
+      }
+    )
+  },
+}

services/track-changes/app/js/HealthChecker.js

@@ -0,0 +1,81 @@
+/* eslint-disable
+    camelcase,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const { ObjectId } = require('./mongodb')
+const request = require('request')
+const async = require('async')
+const settings = require('@overleaf/settings')
+const { port } = settings.internal.trackchanges
+const logger = require('logger-sharelatex')
+const LockManager = require('./LockManager')
+
+module.exports = {
+  check(callback) {
+    const project_id = ObjectId(settings.trackchanges.healthCheck.project_id)
+    const url = `http://localhost:${port}/project/${project_id}`
+    logger.log({ project_id }, 'running health check')
+    const jobs = [
+      cb =>
+        request.get(
+          { url: `http://localhost:${port}/check_lock`, timeout: 3000 },
+          function (err, res, body) {
+            if (err != null) {
+              logger.err(
+                { err, project_id },
+                'error checking lock for health check'
+              )
+              return cb(err)
+            } else if ((res != null ? res.statusCode : undefined) !== 200) {
+              return cb(`status code not 200, it's ${res.statusCode}`)
+            } else {
+              return cb()
+            }
+          }
+        ),
+      cb =>
+        request.post(
+          { url: `${url}/flush`, timeout: 10000 },
+          function (err, res, body) {
+            if (err != null) {
+              logger.err({ err, project_id }, 'error flushing for health check')
+              return cb(err)
+            } else if ((res != null ? res.statusCode : undefined) !== 204) {
+              return cb(`status code not 204, it's ${res.statusCode}`)
+            } else {
+              return cb()
+            }
+          }
+        ),
+      cb =>
+        request.get(
+          { url: `${url}/updates`, timeout: 10000 },
+          function (err, res, body) {
+            if (err != null) {
+              logger.err(
+                { err, project_id },
+                'error getting updates for health check'
+              )
+              return cb(err)
+            } else if ((res != null ? res.statusCode : undefined) !== 200) {
+              return cb(`status code not 200, it's ${res.statusCode}`)
+            } else {
+              return cb()
+            }
+          }
+        ),
+    ]
+    return async.series(jobs, callback)
+  },
+
+  checkLock(callback) {
+    return LockManager.healthCheck(callback)
+  },
+}

services/track-changes/app/js/HttpController.js

@@ -0,0 +1,340 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let HttpController
+const UpdatesManager = require('./UpdatesManager')
+const DiffManager = require('./DiffManager')
+const PackManager = require('./PackManager')
+const RestoreManager = require('./RestoreManager')
+const logger = require('logger-sharelatex')
+const HealthChecker = require('./HealthChecker')
+const _ = require('underscore')
+
+module.exports = HttpController = {
+  flushDoc(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { doc_id } = req.params
+    const { project_id } = req.params
+    logger.log({ project_id, doc_id }, 'compressing doc history')
+    return UpdatesManager.processUncompressedUpdatesWithLock(
+      project_id,
+      doc_id,
+      function (error) {
+        if (error != null) {
+          return next(error)
+        }
+        return res.sendStatus(204)
+      }
+    )
+  },
+
+  flushProject(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { project_id } = req.params
+    logger.log({ project_id }, 'compressing project history')
+    return UpdatesManager.processUncompressedUpdatesForProject(
+      project_id,
+      function (error) {
+        if (error != null) {
+          return next(error)
+        }
+        return res.sendStatus(204)
+      }
+    )
+  },
+
+  flushAll(req, res, next) {
+    // limit on projects to flush or -1 for all (default)
+    if (next == null) {
+      next = function (error) {}
+    }
+    const limit = req.query.limit != null ? parseInt(req.query.limit, 10) : -1
+    logger.log({ limit }, 'flushing all projects')
+    return UpdatesManager.flushAll(limit, function (error, result) {
+      if (error != null) {
+        return next(error)
+      }
+      const { failed, succeeded, all } = result
+      const status = `${succeeded.length} succeeded, ${failed.length} failed`
+      if (limit === 0) {
+        return res
+          .status(200)
+          .send(`${status}\nwould flush:\n${all.join('\n')}\n`)
+      } else if (failed.length > 0) {
+        logger.log({ failed, succeeded }, 'error flushing projects')
+        return res
+          .status(500)
+          .send(`${status}\nfailed to flush:\n${failed.join('\n')}\n`)
+      } else {
+        return res
+          .status(200)
+          .send(
+            `${status}\nflushed ${succeeded.length} projects of ${all.length}\n`
+          )
+      }
+    })
+  },
+
+  checkDanglingUpdates(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    logger.log('checking dangling updates')
+    return UpdatesManager.getDanglingUpdates(function (error, result) {
+      if (error != null) {
+        return next(error)
+      }
+      if (result.length > 0) {
+        logger.log({ dangling: result }, 'found dangling updates')
+        return res.status(500).send(`dangling updates:\n${result.join('\n')}\n`)
+      } else {
+        return res.status(200).send('no dangling updates found\n')
+      }
+    })
+  },
+
+  checkDoc(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { doc_id } = req.params
+    const { project_id } = req.params
+    logger.log({ project_id, doc_id }, 'checking doc history')
+    return DiffManager.getDocumentBeforeVersion(
+      project_id,
+      doc_id,
+      1,
+      function (error, document, rewoundUpdates) {
+        if (error != null) {
+          return next(error)
+        }
+        const broken = []
+        for (const update of Array.from(rewoundUpdates)) {
+          for (const op of Array.from(update.op)) {
+            if (op.broken === true) {
+              broken.push(op)
+            }
+          }
+        }
+        if (broken.length > 0) {
+          return res.send(broken)
+        } else {
+          return res.sendStatus(204)
+        }
+      }
+    )
+  },
+
+  getDiff(req, res, next) {
+    let from, to
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { doc_id } = req.params
+    const { project_id } = req.params
+
+    if (req.query.from != null) {
+      from = parseInt(req.query.from, 10)
+    } else {
+      from = null
+    }
+    if (req.query.to != null) {
+      to = parseInt(req.query.to, 10)
+    } else {
+      to = null
+    }
+
+    logger.log({ project_id, doc_id, from, to }, 'getting diff')
+    return DiffManager.getDiff(
+      project_id,
+      doc_id,
+      from,
+      to,
+      function (error, diff) {
+        if (error != null) {
+          return next(error)
+        }
+        return res.json({ diff })
+      }
+    )
+  },
+
+  getUpdates(req, res, next) {
+    let before, min_count
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { project_id } = req.params
+
+    if (req.query.before != null) {
+      before = parseInt(req.query.before, 10)
+    }
+    if (req.query.min_count != null) {
+      min_count = parseInt(req.query.min_count, 10)
+    }
+
+    return UpdatesManager.getSummarizedProjectUpdates(
+      project_id,
+      { before, min_count },
+      function (error, updates, nextBeforeTimestamp) {
+        if (error != null) {
+          return next(error)
+        }
+        return res.json({
+          updates,
+          nextBeforeTimestamp,
+        })
+      }
+    )
+  },
+
+  exportProject(req, res, next) {
+    // The project history can be huge:
+    //  - updates can weight MBs for insert/delete of full doc
+    //  - multiple updates form a pack
+    // Flush updates per pack onto the wire.
+    const { project_id } = req.params
+    logger.log({ project_id }, 'exporting project history')
+    UpdatesManager.exportProject(
+      project_id,
+      function (err, { updates, userIds }, confirmWrite) {
+        const abortStreaming = req.aborted || res.finished || res.destroyed
+        if (abortStreaming) {
+          // Tell the producer to stop emitting data
+          if (confirmWrite) confirmWrite(new Error('stop'))
+          return
+        }
+        const hasStartedStreamingResponse = res.headersSent
+        if (err) {
+          logger.error({ project_id, err }, 'export failed')
+          if (!hasStartedStreamingResponse) {
+            // Generate a nice 500
+            return next(err)
+          } else {
+            // Stop streaming
+            return res.destroy()
+          }
+        }
+        // Compose the response incrementally
+        const isFirstWrite = !hasStartedStreamingResponse
+        const isLastWrite = updates.length === 0
+        if (isFirstWrite) {
+          // The first write will emit the 200 status, headers and start of the
+          //  response payload (open array)
+          res.setHeader('Content-Type', 'application/json')
+          res.setHeader('Trailer', 'X-User-Ids')
+          res.writeHead(200)
+          res.write('[')
+        }
+        if (!isFirstWrite && !isLastWrite) {
+          // Starting from the 2nd non-empty write, emit a continuing comma.
+          // write 1: [updates1
+          // write 2: ,updates2
+          // write 3: ,updates3
+          // write N: ]
+          res.write(',')
+        }
+
+        // Every write will emit a blob onto the response stream:
+        // '[update1,update2,...]'
+        //   ^^^^^^^^^^^^^^^^^^^
+        res.write(JSON.stringify(updates).slice(1, -1), confirmWrite)
+
+        if (isLastWrite) {
+          // The last write will have no updates and will finish the response
+          //  payload (close array) and emit the userIds as trailer.
+          res.addTrailers({ 'X-User-Ids': JSON.stringify(userIds) })
+          res.end(']')
+        }
+      }
+    )
+  },
+
+  restore(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    let { doc_id, project_id, version } = req.params
+    const user_id = req.headers['x-user-id']
+    version = parseInt(version, 10)
+    return RestoreManager.restoreToBeforeVersion(
+      project_id,
+      doc_id,
+      version,
+      user_id,
+      function (error) {
+        if (error != null) {
+          return next(error)
+        }
+        return res.sendStatus(204)
+      }
+    )
+  },
+
+  pushDocHistory(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { project_id } = req.params
+    const { doc_id } = req.params
+    logger.log({ project_id, doc_id }, 'pushing all finalised changes to s3')
+    return PackManager.pushOldPacks(project_id, doc_id, function (error) {
+      if (error != null) {
+        return next(error)
+      }
+      return res.sendStatus(204)
+    })
+  },
+
+  pullDocHistory(req, res, next) {
+    if (next == null) {
+      next = function (error) {}
+    }
+    const { project_id } = req.params
+    const { doc_id } = req.params
+    logger.log({ project_id, doc_id }, 'pulling all packs from s3')
+    return PackManager.pullOldPacks(project_id, doc_id, function (error) {
+      if (error != null) {
+        return next(error)
+      }
+      return res.sendStatus(204)
+    })
+  },
+
+  healthCheck(req, res) {
+    return HealthChecker.check(function (err) {
+      if (err != null) {
+        logger.err({ err }, 'error performing health check')
+        return res.sendStatus(500)
+      } else {
+        return res.sendStatus(200)
+      }
+    })
+  },
+
+  checkLock(req, res) {
+    return HealthChecker.checkLock(function (err) {
+      if (err != null) {
+        logger.err({ err }, 'error performing lock check')
+        return res.sendStatus(500)
+      } else {
+        return res.sendStatus(200)
+      }
+    })
+  },
+}

services/track-changes/app/js/LockManager.js

@@ -0,0 +1,164 @@
+/* eslint-disable
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let LockManager
+const Settings = require('@overleaf/settings')
+const redis = require('@overleaf/redis-wrapper')
+const rclient = redis.createClient(Settings.redis.lock)
+const os = require('os')
+const crypto = require('crypto')
+const logger = require('logger-sharelatex')
+
+const HOST = os.hostname()
+const PID = process.pid
+const RND = crypto.randomBytes(4).toString('hex')
+let COUNT = 0
+
+module.exports = LockManager = {
+  LOCK_TEST_INTERVAL: 50, // 50ms between each test of the lock
+  MAX_LOCK_WAIT_TIME: 10000, // 10s maximum time to spend trying to get the lock
+  LOCK_TTL: 300, // seconds (allow 5 minutes for any operation to complete)
+
+  // Use a signed lock value as described in
+  // http://redis.io/topics/distlock#correct-implementation-with-a-single-instance
+  // to prevent accidental unlocking by multiple processes
+  randomLock() {
+    const time = Date.now()
+    return `locked:host=${HOST}:pid=${PID}:random=${RND}:time=${time}:count=${COUNT++}`
+  },
+
+  unlockScript:
+    'if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("del", KEYS[1]) else return 0 end',
+
+  tryLock(key, callback) {
+    if (callback == null) {
+      callback = function (err, gotLock) {}
+    }
+    const lockValue = LockManager.randomLock()
+    return rclient.set(
+      key,
+      lockValue,
+      'EX',
+      this.LOCK_TTL,
+      'NX',
+      function (err, gotLock) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (gotLock === 'OK') {
+          return callback(err, true, lockValue)
+        } else {
+          return callback(err, false)
+        }
+      }
+    )
+  },
+
+  getLock(key, callback) {
+    let attempt
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    const startTime = Date.now()
+    return (attempt = function () {
+      if (Date.now() - startTime > LockManager.MAX_LOCK_WAIT_TIME) {
+        const e = new Error('Timeout')
+        e.key = key
+        return callback(e)
+      }
+
+      return LockManager.tryLock(key, function (error, gotLock, lockValue) {
+        if (error != null) {
+          return callback(error)
+        }
+        if (gotLock) {
+          return callback(null, lockValue)
+        } else {
+          return setTimeout(attempt, LockManager.LOCK_TEST_INTERVAL)
+        }
+      })
+    })()
+  },
+
+  checkLock(key, callback) {
+    if (callback == null) {
+      callback = function (err, isFree) {}
+    }
+    return rclient.exists(key, function (err, exists) {
+      if (err != null) {
+        return callback(err)
+      }
+      exists = parseInt(exists)
+      if (exists === 1) {
+        return callback(err, false)
+      } else {
+        return callback(err, true)
+      }
+    })
+  },
+
+  releaseLock(key, lockValue, callback) {
+    return rclient.eval(
+      LockManager.unlockScript,
+      1,
+      key,
+      lockValue,
+      function (err, result) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (result != null && result !== 1) {
+          // successful unlock should release exactly one key
+          logger.error(
+            { key, lockValue, redis_err: err, redis_result: result },
+            'unlocking error'
+          )
+          return callback(new Error('tried to release timed out lock'))
+        }
+        return callback(err, result)
+      }
+    )
+  },
+
+  runWithLock(key, runner, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return LockManager.getLock(key, function (error, lockValue) {
+      if (error != null) {
+        return callback(error)
+      }
+      return runner(error1 =>
+        LockManager.releaseLock(key, lockValue, function (error2) {
+          error = error1 || error2
+          if (error != null) {
+            return callback(error)
+          }
+          return callback()
+        })
+      )
+    })
+  },
+
+  healthCheck(callback) {
+    const action = releaseLock => releaseLock()
+    return LockManager.runWithLock(
+      `HistoryLock:HealthCheck:host=${HOST}:pid=${PID}:random=${RND}`,
+      action,
+      callback
+    )
+  },
+
+  close(callback) {
+    rclient.quit()
+    return rclient.once('end', callback)
+  },
+}

services/track-changes/app/js/MongoAWS.js

@@ -0,0 +1,199 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let MongoAWS
+const settings = require('@overleaf/settings')
+const logger = require('logger-sharelatex')
+const AWS = require('aws-sdk')
+const S3S = require('s3-streams')
+const { db, ObjectId } = require('./mongodb')
+const JSONStream = require('JSONStream')
+const ReadlineStream = require('byline')
+const zlib = require('zlib')
+const Metrics = require('@overleaf/metrics')
+
+const DAYS = 24 * 3600 * 1000 // one day in milliseconds
+
+const createStream = function (streamConstructor, project_id, doc_id, pack_id) {
+  const AWS_CONFIG = {
+    accessKeyId: settings.trackchanges.s3.key,
+    secretAccessKey: settings.trackchanges.s3.secret,
+    endpoint: settings.trackchanges.s3.endpoint,
+    s3ForcePathStyle: settings.trackchanges.s3.pathStyle,
+  }
+
+  return streamConstructor(new AWS.S3(AWS_CONFIG), {
+    Bucket: settings.trackchanges.stores.doc_history,
+    Key: project_id + '/changes-' + doc_id + '/pack-' + pack_id,
+  })
+}
+
+module.exports = MongoAWS = {
+  archivePack(project_id, doc_id, pack_id, _callback) {
+    if (_callback == null) {
+      _callback = function (error) {}
+    }
+    const callback = function (...args) {
+      _callback(...Array.from(args || []))
+      return (_callback = function () {})
+    }
+
+    const query = {
+      _id: ObjectId(pack_id),
+      doc_id: ObjectId(doc_id),
+    }
+
+    if (project_id == null) {
+      return callback(new Error('invalid project id'))
+    }
+    if (doc_id == null) {
+      return callback(new Error('invalid doc id'))
+    }
+    if (pack_id == null) {
+      return callback(new Error('invalid pack id'))
+    }
+
+    logger.log({ project_id, doc_id, pack_id }, 'uploading data to s3')
+
+    const upload = createStream(S3S.WriteStream, project_id, doc_id, pack_id)
+
+    return db.docHistory.findOne(query, function (err, result) {
+      if (err != null) {
+        return callback(err)
+      }
+      if (result == null) {
+        return callback(new Error('cannot find pack to send to s3'))
+      }
+      if (result.expiresAt != null) {
+        return callback(new Error('refusing to send pack with TTL to s3'))
+      }
+      const uncompressedData = JSON.stringify(result)
+      if (uncompressedData.indexOf('\u0000') !== -1) {
+        const error = new Error('null bytes found in upload')
+        logger.error({ err: error, project_id, doc_id, pack_id }, error.message)
+        return callback(error)
+      }
+      return zlib.gzip(uncompressedData, function (err, buf) {
+        logger.log(
+          {
+            project_id,
+            doc_id,
+            pack_id,
+            origSize: uncompressedData.length,
+            newSize: buf.length,
+          },
+          'compressed pack'
+        )
+        if (err != null) {
+          return callback(err)
+        }
+        upload.on('error', err => callback(err))
+        upload.on('finish', function () {
+          Metrics.inc('archive-pack')
+          logger.log({ project_id, doc_id, pack_id }, 'upload to s3 completed')
+          return callback(null)
+        })
+        upload.write(buf)
+        return upload.end()
+      })
+    })
+  },
+
+  readArchivedPack(project_id, doc_id, pack_id, _callback) {
+    if (_callback == null) {
+      _callback = function (error, result) {}
+    }
+    const callback = function (...args) {
+      _callback(...Array.from(args || []))
+      return (_callback = function () {})
+    }
+
+    if (project_id == null) {
+      return callback(new Error('invalid project id'))
+    }
+    if (doc_id == null) {
+      return callback(new Error('invalid doc id'))
+    }
+    if (pack_id == null) {
+      return callback(new Error('invalid pack id'))
+    }
+
+    logger.log({ project_id, doc_id, pack_id }, 'downloading data from s3')
+
+    const download = createStream(S3S.ReadStream, project_id, doc_id, pack_id)
+
+    const inputStream = download
+      .on('open', obj => 1)
+      .on('error', err => callback(err))
+
+    const gunzip = zlib.createGunzip()
+    gunzip.setEncoding('utf8')
+    gunzip.on('error', function (err) {
+      logger.log(
+        { project_id, doc_id, pack_id, err },
+        'error uncompressing gzip stream'
+      )
+      return callback(err)
+    })
+
+    const outputStream = inputStream.pipe(gunzip)
+    const parts = []
+    outputStream.on('error', err => callback(err))
+    outputStream.on('end', function () {
+      let object
+      logger.log({ project_id, doc_id, pack_id }, 'download from s3 completed')
+      try {
+        object = JSON.parse(parts.join(''))
+      } catch (e) {
+        return callback(e)
+      }
+      object._id = ObjectId(object._id)
+      object.doc_id = ObjectId(object.doc_id)
+      object.project_id = ObjectId(object.project_id)
+      for (const op of Array.from(object.pack)) {
+        if (op._id != null) {
+          op._id = ObjectId(op._id)
+        }
+      }
+      return callback(null, object)
+    })
+    return outputStream.on('data', data => parts.push(data))
+  },
+
+  unArchivePack(project_id, doc_id, pack_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return MongoAWS.readArchivedPack(
+      project_id,
+      doc_id,
+      pack_id,
+      function (err, object) {
+        if (err != null) {
+          return callback(err)
+        }
+        Metrics.inc('unarchive-pack')
+        // allow the object to expire, we can always retrieve it again
+        object.expiresAt = new Date(Date.now() + 7 * DAYS)
+        logger.log({ project_id, doc_id, pack_id }, 'inserting object from s3')
+        return db.docHistory.insertOne(object, (err, confirmation) => {
+          if (err) return callback(err)
+          object._id = confirmation.insertedId
+          callback(null, object)
+        })
+      }
+    )
+  },
+}

services/track-changes/app/js/MongoManager.js

@@ -0,0 +1,202 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let MongoManager
+const { db, ObjectId } = require('./mongodb')
+const PackManager = require('./PackManager')
+const async = require('async')
+const _ = require('underscore')
+const metrics = require('@overleaf/metrics')
+const logger = require('logger-sharelatex')
+
+module.exports = MongoManager = {
+  getLastCompressedUpdate(doc_id, callback) {
+    if (callback == null) {
+      callback = function (error, update) {}
+    }
+    return db.docHistory
+      .find(
+        { doc_id: ObjectId(doc_id.toString()) },
+        // only return the last entry in a pack
+        { projection: { pack: { $slice: -1 } } }
+      )
+      .sort({ v: -1 })
+      .limit(1)
+      .toArray(function (error, compressedUpdates) {
+        if (error != null) {
+          return callback(error)
+        }
+        return callback(null, compressedUpdates[0] || null)
+      })
+  },
+
+  peekLastCompressedUpdate(doc_id, callback) {
+    // under normal use we pass back the last update as
+    // callback(null,update,version).
+    //
+    // when we have an existing last update but want to force a new one
+    // to start, we pass it back as callback(null,null,version), just
+    // giving the version so we can check consistency.
+    if (callback == null) {
+      callback = function (error, update, version) {}
+    }
+    return MongoManager.getLastCompressedUpdate(
+      doc_id,
+      function (error, update) {
+        if (error != null) {
+          return callback(error)
+        }
+        if (update != null) {
+          if (update.broken) {
+            // marked as broken so we will force a new op
+            return callback(null, null)
+          } else if (update.pack != null) {
+            if (update.finalised) {
+              // no more ops can be appended
+              return callback(
+                null,
+                null,
+                update.pack[0] != null ? update.pack[0].v : undefined
+              )
+            } else {
+              return callback(
+                null,
+                update,
+                update.pack[0] != null ? update.pack[0].v : undefined
+              )
+            }
+          } else {
+            return callback(null, update, update.v)
+          }
+        } else {
+          return PackManager.getLastPackFromIndex(
+            doc_id,
+            function (error, pack) {
+              if (error != null) {
+                return callback(error)
+              }
+              if (
+                (pack != null ? pack.inS3 : undefined) != null &&
+                (pack != null ? pack.v_end : undefined) != null
+              ) {
+                return callback(null, null, pack.v_end)
+              }
+              return callback(null, null)
+            }
+          )
+        }
+      }
+    )
+  },
+
+  backportProjectId(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return db.docHistory.updateMany(
+      {
+        doc_id: ObjectId(doc_id.toString()),
+        project_id: { $exists: false },
+      },
+      {
+        $set: { project_id: ObjectId(project_id.toString()) },
+      },
+      callback
+    )
+  },
+
+  getProjectMetaData(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, metadata) {}
+    }
+    return db.projectHistoryMetaData.findOne(
+      {
+        project_id: ObjectId(project_id.toString()),
+      },
+      callback
+    )
+  },
+
+  setProjectMetaData(project_id, metadata, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return db.projectHistoryMetaData.updateOne(
+      {
+        project_id: ObjectId(project_id),
+      },
+      {
+        $set: metadata,
+      },
+      {
+        upsert: true,
+      },
+      callback
+    )
+  },
+
+  upgradeHistory(project_id, callback) {
+    // preserve the project's existing history
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return db.docHistory.updateMany(
+      {
+        project_id: ObjectId(project_id),
+        temporary: true,
+        expiresAt: { $exists: true },
+      },
+      {
+        $set: { temporary: false },
+        $unset: { expiresAt: '' },
+      },
+      callback
+    )
+  },
+
+  ensureIndices() {
+    // For finding all updates that go into a diff for a doc
+    db.docHistory.ensureIndex({ doc_id: 1, v: 1 }, { background: true })
+    // For finding all updates that affect a project
+    db.docHistory.ensureIndex(
+      { project_id: 1, 'meta.end_ts': 1 },
+      { background: true }
+    )
+    // For finding updates that don't yet have a project_id and need it inserting
+    db.docHistory.ensureIndex(
+      { doc_id: 1, project_id: 1 },
+      { background: true }
+    )
+    // For finding project meta-data
+    db.projectHistoryMetaData.ensureIndex(
+      { project_id: 1 },
+      { background: true }
+    )
+    // TTL index for auto deleting week old temporary ops
+    db.docHistory.ensureIndex(
+      { expiresAt: 1 },
+      { expireAfterSeconds: 0, background: true }
+    )
+    // For finding packs to be checked for archiving
+    db.docHistory.ensureIndex({ last_checked: 1 }, { background: true })
+    // For finding archived packs
+    return db.docHistoryIndex.ensureIndex(
+      { project_id: 1 },
+      { background: true }
+    )
+  },
+}
+;['getLastCompressedUpdate', 'getProjectMetaData', 'setProjectMetaData'].map(
+  method =>
+    metrics.timeAsyncMethod(MongoManager, method, 'mongo.MongoManager', logger)
+)

services/track-changes/app/js/PackManager.js

@@ -0,0 +1,1171 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS205: Consider reworking code to avoid use of IIFEs
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let PackManager
+const async = require('async')
+const _ = require('underscore')
+const Bson = require('bson')
+const BSON = new Bson()
+const { db, ObjectId } = require('./mongodb')
+const logger = require('logger-sharelatex')
+const LockManager = require('./LockManager')
+const MongoAWS = require('./MongoAWS')
+const Metrics = require('@overleaf/metrics')
+const ProjectIterator = require('./ProjectIterator')
+const Settings = require('@overleaf/settings')
+const keys = Settings.redis.lock.key_schema
+
+// Sharejs operations are stored in a 'pack' object
+//
+//  e.g.  a single sharejs update looks like
+//
+//   {
+//     "doc_id" : 549dae9e0a2a615c0c7f0c98,
+//     "project_id" : 549dae9c0a2a615c0c7f0c8c,
+//     "op" : [ {"p" : 6981,	"d" : "?"	} ],
+//     "meta" : {	"user_id" : 52933..., "start_ts" : 1422310693931,	"end_ts" : 1422310693931 },
+//     "v" : 17082
+//   }
+//
+//  and a pack looks like this
+//
+//   {
+//     "doc_id" : 549dae9e0a2a615c0c7f0c98,
+//     "project_id" : 549dae9c0a2a615c0c7f0c8c,
+//     "pack" : [ U1, U2, U3, ...., UN],
+//     "meta" : {	"user_id" : 52933..., "start_ts" : 1422310693931,	"end_ts" : 1422310693931 },
+//     "v" : 17082
+//     "v_end" : ...
+//   }
+//
+//  where U1, U2, U3, .... are single updates stripped of their
+//  doc_id and project_id fields (which are the same for all the
+//  updates in the pack).
+//
+//  The pack itself has v and meta fields, this makes it possible to
+//  treat packs and single updates in a similar way.
+//
+//  The v field of the pack itself is from the first entry U1, the
+//  v_end field from UN.  The meta.end_ts field of the pack itself is
+//  from the last entry UN, the meta.start_ts field from U1.
+
+const DAYS = 24 * 3600 * 1000 // one day in milliseconds
+
+module.exports = PackManager = {
+  MAX_SIZE: 1024 * 1024, // make these configurable parameters
+  MAX_COUNT: 1024,
+
+  insertCompressedUpdates(
+    project_id,
+    doc_id,
+    lastUpdate,
+    newUpdates,
+    temporary,
+    callback
+  ) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    if (newUpdates.length === 0) {
+      return callback()
+    }
+
+    // never append permanent ops to a pack that will expire
+    if (
+      (lastUpdate != null ? lastUpdate.expiresAt : undefined) != null &&
+      !temporary
+    ) {
+      lastUpdate = null
+    }
+
+    const updatesToFlush = []
+    const updatesRemaining = newUpdates.slice()
+
+    let n = (lastUpdate != null ? lastUpdate.n : undefined) || 0
+    let sz = (lastUpdate != null ? lastUpdate.sz : undefined) || 0
+
+    while (
+      updatesRemaining.length &&
+      n < PackManager.MAX_COUNT &&
+      sz < PackManager.MAX_SIZE
+    ) {
+      const nextUpdate = updatesRemaining[0]
+      const nextUpdateSize = BSON.calculateObjectSize(nextUpdate)
+      if (nextUpdateSize + sz > PackManager.MAX_SIZE && n > 0) {
+        break
+      }
+      n++
+      sz += nextUpdateSize
+      updatesToFlush.push(updatesRemaining.shift())
+    }
+
+    return PackManager.flushCompressedUpdates(
+      project_id,
+      doc_id,
+      lastUpdate,
+      updatesToFlush,
+      temporary,
+      function (error) {
+        if (error != null) {
+          return callback(error)
+        }
+        return PackManager.insertCompressedUpdates(
+          project_id,
+          doc_id,
+          null,
+          updatesRemaining,
+          temporary,
+          callback
+        )
+      }
+    )
+  },
+
+  flushCompressedUpdates(
+    project_id,
+    doc_id,
+    lastUpdate,
+    newUpdates,
+    temporary,
+    callback
+  ) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    if (newUpdates.length === 0) {
+      return callback()
+    }
+
+    let canAppend = false
+    // check if it is safe to append to an existing pack
+    if (lastUpdate != null) {
+      if (!temporary && lastUpdate.expiresAt == null) {
+        // permanent pack appends to permanent pack
+        canAppend = true
+      }
+      const age =
+        Date.now() -
+        (lastUpdate.meta != null ? lastUpdate.meta.start_ts : undefined)
+      if (temporary && lastUpdate.expiresAt != null && age < 1 * DAYS) {
+        // temporary pack appends to temporary pack if same day
+        canAppend = true
+      }
+    }
+
+    if (canAppend) {
+      return PackManager.appendUpdatesToExistingPack(
+        project_id,
+        doc_id,
+        lastUpdate,
+        newUpdates,
+        temporary,
+        callback
+      )
+    } else {
+      return PackManager.insertUpdatesIntoNewPack(
+        project_id,
+        doc_id,
+        newUpdates,
+        temporary,
+        callback
+      )
+    }
+  },
+
+  insertUpdatesIntoNewPack(
+    project_id,
+    doc_id,
+    newUpdates,
+    temporary,
+    callback
+  ) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    const first = newUpdates[0]
+    const last = newUpdates[newUpdates.length - 1]
+    const n = newUpdates.length
+    const sz = BSON.calculateObjectSize(newUpdates)
+    const newPack = {
+      project_id: ObjectId(project_id.toString()),
+      doc_id: ObjectId(doc_id.toString()),
+      pack: newUpdates,
+      n,
+      sz,
+      meta: {
+        start_ts: first.meta.start_ts,
+        end_ts: last.meta.end_ts,
+      },
+      v: first.v,
+      v_end: last.v,
+      temporary,
+    }
+    if (temporary) {
+      newPack.expiresAt = new Date(Date.now() + 7 * DAYS)
+      newPack.last_checked = new Date(Date.now() + 30 * DAYS) // never check temporary packs
+    }
+    logger.log(
+      { project_id, doc_id, newUpdates },
+      'inserting updates into new pack'
+    )
+    return db.docHistory.insertOne(newPack, function (err) {
+      if (err != null) {
+        return callback(err)
+      }
+      Metrics.inc(`insert-pack-${temporary ? 'temporary' : 'permanent'}`)
+      if (temporary) {
+        return callback()
+      } else {
+        return PackManager.updateIndex(project_id, doc_id, callback)
+      }
+    })
+  },
+
+  appendUpdatesToExistingPack(
+    project_id,
+    doc_id,
+    lastUpdate,
+    newUpdates,
+    temporary,
+    callback
+  ) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    const first = newUpdates[0]
+    const last = newUpdates[newUpdates.length - 1]
+    const n = newUpdates.length
+    const sz = BSON.calculateObjectSize(newUpdates)
+    const query = {
+      _id: lastUpdate._id,
+      project_id: ObjectId(project_id.toString()),
+      doc_id: ObjectId(doc_id.toString()),
+      pack: { $exists: true },
+    }
+    const update = {
+      $push: {
+        pack: { $each: newUpdates },
+      },
+      $inc: {
+        n: n,
+        sz: sz,
+      },
+      $set: {
+        'meta.end_ts': last.meta.end_ts,
+        v_end: last.v,
+      },
+    }
+    if (lastUpdate.expiresAt && temporary) {
+      update.$set.expiresAt = new Date(Date.now() + 7 * DAYS)
+    }
+    logger.log(
+      { project_id, doc_id, lastUpdate, newUpdates },
+      'appending updates to existing pack'
+    )
+    Metrics.inc(`append-pack-${temporary ? 'temporary' : 'permanent'}`)
+    return db.docHistory.updateOne(query, update, callback)
+  },
+
+  // Retrieve all changes for a document
+
+  getOpsByVersionRange(project_id, doc_id, fromVersion, toVersion, callback) {
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    return PackManager.loadPacksByVersionRange(
+      project_id,
+      doc_id,
+      fromVersion,
+      toVersion,
+      function (error) {
+        const query = { doc_id: ObjectId(doc_id.toString()) }
+        if (toVersion != null) {
+          query.v = { $lte: toVersion }
+        }
+        if (fromVersion != null) {
+          query.v_end = { $gte: fromVersion }
+        }
+        // console.log "query:", query
+        return db.docHistory
+          .find(query)
+          .sort({ v: -1 })
+          .toArray(function (err, result) {
+            if (err != null) {
+              return callback(err)
+            }
+            // console.log "getOpsByVersionRange:", err, result
+            const updates = []
+            const opInRange = function (op, from, to) {
+              if (fromVersion != null && op.v < fromVersion) {
+                return false
+              }
+              if (toVersion != null && op.v > toVersion) {
+                return false
+              }
+              return true
+            }
+            for (const docHistory of Array.from(result)) {
+              // console.log 'adding', docHistory.pack
+              for (const op of Array.from(docHistory.pack.reverse())) {
+                if (opInRange(op, fromVersion, toVersion)) {
+                  op.project_id = docHistory.project_id
+                  op.doc_id = docHistory.doc_id
+                  // console.log "added op", op.v, fromVersion, toVersion
+                  updates.push(op)
+                }
+              }
+            }
+            return callback(null, updates)
+          })
+      }
+    )
+  },
+
+  loadPacksByVersionRange(
+    project_id,
+    doc_id,
+    fromVersion,
+    toVersion,
+    callback
+  ) {
+    return PackManager.getIndex(doc_id, function (err, indexResult) {
+      let pack
+      if (err != null) {
+        return callback(err)
+      }
+      const indexPacks =
+        (indexResult != null ? indexResult.packs : undefined) || []
+      const packInRange = function (pack, from, to) {
+        if (fromVersion != null && pack.v_end < fromVersion) {
+          return false
+        }
+        if (toVersion != null && pack.v > toVersion) {
+          return false
+        }
+        return true
+      }
+      const neededIds = (() => {
+        const result = []
+        for (pack of Array.from(indexPacks)) {
+          if (packInRange(pack, fromVersion, toVersion)) {
+            result.push(pack._id)
+          }
+        }
+        return result
+      })()
+      if (neededIds.length) {
+        return PackManager.fetchPacksIfNeeded(
+          project_id,
+          doc_id,
+          neededIds,
+          callback
+        )
+      } else {
+        return callback()
+      }
+    })
+  },
+
+  fetchPacksIfNeeded(project_id, doc_id, pack_ids, callback) {
+    let id
+    return db.docHistory
+      .find(
+        { _id: { $in: pack_ids.map(ObjectId) } },
+        { projection: { _id: 1 } }
+      )
+      .toArray(function (err, loadedPacks) {
+        if (err != null) {
+          return callback(err)
+        }
+        const allPackIds = (() => {
+          const result1 = []
+          for (id of Array.from(pack_ids)) {
+            result1.push(id.toString())
+          }
+          return result1
+        })()
+        const loadedPackIds = Array.from(loadedPacks).map(pack =>
+          pack._id.toString()
+        )
+        const packIdsToFetch = _.difference(allPackIds, loadedPackIds)
+        logger.log(
+          { project_id, doc_id, loadedPackIds, allPackIds, packIdsToFetch },
+          'analysed packs'
+        )
+        if (packIdsToFetch.length === 0) {
+          return callback()
+        }
+        return async.eachLimit(
+          packIdsToFetch,
+          4,
+          (pack_id, cb) =>
+            MongoAWS.unArchivePack(project_id, doc_id, pack_id, cb),
+          function (err) {
+            if (err != null) {
+              return callback(err)
+            }
+            logger.log({ project_id, doc_id }, 'done unarchiving')
+            return callback()
+          }
+        )
+      })
+  },
+
+  // Retrieve all changes across a project
+
+  makeProjectIterator(project_id, before, callback) {
+    // get all the docHistory Entries
+    return db.docHistory
+      .find(
+        { project_id: ObjectId(project_id) },
+        { projection: { pack: false } }
+      )
+      .sort({ 'meta.end_ts': -1 })
+      .toArray(function (err, packs) {
+        let pack
+        if (err != null) {
+          return callback(err)
+        }
+        const allPacks = []
+        const seenIds = {}
+        for (pack of Array.from(packs)) {
+          allPacks.push(pack)
+          seenIds[pack._id] = true
+        }
+        return db.docHistoryIndex
+          .find({ project_id: ObjectId(project_id) })
+          .toArray(function (err, indexes) {
+            if (err != null) {
+              return callback(err)
+            }
+            for (const index of Array.from(indexes)) {
+              for (pack of Array.from(index.packs)) {
+                if (!seenIds[pack._id]) {
+                  pack.project_id = index.project_id
+                  pack.doc_id = index._id
+                  pack.fromIndex = true
+                  allPacks.push(pack)
+                  seenIds[pack._id] = true
+                }
+              }
+            }
+            return callback(
+              null,
+              new ProjectIterator(allPacks, before, PackManager.getPackById)
+            )
+          })
+      })
+  },
+
+  getPackById(project_id, doc_id, pack_id, callback) {
+    return db.docHistory.findOne({ _id: pack_id }, function (err, pack) {
+      if (err != null) {
+        return callback(err)
+      }
+      if (pack == null) {
+        return MongoAWS.unArchivePack(project_id, doc_id, pack_id, callback)
+      } else if (pack.expiresAt != null && pack.temporary === false) {
+        // we only need to touch the TTL when listing the changes in the project
+        // because diffs on individual documents are always done after that
+        return PackManager.increaseTTL(pack, callback)
+        // only do this for cached packs, not temporary ones to avoid older packs
+        // being kept longer than newer ones (which messes up the last update version)
+      } else {
+        return callback(null, pack)
+      }
+    })
+  },
+
+  increaseTTL(pack, callback) {
+    if (pack.expiresAt < new Date(Date.now() + 6 * DAYS)) {
+      // update cache expiry since we are using this pack
+      return db.docHistory.updateOne(
+        { _id: pack._id },
+        { $set: { expiresAt: new Date(Date.now() + 7 * DAYS) } },
+        err => callback(err, pack)
+      )
+    } else {
+      return callback(null, pack)
+    }
+  },
+
+  // Manage docHistoryIndex collection
+
+  getIndex(doc_id, callback) {
+    return db.docHistoryIndex.findOne(
+      { _id: ObjectId(doc_id.toString()) },
+      callback
+    )
+  },
+
+  getPackFromIndex(doc_id, pack_id, callback) {
+    return db.docHistoryIndex.findOne(
+      { _id: ObjectId(doc_id.toString()), 'packs._id': pack_id },
+      { projection: { 'packs.$': 1 } },
+      callback
+    )
+  },
+
+  getLastPackFromIndex(doc_id, callback) {
+    return db.docHistoryIndex.findOne(
+      { _id: ObjectId(doc_id.toString()) },
+      { projection: { packs: { $slice: -1 } } },
+      function (err, indexPack) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (indexPack == null) {
+          return callback()
+        }
+        return callback(null, indexPack[0])
+      }
+    )
+  },
+
+  getIndexWithKeys(doc_id, callback) {
+    return PackManager.getIndex(doc_id, function (err, index) {
+      if (err != null) {
+        return callback(err)
+      }
+      if (index == null) {
+        return callback()
+      }
+      for (const pack of Array.from(
+        (index != null ? index.packs : undefined) || []
+      )) {
+        index[pack._id] = pack
+      }
+      return callback(null, index)
+    })
+  },
+
+  initialiseIndex(project_id, doc_id, callback) {
+    return PackManager.findCompletedPacks(
+      project_id,
+      doc_id,
+      function (err, packs) {
+        // console.log 'err', err, 'packs', packs, packs?.length
+        if (err != null) {
+          return callback(err)
+        }
+        if (packs == null) {
+          return callback()
+        }
+        return PackManager.insertPacksIntoIndexWithLock(
+          project_id,
+          doc_id,
+          packs,
+          callback
+        )
+      }
+    )
+  },
+
+  updateIndex(project_id, doc_id, callback) {
+    // find all packs prior to current pack
+    return PackManager.findUnindexedPacks(
+      project_id,
+      doc_id,
+      function (err, newPacks) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (newPacks == null || newPacks.length === 0) {
+          return callback()
+        }
+        return PackManager.insertPacksIntoIndexWithLock(
+          project_id,
+          doc_id,
+          newPacks,
+          function (err) {
+            if (err != null) {
+              return callback(err)
+            }
+            logger.log(
+              { project_id, doc_id, newPacks },
+              'added new packs to index'
+            )
+            return callback()
+          }
+        )
+      }
+    )
+  },
+
+  findCompletedPacks(project_id, doc_id, callback) {
+    const query = {
+      doc_id: ObjectId(doc_id.toString()),
+      expiresAt: { $exists: false },
+    }
+    return db.docHistory
+      .find(query, { projection: { pack: false } })
+      .sort({ v: 1 })
+      .toArray(function (err, packs) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (packs == null) {
+          return callback()
+        }
+        if (!(packs != null ? packs.length : undefined)) {
+          return callback()
+        }
+        const last = packs.pop() // discard the last pack, if it's still in progress
+        if (last.finalised) {
+          packs.push(last)
+        } // it's finalised so we push it back to archive it
+        return callback(null, packs)
+      })
+  },
+
+  findPacks(project_id, doc_id, callback) {
+    const query = {
+      doc_id: ObjectId(doc_id.toString()),
+      expiresAt: { $exists: false },
+    }
+    return db.docHistory
+      .find(query, { projection: { pack: false } })
+      .sort({ v: 1 })
+      .toArray(function (err, packs) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (packs == null) {
+          return callback()
+        }
+        if (!(packs != null ? packs.length : undefined)) {
+          return callback()
+        }
+        return callback(null, packs)
+      })
+  },
+
+  findUnindexedPacks(project_id, doc_id, callback) {
+    return PackManager.getIndexWithKeys(doc_id, function (err, indexResult) {
+      if (err != null) {
+        return callback(err)
+      }
+      return PackManager.findCompletedPacks(
+        project_id,
+        doc_id,
+        function (err, historyPacks) {
+          let pack
+          if (err != null) {
+            return callback(err)
+          }
+          if (historyPacks == null) {
+            return callback()
+          }
+          // select only the new packs not already in the index
+          let newPacks = (() => {
+            const result = []
+            for (pack of Array.from(historyPacks)) {
+              if (
+                (indexResult != null ? indexResult[pack._id] : undefined) ==
+                null
+              ) {
+                result.push(pack)
+              }
+            }
+            return result
+          })()
+          newPacks = (() => {
+            const result1 = []
+            for (pack of Array.from(newPacks)) {
+              result1.push(
+                _.omit(
+                  pack,
+                  'doc_id',
+                  'project_id',
+                  'n',
+                  'sz',
+                  'last_checked',
+                  'finalised'
+                )
+              )
+            }
+            return result1
+          })()
+          if (newPacks.length) {
+            logger.log(
+              { project_id, doc_id, n: newPacks.length },
+              'found new packs'
+            )
+          }
+          return callback(null, newPacks)
+        }
+      )
+    })
+  },
+
+  insertPacksIntoIndexWithLock(project_id, doc_id, newPacks, callback) {
+    return LockManager.runWithLock(
+      keys.historyIndexLock({ doc_id }),
+      releaseLock =>
+        PackManager._insertPacksIntoIndex(
+          project_id,
+          doc_id,
+          newPacks,
+          releaseLock
+        ),
+      callback
+    )
+  },
+
+  _insertPacksIntoIndex(project_id, doc_id, newPacks, callback) {
+    return db.docHistoryIndex.updateOne(
+      { _id: ObjectId(doc_id.toString()) },
+      {
+        $setOnInsert: { project_id: ObjectId(project_id.toString()) },
+        $push: {
+          packs: { $each: newPacks, $sort: { v: 1 } },
+        },
+      },
+      {
+        upsert: true,
+      },
+      callback
+    )
+  },
+
+  // Archiving packs to S3
+
+  archivePack(project_id, doc_id, pack_id, callback) {
+    const clearFlagOnError = function (err, cb) {
+      if (err != null) {
+        // clear the inS3 flag on error
+        return PackManager.clearPackAsArchiveInProgress(
+          project_id,
+          doc_id,
+          pack_id,
+          function (err2) {
+            if (err2 != null) {
+              return cb(err2)
+            }
+            return cb(err)
+          }
+        )
+      } else {
+        return cb()
+      }
+    }
+    return async.series(
+      [
+        cb =>
+          PackManager.checkArchiveNotInProgress(
+            project_id,
+            doc_id,
+            pack_id,
+            cb
+          ),
+        cb =>
+          PackManager.markPackAsArchiveInProgress(
+            project_id,
+            doc_id,
+            pack_id,
+            cb
+          ),
+        cb =>
+          MongoAWS.archivePack(project_id, doc_id, pack_id, err =>
+            clearFlagOnError(err, cb)
+          ),
+        cb =>
+          PackManager.checkArchivedPack(project_id, doc_id, pack_id, err =>
+            clearFlagOnError(err, cb)
+          ),
+        cb => PackManager.markPackAsArchived(project_id, doc_id, pack_id, cb),
+        cb =>
+          PackManager.setTTLOnArchivedPack(
+            project_id,
+            doc_id,
+            pack_id,
+            callback
+          ),
+      ],
+      callback
+    )
+  },
+
+  checkArchivedPack(project_id, doc_id, pack_id, callback) {
+    return db.docHistory.findOne({ _id: pack_id }, function (err, pack) {
+      if (err != null) {
+        return callback(err)
+      }
+      if (pack == null) {
+        return callback(new Error('pack not found'))
+      }
+      return MongoAWS.readArchivedPack(
+        project_id,
+        doc_id,
+        pack_id,
+        function (err, result) {
+          delete result.last_checked
+          delete pack.last_checked
+          // need to compare ids as ObjectIds with .equals()
+          for (const key of ['_id', 'project_id', 'doc_id']) {
+            if (result[key].equals(pack[key])) {
+              result[key] = pack[key]
+            }
+          }
+          for (let i = 0; i < result.pack.length; i++) {
+            const op = result.pack[i]
+            if (op._id != null && op._id.equals(pack.pack[i]._id)) {
+              op._id = pack.pack[i]._id
+            }
+          }
+          if (_.isEqual(pack, result)) {
+            return callback()
+          } else {
+            logger.err(
+              {
+                pack,
+                result,
+                jsondiff: JSON.stringify(pack) === JSON.stringify(result),
+              },
+              'difference when comparing packs'
+            )
+            return callback(
+              new Error('pack retrieved from s3 does not match pack in mongo')
+            )
+          }
+        }
+      )
+    })
+  },
+  // Extra methods to test archive/unarchive for a doc_id
+
+  pushOldPacks(project_id, doc_id, callback) {
+    return PackManager.findPacks(project_id, doc_id, function (err, packs) {
+      if (err != null) {
+        return callback(err)
+      }
+      if (!(packs != null ? packs.length : undefined)) {
+        return callback()
+      }
+      return PackManager.processOldPack(
+        project_id,
+        doc_id,
+        packs[0]._id,
+        callback
+      )
+    })
+  },
+
+  pullOldPacks(project_id, doc_id, callback) {
+    return PackManager.loadPacksByVersionRange(
+      project_id,
+      doc_id,
+      null,
+      null,
+      callback
+    )
+  },
+
+  // Processing old packs via worker
+
+  processOldPack(project_id, doc_id, pack_id, callback) {
+    const markAsChecked = err =>
+      PackManager.markPackAsChecked(
+        project_id,
+        doc_id,
+        pack_id,
+        function (err2) {
+          if (err2 != null) {
+            return callback(err2)
+          }
+          return callback(err)
+        }
+      )
+    logger.log({ project_id, doc_id }, 'processing old packs')
+    return db.docHistory.findOne({ _id: pack_id }, function (err, pack) {
+      if (err != null) {
+        return markAsChecked(err)
+      }
+      if (pack == null) {
+        return markAsChecked()
+      }
+      if (pack.expiresAt != null) {
+        return callback()
+      } // return directly
+      return PackManager.finaliseIfNeeded(
+        project_id,
+        doc_id,
+        pack._id,
+        pack,
+        function (err) {
+          if (err != null) {
+            return markAsChecked(err)
+          }
+          return PackManager.updateIndexIfNeeded(
+            project_id,
+            doc_id,
+            function (err) {
+              if (err != null) {
+                return markAsChecked(err)
+              }
+              return PackManager.findUnarchivedPacks(
+                project_id,
+                doc_id,
+                function (err, unarchivedPacks) {
+                  if (err != null) {
+                    return markAsChecked(err)
+                  }
+                  if (
+                    !(unarchivedPacks != null
+                      ? unarchivedPacks.length
+                      : undefined)
+                  ) {
+                    logger.log(
+                      { project_id, doc_id },
+                      'no packs need archiving'
+                    )
+                    return markAsChecked()
+                  }
+                  return async.eachSeries(
+                    unarchivedPacks,
+                    (pack, cb) =>
+                      PackManager.archivePack(project_id, doc_id, pack._id, cb),
+                    function (err) {
+                      if (err != null) {
+                        return markAsChecked(err)
+                      }
+                      logger.log({ project_id, doc_id }, 'done processing')
+                      return markAsChecked()
+                    }
+                  )
+                }
+              )
+            }
+          )
+        }
+      )
+    })
+  },
+
+  finaliseIfNeeded(project_id, doc_id, pack_id, pack, callback) {
+    const sz = pack.sz / (1024 * 1024) // in fractions of a megabyte
+    const n = pack.n / 1024 // in fraction of 1024 ops
+    const age = (Date.now() - pack.meta.end_ts) / DAYS
+    if (age < 30) {
+      // always keep if less than 1 month old
+      logger.log({ project_id, doc_id, pack_id, age }, 'less than 30 days old')
+      return callback()
+    }
+    // compute an archiving threshold which decreases for each month of age
+    const archive_threshold = 30 / age
+    if (sz > archive_threshold || n > archive_threshold || age > 90) {
+      logger.log(
+        { project_id, doc_id, pack_id, age, archive_threshold, sz, n },
+        'meets archive threshold'
+      )
+      return PackManager.markPackAsFinalisedWithLock(
+        project_id,
+        doc_id,
+        pack_id,
+        callback
+      )
+    } else {
+      logger.log(
+        { project_id, doc_id, pack_id, age, archive_threshold, sz, n },
+        'does not meet archive threshold'
+      )
+      return callback()
+    }
+  },
+
+  markPackAsFinalisedWithLock(project_id, doc_id, pack_id, callback) {
+    return LockManager.runWithLock(
+      keys.historyLock({ doc_id }),
+      releaseLock =>
+        PackManager._markPackAsFinalised(
+          project_id,
+          doc_id,
+          pack_id,
+          releaseLock
+        ),
+      callback
+    )
+  },
+
+  _markPackAsFinalised(project_id, doc_id, pack_id, callback) {
+    logger.log({ project_id, doc_id, pack_id }, 'marking pack as finalised')
+    return db.docHistory.updateOne(
+      { _id: pack_id },
+      { $set: { finalised: true } },
+      callback
+    )
+  },
+
+  updateIndexIfNeeded(project_id, doc_id, callback) {
+    logger.log({ project_id, doc_id }, 'archiving old packs')
+    return PackManager.getIndexWithKeys(doc_id, function (err, index) {
+      if (err != null) {
+        return callback(err)
+      }
+      if (index == null) {
+        return PackManager.initialiseIndex(project_id, doc_id, callback)
+      } else {
+        return PackManager.updateIndex(project_id, doc_id, callback)
+      }
+    })
+  },
+
+  markPackAsChecked(project_id, doc_id, pack_id, callback) {
+    logger.log({ project_id, doc_id, pack_id }, 'marking pack as checked')
+    return db.docHistory.updateOne(
+      { _id: pack_id },
+      { $currentDate: { last_checked: true } },
+      callback
+    )
+  },
+
+  findUnarchivedPacks(project_id, doc_id, callback) {
+    return PackManager.getIndex(doc_id, function (err, indexResult) {
+      if (err != null) {
+        return callback(err)
+      }
+      const indexPacks =
+        (indexResult != null ? indexResult.packs : undefined) || []
+      const unArchivedPacks = (() => {
+        const result = []
+        for (const pack of Array.from(indexPacks)) {
+          if (pack.inS3 == null) {
+            result.push(pack)
+          }
+        }
+        return result
+      })()
+      if (unArchivedPacks.length) {
+        logger.log(
+          { project_id, doc_id, n: unArchivedPacks.length },
+          'find unarchived packs'
+        )
+      }
+      return callback(null, unArchivedPacks)
+    })
+  },
+
+  // Archive locking flags
+
+  checkArchiveNotInProgress(project_id, doc_id, pack_id, callback) {
+    logger.log(
+      { project_id, doc_id, pack_id },
+      'checking if archive in progress'
+    )
+    return PackManager.getPackFromIndex(
+      doc_id,
+      pack_id,
+      function (err, result) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (result == null) {
+          return callback(new Error('pack not found in index'))
+        }
+        if (result.inS3) {
+          return callback(new Error('pack archiving already done'))
+        } else if (result.inS3 != null) {
+          return callback(new Error('pack archiving already in progress'))
+        } else {
+          return callback()
+        }
+      }
+    )
+  },
+
+  markPackAsArchiveInProgress(project_id, doc_id, pack_id, callback) {
+    logger.log(
+      { project_id, doc_id },
+      'marking pack as archive in progress status'
+    )
+    return db.docHistoryIndex.findOneAndUpdate(
+      {
+        _id: ObjectId(doc_id.toString()),
+        packs: { $elemMatch: { _id: pack_id, inS3: { $exists: false } } },
+      },
+      { $set: { 'packs.$.inS3': false } },
+      { projection: { 'packs.$': 1 } },
+      function (err, result) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (!result.value) {
+          return callback(new Error('archive is already in progress'))
+        }
+        logger.log(
+          { project_id, doc_id, pack_id },
+          'marked as archive in progress'
+        )
+        return callback()
+      }
+    )
+  },
+
+  clearPackAsArchiveInProgress(project_id, doc_id, pack_id, callback) {
+    logger.log(
+      { project_id, doc_id, pack_id },
+      'clearing as archive in progress'
+    )
+    return db.docHistoryIndex.updateOne(
+      {
+        _id: ObjectId(doc_id.toString()),
+        packs: { $elemMatch: { _id: pack_id, inS3: false } },
+      },
+      { $unset: { 'packs.$.inS3': true } },
+      callback
+    )
+  },
+
+  markPackAsArchived(project_id, doc_id, pack_id, callback) {
+    logger.log({ project_id, doc_id, pack_id }, 'marking pack as archived')
+    return db.docHistoryIndex.findOneAndUpdate(
+      {
+        _id: ObjectId(doc_id.toString()),
+        packs: { $elemMatch: { _id: pack_id, inS3: false } },
+      },
+      { $set: { 'packs.$.inS3': true } },
+      { projection: { 'packs.$': 1 } },
+      function (err, result) {
+        if (err != null) {
+          return callback(err)
+        }
+        if (!result.value) {
+          return callback(new Error('archive is not marked as progress'))
+        }
+        logger.log({ project_id, doc_id, pack_id }, 'marked as archived')
+        return callback()
+      }
+    )
+  },
+
+  setTTLOnArchivedPack(project_id, doc_id, pack_id, callback) {
+    return db.docHistory.updateOne(
+      { _id: pack_id },
+      { $set: { expiresAt: new Date(Date.now() + 1 * DAYS) } },
+      function (err) {
+        if (err) {
+          return callback(err)
+        }
+        logger.log({ project_id, doc_id, pack_id }, 'set expiry on pack')
+        return callback()
+      }
+    )
+  },
+}
+
+//	_getOneDayInFutureWithRandomDelay: ->
+//		thirtyMins = 1000 * 60 * 30
+//		randomThirtyMinMax = Math.ceil(Math.random() * thirtyMins)
+//		return new Date(Date.now() + randomThirtyMinMax + 1*DAYS)

services/track-changes/app/js/PackWorker.js

@@ -0,0 +1,212 @@
+/* eslint-disable
+    camelcase,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS103: Rewrite code to no longer use __guard__
+ * DS205: Consider reworking code to avoid use of IIFEs
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let LIMIT, pending
+let project_id, doc_id
+const { callbackify } = require('util')
+const Settings = require('@overleaf/settings')
+const async = require('async')
+const _ = require('underscore')
+const { db, ObjectId, waitForDb, closeDb } = require('./mongodb')
+const fs = require('fs')
+const Metrics = require('@overleaf/metrics')
+Metrics.initialize('track-changes')
+const logger = require('logger-sharelatex')
+logger.initialize('track-changes-packworker')
+if ((Settings.sentry != null ? Settings.sentry.dsn : undefined) != null) {
+  logger.initializeErrorReporting(Settings.sentry.dsn)
+}
+
+const DAYS = 24 * 3600 * 1000
+
+const LockManager = require('./LockManager')
+const PackManager = require('./PackManager')
+
+// this worker script is forked by the main process to look for
+// document histories which can be archived
+
+const source = process.argv[2]
+const DOCUMENT_PACK_DELAY = Number(process.argv[3]) || 1000
+const TIMEOUT = Number(process.argv[4]) || 30 * 60 * 1000
+let COUNT = 0 // number processed
+let TOTAL = 0 // total number to process
+
+if (!source.match(/^[0-9]+$/)) {
+  const file = fs.readFileSync(source)
+  const result = (() => {
+    const result1 = []
+    for (const line of Array.from(file.toString().split('\n'))) {
+      ;[project_id, doc_id] = Array.from(line.split(' '))
+      result1.push({ doc_id, project_id })
+    }
+    return result1
+  })()
+  pending = _.filter(result, row =>
+    __guard__(row != null ? row.doc_id : undefined, x =>
+      x.match(/^[a-f0-9]{24}$/)
+    )
+  )
+} else {
+  LIMIT = Number(process.argv[2]) || 1000
+}
+
+let shutDownRequested = false
+const shutDownTimer = setTimeout(function () {
+  logger.log('pack timed out, requesting shutdown')
+  // start the shutdown on the next pack
+  shutDownRequested = true
+  // do a hard shutdown after a further 5 minutes
+  const hardTimeout = setTimeout(function () {
+    logger.error('HARD TIMEOUT in pack archive worker')
+    return process.exit()
+  }, 5 * 60 * 1000)
+  return hardTimeout.unref()
+}, TIMEOUT)
+
+logger.log(
+  `checking for updates, limit=${LIMIT}, delay=${DOCUMENT_PACK_DELAY}, timeout=${TIMEOUT}`
+)
+
+const finish = function () {
+  if (shutDownTimer != null) {
+    logger.log('cancelling timeout')
+    clearTimeout(shutDownTimer)
+  }
+  logger.log('closing db')
+  callbackify(closeDb)(function () {
+    logger.log('closing LockManager Redis Connection')
+    return LockManager.close(function () {
+      logger.log(
+        { processedCount: COUNT, allCount: TOTAL },
+        'ready to exit from pack archive worker'
+      )
+      const hardTimeout = setTimeout(function () {
+        logger.error('hard exit from pack archive worker')
+        return process.exit(1)
+      }, 5 * 1000)
+      return hardTimeout.unref()
+    })
+  })
+}
+
+process.on('exit', code => logger.log({ code }, 'pack archive worker exited'))
+
+const processUpdates = pending =>
+  async.eachSeries(
+    pending,
+    function (result, callback) {
+      let _id
+      ;({ _id, project_id, doc_id } = result)
+      COUNT++
+      logger.log({ project_id, doc_id }, `processing ${COUNT}/${TOTAL}`)
+      if (project_id == null || doc_id == null) {
+        logger.log(
+          { project_id, doc_id },
+          'skipping pack, missing project/doc id'
+        )
+        return callback()
+      }
+      const handler = function (err, result) {
+        if (err != null && err.code === 'InternalError' && err.retryable) {
+          logger.warn(
+            { err, result },
+            'ignoring S3 error in pack archive worker'
+          )
+          // Ignore any s3 errors due to random problems
+          err = null
+        }
+        if (err != null) {
+          logger.error({ err, result }, 'error in pack archive worker')
+          return callback(err)
+        }
+        if (shutDownRequested) {
+          logger.warn('shutting down pack archive worker')
+          return callback(new Error('shutdown'))
+        }
+        return setTimeout(() => callback(err, result), DOCUMENT_PACK_DELAY)
+      }
+      if (_id == null) {
+        return PackManager.pushOldPacks(project_id, doc_id, handler)
+      } else {
+        return PackManager.processOldPack(project_id, doc_id, _id, handler)
+      }
+    },
+    function (err, results) {
+      if (err != null && err.message !== 'shutdown') {
+        logger.error({ err }, 'error in pack archive worker processUpdates')
+      }
+      return finish()
+    }
+  )
+// find the packs which can be archived
+
+const ObjectIdFromDate = function (date) {
+  const id = Math.floor(date.getTime() / 1000).toString(16) + '0000000000000000'
+  return ObjectId(id)
+}
+
+// new approach, two passes
+// find packs to be marked as finalised:true, those which have a newer pack present
+// then only consider finalised:true packs for archiving
+
+waitForDb()
+  .then(() => {
+    if (pending != null) {
+      logger.log(`got ${pending.length} entries from ${source}`)
+      processUpdates(pending)
+    } else {
+      processFromOneWeekAgo()
+    }
+  })
+  .catch(err => {
+    logger.fatal({ err }, 'cannot connect to mongo, exiting')
+    process.exit(1)
+  })
+
+function processFromOneWeekAgo() {
+  const oneWeekAgo = new Date(Date.now() - 7 * DAYS)
+  db.docHistory
+    .find(
+      {
+        expiresAt: { $exists: false },
+        project_id: { $exists: true },
+        v_end: { $exists: true },
+        _id: { $lt: ObjectIdFromDate(oneWeekAgo) },
+        last_checked: { $lt: oneWeekAgo },
+      },
+      { projection: { _id: 1, doc_id: 1, project_id: 1 } }
+    )
+    .sort({
+      last_checked: 1,
+    })
+    .limit(LIMIT)
+    .toArray(function (err, results) {
+      if (err != null) {
+        logger.log({ err }, 'error checking for updates')
+        finish()
+        return
+      }
+      pending = _.uniq(results, false, result => result.doc_id.toString())
+      TOTAL = pending.length
+      logger.log(`found ${TOTAL} documents to archive`)
+      return processUpdates(pending)
+    })
+}
+
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/app/js/ProjectIterator.js

@@ -0,0 +1,113 @@
+/* eslint-disable
+    no-unmodified-loop-condition,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let ProjectIterator
+const Heap = require('heap')
+
+module.exports =
+  ProjectIterator =
+  ProjectIterator =
+    class ProjectIterator {
+      constructor(packs, before, getPackByIdFn) {
+        this.before = before
+        this.getPackByIdFn = getPackByIdFn
+        const byEndTs = (a, b) =>
+          b.meta.end_ts - a.meta.end_ts || a.fromIndex - b.fromIndex
+        this.packs = packs.slice().sort(byEndTs)
+        this.queue = new Heap(byEndTs)
+      }
+
+      next(callback) {
+        //  what's up next
+        // console.log ">>> top item", iterator.packs[0]
+        const iterator = this
+        const { before } = this
+        const { queue } = iterator
+        const opsToReturn = []
+        let nextPack = iterator.packs[0]
+        let lowWaterMark =
+          (nextPack != null ? nextPack.meta.end_ts : undefined) || 0
+        let nextItem = queue.peek()
+
+        // console.log "queue empty?", queue.empty()
+        // console.log "nextItem", nextItem
+        // console.log "nextItem.meta.end_ts", nextItem?.meta.end_ts
+        // console.log "lowWaterMark", lowWaterMark
+
+        while (
+          before != null &&
+          (nextPack != null ? nextPack.meta.start_ts : undefined) > before
+        ) {
+          // discard pack that is outside range
+          iterator.packs.shift()
+          nextPack = iterator.packs[0]
+          lowWaterMark =
+            (nextPack != null ? nextPack.meta.end_ts : undefined) || 0
+        }
+
+        if (
+          (queue.empty() ||
+            (nextItem != null ? nextItem.meta.end_ts : undefined) <=
+              lowWaterMark) &&
+          nextPack != null
+        ) {
+          // retrieve the next pack and populate the queue
+          return this.getPackByIdFn(
+            nextPack.project_id,
+            nextPack.doc_id,
+            nextPack._id,
+            function (err, pack) {
+              if (err != null) {
+                return callback(err)
+              }
+              iterator.packs.shift() // have now retrieved this pack, remove it
+              // console.log "got pack", pack
+              for (const op of Array.from(pack.pack)) {
+                // console.log "adding op", op
+                if (before == null || op.meta.end_ts < before) {
+                  op.doc_id = nextPack.doc_id
+                  op.project_id = nextPack.project_id
+                  queue.push(op)
+                }
+              }
+              // now try again
+              return iterator.next(callback)
+            }
+          )
+        }
+
+        // console.log "nextItem", nextItem, "lowWaterMark", lowWaterMark
+        while (
+          nextItem != null &&
+          (nextItem != null ? nextItem.meta.end_ts : undefined) > lowWaterMark
+        ) {
+          opsToReturn.push(nextItem)
+          queue.pop()
+          nextItem = queue.peek()
+        }
+
+        // console.log "queue empty?", queue.empty()
+        // console.log "nextPack", nextPack?
+
+        if (queue.empty() && nextPack == null) {
+          // got everything
+          iterator._done = true
+        }
+
+        return callback(null, opsToReturn)
+      }
+
+      done() {
+        return this._done
+      }
+    }

services/track-changes/app/js/RedisManager.js

@@ -0,0 +1,170 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS205: Consider reworking code to avoid use of IIFEs
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let RedisManager
+const Settings = require('@overleaf/settings')
+const redis = require('@overleaf/redis-wrapper')
+const rclient = redis.createClient(Settings.redis.history)
+const Keys = Settings.redis.history.key_schema
+const async = require('async')
+
+module.exports = RedisManager = {
+  getOldestDocUpdates(doc_id, batchSize, callback) {
+    if (callback == null) {
+      callback = function (error, jsonUpdates) {}
+    }
+    const key = Keys.uncompressedHistoryOps({ doc_id })
+    return rclient.lrange(key, 0, batchSize - 1, callback)
+  },
+
+  expandDocUpdates(jsonUpdates, callback) {
+    let rawUpdates
+    if (callback == null) {
+      callback = function (error, rawUpdates) {}
+    }
+    try {
+      rawUpdates = Array.from(jsonUpdates || []).map(update =>
+        JSON.parse(update)
+      )
+    } catch (e) {
+      return callback(e)
+    }
+    return callback(null, rawUpdates)
+  },
+
+  deleteAppliedDocUpdates(project_id, doc_id, docUpdates, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    const multi = rclient.multi()
+    // Delete all the updates which have been applied (exact match)
+    for (const update of Array.from(docUpdates || [])) {
+      multi.lrem(Keys.uncompressedHistoryOps({ doc_id }), 1, update)
+    }
+    return multi.exec(function (error, results) {
+      if (error != null) {
+        return callback(error)
+      }
+      // It's ok to delete the doc_id from the set here. Even though the list
+      // of updates may not be empty, we will continue to process it until it is.
+      return rclient.srem(
+        Keys.docsWithHistoryOps({ project_id }),
+        doc_id,
+        function (error) {
+          if (error != null) {
+            return callback(error)
+          }
+          return callback(null)
+        }
+      )
+    })
+  },
+
+  getDocIdsWithHistoryOps(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, doc_ids) {}
+    }
+    return rclient.smembers(Keys.docsWithHistoryOps({ project_id }), callback)
+  },
+
+  // iterate over keys asynchronously using redis scan (non-blocking)
+  // handle all the cluster nodes or single redis server
+  _getKeys(pattern, callback) {
+    const nodes = (typeof rclient.nodes === 'function'
+      ? rclient.nodes('master')
+      : undefined) || [rclient]
+    const doKeyLookupForNode = (node, cb) =>
+      RedisManager._getKeysFromNode(node, pattern, cb)
+    return async.concatSeries(nodes, doKeyLookupForNode, callback)
+  },
+
+  _getKeysFromNode(node, pattern, callback) {
+    let cursor = 0 // redis iterator
+    const keySet = {} // use hash to avoid duplicate results
+    // scan over all keys looking for pattern
+    var doIteration = cb =>
+      node.scan(
+        cursor,
+        'MATCH',
+        pattern,
+        'COUNT',
+        1000,
+        function (error, reply) {
+          let keys
+          if (error != null) {
+            return callback(error)
+          }
+          ;[cursor, keys] = Array.from(reply)
+          for (const key of Array.from(keys)) {
+            keySet[key] = true
+          }
+          if (cursor === '0') {
+            // note redis returns string result not numeric
+            return callback(null, Object.keys(keySet))
+          } else {
+            return doIteration()
+          }
+        }
+      )
+    return doIteration()
+  },
+
+  // extract ids from keys like DocsWithHistoryOps:57fd0b1f53a8396d22b2c24b
+  // or DocsWithHistoryOps:{57fd0b1f53a8396d22b2c24b} (for redis cluster)
+  _extractIds(keyList) {
+    const ids = (() => {
+      const result = []
+      for (const key of Array.from(keyList)) {
+        const m = key.match(/:\{?([0-9a-f]{24})\}?/) // extract object id
+        result.push(m[1])
+      }
+      return result
+    })()
+    return ids
+  },
+
+  getProjectIdsWithHistoryOps(callback) {
+    if (callback == null) {
+      callback = function (error, project_ids) {}
+    }
+    return RedisManager._getKeys(
+      Keys.docsWithHistoryOps({ project_id: '*' }),
+      function (error, project_keys) {
+        if (error != null) {
+          return callback(error)
+        }
+        const project_ids = RedisManager._extractIds(project_keys)
+        return callback(error, project_ids)
+      }
+    )
+  },
+
+  getAllDocIdsWithHistoryOps(callback) {
+    // return all the docids, to find dangling history entries after
+    // everything is flushed.
+    if (callback == null) {
+      callback = function (error, doc_ids) {}
+    }
+    return RedisManager._getKeys(
+      Keys.uncompressedHistoryOps({ doc_id: '*' }),
+      function (error, doc_keys) {
+        if (error != null) {
+          return callback(error)
+        }
+        const doc_ids = RedisManager._extractIds(doc_keys)
+        return callback(error, doc_ids)
+      }
+    )
+  },
+}

services/track-changes/app/js/RestoreManager.js

@@ -0,0 +1,48 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let RestoreManager
+const DocumentUpdaterManager = require('./DocumentUpdaterManager')
+const DiffManager = require('./DiffManager')
+const logger = require('logger-sharelatex')
+
+module.exports = RestoreManager = {
+  restoreToBeforeVersion(project_id, doc_id, version, user_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    logger.log({ project_id, doc_id, version, user_id }, 'restoring document')
+    return DiffManager.getDocumentBeforeVersion(
+      project_id,
+      doc_id,
+      version,
+      function (error, content) {
+        if (error != null) {
+          return callback(error)
+        }
+        return DocumentUpdaterManager.setDocument(
+          project_id,
+          doc_id,
+          content,
+          user_id,
+          function (error) {
+            if (error != null) {
+              return callback(error)
+            }
+            return callback()
+          }
+        )
+      }
+    )
+  },
+}

services/track-changes/app/js/UpdateCompressor.js

@@ -0,0 +1,340 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    new-cap,
+    no-throw-literal,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS103: Rewrite code to no longer use __guard__
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let oneMinute, twoMegabytes, UpdateCompressor
+const strInject = (s1, pos, s2) => s1.slice(0, pos) + s2 + s1.slice(pos)
+const strRemove = (s1, pos, length) => s1.slice(0, pos) + s1.slice(pos + length)
+
+const { diff_match_patch } = require('../lib/diff_match_patch')
+const dmp = new diff_match_patch()
+
+module.exports = UpdateCompressor = {
+  NOOP: 'noop',
+
+  // Updates come from the doc updater in format
+  // {
+  // 	op:   [ { ... op1 ... }, { ... op2 ... } ]
+  // 	meta: { ts: ..., user_id: ... }
+  // }
+  // but it's easier to work with on op per update, so convert these updates to
+  // our compressed format
+  // [{
+  // 	op: op1
+  // 	meta: { start_ts: ... , end_ts: ..., user_id: ... }
+  // }, {
+  // 	op: op2
+  // 	meta: { start_ts: ... , end_ts: ..., user_id: ... }
+  // }]
+  convertToSingleOpUpdates(updates) {
+    const splitUpdates = []
+    for (const update of Array.from(updates)) {
+      // Reject any non-insert or delete ops, i.e. comments
+      const ops = update.op.filter(o => o.i != null || o.d != null)
+      if (ops.length === 0) {
+        splitUpdates.push({
+          op: UpdateCompressor.NOOP,
+          meta: {
+            start_ts: update.meta.start_ts || update.meta.ts,
+            end_ts: update.meta.end_ts || update.meta.ts,
+            user_id: update.meta.user_id,
+          },
+          v: update.v,
+        })
+      } else {
+        for (const op of Array.from(ops)) {
+          splitUpdates.push({
+            op,
+            meta: {
+              start_ts: update.meta.start_ts || update.meta.ts,
+              end_ts: update.meta.end_ts || update.meta.ts,
+              user_id: update.meta.user_id,
+            },
+            v: update.v,
+          })
+        }
+      }
+    }
+    return splitUpdates
+  },
+
+  concatUpdatesWithSameVersion(updates) {
+    const concattedUpdates = []
+    for (const update of Array.from(updates)) {
+      const lastUpdate = concattedUpdates[concattedUpdates.length - 1]
+      if (lastUpdate != null && lastUpdate.v === update.v) {
+        if (update.op !== UpdateCompressor.NOOP) {
+          lastUpdate.op.push(update.op)
+        }
+      } else {
+        const nextUpdate = {
+          op: [],
+          meta: update.meta,
+          v: update.v,
+        }
+        if (update.op !== UpdateCompressor.NOOP) {
+          nextUpdate.op.push(update.op)
+        }
+        concattedUpdates.push(nextUpdate)
+      }
+    }
+    return concattedUpdates
+  },
+
+  compressRawUpdates(lastPreviousUpdate, rawUpdates) {
+    if (
+      __guard__(
+        lastPreviousUpdate != null ? lastPreviousUpdate.op : undefined,
+        x => x.length
+      ) > 1
+    ) {
+      // if the last previous update was an array op, don't compress onto it.
+      // The avoids cases where array length changes but version number doesn't
+      return [lastPreviousUpdate].concat(
+        UpdateCompressor.compressRawUpdates(null, rawUpdates)
+      )
+    }
+    if (lastPreviousUpdate != null) {
+      rawUpdates = [lastPreviousUpdate].concat(rawUpdates)
+    }
+    let updates = UpdateCompressor.convertToSingleOpUpdates(rawUpdates)
+    updates = UpdateCompressor.compressUpdates(updates)
+    return UpdateCompressor.concatUpdatesWithSameVersion(updates)
+  },
+
+  compressUpdates(updates) {
+    if (updates.length === 0) {
+      return []
+    }
+
+    let compressedUpdates = [updates.shift()]
+    for (const update of Array.from(updates)) {
+      const lastCompressedUpdate = compressedUpdates.pop()
+      if (lastCompressedUpdate != null) {
+        compressedUpdates = compressedUpdates.concat(
+          UpdateCompressor._concatTwoUpdates(lastCompressedUpdate, update)
+        )
+      } else {
+        compressedUpdates.push(update)
+      }
+    }
+
+    return compressedUpdates
+  },
+
+  MAX_TIME_BETWEEN_UPDATES: (oneMinute = 60 * 1000),
+  MAX_UPDATE_SIZE: (twoMegabytes = 2 * 1024 * 1024),
+
+  _concatTwoUpdates(firstUpdate, secondUpdate) {
+    let offset
+    firstUpdate = {
+      op: firstUpdate.op,
+      meta: {
+        user_id: firstUpdate.meta.user_id || null,
+        start_ts: firstUpdate.meta.start_ts || firstUpdate.meta.ts,
+        end_ts: firstUpdate.meta.end_ts || firstUpdate.meta.ts,
+      },
+      v: firstUpdate.v,
+    }
+    secondUpdate = {
+      op: secondUpdate.op,
+      meta: {
+        user_id: secondUpdate.meta.user_id || null,
+        start_ts: secondUpdate.meta.start_ts || secondUpdate.meta.ts,
+        end_ts: secondUpdate.meta.end_ts || secondUpdate.meta.ts,
+      },
+      v: secondUpdate.v,
+    }
+
+    if (firstUpdate.meta.user_id !== secondUpdate.meta.user_id) {
+      return [firstUpdate, secondUpdate]
+    }
+
+    if (
+      secondUpdate.meta.start_ts - firstUpdate.meta.end_ts >
+      UpdateCompressor.MAX_TIME_BETWEEN_UPDATES
+    ) {
+      return [firstUpdate, secondUpdate]
+    }
+
+    const firstOp = firstUpdate.op
+    const secondOp = secondUpdate.op
+
+    const firstSize =
+      (firstOp.i != null ? firstOp.i.length : undefined) ||
+      (firstOp.d != null ? firstOp.d.length : undefined)
+    const secondSize =
+      (secondOp.i != null ? secondOp.i.length : undefined) ||
+      (secondOp.d != null ? secondOp.d.length : undefined)
+
+    // Two inserts
+    if (
+      firstOp.i != null &&
+      secondOp.i != null &&
+      firstOp.p <= secondOp.p &&
+      secondOp.p <= firstOp.p + firstOp.i.length &&
+      firstSize + secondSize < UpdateCompressor.MAX_UPDATE_SIZE
+    ) {
+      return [
+        {
+          meta: {
+            start_ts: firstUpdate.meta.start_ts,
+            end_ts: secondUpdate.meta.end_ts,
+            user_id: firstUpdate.meta.user_id,
+          },
+          op: {
+            p: firstOp.p,
+            i: strInject(firstOp.i, secondOp.p - firstOp.p, secondOp.i),
+          },
+          v: secondUpdate.v,
+        },
+      ]
+      // Two deletes
+    } else if (
+      firstOp.d != null &&
+      secondOp.d != null &&
+      secondOp.p <= firstOp.p &&
+      firstOp.p <= secondOp.p + secondOp.d.length &&
+      firstSize + secondSize < UpdateCompressor.MAX_UPDATE_SIZE
+    ) {
+      return [
+        {
+          meta: {
+            start_ts: firstUpdate.meta.start_ts,
+            end_ts: secondUpdate.meta.end_ts,
+            user_id: firstUpdate.meta.user_id,
+          },
+          op: {
+            p: secondOp.p,
+            d: strInject(secondOp.d, firstOp.p - secondOp.p, firstOp.d),
+          },
+          v: secondUpdate.v,
+        },
+      ]
+      // An insert and then a delete
+    } else if (
+      firstOp.i != null &&
+      secondOp.d != null &&
+      firstOp.p <= secondOp.p &&
+      secondOp.p <= firstOp.p + firstOp.i.length
+    ) {
+      offset = secondOp.p - firstOp.p
+      const insertedText = firstOp.i.slice(offset, offset + secondOp.d.length)
+      // Only trim the insert when the delete is fully contained within in it
+      if (insertedText === secondOp.d) {
+        const insert = strRemove(firstOp.i, offset, secondOp.d.length)
+        return [
+          {
+            meta: {
+              start_ts: firstUpdate.meta.start_ts,
+              end_ts: secondUpdate.meta.end_ts,
+              user_id: firstUpdate.meta.user_id,
+            },
+            op: {
+              p: firstOp.p,
+              i: insert,
+            },
+            v: secondUpdate.v,
+          },
+        ]
+      } else {
+        // This will only happen if the delete extends outside the insert
+        return [firstUpdate, secondUpdate]
+      }
+
+      // A delete then an insert at the same place, likely a copy-paste of a chunk of content
+    } else if (
+      firstOp.d != null &&
+      secondOp.i != null &&
+      firstOp.p === secondOp.p
+    ) {
+      offset = firstOp.p
+      const diff_ops = this.diffAsShareJsOps(firstOp.d, secondOp.i)
+      if (diff_ops.length === 0) {
+        return [
+          {
+            // Noop
+            meta: {
+              start_ts: firstUpdate.meta.start_ts,
+              end_ts: secondUpdate.meta.end_ts,
+              user_id: firstUpdate.meta.user_id,
+            },
+            op: {
+              p: firstOp.p,
+              i: '',
+            },
+            v: secondUpdate.v,
+          },
+        ]
+      } else {
+        return diff_ops.map(function (op) {
+          op.p += offset
+          return {
+            meta: {
+              start_ts: firstUpdate.meta.start_ts,
+              end_ts: secondUpdate.meta.end_ts,
+              user_id: firstUpdate.meta.user_id,
+            },
+            op,
+            v: secondUpdate.v,
+          }
+        })
+      }
+    } else {
+      return [firstUpdate, secondUpdate]
+    }
+  },
+
+  ADDED: 1,
+  REMOVED: -1,
+  UNCHANGED: 0,
+  diffAsShareJsOps(before, after, callback) {
+    if (callback == null) {
+      callback = function (error, ops) {}
+    }
+    const diffs = dmp.diff_main(before, after)
+    dmp.diff_cleanupSemantic(diffs)
+
+    const ops = []
+    let position = 0
+    for (const diff of Array.from(diffs)) {
+      const type = diff[0]
+      const content = diff[1]
+      if (type === this.ADDED) {
+        ops.push({
+          i: content,
+          p: position,
+        })
+        position += content.length
+      } else if (type === this.REMOVED) {
+        ops.push({
+          d: content,
+          p: position,
+        })
+      } else if (type === this.UNCHANGED) {
+        position += content.length
+      } else {
+        throw 'Unknown type'
+      }
+    }
+    return ops
+  },
+}
+
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/app/js/UpdateTrimmer.js

@@ -0,0 +1,80 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS103: Rewrite code to no longer use __guard__
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let UpdateTrimmer
+const MongoManager = require('./MongoManager')
+const WebApiManager = require('./WebApiManager')
+const logger = require('logger-sharelatex')
+
+module.exports = UpdateTrimmer = {
+  shouldTrimUpdates(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, shouldTrim) {}
+    }
+    return MongoManager.getProjectMetaData(
+      project_id,
+      function (error, metadata) {
+        if (error != null) {
+          return callback(error)
+        }
+        if (metadata != null ? metadata.preserveHistory : undefined) {
+          return callback(null, false)
+        } else {
+          return WebApiManager.getProjectDetails(
+            project_id,
+            function (error, details) {
+              if (error != null) {
+                return callback(error)
+              }
+              logger.log({ project_id, details }, 'got details')
+              if (
+                __guard__(
+                  details != null ? details.features : undefined,
+                  x => x.versioning
+                )
+              ) {
+                return MongoManager.setProjectMetaData(
+                  project_id,
+                  { preserveHistory: true },
+                  function (error) {
+                    if (error != null) {
+                      return callback(error)
+                    }
+                    return MongoManager.upgradeHistory(
+                      project_id,
+                      function (error) {
+                        if (error != null) {
+                          return callback(error)
+                        }
+                        return callback(null, false)
+                      }
+                    )
+                  }
+                )
+              } else {
+                return callback(null, true)
+              }
+            }
+          )
+        }
+      }
+    )
+  },
+}
+
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/app/js/UpdatesManager.js

@@ -0,0 +1,888 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS103: Rewrite code to no longer use __guard__
+ * DS205: Consider reworking code to avoid use of IIFEs
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let fiveMinutes, UpdatesManager
+const MongoManager = require('./MongoManager')
+const PackManager = require('./PackManager')
+const RedisManager = require('./RedisManager')
+const UpdateCompressor = require('./UpdateCompressor')
+const LockManager = require('./LockManager')
+const WebApiManager = require('./WebApiManager')
+const UpdateTrimmer = require('./UpdateTrimmer')
+const logger = require('logger-sharelatex')
+const async = require('async')
+const _ = require('underscore')
+const Settings = require('@overleaf/settings')
+const keys = Settings.redis.lock.key_schema
+
+module.exports = UpdatesManager = {
+  compressAndSaveRawUpdates(
+    project_id,
+    doc_id,
+    rawUpdates,
+    temporary,
+    callback
+  ) {
+    let i
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    const { length } = rawUpdates
+    if (length === 0) {
+      return callback()
+    }
+
+    // check that ops are in the correct order
+    for (i = 0; i < rawUpdates.length; i++) {
+      const op = rawUpdates[i]
+      if (i > 0) {
+        const thisVersion = op != null ? op.v : undefined
+        const prevVersion = __guard__(rawUpdates[i - 1], x => x.v)
+        if (!(prevVersion < thisVersion)) {
+          logger.error(
+            {
+              project_id,
+              doc_id,
+              rawUpdates,
+              temporary,
+              thisVersion,
+              prevVersion,
+            },
+            'op versions out of order'
+          )
+        }
+      }
+    }
+
+    // FIXME: we no longer need the lastCompressedUpdate, so change functions not to need it
+    // CORRECTION:  we do use it to log the time in case of error
+    return MongoManager.peekLastCompressedUpdate(
+      doc_id,
+      function (error, lastCompressedUpdate, lastVersion) {
+        // lastCompressedUpdate is the most recent update in Mongo, and
+        // lastVersion is its sharejs version number.
+        //
+        // The peekLastCompressedUpdate method may pass the update back
+        // as 'null' (for example if the previous compressed update has
+        // been archived).  In this case it can still pass back the
+        // lastVersion from the update to allow us to check consistency.
+        let op
+        if (error != null) {
+          return callback(error)
+        }
+
+        // Ensure that raw updates start where lastVersion left off
+        if (lastVersion != null) {
+          const discardedUpdates = []
+          rawUpdates = rawUpdates.slice(0)
+          while (rawUpdates[0] != null && rawUpdates[0].v <= lastVersion) {
+            discardedUpdates.push(rawUpdates.shift())
+          }
+          if (discardedUpdates.length) {
+            logger.error(
+              { project_id, doc_id, discardedUpdates, temporary, lastVersion },
+              'discarded updates already present'
+            )
+          }
+
+          if (rawUpdates[0] != null && rawUpdates[0].v !== lastVersion + 1) {
+            const ts = __guard__(
+              lastCompressedUpdate != null
+                ? lastCompressedUpdate.meta
+                : undefined,
+              x1 => x1.end_ts
+            )
+            const last_timestamp = ts != null ? new Date(ts) : 'unknown time'
+            error = new Error(
+              `Tried to apply raw op at version ${rawUpdates[0].v} to last compressed update with version ${lastVersion} from ${last_timestamp}`
+            )
+            logger.error(
+              {
+                err: error,
+                doc_id,
+                project_id,
+                prev_end_ts: ts,
+                temporary,
+                lastCompressedUpdate,
+              },
+              'inconsistent doc versions'
+            )
+            if (
+              (Settings.trackchanges != null
+                ? Settings.trackchanges.continueOnError
+                : undefined) &&
+              rawUpdates[0].v > lastVersion + 1
+            ) {
+              // we have lost some ops - continue to write into the database, we can't recover at this point
+              lastCompressedUpdate = null
+            } else {
+              return callback(error)
+            }
+          }
+        }
+
+        if (rawUpdates.length === 0) {
+          return callback()
+        }
+
+        // some old large ops in redis need to be rejected, they predate
+        // the size limit that now prevents them going through the system
+        const REJECT_LARGE_OP_SIZE = 4 * 1024 * 1024
+        for (var rawUpdate of Array.from(rawUpdates)) {
+          const opSizes = (() => {
+            const result = []
+            for (op of Array.from(
+              (rawUpdate != null ? rawUpdate.op : undefined) || []
+            )) {
+              result.push(
+                (op.i != null ? op.i.length : undefined) ||
+                  (op.d != null ? op.d.length : undefined)
+              )
+            }
+            return result
+          })()
+          const size = _.max(opSizes)
+          if (size > REJECT_LARGE_OP_SIZE) {
+            error = new Error(
+              `dropped op exceeding maximum allowed size of ${REJECT_LARGE_OP_SIZE}`
+            )
+            logger.error(
+              { err: error, doc_id, project_id, size, rawUpdate },
+              'dropped op - too big'
+            )
+            rawUpdate.op = []
+          }
+        }
+
+        const compressedUpdates = UpdateCompressor.compressRawUpdates(
+          null,
+          rawUpdates
+        )
+        return PackManager.insertCompressedUpdates(
+          project_id,
+          doc_id,
+          lastCompressedUpdate,
+          compressedUpdates,
+          temporary,
+          function (error, result) {
+            if (error != null) {
+              return callback(error)
+            }
+            if (result != null) {
+              logger.log(
+                {
+                  project_id,
+                  doc_id,
+                  orig_v:
+                    lastCompressedUpdate != null
+                      ? lastCompressedUpdate.v
+                      : undefined,
+                  new_v: result.v,
+                },
+                'inserted updates into pack'
+              )
+            }
+            return callback()
+          }
+        )
+      }
+    )
+  },
+
+  // Check whether the updates are temporary (per-project property)
+  _prepareProjectForUpdates(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, temporary) {}
+    }
+    return UpdateTrimmer.shouldTrimUpdates(
+      project_id,
+      function (error, temporary) {
+        if (error != null) {
+          return callback(error)
+        }
+        return callback(null, temporary)
+      }
+    )
+  },
+
+  // Check for project id on document history (per-document property)
+  _prepareDocForUpdates(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return MongoManager.backportProjectId(project_id, doc_id, function (error) {
+      if (error != null) {
+        return callback(error)
+      }
+      return callback(null)
+    })
+  },
+
+  // Apply updates for specific project/doc after preparing at project and doc level
+  REDIS_READ_BATCH_SIZE: 100,
+  processUncompressedUpdates(project_id, doc_id, temporary, callback) {
+    // get the updates as strings from redis (so we can delete them after they are applied)
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return RedisManager.getOldestDocUpdates(
+      doc_id,
+      UpdatesManager.REDIS_READ_BATCH_SIZE,
+      function (error, docUpdates) {
+        if (error != null) {
+          return callback(error)
+        }
+        const { length } = docUpdates
+        // parse the redis strings into ShareJs updates
+        return RedisManager.expandDocUpdates(
+          docUpdates,
+          function (error, rawUpdates) {
+            if (error != null) {
+              logger.err(
+                { project_id, doc_id, docUpdates },
+                'failed to parse docUpdates'
+              )
+              return callback(error)
+            }
+            logger.log(
+              { project_id, doc_id, rawUpdates },
+              'retrieved raw updates from redis'
+            )
+            return UpdatesManager.compressAndSaveRawUpdates(
+              project_id,
+              doc_id,
+              rawUpdates,
+              temporary,
+              function (error) {
+                if (error != null) {
+                  return callback(error)
+                }
+                logger.log(
+                  { project_id, doc_id },
+                  'compressed and saved doc updates'
+                )
+                // delete the applied updates from redis
+                return RedisManager.deleteAppliedDocUpdates(
+                  project_id,
+                  doc_id,
+                  docUpdates,
+                  function (error) {
+                    if (error != null) {
+                      return callback(error)
+                    }
+                    if (length === UpdatesManager.REDIS_READ_BATCH_SIZE) {
+                      // There might be more updates
+                      logger.log(
+                        { project_id, doc_id },
+                        'continuing processing updates'
+                      )
+                      return setTimeout(
+                        () =>
+                          UpdatesManager.processUncompressedUpdates(
+                            project_id,
+                            doc_id,
+                            temporary,
+                            callback
+                          ),
+                        0
+                      )
+                    } else {
+                      logger.log(
+                        { project_id, doc_id },
+                        'all raw updates processed'
+                      )
+                      return callback()
+                    }
+                  }
+                )
+              }
+            )
+          }
+        )
+      }
+    )
+  },
+
+  // Process updates for a doc when we flush it individually
+  processUncompressedUpdatesWithLock(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return UpdatesManager._prepareProjectForUpdates(
+      project_id,
+      function (error, temporary) {
+        if (error != null) {
+          return callback(error)
+        }
+        return UpdatesManager._processUncompressedUpdatesForDocWithLock(
+          project_id,
+          doc_id,
+          temporary,
+          callback
+        )
+      }
+    )
+  },
+
+  // Process updates for a doc when the whole project is flushed (internal method)
+  _processUncompressedUpdatesForDocWithLock(
+    project_id,
+    doc_id,
+    temporary,
+    callback
+  ) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return UpdatesManager._prepareDocForUpdates(
+      project_id,
+      doc_id,
+      function (error) {
+        if (error != null) {
+          return callback(error)
+        }
+        return LockManager.runWithLock(
+          keys.historyLock({ doc_id }),
+          releaseLock =>
+            UpdatesManager.processUncompressedUpdates(
+              project_id,
+              doc_id,
+              temporary,
+              releaseLock
+            ),
+          callback
+        )
+      }
+    )
+  },
+
+  // Process all updates for a project, only check project-level information once
+  processUncompressedUpdatesForProject(project_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return RedisManager.getDocIdsWithHistoryOps(
+      project_id,
+      function (error, doc_ids) {
+        if (error != null) {
+          return callback(error)
+        }
+        return UpdatesManager._prepareProjectForUpdates(
+          project_id,
+          function (error, temporary) {
+            const jobs = []
+            for (const doc_id of Array.from(doc_ids)) {
+              ;(doc_id =>
+                jobs.push(cb =>
+                  UpdatesManager._processUncompressedUpdatesForDocWithLock(
+                    project_id,
+                    doc_id,
+                    temporary,
+                    cb
+                  )
+                ))(doc_id)
+            }
+            return async.parallelLimit(jobs, 5, callback)
+          }
+        )
+      }
+    )
+  },
+
+  // flush all outstanding changes
+  flushAll(limit, callback) {
+    if (callback == null) {
+      callback = function (error, result) {}
+    }
+    return RedisManager.getProjectIdsWithHistoryOps(function (
+      error,
+      project_ids
+    ) {
+      let project_id
+      if (error != null) {
+        return callback(error)
+      }
+      logger.log(
+        {
+          count: project_ids != null ? project_ids.length : undefined,
+          project_ids,
+        },
+        'found projects'
+      )
+      const jobs = []
+      project_ids = _.shuffle(project_ids) // randomise to avoid hitting same projects each time
+      const selectedProjects =
+        limit < 0 ? project_ids : project_ids.slice(0, limit)
+      for (project_id of Array.from(selectedProjects)) {
+        ;(project_id =>
+          jobs.push(cb =>
+            UpdatesManager.processUncompressedUpdatesForProject(
+              project_id,
+              err => cb(null, { failed: err != null, project_id })
+            )
+          ))(project_id)
+      }
+      return async.series(jobs, function (error, result) {
+        let x
+        if (error != null) {
+          return callback(error)
+        }
+        const failedProjects = (() => {
+          const result1 = []
+          for (x of Array.from(result)) {
+            if (x.failed) {
+              result1.push(x.project_id)
+            }
+          }
+          return result1
+        })()
+        const succeededProjects = (() => {
+          const result2 = []
+          for (x of Array.from(result)) {
+            if (!x.failed) {
+              result2.push(x.project_id)
+            }
+          }
+          return result2
+        })()
+        return callback(null, {
+          failed: failedProjects,
+          succeeded: succeededProjects,
+          all: project_ids,
+        })
+      })
+    })
+  },
+
+  getDanglingUpdates(callback) {
+    if (callback == null) {
+      callback = function (error, doc_ids) {}
+    }
+    return RedisManager.getAllDocIdsWithHistoryOps(function (
+      error,
+      all_doc_ids
+    ) {
+      if (error != null) {
+        return callback(error)
+      }
+      return RedisManager.getProjectIdsWithHistoryOps(function (
+        error,
+        all_project_ids
+      ) {
+        if (error != null) {
+          return callback(error)
+        }
+        // function to get doc_ids for each project
+        const task = cb =>
+          async.concatSeries(
+            all_project_ids,
+            RedisManager.getDocIdsWithHistoryOps,
+            cb
+          )
+        // find the dangling doc ids
+        return task(function (error, project_doc_ids) {
+          const dangling_doc_ids = _.difference(all_doc_ids, project_doc_ids)
+          logger.log(
+            { all_doc_ids, all_project_ids, project_doc_ids, dangling_doc_ids },
+            'checking for dangling doc ids'
+          )
+          return callback(null, dangling_doc_ids)
+        })
+      })
+    })
+  },
+
+  getDocUpdates(project_id, doc_id, options, callback) {
+    if (options == null) {
+      options = {}
+    }
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    return UpdatesManager.processUncompressedUpdatesWithLock(
+      project_id,
+      doc_id,
+      function (error) {
+        if (error != null) {
+          return callback(error)
+        }
+        // console.log "options", options
+        return PackManager.getOpsByVersionRange(
+          project_id,
+          doc_id,
+          options.from,
+          options.to,
+          function (error, updates) {
+            if (error != null) {
+              return callback(error)
+            }
+            return callback(null, updates)
+          }
+        )
+      }
+    )
+  },
+
+  getDocUpdatesWithUserInfo(project_id, doc_id, options, callback) {
+    if (options == null) {
+      options = {}
+    }
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    return UpdatesManager.getDocUpdates(
+      project_id,
+      doc_id,
+      options,
+      function (error, updates) {
+        if (error != null) {
+          return callback(error)
+        }
+        return UpdatesManager.fillUserInfo(updates, function (error, updates) {
+          if (error != null) {
+            return callback(error)
+          }
+          return callback(null, updates)
+        })
+      }
+    )
+  },
+
+  getSummarizedProjectUpdates(project_id, options, callback) {
+    if (options == null) {
+      options = {}
+    }
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    if (!options.min_count) {
+      options.min_count = 25
+    }
+    let summarizedUpdates = []
+    const { before } = options
+    let nextBeforeTimestamp = null
+    return UpdatesManager.processUncompressedUpdatesForProject(
+      project_id,
+      function (error) {
+        if (error != null) {
+          return callback(error)
+        }
+        return PackManager.makeProjectIterator(
+          project_id,
+          before,
+          function (err, iterator) {
+            if (err != null) {
+              return callback(err)
+            }
+            // repeatedly get updates and pass them through the summariser to get an final output with user info
+            return async.whilst(
+              () =>
+                // console.log "checking iterator.done", iterator.done()
+                summarizedUpdates.length < options.min_count &&
+                !iterator.done(),
+
+              cb =>
+                iterator.next(function (err, partialUpdates) {
+                  if (err != null) {
+                    return callback(err)
+                  }
+                  // logger.log {partialUpdates}, 'got partialUpdates'
+                  if (partialUpdates.length === 0) {
+                    return cb()
+                  } // # FIXME should try to avoid this happening
+                  nextBeforeTimestamp =
+                    partialUpdates[partialUpdates.length - 1].meta.end_ts
+                  // add the updates to the summary list
+                  summarizedUpdates = UpdatesManager._summarizeUpdates(
+                    partialUpdates,
+                    summarizedUpdates
+                  )
+                  return cb()
+                }),
+
+              () =>
+                // finally done all updates
+                // console.log 'summarized Updates', summarizedUpdates
+                UpdatesManager.fillSummarizedUserInfo(
+                  summarizedUpdates,
+                  function (err, results) {
+                    if (err != null) {
+                      return callback(err)
+                    }
+                    return callback(
+                      null,
+                      results,
+                      !iterator.done() ? nextBeforeTimestamp : undefined
+                    )
+                  }
+                )
+            )
+          }
+        )
+      }
+    )
+  },
+
+  exportProject(projectId, consumer) {
+    // Flush anything before collecting updates.
+    UpdatesManager.processUncompressedUpdatesForProject(projectId, err => {
+      if (err) return consumer(err)
+
+      // Fetch all the packs.
+      const before = undefined
+      PackManager.makeProjectIterator(projectId, before, (err, iterator) => {
+        if (err) return consumer(err)
+
+        const accumulatedUserIds = new Set()
+
+        async.whilst(
+          () => !iterator.done(),
+
+          cb =>
+            iterator.next((err, updatesFromASinglePack) => {
+              if (err) return cb(err)
+
+              if (updatesFromASinglePack.length === 0) {
+                // This should not happen when `iterator.done() == false`.
+                // Emitting an empty array would signal the consumer the final
+                //  call.
+                return cb()
+              }
+              updatesFromASinglePack.forEach(update => {
+                accumulatedUserIds.add(
+                  // Super defensive access on update details.
+                  String(update && update.meta && update.meta.user_id)
+                )
+              })
+              // Emit updates and wait for the consumer.
+              consumer(null, { updates: updatesFromASinglePack }, cb)
+            }),
+
+          err => {
+            if (err) return consumer(err)
+
+            // Adding undefined can happen for broken updates.
+            accumulatedUserIds.delete('undefined')
+
+            consumer(null, {
+              updates: [],
+              userIds: Array.from(accumulatedUserIds).sort(),
+            })
+          }
+        )
+      })
+    })
+  },
+
+  fetchUserInfo(users, callback) {
+    if (callback == null) {
+      callback = function (error, fetchedUserInfo) {}
+    }
+    const jobs = []
+    const fetchedUserInfo = {}
+    for (const user_id in users) {
+      ;(user_id =>
+        jobs.push(callback =>
+          WebApiManager.getUserInfo(user_id, function (error, userInfo) {
+            if (error != null) {
+              return callback(error)
+            }
+            fetchedUserInfo[user_id] = userInfo
+            return callback()
+          })
+        ))(user_id)
+    }
+
+    return async.series(jobs, function (err) {
+      if (err != null) {
+        return callback(err)
+      }
+      return callback(null, fetchedUserInfo)
+    })
+  },
+
+  fillUserInfo(updates, callback) {
+    let update, user_id
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    const users = {}
+    for (update of Array.from(updates)) {
+      ;({ user_id } = update.meta)
+      if (UpdatesManager._validUserId(user_id)) {
+        users[user_id] = true
+      }
+    }
+
+    return UpdatesManager.fetchUserInfo(
+      users,
+      function (error, fetchedUserInfo) {
+        if (error != null) {
+          return callback(error)
+        }
+        for (update of Array.from(updates)) {
+          ;({ user_id } = update.meta)
+          delete update.meta.user_id
+          if (UpdatesManager._validUserId(user_id)) {
+            update.meta.user = fetchedUserInfo[user_id]
+          }
+        }
+        return callback(null, updates)
+      }
+    )
+  },
+
+  fillSummarizedUserInfo(updates, callback) {
+    let update, user_id, user_ids
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    const users = {}
+    for (update of Array.from(updates)) {
+      user_ids = update.meta.user_ids || []
+      for (user_id of Array.from(user_ids)) {
+        if (UpdatesManager._validUserId(user_id)) {
+          users[user_id] = true
+        }
+      }
+    }
+
+    return UpdatesManager.fetchUserInfo(
+      users,
+      function (error, fetchedUserInfo) {
+        if (error != null) {
+          return callback(error)
+        }
+        for (update of Array.from(updates)) {
+          user_ids = update.meta.user_ids || []
+          update.meta.users = []
+          delete update.meta.user_ids
+          for (user_id of Array.from(user_ids)) {
+            if (UpdatesManager._validUserId(user_id)) {
+              update.meta.users.push(fetchedUserInfo[user_id])
+            } else {
+              update.meta.users.push(null)
+            }
+          }
+        }
+        return callback(null, updates)
+      }
+    )
+  },
+
+  _validUserId(user_id) {
+    if (user_id == null) {
+      return false
+    } else {
+      return !!user_id.match(/^[a-f0-9]{24}$/)
+    }
+  },
+
+  TIME_BETWEEN_DISTINCT_UPDATES: (fiveMinutes = 5 * 60 * 1000),
+  SPLIT_ON_DELETE_SIZE: 16, // characters
+  _summarizeUpdates(updates, existingSummarizedUpdates) {
+    if (existingSummarizedUpdates == null) {
+      existingSummarizedUpdates = []
+    }
+    const summarizedUpdates = existingSummarizedUpdates.slice()
+    let previousUpdateWasBigDelete = false
+    for (const update of Array.from(updates)) {
+      var doc_id
+      const earliestUpdate = summarizedUpdates[summarizedUpdates.length - 1]
+      let shouldConcat = false
+
+      // If a user inserts some text, then deletes a big chunk including that text,
+      // the update we show might concat the insert and delete, and there will be no sign
+      // of that insert having happened, or be able to restore to it (restoring after a big delete is common).
+      // So, we split the summary on 'big' deletes. However, we've stepping backwards in time with
+      // most recent changes considered first, so if this update is a big delete, we want to start
+      // a new summarized update next timge, hence we monitor the previous update.
+      if (previousUpdateWasBigDelete) {
+        shouldConcat = false
+      } else if (
+        earliestUpdate &&
+        earliestUpdate.meta.end_ts - update.meta.start_ts <
+          this.TIME_BETWEEN_DISTINCT_UPDATES
+      ) {
+        // We're going backwards in time through the updates, so only combine if this update starts less than 5 minutes before
+        // the end of current summarized block, so no block spans more than 5 minutes.
+        shouldConcat = true
+      }
+
+      let isBigDelete = false
+      for (const op of Array.from(update.op || [])) {
+        if (op.d != null && op.d.length > this.SPLIT_ON_DELETE_SIZE) {
+          isBigDelete = true
+        }
+      }
+
+      previousUpdateWasBigDelete = isBigDelete
+
+      if (shouldConcat) {
+        // check if the user in this update is already present in the earliest update,
+        // if not, add them to the users list of the earliest update
+        earliestUpdate.meta.user_ids = _.union(earliestUpdate.meta.user_ids, [
+          update.meta.user_id,
+        ])
+
+        doc_id = update.doc_id.toString()
+        const doc = earliestUpdate.docs[doc_id]
+        if (doc != null) {
+          doc.fromV = Math.min(doc.fromV, update.v)
+          doc.toV = Math.max(doc.toV, update.v)
+        } else {
+          earliestUpdate.docs[doc_id] = {
+            fromV: update.v,
+            toV: update.v,
+          }
+        }
+
+        earliestUpdate.meta.start_ts = Math.min(
+          earliestUpdate.meta.start_ts,
+          update.meta.start_ts
+        )
+        earliestUpdate.meta.end_ts = Math.max(
+          earliestUpdate.meta.end_ts,
+          update.meta.end_ts
+        )
+      } else {
+        const newUpdate = {
+          meta: {
+            user_ids: [],
+            start_ts: update.meta.start_ts,
+            end_ts: update.meta.end_ts,
+          },
+          docs: {},
+        }
+
+        newUpdate.docs[update.doc_id.toString()] = {
+          fromV: update.v,
+          toV: update.v,
+        }
+        newUpdate.meta.user_ids.push(update.meta.user_id)
+        summarizedUpdates.push(newUpdate)
+      }
+    }
+
+    return summarizedUpdates
+  },
+}
+
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/app/js/WebApiManager.js

@@ -0,0 +1,116 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let WebApiManager
+const request = require('requestretry') // allow retry on error https://github.com/FGRibreau/node-request-retry
+const logger = require('logger-sharelatex')
+const Settings = require('@overleaf/settings')
+
+// Don't let HTTP calls hang for a long time
+const MAX_HTTP_REQUEST_LENGTH = 15000 // 15 seconds
+
+// DEPRECATED! This method of getting user details via track-changes is deprecated
+// in the way we lay out our services.
+// Instead, web should be responsible for collecting the raw data (user_ids) and
+// filling it out with calls to other services. All API calls should create a
+// tree-like structure as much as possible, with web as the root.
+module.exports = WebApiManager = {
+  sendRequest(url, callback) {
+    if (callback == null) {
+      callback = function (error, body) {}
+    }
+    return request.get(
+      {
+        url: `${Settings.apis.web.url}${url}`,
+        timeout: MAX_HTTP_REQUEST_LENGTH,
+        maxAttempts: 2, // for node-request-retry
+        auth: {
+          user: Settings.apis.web.user,
+          pass: Settings.apis.web.pass,
+          sendImmediately: true,
+        },
+      },
+      function (error, res, body) {
+        if (error != null) {
+          return callback(error)
+        }
+        if (res.statusCode === 404) {
+          logger.log({ url }, 'got 404 from web api')
+          return callback(null, null)
+        }
+        if (res.statusCode >= 200 && res.statusCode < 300) {
+          return callback(null, body)
+        } else {
+          error = new Error(
+            `web returned a non-success status code: ${res.statusCode} (attempts: ${res.attempts})`
+          )
+          return callback(error)
+        }
+      }
+    )
+  },
+
+  getUserInfo(user_id, callback) {
+    if (callback == null) {
+      callback = function (error, userInfo) {}
+    }
+    const url = `/user/${user_id}/personal_info`
+    logger.log({ user_id }, 'getting user info from web')
+    return WebApiManager.sendRequest(url, function (error, body) {
+      let user
+      if (error != null) {
+        logger.error({ err: error, user_id, url }, 'error accessing web')
+        return callback(error)
+      }
+
+      if (body === null) {
+        logger.error({ user_id, url }, 'no user found')
+        return callback(null, null)
+      }
+      try {
+        user = JSON.parse(body)
+      } catch (error1) {
+        error = error1
+        return callback(error)
+      }
+      return callback(null, {
+        id: user.id,
+        email: user.email,
+        first_name: user.first_name,
+        last_name: user.last_name,
+      })
+    })
+  },
+
+  getProjectDetails(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, details) {}
+    }
+    const url = `/project/${project_id}/details`
+    logger.log({ project_id }, 'getting project details from web')
+    return WebApiManager.sendRequest(url, function (error, body) {
+      let project
+      if (error != null) {
+        logger.error({ err: error, project_id, url }, 'error accessing web')
+        return callback(error)
+      }
+
+      try {
+        project = JSON.parse(body)
+      } catch (error1) {
+        error = error1
+        return callback(error)
+      }
+      return callback(null, project)
+    })
+  },
+}

services/track-changes/app/js/mongodb.js

@@ -0,0 +1,42 @@
+const Settings = require('@overleaf/settings')
+const { MongoClient, ObjectId } = require('mongodb')
+
+const clientPromise = MongoClient.connect(
+  Settings.mongo.url,
+  Settings.mongo.options
+)
+
+let setupDbPromise
+async function waitForDb() {
+  if (!setupDbPromise) {
+    setupDbPromise = setupDb()
+  }
+  await setupDbPromise
+}
+
+const db = {}
+async function setupDb() {
+  const internalDb = (await clientPromise).db()
+
+  db.docHistory = internalDb.collection('docHistory')
+  db.docHistoryIndex = internalDb.collection('docHistoryIndex')
+  db.projectHistoryMetaData = internalDb.collection('projectHistoryMetaData')
+}
+
+async function closeDb() {
+  let client
+  try {
+    client = await clientPromise
+  } catch (e) {
+    // there is nothing to close
+    return
+  }
+  return client.close()
+}
+
+module.exports = {
+  db,
+  ObjectId,
+  closeDb,
+  waitForDb,
+}

services/track-changes/app/lib/diff_match_patch.js

@@ -0,0 +1,2339 @@
+/**
+ * Diff Match and Patch
+ *
+ * Copyright 2006 Google Inc.
+ * http://code.google.com/p/google-diff-match-patch/
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * @fileoverview Computes the difference between two texts to create a patch.
+ * Applies the patch onto another text, allowing for errors.
+ * @author fraser@google.com (Neil Fraser)
+ */
+
+/**
+ * Class containing the diff, match and patch methods.
+ * @constructor
+ */
+function diff_match_patch() {
+  // Defaults.
+  // Redefine these in your program to override the defaults.
+
+  // Number of seconds to map a diff before giving up (0 for infinity).
+  this.Diff_Timeout = 1.0
+  // Cost of an empty edit operation in terms of edit characters.
+  this.Diff_EditCost = 4
+  // At what point is no match declared (0.0 = perfection, 1.0 = very loose).
+  this.Match_Threshold = 0.5
+  // How far to search for a match (0 = exact location, 1000+ = broad match).
+  // A match this many characters away from the expected location will add
+  // 1.0 to the score (0.0 is a perfect match).
+  this.Match_Distance = 1000
+  // When deleting a large block of text (over ~64 characters), how close do
+  // the contents have to be to match the expected contents. (0.0 = perfection,
+  // 1.0 = very loose).  Note that Match_Threshold controls how closely the
+  // end points of a delete need to match.
+  this.Patch_DeleteThreshold = 0.5
+  // Chunk size for context length.
+  this.Patch_Margin = 4
+
+  // The number of bits in an int.
+  this.Match_MaxBits = 32
+}
+
+//  DIFF FUNCTIONS
+
+/**
+ * The data structure representing a diff is an array of tuples:
+ * [[DIFF_DELETE, 'Hello'], [DIFF_INSERT, 'Goodbye'], [DIFF_EQUAL, ' world.']]
+ * which means: delete 'Hello', add 'Goodbye' and keep ' world.'
+ */
+var DIFF_DELETE = -1
+var DIFF_INSERT = 1
+var DIFF_EQUAL = 0
+
+/** @typedef {{0: number, 1: string}} */
+diff_match_patch.Diff
+
+/**
+ * Find the differences between two texts.  Simplifies the problem by stripping
+ * any common prefix or suffix off the texts before diffing.
+ * @param {string} text1 Old string to be diffed.
+ * @param {string} text2 New string to be diffed.
+ * @param {boolean=} opt_checklines Optional speedup flag. If present and false,
+ *     then don't run a line-level diff first to identify the changed areas.
+ *     Defaults to true, which does a faster, slightly less optimal diff.
+ * @param {number} opt_deadline Optional time when the diff should be complete
+ *     by.  Used internally for recursive calls.  Users should set DiffTimeout
+ *     instead.
+ * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
+ */
+diff_match_patch.prototype.diff_main = function (
+  text1,
+  text2,
+  opt_checklines,
+  opt_deadline
+) {
+  // Set a deadline by which time the diff must be complete.
+  if (typeof opt_deadline === 'undefined') {
+    if (this.Diff_Timeout <= 0) {
+      opt_deadline = Number.MAX_VALUE
+    } else {
+      opt_deadline = new Date().getTime() + this.Diff_Timeout * 1000
+    }
+  }
+  var deadline = opt_deadline
+
+  // Check for null inputs.
+  if (text1 == null || text2 == null) {
+    throw new Error('Null input. (diff_main)')
+  }
+
+  // Check for equality (speedup).
+  if (text1 == text2) {
+    if (text1) {
+      return [[DIFF_EQUAL, text1]]
+    }
+    return []
+  }
+
+  if (typeof opt_checklines === 'undefined') {
+    opt_checklines = true
+  }
+  var checklines = opt_checklines
+
+  // Trim off common prefix (speedup).
+  var commonlength = this.diff_commonPrefix(text1, text2)
+  var commonprefix = text1.substring(0, commonlength)
+  text1 = text1.substring(commonlength)
+  text2 = text2.substring(commonlength)
+
+  // Trim off common suffix (speedup).
+  commonlength = this.diff_commonSuffix(text1, text2)
+  var commonsuffix = text1.substring(text1.length - commonlength)
+  text1 = text1.substring(0, text1.length - commonlength)
+  text2 = text2.substring(0, text2.length - commonlength)
+
+  // Compute the diff on the middle block.
+  var diffs = this.diff_compute_(text1, text2, checklines, deadline)
+
+  // Restore the prefix and suffix.
+  if (commonprefix) {
+    diffs.unshift([DIFF_EQUAL, commonprefix])
+  }
+  if (commonsuffix) {
+    diffs.push([DIFF_EQUAL, commonsuffix])
+  }
+  this.diff_cleanupMerge(diffs)
+  return diffs
+}
+
+/**
+ * Find the differences between two texts.  Assumes that the texts do not
+ * have any common prefix or suffix.
+ * @param {string} text1 Old string to be diffed.
+ * @param {string} text2 New string to be diffed.
+ * @param {boolean} checklines Speedup flag.  If false, then don't run a
+ *     line-level diff first to identify the changed areas.
+ *     If true, then run a faster, slightly less optimal diff.
+ * @param {number} deadline Time when the diff should be complete by.
+ * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
+ * @private
+ */
+diff_match_patch.prototype.diff_compute_ = function (
+  text1,
+  text2,
+  checklines,
+  deadline
+) {
+  var diffs
+
+  if (!text1) {
+    // Just add some text (speedup).
+    return [[DIFF_INSERT, text2]]
+  }
+
+  if (!text2) {
+    // Just delete some text (speedup).
+    return [[DIFF_DELETE, text1]]
+  }
+
+  var longtext = text1.length > text2.length ? text1 : text2
+  var shorttext = text1.length > text2.length ? text2 : text1
+  var i = longtext.indexOf(shorttext)
+  if (i != -1) {
+    // Shorter text is inside the longer text (speedup).
+    diffs = [
+      [DIFF_INSERT, longtext.substring(0, i)],
+      [DIFF_EQUAL, shorttext],
+      [DIFF_INSERT, longtext.substring(i + shorttext.length)],
+    ]
+    // Swap insertions for deletions if diff is reversed.
+    if (text1.length > text2.length) {
+      diffs[0][0] = diffs[2][0] = DIFF_DELETE
+    }
+    return diffs
+  }
+
+  if (shorttext.length == 1) {
+    // Single character string.
+    // After the previous speedup, the character can't be an equality.
+    return [
+      [DIFF_DELETE, text1],
+      [DIFF_INSERT, text2],
+    ]
+  }
+
+  // Check to see if the problem can be split in two.
+  var hm = this.diff_halfMatch_(text1, text2)
+  if (hm) {
+    // A half-match was found, sort out the return data.
+    var text1_a = hm[0]
+    var text1_b = hm[1]
+    var text2_a = hm[2]
+    var text2_b = hm[3]
+    var mid_common = hm[4]
+    // Send both pairs off for separate processing.
+    var diffs_a = this.diff_main(text1_a, text2_a, checklines, deadline)
+    var diffs_b = this.diff_main(text1_b, text2_b, checklines, deadline)
+    // Merge the results.
+    return diffs_a.concat([[DIFF_EQUAL, mid_common]], diffs_b)
+  }
+
+  if (checklines && text1.length > 100 && text2.length > 100) {
+    return this.diff_lineMode_(text1, text2, deadline)
+  }
+
+  return this.diff_bisect_(text1, text2, deadline)
+}
+
+/**
+ * Do a quick line-level diff on both strings, then rediff the parts for
+ * greater accuracy.
+ * This speedup can produce non-minimal diffs.
+ * @param {string} text1 Old string to be diffed.
+ * @param {string} text2 New string to be diffed.
+ * @param {number} deadline Time when the diff should be complete by.
+ * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
+ * @private
+ */
+diff_match_patch.prototype.diff_lineMode_ = function (text1, text2, deadline) {
+  // Scan the text on a line-by-line basis first.
+  var a = this.diff_linesToChars_(text1, text2)
+  text1 = a.chars1
+  text2 = a.chars2
+  var linearray = a.lineArray
+
+  var diffs = this.diff_main(text1, text2, false, deadline)
+
+  // Convert the diff back to original text.
+  this.diff_charsToLines_(diffs, linearray)
+  // Eliminate freak matches (e.g. blank lines)
+  this.diff_cleanupSemantic(diffs)
+
+  // Rediff any replacement blocks, this time character-by-character.
+  // Add a dummy entry at the end.
+  diffs.push([DIFF_EQUAL, ''])
+  var pointer = 0
+  var count_delete = 0
+  var count_insert = 0
+  var text_delete = ''
+  var text_insert = ''
+  while (pointer < diffs.length) {
+    switch (diffs[pointer][0]) {
+      case DIFF_INSERT:
+        count_insert++
+        text_insert += diffs[pointer][1]
+        break
+      case DIFF_DELETE:
+        count_delete++
+        text_delete += diffs[pointer][1]
+        break
+      case DIFF_EQUAL:
+        // Upon reaching an equality, check for prior redundancies.
+        if (count_delete >= 1 && count_insert >= 1) {
+          // Delete the offending records and add the merged ones.
+          diffs.splice(
+            pointer - count_delete - count_insert,
+            count_delete + count_insert
+          )
+          pointer = pointer - count_delete - count_insert
+          var a = this.diff_main(text_delete, text_insert, false, deadline)
+          for (var j = a.length - 1; j >= 0; j--) {
+            diffs.splice(pointer, 0, a[j])
+          }
+          pointer = pointer + a.length
+        }
+        count_insert = 0
+        count_delete = 0
+        text_delete = ''
+        text_insert = ''
+        break
+    }
+    pointer++
+  }
+  diffs.pop() // Remove the dummy entry at the end.
+
+  return diffs
+}
+
+/**
+ * Find the 'middle snake' of a diff, split the problem in two
+ * and return the recursively constructed diff.
+ * See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
+ * @param {string} text1 Old string to be diffed.
+ * @param {string} text2 New string to be diffed.
+ * @param {number} deadline Time at which to bail if not yet complete.
+ * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
+ * @private
+ */
+diff_match_patch.prototype.diff_bisect_ = function (text1, text2, deadline) {
+  // Cache the text lengths to prevent multiple calls.
+  var text1_length = text1.length
+  var text2_length = text2.length
+  var max_d = Math.ceil((text1_length + text2_length) / 2)
+  var v_offset = max_d
+  var v_length = 2 * max_d
+  var v1 = new Array(v_length)
+  var v2 = new Array(v_length)
+  // Setting all elements to -1 is faster in Chrome & Firefox than mixing
+  // integers and undefined.
+  for (var x = 0; x < v_length; x++) {
+    v1[x] = -1
+    v2[x] = -1
+  }
+  v1[v_offset + 1] = 0
+  v2[v_offset + 1] = 0
+  var delta = text1_length - text2_length
+  // If the total number of characters is odd, then the front path will collide
+  // with the reverse path.
+  var front = delta % 2 != 0
+  // Offsets for start and end of k loop.
+  // Prevents mapping of space beyond the grid.
+  var k1start = 0
+  var k1end = 0
+  var k2start = 0
+  var k2end = 0
+  for (var d = 0; d < max_d; d++) {
+    // Bail out if deadline is reached.
+    if (new Date().getTime() > deadline) {
+      break
+    }
+
+    // Walk the front path one step.
+    for (var k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
+      var k1_offset = v_offset + k1
+      var x1
+      if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
+        x1 = v1[k1_offset + 1]
+      } else {
+        x1 = v1[k1_offset - 1] + 1
+      }
+      var y1 = x1 - k1
+      while (
+        x1 < text1_length &&
+        y1 < text2_length &&
+        text1.charAt(x1) == text2.charAt(y1)
+      ) {
+        x1++
+        y1++
+      }
+      v1[k1_offset] = x1
+      if (x1 > text1_length) {
+        // Ran off the right of the graph.
+        k1end += 2
+      } else if (y1 > text2_length) {
+        // Ran off the bottom of the graph.
+        k1start += 2
+      } else if (front) {
+        var k2_offset = v_offset + delta - k1
+        if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
+          // Mirror x2 onto top-left coordinate system.
+          var x2 = text1_length - v2[k2_offset]
+          if (x1 >= x2) {
+            // Overlap detected.
+            return this.diff_bisectSplit_(text1, text2, x1, y1, deadline)
+          }
+        }
+      }
+    }
+
+    // Walk the reverse path one step.
+    for (var k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
+      var k2_offset = v_offset + k2
+      var x2
+      if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
+        x2 = v2[k2_offset + 1]
+      } else {
+        x2 = v2[k2_offset - 1] + 1
+      }
+      var y2 = x2 - k2
+      while (
+        x2 < text1_length &&
+        y2 < text2_length &&
+        text1.charAt(text1_length - x2 - 1) ==
+          text2.charAt(text2_length - y2 - 1)
+      ) {
+        x2++
+        y2++
+      }
+      v2[k2_offset] = x2
+      if (x2 > text1_length) {
+        // Ran off the left of the graph.
+        k2end += 2
+      } else if (y2 > text2_length) {
+        // Ran off the top of the graph.
+        k2start += 2
+      } else if (!front) {
+        var k1_offset = v_offset + delta - k2
+        if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
+          var x1 = v1[k1_offset]
+          var y1 = v_offset + x1 - k1_offset
+          // Mirror x2 onto top-left coordinate system.
+          x2 = text1_length - x2
+          if (x1 >= x2) {
+            // Overlap detected.
+            return this.diff_bisectSplit_(text1, text2, x1, y1, deadline)
+          }
+        }
+      }
+    }
+  }
+  // Diff took too long and hit the deadline or
+  // number of diffs equals number of characters, no commonality at all.
+  return [
+    [DIFF_DELETE, text1],
+    [DIFF_INSERT, text2],
+  ]
+}
+
+/**
+ * Given the location of the 'middle snake', split the diff in two parts
+ * and recurse.
+ * @param {string} text1 Old string to be diffed.
+ * @param {string} text2 New string to be diffed.
+ * @param {number} x Index of split point in text1.
+ * @param {number} y Index of split point in text2.
+ * @param {number} deadline Time at which to bail if not yet complete.
+ * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
+ * @private
+ */
+diff_match_patch.prototype.diff_bisectSplit_ = function (
+  text1,
+  text2,
+  x,
+  y,
+  deadline
+) {
+  var text1a = text1.substring(0, x)
+  var text2a = text2.substring(0, y)
+  var text1b = text1.substring(x)
+  var text2b = text2.substring(y)
+
+  // Compute both diffs serially.
+  var diffs = this.diff_main(text1a, text2a, false, deadline)
+  var diffsb = this.diff_main(text1b, text2b, false, deadline)
+
+  return diffs.concat(diffsb)
+}
+
+/**
+ * Split two texts into an array of strings.  Reduce the texts to a string of
+ * hashes where each Unicode character represents one line.
+ * @param {string} text1 First string.
+ * @param {string} text2 Second string.
+ * @return {{chars1: string, chars2: string, lineArray: !Array.<string>}}
+ *     An object containing the encoded text1, the encoded text2 and
+ *     the array of unique strings.
+ *     The zeroth element of the array of unique strings is intentionally blank.
+ * @private
+ */
+diff_match_patch.prototype.diff_linesToChars_ = function (text1, text2) {
+  var lineArray = [] // e.g. lineArray[4] == 'Hello\n'
+  var lineHash = {} // e.g. lineHash['Hello\n'] == 4
+
+  // '\x00' is a valid character, but various debuggers don't like it.
+  // So we'll insert a junk entry to avoid generating a null character.
+  lineArray[0] = ''
+
+  /**
+   * Split a text into an array of strings.  Reduce the texts to a string of
+   * hashes where each Unicode character represents one line.
+   * Modifies linearray and linehash through being a closure.
+   * @param {string} text String to encode.
+   * @return {string} Encoded string.
+   * @private
+   */
+  function diff_linesToCharsMunge_(text) {
+    var chars = ''
+    // Walk the text, pulling out a substring for each line.
+    // text.split('\n') would would temporarily double our memory footprint.
+    // Modifying text would create many large strings to garbage collect.
+    var lineStart = 0
+    var lineEnd = -1
+    // Keeping our own length variable is faster than looking it up.
+    var lineArrayLength = lineArray.length
+    while (lineEnd < text.length - 1) {
+      lineEnd = text.indexOf('\n', lineStart)
+      if (lineEnd == -1) {
+        lineEnd = text.length - 1
+      }
+      var line = text.substring(lineStart, lineEnd + 1)
+      lineStart = lineEnd + 1
+
+      if (
+        lineHash.hasOwnProperty
+          ? lineHash.hasOwnProperty(line)
+          : lineHash[line] !== undefined
+      ) {
+        chars += String.fromCharCode(lineHash[line])
+      } else {
+        chars += String.fromCharCode(lineArrayLength)
+        lineHash[line] = lineArrayLength
+        lineArray[lineArrayLength++] = line
+      }
+    }
+    return chars
+  }
+
+  var chars1 = diff_linesToCharsMunge_(text1)
+  var chars2 = diff_linesToCharsMunge_(text2)
+  return { chars1: chars1, chars2: chars2, lineArray: lineArray }
+}
+
+/**
+ * Rehydrate the text in a diff from a string of line hashes to real lines of
+ * text.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @param {!Array.<string>} lineArray Array of unique strings.
+ * @private
+ */
+diff_match_patch.prototype.diff_charsToLines_ = function (diffs, lineArray) {
+  for (var x = 0; x < diffs.length; x++) {
+    var chars = diffs[x][1]
+    var text = []
+    for (var y = 0; y < chars.length; y++) {
+      text[y] = lineArray[chars.charCodeAt(y)]
+    }
+    diffs[x][1] = text.join('')
+  }
+}
+
+/**
+ * Determine the common prefix of two strings.
+ * @param {string} text1 First string.
+ * @param {string} text2 Second string.
+ * @return {number} The number of characters common to the start of each
+ *     string.
+ */
+diff_match_patch.prototype.diff_commonPrefix = function (text1, text2) {
+  // Quick check for common null cases.
+  if (!text1 || !text2 || text1.charAt(0) != text2.charAt(0)) {
+    return 0
+  }
+  // Binary search.
+  // Performance analysis: http://neil.fraser.name/news/2007/10/09/
+  var pointermin = 0
+  var pointermax = Math.min(text1.length, text2.length)
+  var pointermid = pointermax
+  var pointerstart = 0
+  while (pointermin < pointermid) {
+    if (
+      text1.substring(pointerstart, pointermid) ==
+      text2.substring(pointerstart, pointermid)
+    ) {
+      pointermin = pointermid
+      pointerstart = pointermin
+    } else {
+      pointermax = pointermid
+    }
+    pointermid = Math.floor((pointermax - pointermin) / 2 + pointermin)
+  }
+  return pointermid
+}
+
+/**
+ * Determine the common suffix of two strings.
+ * @param {string} text1 First string.
+ * @param {string} text2 Second string.
+ * @return {number} The number of characters common to the end of each string.
+ */
+diff_match_patch.prototype.diff_commonSuffix = function (text1, text2) {
+  // Quick check for common null cases.
+  if (
+    !text1 ||
+    !text2 ||
+    text1.charAt(text1.length - 1) != text2.charAt(text2.length - 1)
+  ) {
+    return 0
+  }
+  // Binary search.
+  // Performance analysis: http://neil.fraser.name/news/2007/10/09/
+  var pointermin = 0
+  var pointermax = Math.min(text1.length, text2.length)
+  var pointermid = pointermax
+  var pointerend = 0
+  while (pointermin < pointermid) {
+    if (
+      text1.substring(text1.length - pointermid, text1.length - pointerend) ==
+      text2.substring(text2.length - pointermid, text2.length - pointerend)
+    ) {
+      pointermin = pointermid
+      pointerend = pointermin
+    } else {
+      pointermax = pointermid
+    }
+    pointermid = Math.floor((pointermax - pointermin) / 2 + pointermin)
+  }
+  return pointermid
+}
+
+/**
+ * Determine if the suffix of one string is the prefix of another.
+ * @param {string} text1 First string.
+ * @param {string} text2 Second string.
+ * @return {number} The number of characters common to the end of the first
+ *     string and the start of the second string.
+ * @private
+ */
+diff_match_patch.prototype.diff_commonOverlap_ = function (text1, text2) {
+  // Cache the text lengths to prevent multiple calls.
+  var text1_length = text1.length
+  var text2_length = text2.length
+  // Eliminate the null case.
+  if (text1_length == 0 || text2_length == 0) {
+    return 0
+  }
+  // Truncate the longer string.
+  if (text1_length > text2_length) {
+    text1 = text1.substring(text1_length - text2_length)
+  } else if (text1_length < text2_length) {
+    text2 = text2.substring(0, text1_length)
+  }
+  var text_length = Math.min(text1_length, text2_length)
+  // Quick check for the worst case.
+  if (text1 == text2) {
+    return text_length
+  }
+
+  // Start by looking for a single character match
+  // and increase length until no match is found.
+  // Performance analysis: http://neil.fraser.name/news/2010/11/04/
+  var best = 0
+  var length = 1
+  while (true) {
+    var pattern = text1.substring(text_length - length)
+    var found = text2.indexOf(pattern)
+    if (found == -1) {
+      return best
+    }
+    length += found
+    if (
+      found == 0 ||
+      text1.substring(text_length - length) == text2.substring(0, length)
+    ) {
+      best = length
+      length++
+    }
+  }
+}
+
+/**
+ * Do the two texts share a substring which is at least half the length of the
+ * longer text?
+ * This speedup can produce non-minimal diffs.
+ * @param {string} text1 First string.
+ * @param {string} text2 Second string.
+ * @return {Array.<string>} Five element Array, containing the prefix of
+ *     text1, the suffix of text1, the prefix of text2, the suffix of
+ *     text2 and the common middle.  Or null if there was no match.
+ * @private
+ */
+diff_match_patch.prototype.diff_halfMatch_ = function (text1, text2) {
+  if (this.Diff_Timeout <= 0) {
+    // Don't risk returning a non-optimal diff if we have unlimited time.
+    return null
+  }
+  var longtext = text1.length > text2.length ? text1 : text2
+  var shorttext = text1.length > text2.length ? text2 : text1
+  if (longtext.length < 4 || shorttext.length * 2 < longtext.length) {
+    return null // Pointless.
+  }
+  var dmp = this // 'this' becomes 'window' in a closure.
+
+  /**
+   * Does a substring of shorttext exist within longtext such that the substring
+   * is at least half the length of longtext?
+   * Closure, but does not reference any external variables.
+   * @param {string} longtext Longer string.
+   * @param {string} shorttext Shorter string.
+   * @param {number} i Start index of quarter length substring within longtext.
+   * @return {Array.<string>} Five element Array, containing the prefix of
+   *     longtext, the suffix of longtext, the prefix of shorttext, the suffix
+   *     of shorttext and the common middle.  Or null if there was no match.
+   * @private
+   */
+  function diff_halfMatchI_(longtext, shorttext, i) {
+    // Start with a 1/4 length substring at position i as a seed.
+    var seed = longtext.substring(i, i + Math.floor(longtext.length / 4))
+    var j = -1
+    var best_common = ''
+    var best_longtext_a, best_longtext_b, best_shorttext_a, best_shorttext_b
+    while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
+      var prefixLength = dmp.diff_commonPrefix(
+        longtext.substring(i),
+        shorttext.substring(j)
+      )
+      var suffixLength = dmp.diff_commonSuffix(
+        longtext.substring(0, i),
+        shorttext.substring(0, j)
+      )
+      if (best_common.length < suffixLength + prefixLength) {
+        best_common =
+          shorttext.substring(j - suffixLength, j) +
+          shorttext.substring(j, j + prefixLength)
+        best_longtext_a = longtext.substring(0, i - suffixLength)
+        best_longtext_b = longtext.substring(i + prefixLength)
+        best_shorttext_a = shorttext.substring(0, j - suffixLength)
+        best_shorttext_b = shorttext.substring(j + prefixLength)
+      }
+    }
+    if (best_common.length * 2 >= longtext.length) {
+      return [
+        best_longtext_a,
+        best_longtext_b,
+        best_shorttext_a,
+        best_shorttext_b,
+        best_common,
+      ]
+    } else {
+      return null
+    }
+  }
+
+  // First check if the second quarter is the seed for a half-match.
+  var hm1 = diff_halfMatchI_(
+    longtext,
+    shorttext,
+    Math.ceil(longtext.length / 4)
+  )
+  // Check again based on the third quarter.
+  var hm2 = diff_halfMatchI_(
+    longtext,
+    shorttext,
+    Math.ceil(longtext.length / 2)
+  )
+  var hm
+  if (!hm1 && !hm2) {
+    return null
+  } else if (!hm2) {
+    hm = hm1
+  } else if (!hm1) {
+    hm = hm2
+  } else {
+    // Both matched.  Select the longest.
+    hm = hm1[4].length > hm2[4].length ? hm1 : hm2
+  }
+
+  // A half-match was found, sort out the return data.
+  var text1_a, text1_b, text2_a, text2_b
+  if (text1.length > text2.length) {
+    text1_a = hm[0]
+    text1_b = hm[1]
+    text2_a = hm[2]
+    text2_b = hm[3]
+  } else {
+    text2_a = hm[0]
+    text2_b = hm[1]
+    text1_a = hm[2]
+    text1_b = hm[3]
+  }
+  var mid_common = hm[4]
+  return [text1_a, text1_b, text2_a, text2_b, mid_common]
+}
+
+/**
+ * Reduce the number of edits by eliminating semantically trivial equalities.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ */
+diff_match_patch.prototype.diff_cleanupSemantic = function (diffs) {
+  var changes = false
+  var equalities = [] // Stack of indices where equalities are found.
+  var equalitiesLength = 0 // Keeping our own length var is faster in JS.
+  /** @type {?string} */
+  var lastequality = null
+  // Always equal to diffs[equalities[equalitiesLength - 1]][1]
+  var pointer = 0 // Index of current position.
+  // Number of characters that changed prior to the equality.
+  var length_insertions1 = 0
+  var length_deletions1 = 0
+  // Number of characters that changed after the equality.
+  var length_insertions2 = 0
+  var length_deletions2 = 0
+  while (pointer < diffs.length) {
+    if (diffs[pointer][0] == DIFF_EQUAL) {
+      // Equality found.
+      equalities[equalitiesLength++] = pointer
+      length_insertions1 = length_insertions2
+      length_deletions1 = length_deletions2
+      length_insertions2 = 0
+      length_deletions2 = 0
+      lastequality = diffs[pointer][1]
+    } else {
+      // An insertion or deletion.
+      if (diffs[pointer][0] == DIFF_INSERT) {
+        length_insertions2 += diffs[pointer][1].length
+      } else {
+        length_deletions2 += diffs[pointer][1].length
+      }
+      // Eliminate an equality that is smaller or equal to the edits on both
+      // sides of it.
+      if (
+        lastequality &&
+        lastequality.length <=
+          Math.max(length_insertions1, length_deletions1) &&
+        lastequality.length <= Math.max(length_insertions2, length_deletions2)
+      ) {
+        // Duplicate record.
+        diffs.splice(equalities[equalitiesLength - 1], 0, [
+          DIFF_DELETE,
+          lastequality,
+        ])
+        // Change second copy to insert.
+        diffs[equalities[equalitiesLength - 1] + 1][0] = DIFF_INSERT
+        // Throw away the equality we just deleted.
+        equalitiesLength--
+        // Throw away the previous equality (it needs to be reevaluated).
+        equalitiesLength--
+        pointer = equalitiesLength > 0 ? equalities[equalitiesLength - 1] : -1
+        length_insertions1 = 0 // Reset the counters.
+        length_deletions1 = 0
+        length_insertions2 = 0
+        length_deletions2 = 0
+        lastequality = null
+        changes = true
+      }
+    }
+    pointer++
+  }
+
+  // Normalize the diff.
+  if (changes) {
+    this.diff_cleanupMerge(diffs)
+  }
+  this.diff_cleanupSemanticLossless(diffs)
+
+  // Find any overlaps between deletions and insertions.
+  // e.g: <del>abcxxx</del><ins>xxxdef</ins>
+  //   -> <del>abc</del>xxx<ins>def</ins>
+  // e.g: <del>xxxabc</del><ins>defxxx</ins>
+  //   -> <ins>def</ins>xxx<del>abc</del>
+  // Only extract an overlap if it is as big as the edit ahead or behind it.
+  pointer = 1
+  while (pointer < diffs.length) {
+    if (
+      diffs[pointer - 1][0] == DIFF_DELETE &&
+      diffs[pointer][0] == DIFF_INSERT
+    ) {
+      var deletion = diffs[pointer - 1][1]
+      var insertion = diffs[pointer][1]
+      var overlap_length1 = this.diff_commonOverlap_(deletion, insertion)
+      var overlap_length2 = this.diff_commonOverlap_(insertion, deletion)
+      if (overlap_length1 >= overlap_length2) {
+        if (
+          overlap_length1 >= deletion.length / 2 ||
+          overlap_length1 >= insertion.length / 2
+        ) {
+          // Overlap found.  Insert an equality and trim the surrounding edits.
+          diffs.splice(pointer, 0, [
+            DIFF_EQUAL,
+            insertion.substring(0, overlap_length1),
+          ])
+          diffs[pointer - 1][1] = deletion.substring(
+            0,
+            deletion.length - overlap_length1
+          )
+          diffs[pointer + 1][1] = insertion.substring(overlap_length1)
+          pointer++
+        }
+      } else {
+        if (
+          overlap_length2 >= deletion.length / 2 ||
+          overlap_length2 >= insertion.length / 2
+        ) {
+          // Reverse overlap found.
+          // Insert an equality and swap and trim the surrounding edits.
+          diffs.splice(pointer, 0, [
+            DIFF_EQUAL,
+            deletion.substring(0, overlap_length2),
+          ])
+          diffs[pointer - 1][0] = DIFF_INSERT
+          diffs[pointer - 1][1] = insertion.substring(
+            0,
+            insertion.length - overlap_length2
+          )
+          diffs[pointer + 1][0] = DIFF_DELETE
+          diffs[pointer + 1][1] = deletion.substring(overlap_length2)
+          pointer++
+        }
+      }
+      pointer++
+    }
+    pointer++
+  }
+}
+
+/**
+ * Look for single edits surrounded on both sides by equalities
+ * which can be shifted sideways to align the edit to a word boundary.
+ * e.g: The c<ins>at c</ins>ame. -> The <ins>cat </ins>came.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ */
+diff_match_patch.prototype.diff_cleanupSemanticLossless = function (diffs) {
+  /**
+   * Given two strings, compute a score representing whether the internal
+   * boundary falls on logical boundaries.
+   * Scores range from 6 (best) to 0 (worst).
+   * Closure, but does not reference any external variables.
+   * @param {string} one First string.
+   * @param {string} two Second string.
+   * @return {number} The score.
+   * @private
+   */
+  function diff_cleanupSemanticScore_(one, two) {
+    if (!one || !two) {
+      // Edges are the best.
+      return 6
+    }
+
+    // Each port of this function behaves slightly differently due to
+    // subtle differences in each language's definition of things like
+    // 'whitespace'.  Since this function's purpose is largely cosmetic,
+    // the choice has been made to use each language's native features
+    // rather than force total conformity.
+    var char1 = one.charAt(one.length - 1)
+    var char2 = two.charAt(0)
+    var nonAlphaNumeric1 = char1.match(diff_match_patch.nonAlphaNumericRegex_)
+    var nonAlphaNumeric2 = char2.match(diff_match_patch.nonAlphaNumericRegex_)
+    var whitespace1 =
+      nonAlphaNumeric1 && char1.match(diff_match_patch.whitespaceRegex_)
+    var whitespace2 =
+      nonAlphaNumeric2 && char2.match(diff_match_patch.whitespaceRegex_)
+    var lineBreak1 =
+      whitespace1 && char1.match(diff_match_patch.linebreakRegex_)
+    var lineBreak2 =
+      whitespace2 && char2.match(diff_match_patch.linebreakRegex_)
+    var blankLine1 =
+      lineBreak1 && one.match(diff_match_patch.blanklineEndRegex_)
+    var blankLine2 =
+      lineBreak2 && two.match(diff_match_patch.blanklineStartRegex_)
+
+    if (blankLine1 || blankLine2) {
+      // Five points for blank lines.
+      return 5
+    } else if (lineBreak1 || lineBreak2) {
+      // Four points for line breaks.
+      return 4
+    } else if (nonAlphaNumeric1 && !whitespace1 && whitespace2) {
+      // Three points for end of sentences.
+      return 3
+    } else if (whitespace1 || whitespace2) {
+      // Two points for whitespace.
+      return 2
+    } else if (nonAlphaNumeric1 || nonAlphaNumeric2) {
+      // One point for non-alphanumeric.
+      return 1
+    }
+    return 0
+  }
+
+  var pointer = 1
+  // Intentionally ignore the first and last element (don't need checking).
+  while (pointer < diffs.length - 1) {
+    if (
+      diffs[pointer - 1][0] == DIFF_EQUAL &&
+      diffs[pointer + 1][0] == DIFF_EQUAL
+    ) {
+      // This is a single edit surrounded by equalities.
+      var equality1 = diffs[pointer - 1][1]
+      var edit = diffs[pointer][1]
+      var equality2 = diffs[pointer + 1][1]
+
+      // First, shift the edit as far left as possible.
+      var commonOffset = this.diff_commonSuffix(equality1, edit)
+      if (commonOffset) {
+        var commonString = edit.substring(edit.length - commonOffset)
+        equality1 = equality1.substring(0, equality1.length - commonOffset)
+        edit = commonString + edit.substring(0, edit.length - commonOffset)
+        equality2 = commonString + equality2
+      }
+
+      // Second, step character by character right, looking for the best fit.
+      var bestEquality1 = equality1
+      var bestEdit = edit
+      var bestEquality2 = equality2
+      var bestScore =
+        diff_cleanupSemanticScore_(equality1, edit) +
+        diff_cleanupSemanticScore_(edit, equality2)
+      while (edit.charAt(0) === equality2.charAt(0)) {
+        equality1 += edit.charAt(0)
+        edit = edit.substring(1) + equality2.charAt(0)
+        equality2 = equality2.substring(1)
+        var score =
+          diff_cleanupSemanticScore_(equality1, edit) +
+          diff_cleanupSemanticScore_(edit, equality2)
+        // The >= encourages trailing rather than leading whitespace on edits.
+        if (score >= bestScore) {
+          bestScore = score
+          bestEquality1 = equality1
+          bestEdit = edit
+          bestEquality2 = equality2
+        }
+      }
+
+      if (diffs[pointer - 1][1] != bestEquality1) {
+        // We have an improvement, save it back to the diff.
+        if (bestEquality1) {
+          diffs[pointer - 1][1] = bestEquality1
+        } else {
+          diffs.splice(pointer - 1, 1)
+          pointer--
+        }
+        diffs[pointer][1] = bestEdit
+        if (bestEquality2) {
+          diffs[pointer + 1][1] = bestEquality2
+        } else {
+          diffs.splice(pointer + 1, 1)
+          pointer--
+        }
+      }
+    }
+    pointer++
+  }
+}
+
+// Define some regex patterns for matching boundaries.
+diff_match_patch.nonAlphaNumericRegex_ = /[^a-zA-Z0-9]/
+diff_match_patch.whitespaceRegex_ = /\s/
+diff_match_patch.linebreakRegex_ = /[\r\n]/
+diff_match_patch.blanklineEndRegex_ = /\n\r?\n$/
+diff_match_patch.blanklineStartRegex_ = /^\r?\n\r?\n/
+
+/**
+ * Reduce the number of edits by eliminating operationally trivial equalities.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ */
+diff_match_patch.prototype.diff_cleanupEfficiency = function (diffs) {
+  var changes = false
+  var equalities = [] // Stack of indices where equalities are found.
+  var equalitiesLength = 0 // Keeping our own length var is faster in JS.
+  /** @type {?string} */
+  var lastequality = null
+  // Always equal to diffs[equalities[equalitiesLength - 1]][1]
+  var pointer = 0 // Index of current position.
+  // Is there an insertion operation before the last equality.
+  var pre_ins = false
+  // Is there a deletion operation before the last equality.
+  var pre_del = false
+  // Is there an insertion operation after the last equality.
+  var post_ins = false
+  // Is there a deletion operation after the last equality.
+  var post_del = false
+  while (pointer < diffs.length) {
+    if (diffs[pointer][0] == DIFF_EQUAL) {
+      // Equality found.
+      if (
+        diffs[pointer][1].length < this.Diff_EditCost &&
+        (post_ins || post_del)
+      ) {
+        // Candidate found.
+        equalities[equalitiesLength++] = pointer
+        pre_ins = post_ins
+        pre_del = post_del
+        lastequality = diffs[pointer][1]
+      } else {
+        // Not a candidate, and can never become one.
+        equalitiesLength = 0
+        lastequality = null
+      }
+      post_ins = post_del = false
+    } else {
+      // An insertion or deletion.
+      if (diffs[pointer][0] == DIFF_DELETE) {
+        post_del = true
+      } else {
+        post_ins = true
+      }
+      /*
+       * Five types to be split:
+       * <ins>A</ins><del>B</del>XY<ins>C</ins><del>D</del>
+       * <ins>A</ins>X<ins>C</ins><del>D</del>
+       * <ins>A</ins><del>B</del>X<ins>C</ins>
+       * <ins>A</del>X<ins>C</ins><del>D</del>
+       * <ins>A</ins><del>B</del>X<del>C</del>
+       */
+      if (
+        lastequality &&
+        ((pre_ins && pre_del && post_ins && post_del) ||
+          (lastequality.length < this.Diff_EditCost / 2 &&
+            pre_ins + pre_del + post_ins + post_del == 3))
+      ) {
+        // Duplicate record.
+        diffs.splice(equalities[equalitiesLength - 1], 0, [
+          DIFF_DELETE,
+          lastequality,
+        ])
+        // Change second copy to insert.
+        diffs[equalities[equalitiesLength - 1] + 1][0] = DIFF_INSERT
+        equalitiesLength-- // Throw away the equality we just deleted;
+        lastequality = null
+        if (pre_ins && pre_del) {
+          // No changes made which could affect previous entry, keep going.
+          post_ins = post_del = true
+          equalitiesLength = 0
+        } else {
+          equalitiesLength-- // Throw away the previous equality.
+          pointer = equalitiesLength > 0 ? equalities[equalitiesLength - 1] : -1
+          post_ins = post_del = false
+        }
+        changes = true
+      }
+    }
+    pointer++
+  }
+
+  if (changes) {
+    this.diff_cleanupMerge(diffs)
+  }
+}
+
+/**
+ * Reorder and merge like edit sections.  Merge equalities.
+ * Any edit section can move as long as it doesn't cross an equality.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ */
+diff_match_patch.prototype.diff_cleanupMerge = function (diffs) {
+  diffs.push([DIFF_EQUAL, '']) // Add a dummy entry at the end.
+  var pointer = 0
+  var count_delete = 0
+  var count_insert = 0
+  var text_delete = ''
+  var text_insert = ''
+  var commonlength
+  while (pointer < diffs.length) {
+    switch (diffs[pointer][0]) {
+      case DIFF_INSERT:
+        count_insert++
+        text_insert += diffs[pointer][1]
+        pointer++
+        break
+      case DIFF_DELETE:
+        count_delete++
+        text_delete += diffs[pointer][1]
+        pointer++
+        break
+      case DIFF_EQUAL:
+        // Upon reaching an equality, check for prior redundancies.
+        if (count_delete + count_insert > 1) {
+          if (count_delete !== 0 && count_insert !== 0) {
+            // Factor out any common prefixies.
+            commonlength = this.diff_commonPrefix(text_insert, text_delete)
+            if (commonlength !== 0) {
+              if (
+                pointer - count_delete - count_insert > 0 &&
+                diffs[pointer - count_delete - count_insert - 1][0] ==
+                  DIFF_EQUAL
+              ) {
+                diffs[pointer - count_delete - count_insert - 1][1] +=
+                  text_insert.substring(0, commonlength)
+              } else {
+                diffs.splice(0, 0, [
+                  DIFF_EQUAL,
+                  text_insert.substring(0, commonlength),
+                ])
+                pointer++
+              }
+              text_insert = text_insert.substring(commonlength)
+              text_delete = text_delete.substring(commonlength)
+            }
+            // Factor out any common suffixies.
+            commonlength = this.diff_commonSuffix(text_insert, text_delete)
+            if (commonlength !== 0) {
+              diffs[pointer][1] =
+                text_insert.substring(text_insert.length - commonlength) +
+                diffs[pointer][1]
+              text_insert = text_insert.substring(
+                0,
+                text_insert.length - commonlength
+              )
+              text_delete = text_delete.substring(
+                0,
+                text_delete.length - commonlength
+              )
+            }
+          }
+          // Delete the offending records and add the merged ones.
+          if (count_delete === 0) {
+            diffs.splice(pointer - count_insert, count_delete + count_insert, [
+              DIFF_INSERT,
+              text_insert,
+            ])
+          } else if (count_insert === 0) {
+            diffs.splice(pointer - count_delete, count_delete + count_insert, [
+              DIFF_DELETE,
+              text_delete,
+            ])
+          } else {
+            diffs.splice(
+              pointer - count_delete - count_insert,
+              count_delete + count_insert,
+              [DIFF_DELETE, text_delete],
+              [DIFF_INSERT, text_insert]
+            )
+          }
+          pointer =
+            pointer -
+            count_delete -
+            count_insert +
+            (count_delete ? 1 : 0) +
+            (count_insert ? 1 : 0) +
+            1
+        } else if (pointer !== 0 && diffs[pointer - 1][0] == DIFF_EQUAL) {
+          // Merge this equality with the previous one.
+          diffs[pointer - 1][1] += diffs[pointer][1]
+          diffs.splice(pointer, 1)
+        } else {
+          pointer++
+        }
+        count_insert = 0
+        count_delete = 0
+        text_delete = ''
+        text_insert = ''
+        break
+    }
+  }
+  if (diffs[diffs.length - 1][1] === '') {
+    diffs.pop() // Remove the dummy entry at the end.
+  }
+
+  // Second pass: look for single edits surrounded on both sides by equalities
+  // which can be shifted sideways to eliminate an equality.
+  // e.g: A<ins>BA</ins>C -> <ins>AB</ins>AC
+  var changes = false
+  pointer = 1
+  // Intentionally ignore the first and last element (don't need checking).
+  while (pointer < diffs.length - 1) {
+    if (
+      diffs[pointer - 1][0] == DIFF_EQUAL &&
+      diffs[pointer + 1][0] == DIFF_EQUAL
+    ) {
+      // This is a single edit surrounded by equalities.
+      if (
+        diffs[pointer][1].substring(
+          diffs[pointer][1].length - diffs[pointer - 1][1].length
+        ) == diffs[pointer - 1][1]
+      ) {
+        // Shift the edit over the previous equality.
+        diffs[pointer][1] =
+          diffs[pointer - 1][1] +
+          diffs[pointer][1].substring(
+            0,
+            diffs[pointer][1].length - diffs[pointer - 1][1].length
+          )
+        diffs[pointer + 1][1] = diffs[pointer - 1][1] + diffs[pointer + 1][1]
+        diffs.splice(pointer - 1, 1)
+        changes = true
+      } else if (
+        diffs[pointer][1].substring(0, diffs[pointer + 1][1].length) ==
+        diffs[pointer + 1][1]
+      ) {
+        // Shift the edit over the next equality.
+        diffs[pointer - 1][1] += diffs[pointer + 1][1]
+        diffs[pointer][1] =
+          diffs[pointer][1].substring(diffs[pointer + 1][1].length) +
+          diffs[pointer + 1][1]
+        diffs.splice(pointer + 1, 1)
+        changes = true
+      }
+    }
+    pointer++
+  }
+  // If shifts were made, the diff needs reordering and another shift sweep.
+  if (changes) {
+    this.diff_cleanupMerge(diffs)
+  }
+}
+
+/**
+ * loc is a location in text1, compute and return the equivalent location in
+ * text2.
+ * e.g. 'The cat' vs 'The big cat', 1->1, 5->8
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @param {number} loc Location within text1.
+ * @return {number} Location within text2.
+ */
+diff_match_patch.prototype.diff_xIndex = function (diffs, loc) {
+  var chars1 = 0
+  var chars2 = 0
+  var last_chars1 = 0
+  var last_chars2 = 0
+  var x
+  for (x = 0; x < diffs.length; x++) {
+    if (diffs[x][0] !== DIFF_INSERT) {
+      // Equality or deletion.
+      chars1 += diffs[x][1].length
+    }
+    if (diffs[x][0] !== DIFF_DELETE) {
+      // Equality or insertion.
+      chars2 += diffs[x][1].length
+    }
+    if (chars1 > loc) {
+      // Overshot the location.
+      break
+    }
+    last_chars1 = chars1
+    last_chars2 = chars2
+  }
+  // Was the location was deleted?
+  if (diffs.length != x && diffs[x][0] === DIFF_DELETE) {
+    return last_chars2
+  }
+  // Add the remaining character length.
+  return last_chars2 + (loc - last_chars1)
+}
+
+/**
+ * Convert a diff array into a pretty HTML report.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @return {string} HTML representation.
+ */
+diff_match_patch.prototype.diff_prettyHtml = function (diffs) {
+  var html = []
+  var pattern_amp = /&/g
+  var pattern_lt = /</g
+  var pattern_gt = />/g
+  var pattern_para = /\n/g
+  for (var x = 0; x < diffs.length; x++) {
+    var op = diffs[x][0] // Operation (insert, delete, equal)
+    var data = diffs[x][1] // Text of change.
+    var text = data
+      .replace(pattern_amp, '&amp;')
+      .replace(pattern_lt, '&lt;')
+      .replace(pattern_gt, '&gt;')
+      .replace(pattern_para, '&para;<br>')
+    switch (op) {
+      case DIFF_INSERT:
+        html[x] = '<ins style="background:#e6ffe6;">' + text + '</ins>'
+        break
+      case DIFF_DELETE:
+        html[x] = '<del style="background:#ffe6e6;">' + text + '</del>'
+        break
+      case DIFF_EQUAL:
+        html[x] = '<span>' + text + '</span>'
+        break
+    }
+  }
+  return html.join('')
+}
+
+/**
+ * Compute and return the source text (all equalities and deletions).
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @return {string} Source text.
+ */
+diff_match_patch.prototype.diff_text1 = function (diffs) {
+  var text = []
+  for (var x = 0; x < diffs.length; x++) {
+    if (diffs[x][0] !== DIFF_INSERT) {
+      text[x] = diffs[x][1]
+    }
+  }
+  return text.join('')
+}
+
+/**
+ * Compute and return the destination text (all equalities and insertions).
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @return {string} Destination text.
+ */
+diff_match_patch.prototype.diff_text2 = function (diffs) {
+  var text = []
+  for (var x = 0; x < diffs.length; x++) {
+    if (diffs[x][0] !== DIFF_DELETE) {
+      text[x] = diffs[x][1]
+    }
+  }
+  return text.join('')
+}
+
+/**
+ * Compute the Levenshtein distance; the number of inserted, deleted or
+ * substituted characters.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @return {number} Number of changes.
+ */
+diff_match_patch.prototype.diff_levenshtein = function (diffs) {
+  var levenshtein = 0
+  var insertions = 0
+  var deletions = 0
+  for (var x = 0; x < diffs.length; x++) {
+    var op = diffs[x][0]
+    var data = diffs[x][1]
+    switch (op) {
+      case DIFF_INSERT:
+        insertions += data.length
+        break
+      case DIFF_DELETE:
+        deletions += data.length
+        break
+      case DIFF_EQUAL:
+        // A deletion and an insertion is one substitution.
+        levenshtein += Math.max(insertions, deletions)
+        insertions = 0
+        deletions = 0
+        break
+    }
+  }
+  levenshtein += Math.max(insertions, deletions)
+  return levenshtein
+}
+
+/**
+ * Crush the diff into an encoded string which describes the operations
+ * required to transform text1 into text2.
+ * E.g. =3\t-2\t+ing  -> Keep 3 chars, delete 2 chars, insert 'ing'.
+ * Operations are tab-separated.  Inserted text is escaped using %xx notation.
+ * @param {!Array.<!diff_match_patch.Diff>} diffs Array of diff tuples.
+ * @return {string} Delta text.
+ */
+diff_match_patch.prototype.diff_toDelta = function (diffs) {
+  var text = []
+  for (var x = 0; x < diffs.length; x++) {
+    switch (diffs[x][0]) {
+      case DIFF_INSERT:
+        text[x] = '+' + encodeURI(diffs[x][1])
+        break
+      case DIFF_DELETE:
+        text[x] = '-' + diffs[x][1].length
+        break
+      case DIFF_EQUAL:
+        text[x] = '=' + diffs[x][1].length
+        break
+    }
+  }
+  return text.join('\t').replace(/%20/g, ' ')
+}
+
+/**
+ * Given the original text1, and an encoded string which describes the
+ * operations required to transform text1 into text2, compute the full diff.
+ * @param {string} text1 Source string for the diff.
+ * @param {string} delta Delta text.
+ * @return {!Array.<!diff_match_patch.Diff>} Array of diff tuples.
+ * @throws {!Error} If invalid input.
+ */
+diff_match_patch.prototype.diff_fromDelta = function (text1, delta) {
+  var diffs = []
+  var diffsLength = 0 // Keeping our own length var is faster in JS.
+  var pointer = 0 // Cursor in text1
+  var tokens = delta.split(/\t/g)
+  for (var x = 0; x < tokens.length; x++) {
+    // Each token begins with a one character parameter which specifies the
+    // operation of this token (delete, insert, equality).
+    var param = tokens[x].substring(1)
+    switch (tokens[x].charAt(0)) {
+      case '+':
+        try {
+          diffs[diffsLength++] = [DIFF_INSERT, decodeURI(param)]
+        } catch (ex) {
+          // Malformed URI sequence.
+          throw new Error('Illegal escape in diff_fromDelta: ' + param)
+        }
+        break
+      case '-':
+      // Fall through.
+      case '=':
+        var n = parseInt(param, 10)
+        if (isNaN(n) || n < 0) {
+          throw new Error('Invalid number in diff_fromDelta: ' + param)
+        }
+        var text = text1.substring(pointer, (pointer += n))
+        if (tokens[x].charAt(0) == '=') {
+          diffs[diffsLength++] = [DIFF_EQUAL, text]
+        } else {
+          diffs[diffsLength++] = [DIFF_DELETE, text]
+        }
+        break
+      default:
+        // Blank tokens are ok (from a trailing \t).
+        // Anything else is an error.
+        if (tokens[x]) {
+          throw new Error(
+            'Invalid diff operation in diff_fromDelta: ' + tokens[x]
+          )
+        }
+    }
+  }
+  if (pointer != text1.length) {
+    throw new Error(
+      'Delta length (' +
+        pointer +
+        ') does not equal source text length (' +
+        text1.length +
+        ').'
+    )
+  }
+  return diffs
+}
+
+//  MATCH FUNCTIONS
+
+/**
+ * Locate the best instance of 'pattern' in 'text' near 'loc'.
+ * @param {string} text The text to search.
+ * @param {string} pattern The pattern to search for.
+ * @param {number} loc The location to search around.
+ * @return {number} Best match index or -1.
+ */
+diff_match_patch.prototype.match_main = function (text, pattern, loc) {
+  // Check for null inputs.
+  if (text == null || pattern == null || loc == null) {
+    throw new Error('Null input. (match_main)')
+  }
+
+  loc = Math.max(0, Math.min(loc, text.length))
+  if (text == pattern) {
+    // Shortcut (potentially not guaranteed by the algorithm)
+    return 0
+  } else if (!text.length) {
+    // Nothing to match.
+    return -1
+  } else if (text.substring(loc, loc + pattern.length) == pattern) {
+    // Perfect match at the perfect spot!  (Includes case of null pattern)
+    return loc
+  } else {
+    // Do a fuzzy compare.
+    return this.match_bitap_(text, pattern, loc)
+  }
+}
+
+/**
+ * Locate the best instance of 'pattern' in 'text' near 'loc' using the
+ * Bitap algorithm.
+ * @param {string} text The text to search.
+ * @param {string} pattern The pattern to search for.
+ * @param {number} loc The location to search around.
+ * @return {number} Best match index or -1.
+ * @private
+ */
+diff_match_patch.prototype.match_bitap_ = function (text, pattern, loc) {
+  if (pattern.length > this.Match_MaxBits) {
+    throw new Error('Pattern too long for this browser.')
+  }
+
+  // Initialise the alphabet.
+  var s = this.match_alphabet_(pattern)
+
+  var dmp = this // 'this' becomes 'window' in a closure.
+
+  /**
+   * Compute and return the score for a match with e errors and x location.
+   * Accesses loc and pattern through being a closure.
+   * @param {number} e Number of errors in match.
+   * @param {number} x Location of match.
+   * @return {number} Overall score for match (0.0 = good, 1.0 = bad).
+   * @private
+   */
+  function match_bitapScore_(e, x) {
+    var accuracy = e / pattern.length
+    var proximity = Math.abs(loc - x)
+    if (!dmp.Match_Distance) {
+      // Dodge divide by zero error.
+      return proximity ? 1.0 : accuracy
+    }
+    return accuracy + proximity / dmp.Match_Distance
+  }
+
+  // Highest score beyond which we give up.
+  var score_threshold = this.Match_Threshold
+  // Is there a nearby exact match? (speedup)
+  var best_loc = text.indexOf(pattern, loc)
+  if (best_loc != -1) {
+    score_threshold = Math.min(match_bitapScore_(0, best_loc), score_threshold)
+    // What about in the other direction? (speedup)
+    best_loc = text.lastIndexOf(pattern, loc + pattern.length)
+    if (best_loc != -1) {
+      score_threshold = Math.min(
+        match_bitapScore_(0, best_loc),
+        score_threshold
+      )
+    }
+  }
+
+  // Initialise the bit arrays.
+  var matchmask = 1 << (pattern.length - 1)
+  best_loc = -1
+
+  var bin_min, bin_mid
+  var bin_max = pattern.length + text.length
+  var last_rd
+  for (var d = 0; d < pattern.length; d++) {
+    // Scan for the best match; each iteration allows for one more error.
+    // Run a binary search to determine how far from 'loc' we can stray at this
+    // error level.
+    bin_min = 0
+    bin_mid = bin_max
+    while (bin_min < bin_mid) {
+      if (match_bitapScore_(d, loc + bin_mid) <= score_threshold) {
+        bin_min = bin_mid
+      } else {
+        bin_max = bin_mid
+      }
+      bin_mid = Math.floor((bin_max - bin_min) / 2 + bin_min)
+    }
+    // Use the result from this iteration as the maximum for the next.
+    bin_max = bin_mid
+    var start = Math.max(1, loc - bin_mid + 1)
+    var finish = Math.min(loc + bin_mid, text.length) + pattern.length
+
+    var rd = Array(finish + 2)
+    rd[finish + 1] = (1 << d) - 1
+    for (var j = finish; j >= start; j--) {
+      // The alphabet (s) is a sparse hash, so the following line generates
+      // warnings.
+      var charMatch = s[text.charAt(j - 1)]
+      if (d === 0) {
+        // First pass: exact match.
+        rd[j] = ((rd[j + 1] << 1) | 1) & charMatch
+      } else {
+        // Subsequent passes: fuzzy match.
+        rd[j] =
+          (((rd[j + 1] << 1) | 1) & charMatch) |
+          (((last_rd[j + 1] | last_rd[j]) << 1) | 1) |
+          last_rd[j + 1]
+      }
+      if (rd[j] & matchmask) {
+        var score = match_bitapScore_(d, j - 1)
+        // This match will almost certainly be better than any existing match.
+        // But check anyway.
+        if (score <= score_threshold) {
+          // Told you so.
+          score_threshold = score
+          best_loc = j - 1
+          if (best_loc > loc) {
+            // When passing loc, don't exceed our current distance from loc.
+            start = Math.max(1, 2 * loc - best_loc)
+          } else {
+            // Already passed loc, downhill from here on in.
+            break
+          }
+        }
+      }
+    }
+    // No hope for a (better) match at greater error levels.
+    if (match_bitapScore_(d + 1, loc) > score_threshold) {
+      break
+    }
+    last_rd = rd
+  }
+  return best_loc
+}
+
+/**
+ * Initialise the alphabet for the Bitap algorithm.
+ * @param {string} pattern The text to encode.
+ * @return {!Object} Hash of character locations.
+ * @private
+ */
+diff_match_patch.prototype.match_alphabet_ = function (pattern) {
+  var s = {}
+  for (var i = 0; i < pattern.length; i++) {
+    s[pattern.charAt(i)] = 0
+  }
+  for (var i = 0; i < pattern.length; i++) {
+    s[pattern.charAt(i)] |= 1 << (pattern.length - i - 1)
+  }
+  return s
+}
+
+//  PATCH FUNCTIONS
+
+/**
+ * Increase the context until it is unique,
+ * but don't let the pattern expand beyond Match_MaxBits.
+ * @param {!diff_match_patch.patch_obj} patch The patch to grow.
+ * @param {string} text Source text.
+ * @private
+ */
+diff_match_patch.prototype.patch_addContext_ = function (patch, text) {
+  if (text.length == 0) {
+    return
+  }
+  var pattern = text.substring(patch.start2, patch.start2 + patch.length1)
+  var padding = 0
+
+  // Look for the first and last matches of pattern in text.  If two different
+  // matches are found, increase the pattern length.
+  while (
+    text.indexOf(pattern) != text.lastIndexOf(pattern) &&
+    pattern.length < this.Match_MaxBits - this.Patch_Margin - this.Patch_Margin
+  ) {
+    padding += this.Patch_Margin
+    pattern = text.substring(
+      patch.start2 - padding,
+      patch.start2 + patch.length1 + padding
+    )
+  }
+  // Add one chunk for good luck.
+  padding += this.Patch_Margin
+
+  // Add the prefix.
+  var prefix = text.substring(patch.start2 - padding, patch.start2)
+  if (prefix) {
+    patch.diffs.unshift([DIFF_EQUAL, prefix])
+  }
+  // Add the suffix.
+  var suffix = text.substring(
+    patch.start2 + patch.length1,
+    patch.start2 + patch.length1 + padding
+  )
+  if (suffix) {
+    patch.diffs.push([DIFF_EQUAL, suffix])
+  }
+
+  // Roll back the start points.
+  patch.start1 -= prefix.length
+  patch.start2 -= prefix.length
+  // Extend the lengths.
+  patch.length1 += prefix.length + suffix.length
+  patch.length2 += prefix.length + suffix.length
+}
+
+/**
+ * Compute a list of patches to turn text1 into text2.
+ * Use diffs if provided, otherwise compute it ourselves.
+ * There are four ways to call this function, depending on what data is
+ * available to the caller:
+ * Method 1:
+ * a = text1, b = text2
+ * Method 2:
+ * a = diffs
+ * Method 3 (optimal):
+ * a = text1, b = diffs
+ * Method 4 (deprecated, use method 3):
+ * a = text1, b = text2, c = diffs
+ *
+ * @param {string|!Array.<!diff_match_patch.Diff>} a text1 (methods 1,3,4) or
+ * Array of diff tuples for text1 to text2 (method 2).
+ * @param {string|!Array.<!diff_match_patch.Diff>} opt_b text2 (methods 1,4) or
+ * Array of diff tuples for text1 to text2 (method 3) or undefined (method 2).
+ * @param {string|!Array.<!diff_match_patch.Diff>} opt_c Array of diff tuples
+ * for text1 to text2 (method 4) or undefined (methods 1,2,3).
+ * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
+ */
+diff_match_patch.prototype.patch_make = function (a, opt_b, opt_c) {
+  var text1, diffs
+  if (
+    typeof a === 'string' &&
+    typeof opt_b === 'string' &&
+    typeof opt_c === 'undefined'
+  ) {
+    // Method 1: text1, text2
+    // Compute diffs from text1 and text2.
+    text1 = /** @type {string} */ (a)
+    diffs = this.diff_main(text1, /** @type {string} */ (opt_b), true)
+    if (diffs.length > 2) {
+      this.diff_cleanupSemantic(diffs)
+      this.diff_cleanupEfficiency(diffs)
+    }
+  } else if (
+    a &&
+    typeof a === 'object' &&
+    typeof opt_b === 'undefined' &&
+    typeof opt_c === 'undefined'
+  ) {
+    // Method 2: diffs
+    // Compute text1 from diffs.
+    diffs = /** @type {!Array.<!diff_match_patch.Diff>} */ (a)
+    text1 = this.diff_text1(diffs)
+  } else if (
+    typeof a === 'string' &&
+    opt_b &&
+    typeof opt_b === 'object' &&
+    typeof opt_c === 'undefined'
+  ) {
+    // Method 3: text1, diffs
+    text1 = /** @type {string} */ (a)
+    diffs = /** @type {!Array.<!diff_match_patch.Diff>} */ (opt_b)
+  } else if (
+    typeof a === 'string' &&
+    typeof opt_b === 'string' &&
+    opt_c &&
+    typeof opt_c === 'object'
+  ) {
+    // Method 4: text1, text2, diffs
+    // text2 is not used.
+    text1 = /** @type {string} */ (a)
+    diffs = /** @type {!Array.<!diff_match_patch.Diff>} */ (opt_c)
+  } else {
+    throw new Error('Unknown call format to patch_make.')
+  }
+
+  if (diffs.length === 0) {
+    return [] // Get rid of the null case.
+  }
+  var patches = []
+  var patch = new diff_match_patch.patch_obj()
+  var patchDiffLength = 0 // Keeping our own length var is faster in JS.
+  var char_count1 = 0 // Number of characters into the text1 string.
+  var char_count2 = 0 // Number of characters into the text2 string.
+  // Start with text1 (prepatch_text) and apply the diffs until we arrive at
+  // text2 (postpatch_text).  We recreate the patches one by one to determine
+  // context info.
+  var prepatch_text = text1
+  var postpatch_text = text1
+  for (var x = 0; x < diffs.length; x++) {
+    var diff_type = diffs[x][0]
+    var diff_text = diffs[x][1]
+
+    if (!patchDiffLength && diff_type !== DIFF_EQUAL) {
+      // A new patch starts here.
+      patch.start1 = char_count1
+      patch.start2 = char_count2
+    }
+
+    switch (diff_type) {
+      case DIFF_INSERT:
+        patch.diffs[patchDiffLength++] = diffs[x]
+        patch.length2 += diff_text.length
+        postpatch_text =
+          postpatch_text.substring(0, char_count2) +
+          diff_text +
+          postpatch_text.substring(char_count2)
+        break
+      case DIFF_DELETE:
+        patch.length1 += diff_text.length
+        patch.diffs[patchDiffLength++] = diffs[x]
+        postpatch_text =
+          postpatch_text.substring(0, char_count2) +
+          postpatch_text.substring(char_count2 + diff_text.length)
+        break
+      case DIFF_EQUAL:
+        if (
+          diff_text.length <= 2 * this.Patch_Margin &&
+          patchDiffLength &&
+          diffs.length != x + 1
+        ) {
+          // Small equality inside a patch.
+          patch.diffs[patchDiffLength++] = diffs[x]
+          patch.length1 += diff_text.length
+          patch.length2 += diff_text.length
+        } else if (diff_text.length >= 2 * this.Patch_Margin) {
+          // Time for a new patch.
+          if (patchDiffLength) {
+            this.patch_addContext_(patch, prepatch_text)
+            patches.push(patch)
+            patch = new diff_match_patch.patch_obj()
+            patchDiffLength = 0
+            // Unlike Unidiff, our patch lists have a rolling context.
+            // http://code.google.com/p/google-diff-match-patch/wiki/Unidiff
+            // Update prepatch text & pos to reflect the application of the
+            // just completed patch.
+            prepatch_text = postpatch_text
+            char_count1 = char_count2
+          }
+        }
+        break
+    }
+
+    // Update the current character count.
+    if (diff_type !== DIFF_INSERT) {
+      char_count1 += diff_text.length
+    }
+    if (diff_type !== DIFF_DELETE) {
+      char_count2 += diff_text.length
+    }
+  }
+  // Pick up the leftover patch if not empty.
+  if (patchDiffLength) {
+    this.patch_addContext_(patch, prepatch_text)
+    patches.push(patch)
+  }
+
+  return patches
+}
+
+/**
+ * Given an array of patches, return another array that is identical.
+ * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
+ * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
+ */
+diff_match_patch.prototype.patch_deepCopy = function (patches) {
+  // Making deep copies is hard in JavaScript.
+  var patchesCopy = []
+  for (var x = 0; x < patches.length; x++) {
+    var patch = patches[x]
+    var patchCopy = new diff_match_patch.patch_obj()
+    patchCopy.diffs = []
+    for (var y = 0; y < patch.diffs.length; y++) {
+      patchCopy.diffs[y] = patch.diffs[y].slice()
+    }
+    patchCopy.start1 = patch.start1
+    patchCopy.start2 = patch.start2
+    patchCopy.length1 = patch.length1
+    patchCopy.length2 = patch.length2
+    patchesCopy[x] = patchCopy
+  }
+  return patchesCopy
+}
+
+/**
+ * Merge a set of patches onto the text.  Return a patched text, as well
+ * as a list of true/false values indicating which patches were applied.
+ * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
+ * @param {string} text Old text.
+ * @return {!Array.<string|!Array.<boolean>>} Two element Array, containing the
+ *      new text and an array of boolean values.
+ */
+diff_match_patch.prototype.patch_apply = function (patches, text) {
+  if (patches.length == 0) {
+    return [text, []]
+  }
+
+  // Deep copy the patches so that no changes are made to originals.
+  patches = this.patch_deepCopy(patches)
+
+  var nullPadding = this.patch_addPadding(patches)
+  text = nullPadding + text + nullPadding
+
+  this.patch_splitMax(patches)
+  // delta keeps track of the offset between the expected and actual location
+  // of the previous patch.  If there are patches expected at positions 10 and
+  // 20, but the first patch was found at 12, delta is 2 and the second patch
+  // has an effective expected position of 22.
+  var delta = 0
+  var results = []
+  for (var x = 0; x < patches.length; x++) {
+    var expected_loc = patches[x].start2 + delta
+    var text1 = this.diff_text1(patches[x].diffs)
+    var start_loc
+    var end_loc = -1
+    if (text1.length > this.Match_MaxBits) {
+      // patch_splitMax will only provide an oversized pattern in the case of
+      // a monster delete.
+      start_loc = this.match_main(
+        text,
+        text1.substring(0, this.Match_MaxBits),
+        expected_loc
+      )
+      if (start_loc != -1) {
+        end_loc = this.match_main(
+          text,
+          text1.substring(text1.length - this.Match_MaxBits),
+          expected_loc + text1.length - this.Match_MaxBits
+        )
+        if (end_loc == -1 || start_loc >= end_loc) {
+          // Can't find valid trailing context.  Drop this patch.
+          start_loc = -1
+        }
+      }
+    } else {
+      start_loc = this.match_main(text, text1, expected_loc)
+    }
+    if (start_loc == -1) {
+      // No match found.  :(
+      results[x] = false
+      // Subtract the delta for this failed patch from subsequent patches.
+      delta -= patches[x].length2 - patches[x].length1
+    } else {
+      // Found a match.  :)
+      results[x] = true
+      delta = start_loc - expected_loc
+      var text2
+      if (end_loc == -1) {
+        text2 = text.substring(start_loc, start_loc + text1.length)
+      } else {
+        text2 = text.substring(start_loc, end_loc + this.Match_MaxBits)
+      }
+      if (text1 == text2) {
+        // Perfect match, just shove the replacement text in.
+        text =
+          text.substring(0, start_loc) +
+          this.diff_text2(patches[x].diffs) +
+          text.substring(start_loc + text1.length)
+      } else {
+        // Imperfect match.  Run a diff to get a framework of equivalent
+        // indices.
+        var diffs = this.diff_main(text1, text2, false)
+        if (
+          text1.length > this.Match_MaxBits &&
+          this.diff_levenshtein(diffs) / text1.length >
+            this.Patch_DeleteThreshold
+        ) {
+          // The end points match, but the content is unacceptably bad.
+          results[x] = false
+        } else {
+          this.diff_cleanupSemanticLossless(diffs)
+          var index1 = 0
+          var index2
+          for (var y = 0; y < patches[x].diffs.length; y++) {
+            var mod = patches[x].diffs[y]
+            if (mod[0] !== DIFF_EQUAL) {
+              index2 = this.diff_xIndex(diffs, index1)
+            }
+            if (mod[0] === DIFF_INSERT) {
+              // Insertion
+              text =
+                text.substring(0, start_loc + index2) +
+                mod[1] +
+                text.substring(start_loc + index2)
+            } else if (mod[0] === DIFF_DELETE) {
+              // Deletion
+              text =
+                text.substring(0, start_loc + index2) +
+                text.substring(
+                  start_loc + this.diff_xIndex(diffs, index1 + mod[1].length)
+                )
+            }
+            if (mod[0] !== DIFF_DELETE) {
+              index1 += mod[1].length
+            }
+          }
+        }
+      }
+    }
+  }
+  // Strip the padding off.
+  text = text.substring(nullPadding.length, text.length - nullPadding.length)
+  return [text, results]
+}
+
+/**
+ * Add some padding on text start and end so that edges can match something.
+ * Intended to be called only from within patch_apply.
+ * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
+ * @return {string} The padding string added to each side.
+ */
+diff_match_patch.prototype.patch_addPadding = function (patches) {
+  var paddingLength = this.Patch_Margin
+  var nullPadding = ''
+  for (var x = 1; x <= paddingLength; x++) {
+    nullPadding += String.fromCharCode(x)
+  }
+
+  // Bump all the patches forward.
+  for (var x = 0; x < patches.length; x++) {
+    patches[x].start1 += paddingLength
+    patches[x].start2 += paddingLength
+  }
+
+  // Add some padding on start of first diff.
+  var patch = patches[0]
+  var diffs = patch.diffs
+  if (diffs.length == 0 || diffs[0][0] != DIFF_EQUAL) {
+    // Add nullPadding equality.
+    diffs.unshift([DIFF_EQUAL, nullPadding])
+    patch.start1 -= paddingLength // Should be 0.
+    patch.start2 -= paddingLength // Should be 0.
+    patch.length1 += paddingLength
+    patch.length2 += paddingLength
+  } else if (paddingLength > diffs[0][1].length) {
+    // Grow first equality.
+    var extraLength = paddingLength - diffs[0][1].length
+    diffs[0][1] = nullPadding.substring(diffs[0][1].length) + diffs[0][1]
+    patch.start1 -= extraLength
+    patch.start2 -= extraLength
+    patch.length1 += extraLength
+    patch.length2 += extraLength
+  }
+
+  // Add some padding on end of last diff.
+  patch = patches[patches.length - 1]
+  diffs = patch.diffs
+  if (diffs.length == 0 || diffs[diffs.length - 1][0] != DIFF_EQUAL) {
+    // Add nullPadding equality.
+    diffs.push([DIFF_EQUAL, nullPadding])
+    patch.length1 += paddingLength
+    patch.length2 += paddingLength
+  } else if (paddingLength > diffs[diffs.length - 1][1].length) {
+    // Grow last equality.
+    var extraLength = paddingLength - diffs[diffs.length - 1][1].length
+    diffs[diffs.length - 1][1] += nullPadding.substring(0, extraLength)
+    patch.length1 += extraLength
+    patch.length2 += extraLength
+  }
+
+  return nullPadding
+}
+
+/**
+ * Look through the patches and break up any which are longer than the maximum
+ * limit of the match algorithm.
+ * Intended to be called only from within patch_apply.
+ * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
+ */
+diff_match_patch.prototype.patch_splitMax = function (patches) {
+  var patch_size = this.Match_MaxBits
+  for (var x = 0; x < patches.length; x++) {
+    if (patches[x].length1 <= patch_size) {
+      continue
+    }
+    var bigpatch = patches[x]
+    // Remove the big old patch.
+    patches.splice(x--, 1)
+    var start1 = bigpatch.start1
+    var start2 = bigpatch.start2
+    var precontext = ''
+    while (bigpatch.diffs.length !== 0) {
+      // Create one of several smaller patches.
+      var patch = new diff_match_patch.patch_obj()
+      var empty = true
+      patch.start1 = start1 - precontext.length
+      patch.start2 = start2 - precontext.length
+      if (precontext !== '') {
+        patch.length1 = patch.length2 = precontext.length
+        patch.diffs.push([DIFF_EQUAL, precontext])
+      }
+      while (
+        bigpatch.diffs.length !== 0 &&
+        patch.length1 < patch_size - this.Patch_Margin
+      ) {
+        var diff_type = bigpatch.diffs[0][0]
+        var diff_text = bigpatch.diffs[0][1]
+        if (diff_type === DIFF_INSERT) {
+          // Insertions are harmless.
+          patch.length2 += diff_text.length
+          start2 += diff_text.length
+          patch.diffs.push(bigpatch.diffs.shift())
+          empty = false
+        } else if (
+          diff_type === DIFF_DELETE &&
+          patch.diffs.length == 1 &&
+          patch.diffs[0][0] == DIFF_EQUAL &&
+          diff_text.length > 2 * patch_size
+        ) {
+          // This is a large deletion.  Let it pass in one chunk.
+          patch.length1 += diff_text.length
+          start1 += diff_text.length
+          empty = false
+          patch.diffs.push([diff_type, diff_text])
+          bigpatch.diffs.shift()
+        } else {
+          // Deletion or equality.  Only take as much as we can stomach.
+          diff_text = diff_text.substring(
+            0,
+            patch_size - patch.length1 - this.Patch_Margin
+          )
+          patch.length1 += diff_text.length
+          start1 += diff_text.length
+          if (diff_type === DIFF_EQUAL) {
+            patch.length2 += diff_text.length
+            start2 += diff_text.length
+          } else {
+            empty = false
+          }
+          patch.diffs.push([diff_type, diff_text])
+          if (diff_text == bigpatch.diffs[0][1]) {
+            bigpatch.diffs.shift()
+          } else {
+            bigpatch.diffs[0][1] = bigpatch.diffs[0][1].substring(
+              diff_text.length
+            )
+          }
+        }
+      }
+      // Compute the head context for the next patch.
+      precontext = this.diff_text2(patch.diffs)
+      precontext = precontext.substring(precontext.length - this.Patch_Margin)
+      // Append the end context for this patch.
+      var postcontext = this.diff_text1(bigpatch.diffs).substring(
+        0,
+        this.Patch_Margin
+      )
+      if (postcontext !== '') {
+        patch.length1 += postcontext.length
+        patch.length2 += postcontext.length
+        if (
+          patch.diffs.length !== 0 &&
+          patch.diffs[patch.diffs.length - 1][0] === DIFF_EQUAL
+        ) {
+          patch.diffs[patch.diffs.length - 1][1] += postcontext
+        } else {
+          patch.diffs.push([DIFF_EQUAL, postcontext])
+        }
+      }
+      if (!empty) {
+        patches.splice(++x, 0, patch)
+      }
+    }
+  }
+}
+
+/**
+ * Take a list of patches and return a textual representation.
+ * @param {!Array.<!diff_match_patch.patch_obj>} patches Array of Patch objects.
+ * @return {string} Text representation of patches.
+ */
+diff_match_patch.prototype.patch_toText = function (patches) {
+  var text = []
+  for (var x = 0; x < patches.length; x++) {
+    text[x] = patches[x]
+  }
+  return text.join('')
+}
+
+/**
+ * Parse a textual representation of patches and return a list of Patch objects.
+ * @param {string} textline Text representation of patches.
+ * @return {!Array.<!diff_match_patch.patch_obj>} Array of Patch objects.
+ * @throws {!Error} If invalid input.
+ */
+diff_match_patch.prototype.patch_fromText = function (textline) {
+  var patches = []
+  if (!textline) {
+    return patches
+  }
+  var text = textline.split('\n')
+  var textPointer = 0
+  var patchHeader = /^@@ -(\d+),?(\d*) \+(\d+),?(\d*) @@$/
+  while (textPointer < text.length) {
+    var m = text[textPointer].match(patchHeader)
+    if (!m) {
+      throw new Error('Invalid patch string: ' + text[textPointer])
+    }
+    var patch = new diff_match_patch.patch_obj()
+    patches.push(patch)
+    patch.start1 = parseInt(m[1], 10)
+    if (m[2] === '') {
+      patch.start1--
+      patch.length1 = 1
+    } else if (m[2] == '0') {
+      patch.length1 = 0
+    } else {
+      patch.start1--
+      patch.length1 = parseInt(m[2], 10)
+    }
+
+    patch.start2 = parseInt(m[3], 10)
+    if (m[4] === '') {
+      patch.start2--
+      patch.length2 = 1
+    } else if (m[4] == '0') {
+      patch.length2 = 0
+    } else {
+      patch.start2--
+      patch.length2 = parseInt(m[4], 10)
+    }
+    textPointer++
+
+    while (textPointer < text.length) {
+      var sign = text[textPointer].charAt(0)
+      try {
+        var line = decodeURI(text[textPointer].substring(1))
+      } catch (ex) {
+        // Malformed URI sequence.
+        throw new Error('Illegal escape in patch_fromText: ' + line)
+      }
+      if (sign == '-') {
+        // Deletion.
+        patch.diffs.push([DIFF_DELETE, line])
+      } else if (sign == '+') {
+        // Insertion.
+        patch.diffs.push([DIFF_INSERT, line])
+      } else if (sign == ' ') {
+        // Minor equality.
+        patch.diffs.push([DIFF_EQUAL, line])
+      } else if (sign == '@') {
+        // Start of next patch.
+        break
+      } else if (sign === '') {
+        // Blank line?  Whatever.
+      } else {
+        // WTF?
+        throw new Error('Invalid patch mode "' + sign + '" in: ' + line)
+      }
+      textPointer++
+    }
+  }
+  return patches
+}
+
+/**
+ * Class representing one patch operation.
+ * @constructor
+ */
+diff_match_patch.patch_obj = function () {
+  /** @type {!Array.<!diff_match_patch.Diff>} */
+  this.diffs = []
+  /** @type {?number} */
+  this.start1 = null
+  /** @type {?number} */
+  this.start2 = null
+  /** @type {number} */
+  this.length1 = 0
+  /** @type {number} */
+  this.length2 = 0
+}
+
+/**
+ * Emmulate GNU diff's format.
+ * Header: @@ -382,8 +481,9 @@
+ * Indicies are printed as 1-based, not 0-based.
+ * @return {string} The GNU diff string.
+ */
+diff_match_patch.patch_obj.prototype.toString = function () {
+  var coords1, coords2
+  if (this.length1 === 0) {
+    coords1 = this.start1 + ',0'
+  } else if (this.length1 == 1) {
+    coords1 = this.start1 + 1
+  } else {
+    coords1 = this.start1 + 1 + ',' + this.length1
+  }
+  if (this.length2 === 0) {
+    coords2 = this.start2 + ',0'
+  } else if (this.length2 == 1) {
+    coords2 = this.start2 + 1
+  } else {
+    coords2 = this.start2 + 1 + ',' + this.length2
+  }
+  var text = ['@@ -' + coords1 + ' +' + coords2 + ' @@\n']
+  var op
+  // Escape the body of the patch with %xx notation.
+  for (var x = 0; x < this.diffs.length; x++) {
+    switch (this.diffs[x][0]) {
+      case DIFF_INSERT:
+        op = '+'
+        break
+      case DIFF_DELETE:
+        op = '-'
+        break
+      case DIFF_EQUAL:
+        op = ' '
+        break
+    }
+    text[x + 1] = op + encodeURI(this.diffs[x][1]) + '\n'
+  }
+  return text.join('').replace(/%20/g, ' ')
+}
+
+// Export these global variables so that they survive Google's JS compiler.
+// In a browser, 'this' will be 'window'.
+// Users of node.js should 'require' the uncompressed version since Google's
+// JS compiler may break the following exports for non-browser environments.
+this.diff_match_patch = diff_match_patch
+this.DIFF_DELETE = DIFF_DELETE
+this.DIFF_INSERT = DIFF_INSERT
+this.DIFF_EQUAL = DIFF_EQUAL

services/track-changes/buildscript.txt

@@ -0,0 +1,8 @@
+track-changes
+--dependencies=mongo,redis,s3
+--docker-repos=gcr.io/overleaf-ops
+--env-add=AWS_BUCKET=bucket
+--env-pass-through=
+--node-version=12.22.3
+--public-repo=True
+--script-version=3.11.0

services/track-changes/config/settings.defaults.js

@@ -0,0 +1,90 @@
+const Path = require('path')
+const TMP_DIR =
+  process.env.TMP_PATH || Path.resolve(Path.join(__dirname, '../../', 'tmp'))
+
+module.exports = {
+  mongo: {
+    options: {
+      useUnifiedTopology:
+        (process.env.MONGO_USE_UNIFIED_TOPOLOGY || 'true') === 'true',
+    },
+    url:
+      process.env.MONGO_CONNECTION_STRING ||
+      `mongodb://${process.env.MONGO_HOST || 'localhost'}/sharelatex`,
+  },
+
+  internal: {
+    trackchanges: {
+      port: 3015,
+      host: process.env.LISTEN_ADDRESS || 'localhost',
+    },
+  },
+  apis: {
+    documentupdater: {
+      url: `http://${
+        process.env.DOCUMENT_UPDATER_HOST ||
+        process.env.DOCUPDATER_HOST ||
+        'localhost'
+      }:3003`,
+    },
+    docstore: {
+      url: `http://${process.env.DOCSTORE_HOST || 'localhost'}:3016`,
+    },
+    web: {
+      url: `http://${
+        process.env.WEB_API_HOST || process.env.WEB_HOST || 'localhost'
+      }:${process.env.WEB_API_PORT || process.env.WEB_PORT || 3000}`,
+      user: process.env.WEB_API_USER || 'sharelatex',
+      pass: process.env.WEB_API_PASSWORD || 'password',
+    },
+  },
+  redis: {
+    lock: {
+      host: process.env.REDIS_HOST || 'localhost',
+      port: process.env.REDIS_PORT || 6379,
+      password: process.env.REDIS_PASSWORD || '',
+      key_schema: {
+        historyLock({ doc_id: docId }) {
+          return `HistoryLock:{${docId}}`
+        },
+        historyIndexLock({ project_id: projectId }) {
+          return `HistoryIndexLock:{${projectId}}`
+        },
+      },
+    },
+    history: {
+      host: process.env.REDIS_HOST || 'localhost',
+      port: process.env.REDIS_PORT || 6379,
+      password: process.env.REDIS_PASSWORD || '',
+      key_schema: {
+        uncompressedHistoryOps({ doc_id: docId }) {
+          return `UncompressedHistoryOps:{${docId}}`
+        },
+        docsWithHistoryOps({ project_id: projectId }) {
+          return `DocsWithHistoryOps:{${projectId}}`
+        },
+      },
+    },
+  },
+
+  trackchanges: {
+    s3: {
+      key: process.env.AWS_ACCESS_KEY_ID,
+      secret: process.env.AWS_SECRET_ACCESS_KEY,
+      endpoint: process.env.AWS_S3_ENDPOINT,
+      pathStyle: process.env.AWS_S3_PATH_STYLE === 'true',
+    },
+    stores: {
+      doc_history: process.env.AWS_BUCKET,
+    },
+    continueOnError: process.env.TRACK_CHANGES_CONTINUE_ON_ERROR || false,
+  },
+
+  path: {
+    dumpFolder: Path.join(TMP_DIR, 'dumpFolder'),
+  },
+
+  sentry: {
+    dsn: process.env.SENTRY_DSN,
+  },
+}

services/track-changes/docker-compose.ci.yml

@@ -0,0 +1,72 @@
+# This file was auto-generated, do not edit it directly.
+# Instead run bin/update_build_scripts from
+# https://github.com/sharelatex/sharelatex-dev-environment
+
+version: "2.3"
+
+services:
+  test_unit:
+    image: ci/$PROJECT_NAME:$BRANCH_NAME-$BUILD_NUMBER
+    user: node
+    command: npm run test:unit:_run
+    environment:
+      NODE_ENV: test
+      NODE_OPTIONS: "--unhandled-rejections=strict"
+
+
+  test_acceptance:
+    build: .
+    image: ci/$PROJECT_NAME:$BRANCH_NAME-$BUILD_NUMBER
+    environment:
+      ELASTIC_SEARCH_DSN: es:9200
+      REDIS_HOST: redis
+      QUEUES_REDIS_HOST: redis
+      MONGO_HOST: mongo
+      POSTGRES_HOST: postgres
+      AWS_S3_ENDPOINT: http://s3:9090
+      AWS_S3_PATH_STYLE: 'true'
+      AWS_ACCESS_KEY_ID: fake
+      AWS_SECRET_ACCESS_KEY: fake
+      MOCHA_GREP: ${MOCHA_GREP}
+      NODE_ENV: test
+      NODE_OPTIONS: "--unhandled-rejections=strict"
+      AWS_BUCKET: bucket
+    depends_on:
+      mongo:
+        condition: service_healthy
+      redis:
+        condition: service_healthy
+      s3:
+        condition: service_healthy
+    user: node
+    command: npm run test:acceptance:_run
+
+
+  tar:
+    build: .
+    image: ci/$PROJECT_NAME:$BRANCH_NAME-$BUILD_NUMBER
+    volumes:
+      - ./:/tmp/build/
+    command: tar -czf /tmp/build/build.tar.gz --exclude=build.tar.gz --exclude-vcs .
+    user: root
+  redis:
+    image: redis
+    healthcheck:
+      test: ping="$$(redis-cli ping)" && [ "$$ping" = 'PONG' ]
+      interval: 1s
+      retries: 20
+
+  mongo:
+    image: mongo:4.0
+    healthcheck:
+      test: "mongo --quiet localhost/test --eval 'quit(db.runCommand({ ping: 1 }).ok ? 0 : 1)'"
+      interval: 1s
+      retries: 20
+  s3:
+    image: adobe/s3mock
+    environment:
+      - initialBuckets=fake_user_files,fake_template_files,fake_public_files,bucket
+    healthcheck:
+      test: wget --quiet --output-document=/dev/null http://localhost:9090
+      interval: 1s
+      retries: 20

services/track-changes/docker-compose.yml

@@ -0,0 +1,71 @@
+# This file was auto-generated, do not edit it directly.
+# Instead run bin/update_build_scripts from
+# https://github.com/sharelatex/sharelatex-dev-environment
+
+version: "2.3"
+
+services:
+  test_unit:
+    image: node:12.22.3
+    volumes:
+      - .:/app
+    working_dir: /app
+    environment:
+      MOCHA_GREP: ${MOCHA_GREP}
+      NODE_ENV: test
+      NODE_OPTIONS: "--unhandled-rejections=strict"
+    command: npm run --silent test:unit
+    user: node
+
+  test_acceptance:
+    image: node:12.22.3
+    volumes:
+      - .:/app
+    working_dir: /app
+    environment:
+      ELASTIC_SEARCH_DSN: es:9200
+      REDIS_HOST: redis
+      QUEUES_REDIS_HOST: redis
+      MONGO_HOST: mongo
+      POSTGRES_HOST: postgres
+      AWS_S3_ENDPOINT: http://s3:9090
+      AWS_S3_PATH_STYLE: 'true'
+      AWS_ACCESS_KEY_ID: fake
+      AWS_SECRET_ACCESS_KEY: fake
+      MOCHA_GREP: ${MOCHA_GREP}
+      LOG_LEVEL: ERROR
+      NODE_ENV: test
+      NODE_OPTIONS: "--unhandled-rejections=strict"
+      AWS_BUCKET: bucket
+    user: node
+    depends_on:
+      mongo:
+        condition: service_healthy
+      redis:
+        condition: service_healthy
+      s3:
+        condition: service_healthy
+    command: npm run --silent test:acceptance
+
+  redis:
+    image: redis
+    healthcheck:
+      test: ping=$$(redis-cli ping) && [ "$$ping" = 'PONG' ]
+      interval: 1s
+      retries: 20
+
+  mongo:
+    image: mongo:4.0
+    healthcheck:
+      test: "mongo --quiet localhost/test --eval 'quit(db.runCommand({ ping: 1 }).ok ? 0 : 1)'"
+      interval: 1s
+      retries: 20
+
+  s3:
+    image: adobe/s3mock
+    environment:
+      - initialBuckets=fake_user_files,fake_template_files,fake_public_files,bucket
+    healthcheck:
+      test: wget --quiet --output-document=/dev/null http://localhost:9090
+      interval: 1s
+      retries: 20

services/track-changes/nodemon.json

@@ -0,0 +1,17 @@
+{
+  "ignore": [
+    ".git",
+    "node_modules/"
+  ],
+  "verbose": true,
+  "legacyWatch": true,
+  "execMap": {
+    "js": "npm run start"
+  },
+  "watch": [
+    "app/js/",
+    "app.js",
+    "config/"
+  ],
+  "ext": "js"
+}

services/track-changes/pack.sh

@@ -0,0 +1,24 @@
+#!/bin/bash -x
+
+# find all the docHistories with unpacked ops and pack them
+
+# need to keep track of docs already done
+
+HOST=${1:-"localhost:3015"}
+T=${2:-10}
+
+echo packing all docHistory on $HOST with delay of $T
+for n in $(seq 5 -1 1) ; do
+    echo starting in $n seconds
+    sleep 1
+done
+
+while docs=$(curl "$HOST/doc/list?limit=1000&doc_id=$last_doc"); do
+    if [ -z "$docs" ] ; then break ; fi
+    for d in $docs ; do 
+	echo "packing $d"
+	curl -X POST "$HOST/doc/$d/pack"
+	sleep $T
+	last_doc=$d
+    done
+done

services/track-changes/package-lock.json

@@ -0,0 +1,5794 @@
+{
+  "name": "history-sharelatex",
+  "version": "0.1.4",
+  "lockfileVersion": 1,
+  "requires": true,
+  "dependencies": {
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+      "dev": true,
+      "requires": {
+        "@babel/highlight": "^7.10.4"
+      }
+    },
+    "@babel/helper-validator-identifier": {
+      "version": "7.14.5",
+      "resolved": "https://registry.npmjs.org/@babel/helper-validator-identifier/-/helper-validator-identifier-7.14.5.tgz",
+      "integrity": "sha512-5lsetuxCLilmVGyiLEfoHBRX8UCFD+1m2x3Rj97WrW3V7H3u4RWRXA4evMjImCsin2J2YT0QaVDGf+z8ondbAg==",
+      "dev": true
+    },
+    "@babel/highlight": {
+      "version": "7.14.5",
+      "resolved": "https://registry.npmjs.org/@babel/highlight/-/highlight-7.14.5.tgz",
+      "integrity": "sha512-qf9u2WFWVV0MppaL877j2dBtQIDgmidgjGk5VIMw3OadXvYaXn66U1BFlH2t4+t3i+8PhedppRv+i40ABzd+gg==",
+      "dev": true,
+      "requires": {
+        "@babel/helper-validator-identifier": "^7.14.5",
+        "chalk": "^2.0.0",
+        "js-tokens": "^4.0.0"
+      }
+    },
+    "@eslint/eslintrc": {
+      "version": "0.4.2",
+      "resolved": "https://registry.npmjs.org/@eslint/eslintrc/-/eslintrc-0.4.2.tgz",
+      "integrity": "sha512-8nmGq/4ycLpIwzvhI4tNDmQztZ8sp+hI7cyG8i1nQDhkAbRzHpXPidRAHlNvCZQpJTKw5ItIpMw9RSToGF00mg==",
+      "dev": true,
+      "requires": {
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+        "debug": "^4.1.1",
+        "espree": "^7.3.0",
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+        "js-yaml": "^3.13.1",
+        "minimatch": "^3.0.4",
+        "strip-json-comments": "^3.1.1"
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+          }
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+        "fast-deep-equal": {
+          "version": "3.1.3",
+          "resolved": "https://registry.npmjs.org/fast-deep-equal/-/fast-deep-equal-3.1.3.tgz",
+          "integrity": "sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==",
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+        }
+      }
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+          }
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+      }
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+    "@google-cloud/debug-agent": {
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+      "requires": {
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+          "version": "2.0.0",
+          "resolved": "https://registry.npmjs.org/is-fullwidth-code-point/-/is-fullwidth-code-point-2.0.0.tgz",
+          "integrity": "sha512-VHskAKYM8RfSFXwee5t5cbN5PZeq1Wrh6qd5bkyiXIf6UQcN6w/A0eXM9r6t8d+GYOh+o6ZhiEnb88LN/Y8m2w=="
+        },
+        "string-width": {
+          "version": "2.1.1",
+          "resolved": "https://registry.npmjs.org/string-width/-/string-width-2.1.1.tgz",
+          "integrity": "sha512-nOqH59deCq9SRHlxq1Aw85Jnt4w6KvLKqWVik6oA9ZklXLNIOlqg4F2yrT1MVaTjAqvVwdfeZ7w7aCvJD7ugkw==",
+          "requires": {
+            "is-fullwidth-code-point": "^2.0.0",
+            "strip-ansi": "^4.0.0"
+          }
+        },
+        "strip-ansi": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/strip-ansi/-/strip-ansi-4.0.0.tgz",
+          "integrity": "sha512-4XaJ2zQdCzROZDivEVIDPkcQn8LMFSa8kj8Gxb/Lnwzv9A8VctNZ+lfivC/sV3ivW8ElJTERXZoPBRrZKkNKow==",
+          "requires": {
+            "ansi-regex": "^3.0.0"
+          }
+        }
+      }
+    },
+    "word-wrap": {
+      "version": "1.2.3",
+      "resolved": "https://registry.npmjs.org/word-wrap/-/word-wrap-1.2.3.tgz",
+      "integrity": "sha512-Hz/mrNwitNRh/HUAtM/VT/5VH+ygD6DV7mYKZAtHOrbs8U7lvPS6xf7EJKMF0uW1KJCl0H701g3ZGus+muE5vQ==",
+      "dev": true
+    },
+    "workerpool": {
+      "version": "6.1.0",
+      "resolved": "https://registry.npmjs.org/workerpool/-/workerpool-6.1.0.tgz",
+      "integrity": "sha512-toV7q9rWNYha963Pl/qyeZ6wG+3nnsyvolaNUS8+R5Wtw6qJPTxIlOP1ZSvcGhEJw+l3HMMmtiNo9Gl61G4GVg==",
+      "dev": true
+    },
+    "wrap-ansi": {
+      "version": "7.0.0",
+      "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-7.0.0.tgz",
+      "integrity": "sha512-YVGIj2kamLSTxw6NsZjoBxfSwsn0ycdesmc4p+Q21c5zPuZ1pl+NfxVdxPtdHvmNVOQ6XSYG4AUtyt/Fi7D16Q==",
+      "dev": true,
+      "requires": {
+        "string-width": "^4.1.0",
+        "strip-ansi": "^6.0.0"
+      }
+    },
+    "wrappy": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
+      "integrity": "sha512-l4Sp/DRseor9wL6EvV2+TuQn63dMkPjZ/sp9XkghTEbV9KlPS1xUsZ3u7/IQO4wxtcFB4bgpQPRcR3QCvezPcQ=="
+    },
+    "xml2js": {
+      "version": "0.4.19",
+      "resolved": "https://registry.npmjs.org/xml2js/-/xml2js-0.4.19.tgz",
+      "integrity": "sha512-esZnJZJOiJR9wWKMyuvSE1y6Dq5LCuJanqhxslH2bxM6duahNZ+HMpCLhBQGZkbX6xRf8x1Y2eJlgt2q3qo49Q==",
+      "requires": {
+        "sax": ">=0.6.0",
+        "xmlbuilder": "~9.0.1"
+      }
+    },
+    "xmlbuilder": {
+      "version": "9.0.7",
+      "resolved": "https://registry.npmjs.org/xmlbuilder/-/xmlbuilder-9.0.7.tgz",
+      "integrity": "sha512-7YXTQc3P2l9+0rjaUbLwMKRhtmwg1M1eDf6nag7urC7pIPYLD9W/jmzQ4ptRSUbodw5S0jfoGTflLemQibSpeQ=="
+    },
+    "y18n": {
+      "version": "5.0.8",
+      "resolved": "https://registry.npmjs.org/y18n/-/y18n-5.0.8.tgz",
+      "integrity": "sha512-0pfFzegeDWJHJIAmTLRP2DwHjdF5s7jo9tuztdQxAhINCdvS+3nGINqPd00AphqJR/0LhANUS6/+7SCb98YOfA==",
+      "dev": true
+    },
+    "yallist": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/yallist/-/yallist-3.1.1.tgz",
+      "integrity": "sha512-a4UGQaWPH59mOXUYnAG2ewncQS4i4F43Tv3JoAM+s2VDAmS9NsK8GpDMLrCHPksFT7h3K6TOoUNn2pb7RoXx4g=="
+    },
+    "yargs": {
+      "version": "16.2.0",
+      "resolved": "https://registry.npmjs.org/yargs/-/yargs-16.2.0.tgz",
+      "integrity": "sha512-D1mvvtDG0L5ft/jGWkLpG1+m0eQxOfaBvTNELraWj22wSVUMWxZUvYgJYcKh6jGGIkJFhH4IZPQhR4TKpc8mBw==",
+      "dev": true,
+      "requires": {
+        "cliui": "^7.0.2",
+        "escalade": "^3.1.1",
+        "get-caller-file": "^2.0.5",
+        "require-directory": "^2.1.1",
+        "string-width": "^4.2.0",
+        "y18n": "^5.0.5",
+        "yargs-parser": "^20.2.2"
+      }
+    },
+    "yargs-parser": {
+      "version": "20.2.4",
+      "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-20.2.4.tgz",
+      "integrity": "sha512-WOkpgNhPTlE73h4VFAFsOnomJVaovO8VqLDzy5saChRBFQFBoMYirowyW+Q9HB4HFF4Z7VZTiG3iSzJJA29yRA==",
+      "dev": true
+    },
+    "yargs-unparser": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/yargs-unparser/-/yargs-unparser-2.0.0.tgz",
+      "integrity": "sha512-7pRTIA9Qc1caZ0bZ6RYRGbHJthJWuakf+WmHK0rVeLkNrrGhfoabBNdue6kdINI6r4if7ocq9aD/n7xwKOdzOA==",
+      "dev": true,
+      "requires": {
+        "camelcase": "^6.0.0",
+        "decamelize": "^4.0.0",
+        "flat": "^5.0.2",
+        "is-plain-obj": "^2.1.0"
+      }
+    },
+    "yn": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/yn/-/yn-3.1.1.tgz",
+      "integrity": "sha512-Ux4ygGWsu2c7isFWe8Yu1YluJmqVhxqK2cLXNQA5AcC3QfbGNpM7fu0Y8b/z16pXLnFxZYvWhd3fhBY9DLmC6Q=="
+    },
+    "yocto-queue": {
+      "version": "0.1.0",
+      "resolved": "https://registry.npmjs.org/yocto-queue/-/yocto-queue-0.1.0.tgz",
+      "integrity": "sha512-rVksvsnNCdJ/ohGc6xgPwyN8eheCxsiLM8mxuE/t/mOVqJewPuO1miLpTHQiRgTKCLexL4MeAFVagts7HmNZ2Q=="
+    }
+  }
+}

services/track-changes/package.json

@@ -0,0 +1,66 @@
+{
+  "name": "history-sharelatex",
+  "version": "0.1.4",
+  "description": "An API for saving and compressing individual document updates into a browsable history",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/sharelatex/track-changes-sharelatex.git"
+  },
+  "scripts": {
+    "start": "node $NODE_APP_OPTIONS app.js",
+    "test:acceptance:_run": "mocha --recursive --reporter spec --timeout 15000 --exit $@ test/acceptance/js",
+    "test:acceptance": "npm run test:acceptance:_run -- --grep=$MOCHA_GREP",
+    "test:unit:_run": "mocha --recursive --reporter spec $@ test/unit/js",
+    "test:unit": "npm run test:unit:_run -- --grep=$MOCHA_GREP",
+    "nodemon": "nodemon --config nodemon.json",
+    "lint": "eslint --max-warnings 0 --format unix .",
+    "format": "prettier --list-different $PWD/'**/*.js'",
+    "format:fix": "prettier --write $PWD/'**/*.js'",
+    "lint:fix": "eslint --fix ."
+  },
+  "dependencies": {
+    "@overleaf/metrics": "^3.5.1",
+    "@overleaf/o-error": "^3.1.0",
+    "@overleaf/redis-wrapper": "^2.0.0",
+    "@overleaf/settings": "^2.1.1",
+    "JSONStream": "^1.3.5",
+    "async": "^2.6.3",
+    "aws-sdk": "^2.643.0",
+    "body-parser": "^1.19.0",
+    "bson": "^1.1.5",
+    "bunyan": "^1.8.15",
+    "byline": "^5.0.0",
+    "express": "4.17.1",
+    "heap": "^0.2.6",
+    "line-reader": "^0.4.0",
+    "logger-sharelatex": "^2.2.0",
+    "mongo-uri": "^0.1.2",
+    "mongodb": "^3.6.0",
+    "redis": "~0.10.1",
+    "request": "~2.88.2",
+    "requestretry": "^4.1.0",
+    "s3-streams": "^0.4.0",
+    "underscore": "~1.13.1"
+  },
+  "devDependencies": {
+    "chai": "^4.2.0",
+    "chai-as-promised": "^7.1.1",
+    "cli": "^1.0.1",
+    "eslint": "^7.21.0",
+    "eslint-config-prettier": "^8.1.0",
+    "eslint-config-standard": "^16.0.2",
+    "eslint-plugin-chai-expect": "^2.2.0",
+    "eslint-plugin-chai-friendly": "^0.6.0",
+    "eslint-plugin-import": "^2.22.1",
+    "eslint-plugin-mocha": "^8.0.0",
+    "eslint-plugin-node": "^11.1.0",
+    "eslint-plugin-prettier": "^3.1.2",
+    "eslint-plugin-promise": "^4.2.1",
+    "memorystream": "0.3.1",
+    "mocha": "^8.3.2",
+    "prettier": "^2.2.1",
+    "sandboxed-module": "~2.0.3",
+    "sinon": "~9.0.1",
+    "timekeeper": "2.2.0"
+  }
+}

services/track-changes/test/acceptance/deps/Dockerfile.s3mock

@@ -0,0 +1,4 @@
+FROM adobe/s3mock
+RUN apk add --update --no-cache curl
+COPY healthcheck.sh /healthcheck.sh
+HEALTHCHECK --interval=1s --timeout=1s --retries=30 CMD /healthcheck.sh http://localhost:9090

services/track-changes/test/acceptance/deps/healthcheck.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# health check to allow 404 status code as valid
+STATUSCODE=$(curl --silent --output /dev/null --write-out "%{http_code}" $1)
+# will be 000 on non-http error (e.g. connection failure)
+if test $STATUSCODE -ge 500 || test $STATUSCODE -lt 200; then
+  exit 1
+fi
+exit 0

services/track-changes/test/acceptance/js/AppendingUpdatesTests.js

@@ -0,0 +1,587 @@
+/* eslint-disable
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { ObjectId } = require('../../../app/js/mongodb')
+const Settings = require('@overleaf/settings')
+const request = require('request')
+const rclient = require('redis').createClient(Settings.redis.history) // Only works locally for now
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+const MockWebApi = require('./helpers/MockWebApi')
+
+describe('Appending doc ops to the history', function () {
+  before(function (done) {
+    return TrackChangesApp.ensureRunning(done)
+  })
+
+  describe('when the history does not exist yet', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [{ i: 'f', p: 3 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+          {
+            op: [{ i: 'o', p: 4 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 4,
+          },
+          {
+            op: [{ i: 'o', p: 5 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 5,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              this.updates = updates
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    it('should insert the compressed op into mongo', function () {
+      return expect(this.updates[0].pack[0].op).to.deep.equal([
+        {
+          p: 3,
+          i: 'foo',
+        },
+      ])
+    })
+
+    it('should insert the correct version number into mongo', function () {
+      return expect(this.updates[0].v).to.equal(5)
+    })
+
+    it('should store the doc id', function () {
+      return expect(this.updates[0].doc_id.toString()).to.equal(this.doc_id)
+    })
+
+    it('should store the project id', function () {
+      return expect(this.updates[0].project_id.toString()).to.equal(
+        this.project_id
+      )
+    })
+
+    return it('should clear the doc from the DocsWithHistoryOps set', function (done) {
+      rclient.sismember(
+        `DocsWithHistoryOps:${this.project_id}`,
+        this.doc_id,
+        (error, member) => {
+          member.should.equal(0)
+          return done()
+        }
+      )
+      return null
+    })
+  })
+
+  describe('when the history has already been started', function () {
+    beforeEach(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [{ i: 'f', p: 3 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+          {
+            op: [{ i: 'o', p: 4 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 4,
+          },
+          {
+            op: [{ i: 'o', p: 5 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 5,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    describe('when the updates are recent and from the same user', function () {
+      beforeEach(function (done) {
+        TrackChangesClient.pushRawUpdates(
+          this.project_id,
+          this.doc_id,
+          [
+            {
+              op: [{ i: 'b', p: 6 }],
+              meta: { ts: Date.now(), user_id: this.user_id },
+              v: 6,
+            },
+            {
+              op: [{ i: 'a', p: 7 }],
+              meta: { ts: Date.now(), user_id: this.user_id },
+              v: 7,
+            },
+            {
+              op: [{ i: 'r', p: 8 }],
+              meta: { ts: Date.now(), user_id: this.user_id },
+              v: 8,
+            },
+          ],
+          error => {
+            if (error != null) {
+              throw error
+            }
+            return TrackChangesClient.flushAndGetCompressedUpdates(
+              this.project_id,
+              this.doc_id,
+              (error, updates) => {
+                this.updates = updates
+                if (error != null) {
+                  throw error
+                }
+                return done()
+              }
+            )
+          }
+        )
+        return null
+      })
+
+      it('should combine all the updates into one pack', function () {
+        return expect(this.updates[0].pack[1].op).to.deep.equal([
+          {
+            p: 6,
+            i: 'bar',
+          },
+        ])
+      })
+
+      return it('should insert the correct version number into mongo', function () {
+        return expect(this.updates[0].v_end).to.equal(8)
+      })
+    })
+
+    return describe('when the updates are far apart', function () {
+      beforeEach(function (done) {
+        const oneDay = 24 * 60 * 60 * 1000
+        TrackChangesClient.pushRawUpdates(
+          this.project_id,
+          this.doc_id,
+          [
+            {
+              op: [{ i: 'b', p: 6 }],
+              meta: { ts: Date.now() + oneDay, user_id: this.user_id },
+              v: 6,
+            },
+            {
+              op: [{ i: 'a', p: 7 }],
+              meta: { ts: Date.now() + oneDay, user_id: this.user_id },
+              v: 7,
+            },
+            {
+              op: [{ i: 'r', p: 8 }],
+              meta: { ts: Date.now() + oneDay, user_id: this.user_id },
+              v: 8,
+            },
+          ],
+          error => {
+            if (error != null) {
+              throw error
+            }
+            return TrackChangesClient.flushAndGetCompressedUpdates(
+              this.project_id,
+              this.doc_id,
+              (error, updates) => {
+                this.updates = updates
+                if (error != null) {
+                  throw error
+                }
+                return done()
+              }
+            )
+          }
+        )
+        return null
+      })
+
+      return it('should combine the updates into one pack', function () {
+        expect(this.updates[0].pack[0].op).to.deep.equal([
+          {
+            p: 3,
+            i: 'foo',
+          },
+        ])
+        return expect(this.updates[0].pack[1].op).to.deep.equal([
+          {
+            p: 6,
+            i: 'bar',
+          },
+        ])
+      })
+    })
+  })
+
+  describe('when the updates need processing in batches', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+      const updates = []
+      this.expectedOp = [{ p: 0, i: '' }]
+      for (let i = 0; i <= 250; i++) {
+        updates.push({
+          op: [{ i: 'a', p: 0 }],
+          meta: { ts: Date.now(), user_id: this.user_id },
+          v: i,
+        })
+        this.expectedOp[0].i = `a${this.expectedOp[0].i}`
+      }
+
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        updates,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates1) => {
+              this.updates = updates1
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    it('should concat the compressed op into mongo', function () {
+      return expect(this.updates[0].pack.length).to.deep.equal(3)
+    }) // batch size is 100
+
+    return it('should insert the correct version number into mongo', function () {
+      return expect(this.updates[0].v_end).to.equal(250)
+    })
+  })
+
+  describe('when there are multiple ops in each update', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+      const oneDay = 24 * 60 * 60 * 1000
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [
+              { i: 'f', p: 3 },
+              { i: 'o', p: 4 },
+              { i: 'o', p: 5 },
+            ],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+          {
+            op: [
+              { i: 'b', p: 6 },
+              { i: 'a', p: 7 },
+              { i: 'r', p: 8 },
+            ],
+            meta: { ts: Date.now() + oneDay, user_id: this.user_id },
+            v: 4,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              this.updates = updates
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    it('should insert the compressed ops into mongo', function () {
+      expect(this.updates[0].pack[0].op).to.deep.equal([
+        {
+          p: 3,
+          i: 'foo',
+        },
+      ])
+      return expect(this.updates[0].pack[1].op).to.deep.equal([
+        {
+          p: 6,
+          i: 'bar',
+        },
+      ])
+    })
+
+    return it('should insert the correct version numbers into mongo', function () {
+      expect(this.updates[0].pack[0].v).to.equal(3)
+      return expect(this.updates[0].pack[1].v).to.equal(4)
+    })
+  })
+
+  describe('when there is a no-op update', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+      const oneDay = 24 * 60 * 60 * 1000
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+          {
+            op: [{ i: 'foo', p: 3 }],
+            meta: { ts: Date.now() + oneDay, user_id: this.user_id },
+            v: 4,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              this.updates = updates
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    it('should insert the compressed no-op into mongo', function () {
+      return expect(this.updates[0].pack[0].op).to.deep.equal([])
+    })
+
+    it('should insert the compressed next update into mongo', function () {
+      return expect(this.updates[0].pack[1].op).to.deep.equal([
+        {
+          p: 3,
+          i: 'foo',
+        },
+      ])
+    })
+
+    return it('should insert the correct version numbers into mongo', function () {
+      expect(this.updates[0].pack[0].v).to.equal(3)
+      return expect(this.updates[0].pack[1].v).to.equal(4)
+    })
+  })
+
+  describe('when there is a comment update', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [
+              { c: 'foo', p: 3 },
+              { d: 'bar', p: 6 },
+            ],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              this.updates = updates
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    it('should ignore the comment op', function () {
+      return expect(this.updates[0].pack[0].op).to.deep.equal([
+        { d: 'bar', p: 6 },
+      ])
+    })
+
+    return it('should insert the correct version numbers into mongo', function () {
+      return expect(this.updates[0].pack[0].v).to.equal(3)
+    })
+  })
+
+  describe('when the project has versioning enabled', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: true } }
+
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [{ i: 'f', p: 3 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              this.updates = updates
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    return it('should not add a expiresAt entry in the update in mongo', function () {
+      return expect(this.updates[0].expiresAt).to.be.undefined
+    })
+  })
+
+  return describe('when the project does not have versioning enabled', function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: false } }
+
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [{ i: 'f', p: 3 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushAndGetCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            (error, updates) => {
+              this.updates = updates
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    return it('should add a expiresAt entry in the update in mongo', function () {
+      return expect(this.updates[0].expiresAt).to.exist
+    })
+  })
+})

services/track-changes/test/acceptance/js/ArchivingUpdatesTests.js

@@ -0,0 +1,322 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-undef,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS103: Rewrite code to no longer use __guard__
+ * DS202: Simplify dynamic range loops
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { db, ObjectId } = require('../../../app/js/mongodb')
+const Settings = require('@overleaf/settings')
+const request = require('request')
+const rclient = require('redis').createClient(Settings.redis.history) // Only works locally for now
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+const MockDocStoreApi = require('./helpers/MockDocStoreApi')
+const MockWebApi = require('./helpers/MockWebApi')
+
+describe('Archiving updates', function () {
+  before(function (done) {
+    if (
+      __guard__(
+        __guard__(
+          Settings != null ? Settings.trackchanges : undefined,
+          x1 => x1.s3
+        ),
+        x => x.key.length
+      ) < 1
+    ) {
+      const message = new Error('s3 keys not setup, this test setup will fail')
+      return done(message)
+    }
+
+    return TrackChangesClient.waitForS3(done)
+  })
+
+  before(function (done) {
+    this.now = Date.now()
+    this.to = this.now
+    this.user_id = ObjectId().toString()
+    this.user_id_2 = ObjectId().toString()
+    this.doc_id = ObjectId().toString()
+    this.project_id = ObjectId().toString()
+
+    this.minutes = 60 * 1000
+    this.hours = 60 * this.minutes
+
+    MockWebApi.projects[this.project_id] = {
+      features: {
+        versioning: true,
+      },
+    }
+    sinon.spy(MockWebApi, 'getProjectDetails')
+
+    MockWebApi.users[this.user_id] = this.user = {
+      email: 'user@sharelatex.com',
+      first_name: 'Leo',
+      last_name: 'Lion',
+      id: this.user_id,
+    }
+    sinon.spy(MockWebApi, 'getUserInfo')
+
+    MockDocStoreApi.docs[this.doc_id] = this.doc = {
+      _id: this.doc_id,
+      project_id: this.project_id,
+    }
+    sinon.spy(MockDocStoreApi, 'getAllDoc')
+
+    this.updates = []
+    for (
+      let i = 0, end = 512 + 10, asc = end >= 0;
+      asc ? i <= end : i >= end;
+      asc ? i++ : i--
+    ) {
+      this.updates.push({
+        op: [{ i: 'a', p: 0 }],
+        meta: { ts: this.now + (i - 2048) * this.hours, user_id: this.user_id },
+        v: 2 * i + 1,
+      })
+      this.updates.push({
+        op: [{ i: 'b', p: 0 }],
+        meta: {
+          ts: this.now + (i - 2048) * this.hours + 10 * this.minutes,
+          user_id: this.user_id_2,
+        },
+        v: 2 * i + 2,
+      })
+    }
+    TrackChangesApp.ensureRunning(() => {
+      return TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        this.updates,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushDoc(
+            this.project_id,
+            this.doc_id,
+            error => {
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+    })
+    return null
+  })
+
+  after(function (done) {
+    MockWebApi.getUserInfo.restore()
+    return db.docHistory.deleteMany(
+      { project_id: ObjectId(this.project_id) },
+      () => {
+        return db.docHistoryIndex.remove(
+          { project_id: ObjectId(this.project_id) },
+          () => {
+            return TrackChangesClient.removeS3Doc(
+              this.project_id,
+              this.doc_id,
+              done
+            )
+          }
+        )
+      }
+    )
+  })
+
+  function testExportFeature() {
+    describe('exporting the project', function () {
+      before('fetch export', function (done) {
+        TrackChangesClient.exportProject(
+          this.project_id,
+          (error, updates, userIds) => {
+            if (error) {
+              return done(error)
+            }
+            this.exportedUpdates = updates
+            this.exportedUserIds = userIds
+            done()
+          }
+        )
+      })
+
+      it('should include all the imported updates, with ids, sorted by timestamp', function () {
+        // Add a safe guard for an empty array matching an empty export.
+        expect(this.updates).to.have.length(1024 + 22)
+
+        const expectedExportedUpdates = this.updates
+          .slice()
+          .reverse()
+          .map(update => {
+            // clone object, updates are created once in before handler
+            const exportedUpdate = Object.assign({}, update)
+            exportedUpdate.meta = Object.assign({}, update.meta)
+
+            exportedUpdate.doc_id = this.doc_id
+            exportedUpdate.project_id = this.project_id
+
+            // This is for merged updates, which does not apply here.
+            exportedUpdate.meta.start_ts = exportedUpdate.meta.end_ts =
+              exportedUpdate.meta.ts
+            delete exportedUpdate.meta.ts
+            return exportedUpdate
+          })
+        expect(this.exportedUpdates).to.deep.equal(expectedExportedUpdates)
+        expect(this.exportedUserIds).to.deep.equal([
+          this.user_id,
+          this.user_id_2,
+        ])
+      })
+    })
+  }
+
+  describe("before archiving a doc's updates", function () {
+    testExportFeature()
+  })
+
+  describe("archiving a doc's updates", function () {
+    before(function (done) {
+      TrackChangesClient.pushDocHistory(this.project_id, this.doc_id, error => {
+        if (error != null) {
+          throw error
+        }
+        return done()
+      })
+      return null
+    })
+
+    it('should have one cached pack', function (done) {
+      return db.docHistory.count(
+        { doc_id: ObjectId(this.doc_id), expiresAt: { $exists: true } },
+        (error, count) => {
+          if (error != null) {
+            throw error
+          }
+          count.should.equal(1)
+          return done()
+        }
+      )
+    })
+
+    it('should have one remaining pack after cache is expired', function (done) {
+      return db.docHistory.deleteMany(
+        {
+          doc_id: ObjectId(this.doc_id),
+          expiresAt: { $exists: true },
+        },
+        (err, result) => {
+          if (typeof error !== 'undefined' && error !== null) {
+            throw error
+          }
+          return db.docHistory.count(
+            { doc_id: ObjectId(this.doc_id) },
+            (error, count) => {
+              if (error != null) {
+                throw error
+              }
+              count.should.equal(1)
+              return done()
+            }
+          )
+        }
+      )
+    })
+
+    it('should have a docHistoryIndex entry marked as inS3', function (done) {
+      return db.docHistoryIndex.findOne(
+        { _id: ObjectId(this.doc_id) },
+        (error, index) => {
+          if (error != null) {
+            throw error
+          }
+          index.packs[0].inS3.should.equal(true)
+          return done()
+        }
+      )
+    })
+
+    it('should have a docHistoryIndex entry with the last version', function (done) {
+      return db.docHistoryIndex.findOne(
+        { _id: ObjectId(this.doc_id) },
+        (error, index) => {
+          if (error != null) {
+            throw error
+          }
+          index.packs[0].v_end.should.equal(1024)
+          return done()
+        }
+      )
+    })
+
+    it('should store 1024 doc changes in S3 in one pack', function (done) {
+      return db.docHistoryIndex.findOne(
+        { _id: ObjectId(this.doc_id) },
+        (error, index) => {
+          if (error != null) {
+            throw error
+          }
+          const pack_id = index.packs[0]._id
+          return TrackChangesClient.getS3Doc(
+            this.project_id,
+            this.doc_id,
+            pack_id,
+            (error, doc) => {
+              doc.n.should.equal(1024)
+              doc.pack.length.should.equal(1024)
+              return done()
+            }
+          )
+        }
+      )
+    })
+
+    testExportFeature()
+  })
+
+  return describe("unarchiving a doc's updates", function () {
+    before(function (done) {
+      TrackChangesClient.pullDocHistory(this.project_id, this.doc_id, error => {
+        if (error != null) {
+          throw error
+        }
+        return done()
+      })
+      return null
+    })
+
+    return it('should restore both packs', function (done) {
+      return db.docHistory.count(
+        { doc_id: ObjectId(this.doc_id) },
+        (error, count) => {
+          if (error != null) {
+            throw error
+          }
+          count.should.equal(2)
+          return done()
+        }
+      )
+    })
+  })
+})
+
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/test/acceptance/js/ExportProjectTests.js

@@ -0,0 +1,34 @@
+const { expect } = require('chai')
+const { ObjectId } = require('../../../app/js/mongodb')
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+
+describe('ExportProject', function () {
+  before('start app', function (done) {
+    TrackChangesApp.ensureRunning(done)
+  })
+
+  describe('when there are no updates', function () {
+    before('fetch export', function (done) {
+      TrackChangesClient.exportProject(
+        ObjectId(),
+        (error, updates, userIds) => {
+          if (error) {
+            return done(error)
+          }
+          this.exportedUpdates = updates
+          this.exportedUserIds = userIds
+          done()
+        }
+      )
+    })
+
+    it('should export an empty array', function () {
+      expect(this.exportedUpdates).to.deep.equal([])
+      expect(this.exportedUserIds).to.deep.equal([])
+    })
+  })
+
+  // see ArchivingUpdatesTests for tests with data in mongo/s3
+})

services/track-changes/test/acceptance/js/FlushingUpdatesTests.js

@@ -0,0 +1,273 @@
+/* eslint-disable
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { ObjectId } = require('../../../app/js/mongodb')
+const Settings = require('@overleaf/settings')
+const request = require('request')
+const rclient = require('redis').createClient(Settings.redis.history) // Only works locally for now
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+const MockWebApi = require('./helpers/MockWebApi')
+
+describe('Flushing updates', function () {
+  before(function (done) {
+    return TrackChangesApp.ensureRunning(done)
+  })
+
+  describe("flushing a doc's updates", function () {
+    before(function (done) {
+      this.project_id = ObjectId().toString()
+      this.doc_id = ObjectId().toString()
+      this.user_id = ObjectId().toString()
+      MockWebApi.projects[this.project_id] = { features: { versioning: true } }
+
+      TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        [
+          {
+            op: [{ i: 'f', p: 3 }],
+            meta: { ts: Date.now(), user_id: this.user_id },
+            v: 3,
+          },
+        ],
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.flushDoc(
+            this.project_id,
+            this.doc_id,
+            error => {
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+      return null
+    })
+
+    return it('should flush the op into mongo', function (done) {
+      TrackChangesClient.getCompressedUpdates(this.doc_id, (error, updates) => {
+        expect(updates[0].pack[0].op).to.deep.equal([
+          {
+            p: 3,
+            i: 'f',
+          },
+        ])
+        return done()
+      })
+      return null
+    })
+  })
+
+  return describe("flushing a project's updates", function () {
+    describe('with versioning enabled', function () {
+      before(function (done) {
+        this.project_id = ObjectId().toString()
+        this.doc_id = ObjectId().toString()
+        this.user_id = ObjectId().toString()
+
+        this.weeks = 7 * 24 * 60 * 60 * 1000
+
+        MockWebApi.projects[this.project_id] = {
+          features: {
+            versioning: true,
+          },
+        }
+
+        TrackChangesClient.pushRawUpdates(
+          this.project_id,
+          this.doc_id,
+          [
+            {
+              op: [{ i: 'g', p: 2 }],
+              meta: { ts: Date.now() - 2 * this.weeks, user_id: this.user_id },
+              v: 2,
+            },
+            {
+              op: [{ i: 'f', p: 3 }],
+              meta: { ts: Date.now(), user_id: this.user_id },
+              v: 3,
+            },
+          ],
+          error => {
+            if (error != null) {
+              throw error
+            }
+            return TrackChangesClient.flushProject(this.project_id, error => {
+              if (error != null) {
+                throw error
+              }
+              return done()
+            })
+          }
+        )
+        return null
+      })
+
+      it('should not mark the updates for deletion', function (done) {
+        TrackChangesClient.getCompressedUpdates(
+          this.doc_id,
+          (error, updates) => {
+            expect(updates[0].expiresAt).to.not.exist
+            return done()
+          }
+        )
+        return null
+      })
+
+      return it('should preserve history forever', function (done) {
+        TrackChangesClient.getProjectMetaData(
+          this.project_id,
+          (error, project) => {
+            expect(project.preserveHistory).to.equal(true)
+            return done()
+          }
+        )
+        return null
+      })
+    })
+
+    describe('without versioning enabled', function () {
+      before(function (done) {
+        this.project_id = ObjectId().toString()
+        this.doc_id = ObjectId().toString()
+        this.user_id = ObjectId().toString()
+
+        this.weeks = 7 * 24 * 60 * 60 * 1000
+
+        MockWebApi.projects[this.project_id] = {
+          features: {
+            versioning: false,
+          },
+        }
+
+        TrackChangesClient.pushRawUpdates(
+          this.project_id,
+          this.doc_id,
+          [
+            {
+              op: [{ i: 'g', p: 2 }],
+              meta: { ts: Date.now() - 2 * this.weeks, user_id: this.user_id },
+              v: 2,
+            },
+            {
+              op: [{ i: 'f', p: 3 }],
+              meta: { ts: Date.now(), user_id: this.user_id },
+              v: 3,
+            },
+          ],
+          error => {
+            if (error != null) {
+              throw error
+            }
+            return TrackChangesClient.flushProject(this.project_id, error => {
+              if (error != null) {
+                throw error
+              }
+              return done()
+            })
+          }
+        )
+        return null
+      })
+
+      return it('should mark the updates for deletion', function (done) {
+        TrackChangesClient.getCompressedUpdates(
+          this.doc_id,
+          (error, updates) => {
+            expect(updates[0].expiresAt).to.exist
+            return done()
+          }
+        )
+        return null
+      })
+    })
+
+    return describe('without versioning enabled but with preserveHistory set to true', function () {
+      before(function (done) {
+        this.project_id = ObjectId().toString()
+        this.doc_id = ObjectId().toString()
+        this.user_id = ObjectId().toString()
+
+        this.weeks = 7 * 24 * 60 * 60 * 1000
+
+        MockWebApi.projects[this.project_id] = {
+          features: {
+            versioning: false,
+          },
+        }
+
+        TrackChangesClient.setPreserveHistoryForProject(
+          this.project_id,
+          error => {
+            if (error != null) {
+              throw error
+            }
+            return TrackChangesClient.pushRawUpdates(
+              this.project_id,
+              this.doc_id,
+              [
+                {
+                  op: [{ i: 'g', p: 2 }],
+                  meta: {
+                    ts: Date.now() - 2 * this.weeks,
+                    user_id: this.user_id,
+                  },
+                  v: 2,
+                },
+                {
+                  op: [{ i: 'f', p: 3 }],
+                  meta: { ts: Date.now(), user_id: this.user_id },
+                  v: 3,
+                },
+              ],
+              error => {
+                if (error != null) {
+                  throw error
+                }
+                return TrackChangesClient.flushProject(
+                  this.project_id,
+                  error => {
+                    if (error != null) {
+                      throw error
+                    }
+                    return done()
+                  }
+                )
+              }
+            )
+          }
+        )
+        return null
+      })
+
+      return it('should not mark the updates for deletion', function (done) {
+        TrackChangesClient.getCompressedUpdates(
+          this.doc_id,
+          (error, updates) => {
+            expect(updates[0].expiresAt).to.not.exist
+            return done()
+          }
+        )
+        return null
+      })
+    })
+  })
+})

services/track-changes/test/acceptance/js/GettingADiffTests.js

@@ -0,0 +1,127 @@
+/* eslint-disable
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { ObjectId } = require('../../../app/js/mongodb')
+const Settings = require('@overleaf/settings')
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+const MockDocUpdaterApi = require('./helpers/MockDocUpdaterApi')
+const MockWebApi = require('./helpers/MockWebApi')
+
+describe('Getting a diff', function () {
+  beforeEach(function (done) {
+    sinon.spy(MockDocUpdaterApi, 'getDoc')
+
+    this.now = Date.now()
+    this.from = this.now - 100000000
+    this.to = this.now
+    this.user_id = ObjectId().toString()
+    this.doc_id = ObjectId().toString()
+    this.project_id = ObjectId().toString()
+    MockWebApi.projects[this.project_id] = { features: { versioning: true } }
+
+    MockWebApi.users[this.user_id] = this.user = {
+      email: 'user@sharelatex.com',
+      first_name: 'Leo',
+      last_name: 'Lion',
+      id: this.user_id,
+    }
+    sinon.spy(MockWebApi, 'getUserInfo')
+
+    const twoMinutes = 2 * 60 * 1000
+
+    this.updates = [
+      {
+        op: [{ i: 'one ', p: 0 }],
+        meta: { ts: this.from - twoMinutes, user_id: this.user_id },
+        v: 3,
+      },
+      {
+        op: [{ i: 'two ', p: 4 }],
+        meta: { ts: this.from + twoMinutes, user_id: this.user_id },
+        v: (this.fromVersion = 4),
+      },
+      {
+        op: [{ i: 'three ', p: 8 }],
+        meta: { ts: this.to - twoMinutes, user_id: this.user_id },
+        v: (this.toVersion = 5),
+      },
+      {
+        op: [{ i: 'four', p: 14 }],
+        meta: { ts: this.to + twoMinutes, user_id: this.user_id },
+        v: 6,
+      },
+    ]
+    this.lines = ['one two three four']
+    this.expected_diff = [
+      { u: 'one ' },
+      {
+        i: 'two three ',
+        meta: {
+          start_ts: this.from + twoMinutes,
+          end_ts: this.to - twoMinutes,
+          user: this.user,
+        },
+      },
+    ]
+
+    MockDocUpdaterApi.docs[this.doc_id] = {
+      lines: this.lines,
+      version: 7,
+    }
+    TrackChangesApp.ensureRunning(() => {
+      return TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        this.updates,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.getDiff(
+            this.project_id,
+            this.doc_id,
+            this.fromVersion,
+            this.toVersion,
+            (error, diff) => {
+              if (error != null) {
+                throw error
+              }
+              this.diff = diff.diff
+              return done()
+            }
+          )
+        }
+      )
+    })
+    return null
+  })
+
+  afterEach(function () {
+    MockDocUpdaterApi.getDoc.restore()
+    MockWebApi.getUserInfo.restore()
+    return null
+  })
+
+  it('should return the diff', function () {
+    return expect(this.diff).to.deep.equal(this.expected_diff)
+  })
+
+  return it('should get the doc from the doc updater', function () {
+    MockDocUpdaterApi.getDoc
+      .calledWith(this.project_id, this.doc_id)
+      .should.equal(true)
+    return null
+  })
+})

services/track-changes/test/acceptance/js/GettingUpdatesTests.js

@@ -0,0 +1,185 @@
+/* eslint-disable
+    chai-friendly/no-unused-expressions,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { ObjectId } = require('../../../app/js/mongodb')
+const Settings = require('@overleaf/settings')
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+const MockWebApi = require('./helpers/MockWebApi')
+
+describe('Getting updates', function () {
+  before(function (done) {
+    this.now = Date.now()
+    this.to = this.now
+    this.user_id = ObjectId().toString()
+    this.deleted_user_id = 'deleted_user'
+    this.doc_id = ObjectId().toString()
+    this.project_id = ObjectId().toString()
+
+    this.minutes = 60 * 1000
+    this.hours = 60 * this.minutes
+
+    MockWebApi.projects[this.project_id] = {
+      features: {
+        versioning: true,
+      },
+    }
+
+    MockWebApi.users[this.user_id] = this.user = {
+      email: 'user@sharelatex.com',
+      first_name: 'Leo',
+      last_name: 'Lion',
+      id: this.user_id,
+    }
+    sinon.spy(MockWebApi, 'getUserInfo')
+
+    this.updates = []
+    for (let i = 0; i <= 9; i++) {
+      this.updates.push({
+        op: [{ i: 'a', p: 0 }],
+        meta: {
+          ts: this.now - (9 - i) * this.hours - 2 * this.minutes,
+          user_id: this.user_id,
+        },
+        v: 2 * i + 1,
+      })
+      this.updates.push({
+        op: [{ i: 'b', p: 0 }],
+        meta: { ts: this.now - (9 - i) * this.hours, user_id: this.user_id },
+        v: 2 * i + 2,
+      })
+    }
+    this.updates[0].meta.user_id = this.deleted_user_id
+
+    TrackChangesApp.ensureRunning(() => {
+      return TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        this.updates,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return done()
+        }
+      )
+    })
+    return null
+  })
+  ;({
+    after() {
+      MockWebApi.getUserInfo.restore()
+      return null
+    },
+  })
+
+  describe('getting updates up to the limit', function () {
+    before(function (done) {
+      TrackChangesClient.getUpdates(
+        this.project_id,
+        { before: this.to + 1, min_count: 3 },
+        (error, body) => {
+          if (error != null) {
+            throw error
+          }
+          this.updates = body.updates
+          return done()
+        }
+      )
+      return null
+    })
+
+    it('should fetch the user details from the web api', function () {
+      return MockWebApi.getUserInfo.calledWith(this.user_id).should.equal(true)
+    })
+
+    return it('should return at least the min_count number of summarized updates', function () {
+      const docs1 = {}
+      docs1[this.doc_id] = { toV: 20, fromV: 19 }
+      const docs2 = {}
+      docs2[this.doc_id] = { toV: 18, fromV: 17 }
+      const docs3 = {}
+      docs3[this.doc_id] = { toV: 16, fromV: 15 }
+      return expect(this.updates.slice(0, 3)).to.deep.equal([
+        {
+          docs: docs1,
+          meta: {
+            start_ts: this.to - 2 * this.minutes,
+            end_ts: this.to,
+            users: [this.user],
+          },
+        },
+        {
+          docs: docs2,
+          meta: {
+            start_ts: this.to - 1 * this.hours - 2 * this.minutes,
+            end_ts: this.to - 1 * this.hours,
+            users: [this.user],
+          },
+        },
+        {
+          docs: docs3,
+          meta: {
+            start_ts: this.to - 2 * this.hours - 2 * this.minutes,
+            end_ts: this.to - 2 * this.hours,
+            users: [this.user],
+          },
+        },
+      ])
+    })
+  })
+
+  return describe('getting updates beyond the end of the database', function () {
+    before(function (done) {
+      TrackChangesClient.getUpdates(
+        this.project_id,
+        { before: this.to - 8 * this.hours + 1, min_count: 30 },
+        (error, body) => {
+          if (error != null) {
+            throw error
+          }
+          this.updates = body.updates
+          return done()
+        }
+      )
+      return null
+    })
+
+    return it('should return as many updates as it can', function () {
+      const docs1 = {}
+      docs1[this.doc_id] = { toV: 4, fromV: 3 }
+      const docs2 = {}
+      docs2[this.doc_id] = { toV: 2, fromV: 1 }
+      return expect(this.updates).to.deep.equal([
+        {
+          docs: docs1,
+          meta: {
+            start_ts: this.to - 8 * this.hours - 2 * this.minutes,
+            end_ts: this.to - 8 * this.hours,
+            users: [this.user],
+          },
+        },
+        {
+          docs: docs2,
+          meta: {
+            start_ts: this.to - 9 * this.hours - 2 * this.minutes,
+            end_ts: this.to - 9 * this.hours,
+            users: [this.user, null],
+          },
+        },
+      ])
+    })
+  })
+})

services/track-changes/test/acceptance/js/LockManagerTests.js

@@ -0,0 +1,62 @@
+/* eslint-disable
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const Settings = require('@overleaf/settings')
+const LockManager = require('../../../app/js/LockManager')
+const rclient = require('redis').createClient(Settings.redis.history) // Only works locally for now
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+
+describe('Locking document', function () {
+  before(function (done) {
+    TrackChangesApp.ensureRunning(done)
+    return null
+  })
+
+  return describe('when the lock has expired in redis', function () {
+    before(function (done) {
+      LockManager.LOCK_TTL = 1 // second
+      LockManager.runWithLock(
+        'doc123',
+        releaseA => {
+          // we create a lock A and allow it to expire in redis
+          return setTimeout(
+            () =>
+              // now we create a new lock B and try to release A
+              LockManager.runWithLock(
+                'doc123',
+                releaseB => {
+                  return releaseA()
+                }, // try to release lock A to see if it wipes out lock B
+                error => {}
+              ),
+
+            // we never release lock B so nothing should happen here
+            1500
+          )
+        }, // enough time to wait until the lock has expired
+        error =>
+          // we get here after trying to release lock A
+          done()
+      )
+      return null
+    })
+
+    return it('the new lock should not be removed by the expired locker', function (done) {
+      LockManager.checkLock('doc123', (err, isFree) => {
+        expect(isFree).to.equal(false)
+        return done()
+      })
+      return null
+    })
+  })
+})

services/track-changes/test/acceptance/js/RestoringVersions.js

@@ -0,0 +1,116 @@
+/* eslint-disable
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { ObjectId } = require('../../../app/js/mongodb')
+const Settings = require('@overleaf/settings')
+
+const TrackChangesApp = require('./helpers/TrackChangesApp')
+const TrackChangesClient = require('./helpers/TrackChangesClient')
+const MockDocUpdaterApi = require('./helpers/MockDocUpdaterApi')
+const MockWebApi = require('./helpers/MockWebApi')
+
+describe('Restoring a version', function () {
+  before(function (done) {
+    sinon.spy(MockDocUpdaterApi, 'setDoc')
+
+    this.now = Date.now()
+    this.user_id = ObjectId().toString()
+    this.doc_id = ObjectId().toString()
+    this.project_id = ObjectId().toString()
+    MockWebApi.projects[this.project_id] = { features: { versioning: true } }
+
+    const minutes = 60 * 1000
+
+    this.updates = [
+      {
+        op: [{ i: 'one ', p: 0 }],
+        meta: { ts: this.now - 6 * minutes, user_id: this.user_id },
+        v: 3,
+      },
+      {
+        op: [{ i: 'two ', p: 4 }],
+        meta: { ts: this.now - 4 * minutes, user_id: this.user_id },
+        v: 4,
+      },
+      {
+        op: [{ i: 'three ', p: 8 }],
+        meta: { ts: this.now - 2 * minutes, user_id: this.user_id },
+        v: 5,
+      },
+      {
+        op: [{ i: 'four', p: 14 }],
+        meta: { ts: this.now, user_id: this.user_id },
+        v: 6,
+      },
+    ]
+    this.lines = ['one two three four']
+    this.restored_lines = ['one two ']
+    this.beforeVersion = 5
+
+    MockWebApi.users[this.user_id] = this.user = {
+      email: 'user@sharelatex.com',
+      first_name: 'Leo',
+      last_name: 'Lion',
+      id: this.user_id,
+    }
+
+    MockDocUpdaterApi.docs[this.doc_id] = {
+      lines: this.lines,
+      version: 7,
+    }
+
+    TrackChangesApp.ensureRunning(() => {
+      return TrackChangesClient.pushRawUpdates(
+        this.project_id,
+        this.doc_id,
+        this.updates,
+        error => {
+          if (error != null) {
+            throw error
+          }
+          return TrackChangesClient.restoreDoc(
+            this.project_id,
+            this.doc_id,
+            this.beforeVersion,
+            this.user_id,
+            error => {
+              if (error != null) {
+                throw error
+              }
+              return done()
+            }
+          )
+        }
+      )
+    })
+    return null
+  })
+
+  after(function () {
+    MockDocUpdaterApi.setDoc.restore()
+    return null
+  })
+
+  return it('should set the doc in the doc updater', function () {
+    MockDocUpdaterApi.setDoc
+      .calledWith(
+        this.project_id,
+        this.doc_id,
+        this.restored_lines,
+        this.user_id,
+        true
+      )
+      .should.equal(true)
+    return null
+  })
+})

services/track-changes/test/acceptance/js/helpers/MockDocStoreApi.js

@@ -0,0 +1,54 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let MockDocUpdaterApi
+const express = require('express')
+const app = express()
+
+module.exports = MockDocUpdaterApi = {
+  docs: {},
+
+  getAllDoc(project_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return callback(null, this.docs)
+  },
+
+  run() {
+    app.get('/project/:project_id/doc', (req, res, next) => {
+      return this.getAllDoc(req.params.project_id, (error, docs) => {
+        if (error != null) {
+          res.sendStatus(500)
+        }
+        if (docs == null) {
+          return res.sendStatus(404)
+        } else {
+          return res.send(JSON.stringify(docs))
+        }
+      })
+    })
+
+    return app
+      .listen(3016, error => {
+        if (error != null) {
+          throw error
+        }
+      })
+      .on('error', error => {
+        console.error('error starting MockDocStoreApi:', error.message)
+        return process.exit(1)
+      })
+  },
+}
+
+MockDocUpdaterApi.run()

services/track-changes/test/acceptance/js/helpers/MockDocUpdaterApi.js

@@ -0,0 +1,89 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-undef,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let MockDocUpdaterApi
+const express = require('express')
+const bodyParser = require('body-parser')
+const app = express()
+app.use(bodyParser.json())
+
+module.exports = MockDocUpdaterApi = {
+  docs: {},
+
+  getDoc(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return callback(null, this.docs[doc_id])
+  },
+
+  setDoc(project_id, doc_id, lines, user_id, undoing, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    if (!this.docs[doc_id]) {
+      this.docs[doc_id] = {}
+    }
+    this.docs[doc_id].lines = lines
+    return callback()
+  },
+
+  run() {
+    app.get('/project/:project_id/doc/:doc_id', (req, res, next) => {
+      return this.getDoc(
+        req.params.project_id,
+        req.params.doc_id,
+        (error, doc) => {
+          if (error != null) {
+            res.sendStatus(500)
+          }
+          if (doc == null) {
+            return res.sendStatus(404)
+          } else {
+            return res.send(JSON.stringify(doc))
+          }
+        }
+      )
+    })
+
+    app.post('/project/:project_id/doc/:doc_id', (req, res, next) => {
+      return this.setDoc(
+        req.params.project_id,
+        req.params.doc_id,
+        req.body.lines,
+        req.body.user_id,
+        req.body.undoing,
+        (errr, doc) => {
+          if (typeof error !== 'undefined' && error !== null) {
+            return res.sendStatus(500)
+          } else {
+            return res.sendStatus(204)
+          }
+        }
+      )
+    })
+
+    return app
+      .listen(3003, error => {
+        if (error != null) {
+          throw error
+        }
+      })
+      .on('error', error => {
+        console.error('error starting MockDocUpdaterApi:', error.message)
+        return process.exit(1)
+      })
+  },
+}
+
+MockDocUpdaterApi.run()

services/track-changes/test/acceptance/js/helpers/MockWebApi.js

@@ -0,0 +1,76 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let MockWebApi
+const express = require('express')
+const app = express()
+
+module.exports = MockWebApi = {
+  users: {},
+
+  projects: {},
+
+  getUserInfo(user_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return callback(null, this.users[user_id] || null)
+  },
+
+  getProjectDetails(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, project) {}
+    }
+    return callback(null, this.projects[project_id])
+  },
+
+  run() {
+    app.get('/user/:user_id/personal_info', (req, res, next) => {
+      return this.getUserInfo(req.params.user_id, (error, user) => {
+        if (error != null) {
+          res.sendStatus(500)
+        }
+        if (user == null) {
+          return res.sendStatus(404)
+        } else {
+          return res.send(JSON.stringify(user))
+        }
+      })
+    })
+
+    app.get('/project/:project_id/details', (req, res, next) => {
+      return this.getProjectDetails(req.params.project_id, (error, project) => {
+        if (error != null) {
+          res.sendStatus(500)
+        }
+        if (project == null) {
+          return res.sendStatus(404)
+        } else {
+          return res.send(JSON.stringify(project))
+        }
+      })
+    })
+
+    return app
+      .listen(3000, error => {
+        if (error != null) {
+          throw error
+        }
+      })
+      .on('error', error => {
+        console.error('error starting MockWebApiServer:', error.message)
+        return process.exit(1)
+      })
+  },
+}
+
+MockWebApi.run()

services/track-changes/test/acceptance/js/helpers/TrackChangesApp.js

@@ -0,0 +1,67 @@
+/* eslint-disable
+    handle-callback-err,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS103: Rewrite code to no longer use __guard__
+ * DS205: Consider reworking code to avoid use of IIFEs
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const app = require('../../../../app')
+const { waitForDb } = require('../../../../app/js/mongodb')
+const logger = require('logger-sharelatex')
+const Settings = require('@overleaf/settings')
+
+module.exports = {
+  running: false,
+  initing: false,
+  callbacks: [],
+  ensureRunning(callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    if (this.running) {
+      return callback()
+    } else if (this.initing) {
+      return this.callbacks.push(callback)
+    }
+    this.initing = true
+    this.callbacks.push(callback)
+    waitForDb().then(() => {
+      return app.listen(
+        __guard__(
+          Settings.internal != null
+            ? Settings.internal.trackchanges
+            : undefined,
+          x => x.port
+        ),
+        'localhost',
+        error => {
+          if (error != null) {
+            throw error
+          }
+          this.running = true
+          logger.log('track changes running in dev mode')
+
+          return (() => {
+            const result = []
+            for (callback of Array.from(this.callbacks)) {
+              result.push(callback())
+            }
+            return result
+          })()
+        }
+      )
+    })
+  },
+}
+function __guard__(value, transform) {
+  return typeof value !== 'undefined' && value !== null
+    ? transform(value)
+    : undefined
+}

services/track-changes/test/acceptance/js/helpers/TrackChangesClient.js

@@ -0,0 +1,301 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+let TrackChangesClient
+const async = require('async')
+const zlib = require('zlib')
+const request = require('request')
+const Settings = require('@overleaf/settings')
+const rclient = require('@overleaf/redis-wrapper').createClient(
+  Settings.redis.history
+) // Only works locally for now
+const Keys = Settings.redis.history.key_schema
+const { db, ObjectId } = require('../../../../app/js/mongodb')
+
+const aws = require('aws-sdk')
+const s3 = new aws.S3({
+  accessKeyId: Settings.trackchanges.s3.key,
+  secretAccessKey: Settings.trackchanges.s3.secret,
+  endpoint: Settings.trackchanges.s3.endpoint,
+  s3ForcePathStyle: Settings.trackchanges.s3.pathStyle,
+})
+const S3_BUCKET = Settings.trackchanges.stores.doc_history
+
+module.exports = TrackChangesClient = {
+  flushAndGetCompressedUpdates(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    return TrackChangesClient.flushDoc(project_id, doc_id, error => {
+      if (error != null) {
+        return callback(error)
+      }
+      return TrackChangesClient.getCompressedUpdates(doc_id, callback)
+    })
+  },
+
+  flushDoc(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return request.post(
+      {
+        url: `http://localhost:3015/project/${project_id}/doc/${doc_id}/flush`,
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(204)
+        return callback(error)
+      }
+    )
+  },
+
+  flushProject(project_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return request.post(
+      {
+        url: `http://localhost:3015/project/${project_id}/flush`,
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(204)
+        return callback(error)
+      }
+    )
+  },
+
+  getCompressedUpdates(doc_id, callback) {
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    return db.docHistory
+      .find({ doc_id: ObjectId(doc_id) })
+      .sort({ 'meta.end_ts': 1 })
+      .toArray(callback)
+  },
+
+  getProjectMetaData(project_id, callback) {
+    if (callback == null) {
+      callback = function (error, updates) {}
+    }
+    return db.projectHistoryMetaData.findOne(
+      {
+        project_id: ObjectId(project_id),
+      },
+      callback
+    )
+  },
+
+  setPreserveHistoryForProject(project_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return db.projectHistoryMetaData.updateOne(
+      {
+        project_id: ObjectId(project_id),
+      },
+      {
+        $set: { preserveHistory: true },
+      },
+      {
+        upsert: true,
+      },
+      callback
+    )
+  },
+
+  pushRawUpdates(project_id, doc_id, updates, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return rclient.sadd(
+      Keys.docsWithHistoryOps({ project_id }),
+      doc_id,
+      error => {
+        if (error != null) {
+          return callback(error)
+        }
+        return rclient.rpush(
+          Keys.uncompressedHistoryOps({ doc_id }),
+          ...Array.from(Array.from(updates).map(u => JSON.stringify(u))),
+          callback
+        )
+      }
+    )
+  },
+
+  getDiff(project_id, doc_id, from, to, callback) {
+    if (callback == null) {
+      callback = function (error, diff) {}
+    }
+    return request.get(
+      {
+        url: `http://localhost:3015/project/${project_id}/doc/${doc_id}/diff?from=${from}&to=${to}`,
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(200)
+        return callback(null, JSON.parse(body))
+      }
+    )
+  },
+
+  getUpdates(project_id, options, callback) {
+    if (callback == null) {
+      callback = function (error, body) {}
+    }
+    return request.get(
+      {
+        url: `http://localhost:3015/project/${project_id}/updates?before=${options.before}&min_count=${options.min_count}`,
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(200)
+        return callback(null, JSON.parse(body))
+      }
+    )
+  },
+
+  exportProject(project_id, callback) {
+    request.get(
+      { url: `http://localhost:3015/project/${project_id}/export`, json: true },
+      (error, response, updates) => {
+        if (error) return callback(error)
+        response.statusCode.should.equal(200)
+        callback(null, updates, JSON.parse(response.trailers['x-user-ids']))
+      }
+    )
+  },
+
+  restoreDoc(project_id, doc_id, version, user_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return request.post(
+      {
+        url: `http://localhost:3015/project/${project_id}/doc/${doc_id}/version/${version}/restore`,
+        headers: {
+          'X-User-Id': user_id,
+        },
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(204)
+        return callback(null)
+      }
+    )
+  },
+
+  pushDocHistory(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return request.post(
+      {
+        url: `http://localhost:3015/project/${project_id}/doc/${doc_id}/push`,
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(204)
+        return callback(error)
+      }
+    )
+  },
+
+  pullDocHistory(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error) {}
+    }
+    return request.post(
+      {
+        url: `http://localhost:3015/project/${project_id}/doc/${doc_id}/pull`,
+      },
+      (error, response, body) => {
+        response.statusCode.should.equal(204)
+        return callback(error)
+      }
+    )
+  },
+
+  waitForS3(done, retries) {
+    if (retries == null) {
+      retries = 42
+    }
+    if (!Settings.trackchanges.s3.endpoint) {
+      return done()
+    }
+
+    return request.get(`${Settings.trackchanges.s3.endpoint}/`, (err, res) => {
+      if (res && res.statusCode < 500) {
+        return done()
+      }
+
+      if (retries === 0) {
+        return done(err || new Error(`s3 returned ${res.statusCode}`))
+      }
+
+      return setTimeout(
+        () => TrackChangesClient.waitForS3(done, --retries),
+        1000
+      )
+    })
+  },
+
+  getS3Doc(project_id, doc_id, pack_id, callback) {
+    if (callback == null) {
+      callback = function (error, body) {}
+    }
+    const params = {
+      Bucket: S3_BUCKET,
+      Key: `${project_id}/changes-${doc_id}/pack-${pack_id}`,
+    }
+
+    return s3.getObject(params, (error, data) => {
+      if (error != null) {
+        return callback(error)
+      }
+      const body = data.Body
+      if (body == null) {
+        return callback(new Error('empty response from s3'))
+      }
+      return zlib.gunzip(body, (err, result) => {
+        if (err != null) {
+          return callback(err)
+        }
+        return callback(null, JSON.parse(result.toString()))
+      })
+    })
+  },
+
+  removeS3Doc(project_id, doc_id, callback) {
+    if (callback == null) {
+      callback = function (error, res, body) {}
+    }
+    let params = {
+      Bucket: S3_BUCKET,
+      Prefix: `${project_id}/changes-${doc_id}`,
+    }
+
+    return s3.listObjects(params, (error, data) => {
+      if (error != null) {
+        return callback(error)
+      }
+
+      params = {
+        Bucket: S3_BUCKET,
+        Delete: {
+          Objects: data.Contents.map(s3object => ({ Key: s3object.Key })),
+        },
+      }
+
+      return s3.deleteObjects(params, callback)
+    })
+  },
+}

services/track-changes/test/setup.js

@@ -0,0 +1,21 @@
+const chai = require('chai')
+const SandboxedModule = require('sandboxed-module')
+
+// Chai configuration
+chai.should()
+
+// SandboxedModule configuration
+SandboxedModule.configure({
+  requires: {
+    'logger-sharelatex': {
+      debug() {},
+      log() {},
+      info() {},
+      warn() {},
+      err() {},
+      error() {},
+      fatal() {},
+    },
+  },
+  globals: { Buffer, JSON, console, process },
+})

services/track-changes/test/unit/js/DiffGenerator/DiffGeneratorTests.js

@@ -0,0 +1,456 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/DiffGenerator.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('DiffGenerator', function () {
+  beforeEach(function () {
+    this.DiffGenerator = SandboxedModule.require(modulePath, {})
+    this.ts = Date.now()
+    this.user_id = 'mock-user-id'
+    this.user_id_2 = 'mock-user-id-2'
+    return (this.meta = {
+      start_ts: this.ts,
+      end_ts: this.ts,
+      user_id: this.user_id,
+    })
+  })
+
+  describe('rewindOp', function () {
+    describe('rewinding an insert', function () {
+      return it('should undo the insert', function () {
+        const content = 'hello world'
+        const rewoundContent = this.DiffGenerator.rewindOp(content, {
+          p: 6,
+          i: 'wo',
+        })
+        return rewoundContent.should.equal('hello rld')
+      })
+    })
+
+    describe('rewinding a delete', function () {
+      return it('should undo the delete', function () {
+        const content = 'hello rld'
+        const rewoundContent = this.DiffGenerator.rewindOp(content, {
+          p: 6,
+          d: 'wo',
+        })
+        return rewoundContent.should.equal('hello world')
+      })
+    })
+
+    describe('with an inconsistent update', function () {
+      return it('should throw an error', function () {
+        const content = 'hello world'
+        return expect(() => {
+          return this.DiffGenerator.rewindOp(content, { p: 6, i: 'foo' })
+        }).to.throw(this.DiffGenerator.ConsistencyError)
+      })
+    })
+
+    return describe('with an update which is beyond the length of the content', function () {
+      return it('should undo the insert as if it were at the end of the content', function () {
+        const content = 'foobar'
+        const rewoundContent = this.DiffGenerator.rewindOp(content, {
+          p: 4,
+          i: 'bar',
+        })
+        return rewoundContent.should.equal('foo')
+      })
+    })
+  })
+
+  describe('rewindUpdate', function () {
+    return it('should rewind ops in reverse', function () {
+      const content = 'aaabbbccc'
+      const update = {
+        op: [
+          { p: 3, i: 'bbb' },
+          { p: 6, i: 'ccc' },
+        ],
+      }
+      const rewoundContent = this.DiffGenerator.rewindUpdate(content, update)
+      return rewoundContent.should.equal('aaa')
+    })
+  })
+
+  describe('rewindUpdates', function () {
+    return it('should rewind updates in reverse', function () {
+      const content = 'aaabbbccc'
+      const updates = [
+        { op: [{ p: 3, i: 'bbb' }] },
+        { op: [{ p: 6, i: 'ccc' }] },
+      ]
+      const rewoundContent = this.DiffGenerator.rewindUpdates(content, updates)
+      return rewoundContent.should.equal('aaa')
+    })
+  })
+
+  describe('buildDiff', function () {
+    beforeEach(function () {
+      this.diff = [{ u: 'mock-diff' }]
+      this.content = 'Hello world'
+      this.updates = [
+        { i: 'mock-update-1' },
+        { i: 'mock-update-2' },
+        { i: 'mock-update-3' },
+      ]
+      this.DiffGenerator.applyUpdateToDiff = sinon.stub().returns(this.diff)
+      this.DiffGenerator.compressDiff = sinon.stub().returns(this.diff)
+      return (this.result = this.DiffGenerator.buildDiff(
+        this.content,
+        this.updates
+      ))
+    })
+
+    it('should return the diff', function () {
+      return this.result.should.deep.equal(this.diff)
+    })
+
+    it('should build the content into an initial diff', function () {
+      return this.DiffGenerator.applyUpdateToDiff
+        .calledWith(
+          [
+            {
+              u: this.content,
+            },
+          ],
+          this.updates[0]
+        )
+        .should.equal(true)
+    })
+
+    it('should apply each update', function () {
+      return Array.from(this.updates).map(update =>
+        this.DiffGenerator.applyUpdateToDiff
+          .calledWith(sinon.match.any, update)
+          .should.equal(true)
+      )
+    })
+
+    return it('should compress the diff', function () {
+      return this.DiffGenerator.compressDiff
+        .calledWith(this.diff)
+        .should.equal(true)
+    })
+  })
+
+  describe('compressDiff', function () {
+    describe('with adjacent inserts with the same user_id', function () {
+      return it('should create one update with combined meta data and min/max timestamps', function () {
+        const diff = this.DiffGenerator.compressDiff([
+          {
+            i: 'foo',
+            meta: { start_ts: 10, end_ts: 20, user: { id: this.user_id } },
+          },
+          {
+            i: 'bar',
+            meta: { start_ts: 5, end_ts: 15, user: { id: this.user_id } },
+          },
+        ])
+        return expect(diff).to.deep.equal([
+          {
+            i: 'foobar',
+            meta: { start_ts: 5, end_ts: 20, user: { id: this.user_id } },
+          },
+        ])
+      })
+    })
+
+    describe('with adjacent inserts with different user_ids', function () {
+      return it('should leave the inserts unchanged', function () {
+        const input = [
+          {
+            i: 'foo',
+            meta: { start_ts: 10, end_ts: 20, user: { id: this.user_id } },
+          },
+          {
+            i: 'bar',
+            meta: { start_ts: 5, end_ts: 15, user: { id: this.user_id_2 } },
+          },
+        ]
+        const output = this.DiffGenerator.compressDiff(input)
+        return expect(output).to.deep.equal(input)
+      })
+    })
+
+    describe('with adjacent deletes with the same user_id', function () {
+      return it('should create one update with combined meta data and min/max timestamps', function () {
+        const diff = this.DiffGenerator.compressDiff([
+          {
+            d: 'foo',
+            meta: { start_ts: 10, end_ts: 20, user: { id: this.user_id } },
+          },
+          {
+            d: 'bar',
+            meta: { start_ts: 5, end_ts: 15, user: { id: this.user_id } },
+          },
+        ])
+        return expect(diff).to.deep.equal([
+          {
+            d: 'foobar',
+            meta: { start_ts: 5, end_ts: 20, user: { id: this.user_id } },
+          },
+        ])
+      })
+    })
+
+    return describe('with adjacent deletes with different user_ids', function () {
+      return it('should leave the deletes unchanged', function () {
+        const input = [
+          {
+            d: 'foo',
+            meta: { start_ts: 10, end_ts: 20, user: { id: this.user_id } },
+          },
+          {
+            d: 'bar',
+            meta: { start_ts: 5, end_ts: 15, user: { id: this.user_id_2 } },
+          },
+        ]
+        const output = this.DiffGenerator.compressDiff(input)
+        return expect(output).to.deep.equal(input)
+      })
+    })
+  })
+
+  return describe('applyUpdateToDiff', function () {
+    describe('an insert', function () {
+      it('should insert into the middle of (u)nchanged text', function () {
+        const diff = this.DiffGenerator.applyUpdateToDiff([{ u: 'foobar' }], {
+          op: [{ p: 3, i: 'baz' }],
+          meta: this.meta,
+        })
+        return expect(diff).to.deep.equal([
+          { u: 'foo' },
+          { i: 'baz', meta: this.meta },
+          { u: 'bar' },
+        ])
+      })
+
+      it('should insert into the start of (u)changed text', function () {
+        const diff = this.DiffGenerator.applyUpdateToDiff([{ u: 'foobar' }], {
+          op: [{ p: 0, i: 'baz' }],
+          meta: this.meta,
+        })
+        return expect(diff).to.deep.equal([
+          { i: 'baz', meta: this.meta },
+          { u: 'foobar' },
+        ])
+      })
+
+      it('should insert into the end of (u)changed text', function () {
+        const diff = this.DiffGenerator.applyUpdateToDiff([{ u: 'foobar' }], {
+          op: [{ p: 6, i: 'baz' }],
+          meta: this.meta,
+        })
+        return expect(diff).to.deep.equal([
+          { u: 'foobar' },
+          { i: 'baz', meta: this.meta },
+        ])
+      })
+
+      it('should insert into the middle of (i)inserted text', function () {
+        const diff = this.DiffGenerator.applyUpdateToDiff(
+          [{ i: 'foobar', meta: this.meta }],
+          { op: [{ p: 3, i: 'baz' }], meta: this.meta }
+        )
+        return expect(diff).to.deep.equal([
+          { i: 'foo', meta: this.meta },
+          { i: 'baz', meta: this.meta },
+          { i: 'bar', meta: this.meta },
+        ])
+      })
+
+      return it('should not count deletes in the running length total', function () {
+        const diff = this.DiffGenerator.applyUpdateToDiff(
+          [{ d: 'deleted', meta: this.meta }, { u: 'foobar' }],
+          { op: [{ p: 3, i: 'baz' }], meta: this.meta }
+        )
+        return expect(diff).to.deep.equal([
+          { d: 'deleted', meta: this.meta },
+          { u: 'foo' },
+          { i: 'baz', meta: this.meta },
+          { u: 'bar' },
+        ])
+      })
+    })
+
+    return describe('a delete', function () {
+      describe('deleting unchanged text', function () {
+        it('should delete from the middle of (u)nchanged text', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foobazbar' }],
+            { op: [{ p: 3, d: 'baz' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { u: 'foo' },
+            { d: 'baz', meta: this.meta },
+            { u: 'bar' },
+          ])
+        })
+
+        it('should delete from the start of (u)nchanged text', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foobazbar' }],
+            { op: [{ p: 0, d: 'foo' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { d: 'foo', meta: this.meta },
+            { u: 'bazbar' },
+          ])
+        })
+
+        it('should delete from the end of (u)nchanged text', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foobazbar' }],
+            { op: [{ p: 6, d: 'bar' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { u: 'foobaz' },
+            { d: 'bar', meta: this.meta },
+          ])
+        })
+
+        return it('should delete across multiple (u)changed text parts', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foo' }, { u: 'baz' }, { u: 'bar' }],
+            { op: [{ p: 2, d: 'obazb' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { u: 'fo' },
+            { d: 'o', meta: this.meta },
+            { d: 'baz', meta: this.meta },
+            { d: 'b', meta: this.meta },
+            { u: 'ar' },
+          ])
+        })
+      })
+
+      describe('deleting inserts', function () {
+        it('should delete from the middle of (i)nserted text', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ i: 'foobazbar', meta: this.meta }],
+            { op: [{ p: 3, d: 'baz' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { i: 'foo', meta: this.meta },
+            { i: 'bar', meta: this.meta },
+          ])
+        })
+
+        it('should delete from the start of (u)nchanged text', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ i: 'foobazbar', meta: this.meta }],
+            { op: [{ p: 0, d: 'foo' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([{ i: 'bazbar', meta: this.meta }])
+        })
+
+        it('should delete from the end of (u)nchanged text', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ i: 'foobazbar', meta: this.meta }],
+            { op: [{ p: 6, d: 'bar' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([{ i: 'foobaz', meta: this.meta }])
+        })
+
+        return it('should delete across multiple (u)changed and (i)nserted text parts', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foo' }, { i: 'baz', meta: this.meta }, { u: 'bar' }],
+            { op: [{ p: 2, d: 'obazb' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { u: 'fo' },
+            { d: 'o', meta: this.meta },
+            { d: 'b', meta: this.meta },
+            { u: 'ar' },
+          ])
+        })
+      })
+
+      describe('deleting over existing deletes', function () {
+        return it('should delete across multiple (u)changed and (d)deleted text parts', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foo' }, { d: 'baz', meta: this.meta }, { u: 'bar' }],
+            { op: [{ p: 2, d: 'ob' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { u: 'fo' },
+            { d: 'o', meta: this.meta },
+            { d: 'baz', meta: this.meta },
+            { d: 'b', meta: this.meta },
+            { u: 'ar' },
+          ])
+        })
+      })
+
+      describe("deleting when the text doesn't match", function () {
+        it('should throw an error when deleting from the middle of (u)nchanged text', function () {
+          return expect(() =>
+            this.DiffGenerator.applyUpdateToDiff([{ u: 'foobazbar' }], {
+              op: [{ p: 3, d: 'xxx' }],
+              meta: this.meta,
+            })
+          ).to.throw(this.DiffGenerator.ConsistencyError)
+        })
+
+        it('should throw an error when deleting from the start of (u)nchanged text', function () {
+          return expect(() =>
+            this.DiffGenerator.applyUpdateToDiff([{ u: 'foobazbar' }], {
+              op: [{ p: 0, d: 'xxx' }],
+              meta: this.meta,
+            })
+          ).to.throw(this.DiffGenerator.ConsistencyError)
+        })
+
+        return it('should throw an error when deleting from the end of (u)nchanged text', function () {
+          return expect(() =>
+            this.DiffGenerator.applyUpdateToDiff([{ u: 'foobazbar' }], {
+              op: [{ p: 6, d: 'xxx' }],
+              meta: this.meta,
+            })
+          ).to.throw(this.DiffGenerator.ConsistencyError)
+        })
+      })
+
+      describe('when the last update in the existing diff is a delete', function () {
+        return it('should insert the new update before the delete', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ u: 'foo' }, { d: 'bar', meta: this.meta }],
+            { op: [{ p: 3, i: 'baz' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { u: 'foo' },
+            { i: 'baz', meta: this.meta },
+            { d: 'bar', meta: this.meta },
+          ])
+        })
+      })
+
+      return describe('when the only update in the existing diff is a delete', function () {
+        return it('should insert the new update after the delete', function () {
+          const diff = this.DiffGenerator.applyUpdateToDiff(
+            [{ d: 'bar', meta: this.meta }],
+            { op: [{ p: 0, i: 'baz' }], meta: this.meta }
+          )
+          return expect(diff).to.deep.equal([
+            { d: 'bar', meta: this.meta },
+            { i: 'baz', meta: this.meta },
+          ])
+        })
+      })
+    })
+  })
+})

services/track-changes/test/unit/js/DiffManager/DiffManagerTests.js

@@ -0,0 +1,444 @@
+/* eslint-disable
+    camelcase,
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/DiffManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('DiffManager', function () {
+  beforeEach(function () {
+    this.DiffManager = SandboxedModule.require(modulePath, {
+      requires: {
+        './UpdatesManager': (this.UpdatesManager = {}),
+        './DocumentUpdaterManager': (this.DocumentUpdaterManager = {}),
+        './DiffGenerator': (this.DiffGenerator = {}),
+      },
+    })
+    this.callback = sinon.stub()
+    this.from = new Date()
+    this.to = new Date(Date.now() + 10000)
+    this.project_id = 'mock-project-id'
+    return (this.doc_id = 'mock-doc-id')
+  })
+
+  describe('getLatestDocAndUpdates', function () {
+    beforeEach(function () {
+      this.content = 'hello world'
+      this.version = 42
+      this.updates = ['mock-update-1', 'mock-update-2']
+
+      this.DocumentUpdaterManager.getDocument = sinon
+        .stub()
+        .callsArgWith(2, null, this.content, this.version)
+      return (this.UpdatesManager.getDocUpdatesWithUserInfo = sinon
+        .stub()
+        .callsArgWith(3, null, this.updates))
+    })
+
+    describe('with a fromVersion', function () {
+      beforeEach(function () {
+        return this.DiffManager.getLatestDocAndUpdates(
+          this.project_id,
+          this.doc_id,
+          this.from,
+          this.callback
+        )
+      })
+
+      it('should get the latest version of the doc', function () {
+        return this.DocumentUpdaterManager.getDocument
+          .calledWith(this.project_id, this.doc_id)
+          .should.equal(true)
+      })
+
+      it('should get the latest updates', function () {
+        return this.UpdatesManager.getDocUpdatesWithUserInfo
+          .calledWith(this.project_id, this.doc_id, { from: this.from })
+          .should.equal(true)
+      })
+
+      return it('should call the callback with the content, version and updates', function () {
+        return this.callback
+          .calledWith(null, this.content, this.version, this.updates)
+          .should.equal(true)
+      })
+    })
+
+    return describe('with no fromVersion', function () {
+      beforeEach(function () {
+        return this.DiffManager.getLatestDocAndUpdates(
+          this.project_id,
+          this.doc_id,
+          null,
+          this.callback
+        )
+      })
+
+      it('should get the latest version of the doc', function () {
+        return this.DocumentUpdaterManager.getDocument
+          .calledWith(this.project_id, this.doc_id)
+          .should.equal(true)
+      })
+
+      it('should not get the latest updates', function () {
+        return this.UpdatesManager.getDocUpdatesWithUserInfo.called.should.equal(
+          false
+        )
+      })
+
+      return it('should call the callback with the content, version and blank updates', function () {
+        return this.callback
+          .calledWith(null, this.content, this.version, [])
+          .should.equal(true)
+      })
+    })
+  })
+
+  describe('getDiff', function () {
+    beforeEach(function () {
+      this.content = 'hello world'
+      // Op versions are the version they were applied to, so doc is always one version
+      // ahead.s
+      this.version = 43
+      this.updates = [
+        {
+          op: 'mock-4',
+          v: 42,
+          meta: { start_ts: new Date(this.to.getTime() + 20) },
+        },
+        {
+          op: 'mock-3',
+          v: 41,
+          meta: { start_ts: new Date(this.to.getTime() + 10) },
+        },
+        {
+          op: 'mock-2',
+          v: 40,
+          meta: { start_ts: new Date(this.to.getTime() - 10) },
+        },
+        {
+          op: 'mock-1',
+          v: 39,
+          meta: { start_ts: new Date(this.to.getTime() - 20) },
+        },
+      ]
+      this.fromVersion = 39
+      this.toVersion = 40
+      this.diffed_updates = this.updates.slice(2)
+      this.rewound_content = 'rewound-content'
+      return (this.diff = [{ u: 'mock-diff' }])
+    })
+
+    describe('with matching versions', function () {
+      beforeEach(function () {
+        this.DiffManager.getDocumentBeforeVersion = sinon
+          .stub()
+          .callsArgWith(3, null, this.rewound_content, this.updates)
+        this.DiffGenerator.buildDiff = sinon.stub().returns(this.diff)
+        return this.DiffManager.getDiff(
+          this.project_id,
+          this.doc_id,
+          this.fromVersion,
+          this.toVersion,
+          this.callback
+        )
+      })
+
+      it('should get the latest doc and version with all recent updates', function () {
+        return this.DiffManager.getDocumentBeforeVersion
+          .calledWith(this.project_id, this.doc_id, this.fromVersion)
+          .should.equal(true)
+      })
+
+      it('should generate the diff', function () {
+        return this.DiffGenerator.buildDiff
+          .calledWith(
+            this.rewound_content,
+            this.diffed_updates.slice().reverse()
+          )
+          .should.equal(true)
+      })
+
+      return it('should call the callback with the diff', function () {
+        return this.callback.calledWith(null, this.diff).should.equal(true)
+      })
+    })
+
+    describe('when the updates are inconsistent', function () {
+      beforeEach(function () {
+        this.DiffManager.getLatestDocAndUpdates = sinon
+          .stub()
+          .callsArgWith(3, null, this.content, this.version, this.updates)
+        this.DiffGenerator.buildDiff = sinon
+          .stub()
+          .throws((this.error = new Error('inconsistent!')))
+        this.DiffGenerator.rewindUpdates = sinon.stub()
+        this.DiffManager.getDiff(
+          this.project_id,
+          this.doc_id,
+          this.fromVersion,
+          this.toVersion,
+          this.callback
+        )
+      })
+
+      it('should call the callback with an error', function () {
+        this.callback.calledWith(sinon.match(Error)).should.equal(true)
+        const errorObj = this.callback.args[0][0]
+        expect(errorObj.message).to.include('inconsistent!')
+      })
+    })
+  })
+
+  describe('getDocumentBeforeVersion', function () {
+    beforeEach(function () {
+      this.DiffManager._tryGetDocumentBeforeVersion = sinon.stub()
+      this.document = 'mock-documents'
+      return (this.rewound_updates = 'mock-rewound-updates')
+    })
+
+    describe('succesfully', function () {
+      beforeEach(function () {
+        this.DiffManager._tryGetDocumentBeforeVersion.yields(
+          null,
+          this.document,
+          this.rewound_updates
+        )
+        return this.DiffManager.getDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.version,
+          this.callback
+        )
+      })
+
+      it('should call _tryGetDocumentBeforeVersion', function () {
+        return this.DiffManager._tryGetDocumentBeforeVersion
+          .calledWith(this.project_id, this.doc_id, this.version)
+          .should.equal(true)
+      })
+
+      return it('should call the callback with the response', function () {
+        return this.callback
+          .calledWith(null, this.document, this.rewound_updates)
+          .should.equal(true)
+      })
+    })
+
+    describe('with a retry needed', function () {
+      beforeEach(function () {
+        let retried = false
+        this.DiffManager._tryGetDocumentBeforeVersion = (
+          project_id,
+          doc_id,
+          version,
+          callback
+        ) => {
+          if (!retried) {
+            retried = true
+            const error = new Error()
+            error.retry = true
+            return callback(error)
+          } else {
+            return callback(null, this.document, this.rewound_updates)
+          }
+        }
+        sinon.spy(this.DiffManager, '_tryGetDocumentBeforeVersion')
+        return this.DiffManager.getDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.version,
+          this.callback
+        )
+      })
+
+      it('should call _tryGetDocumentBeforeVersion twice', function () {
+        return this.DiffManager._tryGetDocumentBeforeVersion.calledTwice.should.equal(
+          true
+        )
+      })
+
+      return it('should call the callback with the response', function () {
+        return this.callback
+          .calledWith(null, this.document, this.rewound_updates)
+          .should.equal(true)
+      })
+    })
+
+    describe('with a non-retriable error', function () {
+      beforeEach(function () {
+        this.error = new Error('oops')
+        this.DiffManager._tryGetDocumentBeforeVersion.yields(this.error)
+        return this.DiffManager.getDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.version,
+          this.callback
+        )
+      })
+
+      it('should call _tryGetDocumentBeforeVersion once', function () {
+        return this.DiffManager._tryGetDocumentBeforeVersion.calledOnce.should.equal(
+          true
+        )
+      })
+
+      return it('should call the callback with the error', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+
+    return describe('when retry limit is matched', function () {
+      beforeEach(function () {
+        this.error = new Error('oops')
+        this.error.retry = true
+        this.DiffManager._tryGetDocumentBeforeVersion.yields(this.error)
+        return this.DiffManager.getDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.version,
+          this.callback
+        )
+      })
+
+      it('should call _tryGetDocumentBeforeVersion three times (max retries)', function () {
+        return this.DiffManager._tryGetDocumentBeforeVersion.calledThrice.should.equal(
+          true
+        )
+      })
+
+      return it('should call the callback with the error', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+  })
+
+  return describe('_tryGetDocumentBeforeVersion', function () {
+    beforeEach(function () {
+      this.content = 'hello world'
+      // Op versions are the version they were applied to, so doc is always one version
+      // ahead.s
+      this.version = 43
+      this.updates = [
+        {
+          op: 'mock-4',
+          v: 42,
+          meta: { start_ts: new Date(this.to.getTime() + 20) },
+        },
+        {
+          op: 'mock-3',
+          v: 41,
+          meta: { start_ts: new Date(this.to.getTime() + 10) },
+        },
+        {
+          op: 'mock-2',
+          v: 40,
+          meta: { start_ts: new Date(this.to.getTime() - 10) },
+        },
+        {
+          op: 'mock-1',
+          v: 39,
+          meta: { start_ts: new Date(this.to.getTime() - 20) },
+        },
+      ]
+      this.fromVersion = 39
+      this.rewound_content = 'rewound-content'
+      return (this.diff = [{ u: 'mock-diff' }])
+    })
+
+    describe('with matching versions', function () {
+      beforeEach(function () {
+        this.DiffManager.getLatestDocAndUpdates = sinon
+          .stub()
+          .callsArgWith(3, null, this.content, this.version, this.updates)
+        this.DiffGenerator.rewindUpdates = sinon.spy((content, updates) => {
+          // the rewindUpdates method reverses the 'updates' array
+          updates.reverse()
+          return this.rewound_content
+        })
+        this.rewindUpdatesWithArgs = this.DiffGenerator.rewindUpdates.withArgs(
+          this.content,
+          this.updates.slice().reverse()
+        )
+        return this.DiffManager._tryGetDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.fromVersion,
+          this.callback
+        )
+      })
+
+      it('should get the latest doc and version with all recent updates', function () {
+        return this.DiffManager.getLatestDocAndUpdates
+          .calledWith(this.project_id, this.doc_id, this.fromVersion)
+          .should.equal(true)
+      })
+
+      it('should rewind the diff', function () {
+        return sinon.assert.calledOnce(this.rewindUpdatesWithArgs)
+      })
+
+      return it('should call the callback with the rewound document and updates', function () {
+        return this.callback
+          .calledWith(null, this.rewound_content, this.updates)
+          .should.equal(true)
+      })
+    })
+
+    describe('with mismatching versions', function () {
+      beforeEach(function () {
+        this.version = 50
+        this.updates = [
+          { op: 'mock-1', v: 40 },
+          { op: 'mock-1', v: 39 },
+        ]
+        this.DiffManager.getLatestDocAndUpdates = sinon
+          .stub()
+          .callsArgWith(3, null, this.content, this.version, this.updates)
+        return this.DiffManager._tryGetDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.fromVersion,
+          this.callback
+        )
+      })
+
+      return it('should call the callback with an error with retry = true set', function () {
+        this.callback.calledOnce.should.equal(true)
+        const error = this.callback.args[0][0]
+        return expect(error.retry).to.equal(true)
+      })
+    })
+
+    return describe('when the updates are inconsistent', function () {
+      beforeEach(function () {
+        this.DiffManager.getLatestDocAndUpdates = sinon
+          .stub()
+          .callsArgWith(3, null, this.content, this.version, this.updates)
+        this.DiffGenerator.rewindUpdates = sinon
+          .stub()
+          .throws((this.error = new Error('inconsistent!')))
+        return this.DiffManager.getDocumentBeforeVersion(
+          this.project_id,
+          this.doc_id,
+          this.fromVersion,
+          this.callback
+        )
+      })
+
+      return it('should call the callback with an error', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+  })
+})

services/track-changes/test/unit/js/DocArchive/MongoAWS.js

@@ -0,0 +1,108 @@
+/* eslint-disable
+    handle-callback-err,
+    no-return-assign,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const modulePath = '../../../../app/js/MongoAWS.js'
+const SandboxedModule = require('sandboxed-module')
+const { ObjectId } = require('mongodb')
+const MemoryStream = require('memorystream')
+const zlib = require('zlib')
+
+describe('MongoAWS', function () {
+  beforeEach(function () {
+    this.MongoAWS = SandboxedModule.require(modulePath, {
+      singleOnly: true,
+      requires: {
+        '@overleaf/settings': (this.settings = {
+          trackchanges: {
+            s3: {
+              secret: 's3-secret',
+              key: 's3-key',
+            },
+            stores: {
+              doc_history: 's3-bucket',
+            },
+          },
+        }),
+        child_process: (this.child_process = {}),
+        'mongo-uri': (this.mongouri = {}),
+        'aws-sdk': (this.awssdk = {}),
+        fs: (this.fs = {}),
+        's3-streams': (this.S3S = {}),
+        './mongodb': { db: (this.db = {}), ObjectId },
+        JSONStream: (this.JSONStream = {}),
+        'readline-stream': (this.readline = sinon.stub()),
+        '@overleaf/metrics': { inc() {} },
+      },
+    })
+
+    this.project_id = ObjectId().toString()
+    this.doc_id = ObjectId().toString()
+    this.pack_id = ObjectId()
+    this.update = { v: 123 }
+    return (this.callback = sinon.stub())
+  })
+
+  describe('archivePack', function () {
+    beforeEach(function (done) {
+      this.awssdk.config = { update: sinon.stub() }
+      this.awssdk.S3 = sinon.stub()
+      this.S3S.WriteStream = () => MemoryStream.createWriteStream()
+      this.db.docHistory = {}
+      this.db.docHistory.findOne = sinon
+        .stub()
+        .callsArgWith(1, null, { pack: 'hello' })
+
+      return this.MongoAWS.archivePack(
+        this.project_id,
+        this.doc_id,
+        this.pack_id,
+        (err, result) => {
+          this.callback()
+          return done()
+        }
+      )
+    })
+
+    return it('should call the callback', function () {
+      return this.callback.called.should.equal(true)
+    })
+  })
+
+  return describe('unArchivePack', function () {
+    beforeEach(function (done) {
+      return zlib.gzip('{"pack":"123"}', (err, zbuf) => {
+        this.awssdk.config = { update: sinon.stub() }
+        this.awssdk.S3 = sinon.stub()
+        this.S3S.ReadStream = () =>
+          MemoryStream.createReadStream(zbuf, { readable: true })
+        this.db.docHistory = {}
+        this.db.docHistory.insertOne = sinon
+          .stub()
+          .yields(null, { insertedId: ObjectId() })
+
+        return this.MongoAWS.unArchivePack(
+          this.project_id,
+          this.doc_id,
+          this.pack_id,
+          (err, result) => {
+            this.callback()
+            return done()
+          }
+        )
+      })
+    })
+
+    return it('should call db.docHistory.insert', function () {
+      return this.db.docHistory.insertOne.called.should.equal(true)
+    })
+  })
+})

services/track-changes/test/unit/js/DocumentUpdaterManager/DocumentUpdaterManagerTests.js

@@ -0,0 +1,199 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/DocumentUpdaterManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('DocumentUpdaterManager', function () {
+  beforeEach(function () {
+    this.DocumentUpdaterManager = SandboxedModule.require(modulePath, {
+      requires: {
+        request: (this.request = {}),
+        '@overleaf/settings': (this.settings = {
+          apis: { documentupdater: { url: 'http://example.com' } },
+        }),
+      },
+    })
+    this.callback = sinon.stub()
+    this.lines = ['one', 'two', 'three']
+    return (this.version = 42)
+  })
+
+  describe('getDocument', function () {
+    describe('successfully', function () {
+      beforeEach(function () {
+        this.body = JSON.stringify({
+          lines: this.lines,
+          version: this.version,
+          ops: [],
+        })
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 200 }, this.body)
+        return this.DocumentUpdaterManager.getDocument(
+          this.project_id,
+          this.doc_id,
+          this.callback
+        )
+      })
+
+      it('should get the document from the document updater', function () {
+        const url = `${this.settings.apis.documentupdater.url}/project/${this.project_id}/doc/${this.doc_id}`
+        return this.request.get.calledWith(url).should.equal(true)
+      })
+
+      return it('should call the callback with the content and version', function () {
+        return this.callback
+          .calledWith(null, this.lines.join('\n'), this.version)
+          .should.equal(true)
+      })
+    })
+
+    describe('when the document updater API returns an error', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(
+            1,
+            (this.error = new Error('something went wrong')),
+            null,
+            null
+          )
+        return this.DocumentUpdaterManager.getDocument(
+          this.project_id,
+          this.doc_id,
+          this.callback
+        )
+      })
+
+      return it('should return an error to the callback', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+
+    return describe('when the document updater returns a failure error code', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 500 }, '')
+        return this.DocumentUpdaterManager.getDocument(
+          this.project_id,
+          this.doc_id,
+          this.callback
+        )
+      })
+
+      return it('should return the callback with an error', function () {
+        return this.callback
+          .calledWith(
+            sinon.match.has(
+              'message',
+              'doc updater returned a non-success status code: 500'
+            )
+          )
+          .should.equal(true)
+      })
+    })
+  })
+
+  return describe('setDocument', function () {
+    beforeEach(function () {
+      this.content = 'mock content'
+      return (this.user_id = 'user-id-123')
+    })
+
+    describe('successfully', function () {
+      beforeEach(function () {
+        this.request.post = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 200 })
+        return this.DocumentUpdaterManager.setDocument(
+          this.project_id,
+          this.doc_id,
+          this.content,
+          this.user_id,
+          this.callback
+        )
+      })
+
+      it('should set the document in the document updater', function () {
+        const url = `${this.settings.apis.documentupdater.url}/project/${this.project_id}/doc/${this.doc_id}`
+        return this.request.post
+          .calledWith({
+            url,
+            json: {
+              lines: this.content.split('\n'),
+              source: 'restore',
+              user_id: this.user_id,
+              undoing: true,
+            },
+          })
+          .should.equal(true)
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.calledWith(null).should.equal(true)
+      })
+    })
+
+    describe('when the document updater API returns an error', function () {
+      beforeEach(function () {
+        this.request.post = sinon
+          .stub()
+          .callsArgWith(
+            1,
+            (this.error = new Error('something went wrong')),
+            null,
+            null
+          )
+        return this.DocumentUpdaterManager.setDocument(
+          this.project_id,
+          this.doc_id,
+          this.content,
+          this.user_id,
+          this.callback
+        )
+      })
+
+      return it('should return an error to the callback', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+
+    return describe('when the document updater returns a failure error code', function () {
+      beforeEach(function () {
+        this.request.post = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 500 }, '')
+        return this.DocumentUpdaterManager.setDocument(
+          this.project_id,
+          this.doc_id,
+          this.content,
+          this.user_id,
+          this.callback
+        )
+      })
+
+      return it('should return the callback with an error', function () {
+        return this.callback
+          .calledWith(
+            sinon.match.has(
+              'message',
+              'doc updater returned a non-success status code: 500'
+            )
+          )
+          .should.equal(true)
+      })
+    })
+  })
+})

services/track-changes/test/unit/js/HttpController/HttpControllerTests.js

@@ -0,0 +1,199 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/HttpController.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('HttpController', function () {
+  beforeEach(function () {
+    this.HttpController = SandboxedModule.require(modulePath, {
+      singleOnly: true,
+      requires: {
+        './UpdatesManager': (this.UpdatesManager = {}),
+        './DiffManager': (this.DiffManager = {}),
+        './RestoreManager': (this.RestoreManager = {}),
+        './PackManager': (this.PackManager = {}),
+        './DocArchiveManager': (this.DocArchiveManager = {}),
+        './HealthChecker': (this.HealthChecker = {}),
+      },
+    })
+    this.doc_id = 'doc-id-123'
+    this.project_id = 'project-id-123'
+    this.next = sinon.stub()
+    this.user_id = 'mock-user-123'
+    return (this.now = Date.now())
+  })
+
+  describe('flushDoc', function () {
+    beforeEach(function () {
+      this.req = {
+        params: {
+          doc_id: this.doc_id,
+          project_id: this.project_id,
+        },
+      }
+      this.res = { sendStatus: sinon.stub() }
+      this.UpdatesManager.processUncompressedUpdatesWithLock = sinon
+        .stub()
+        .callsArg(2)
+      return this.HttpController.flushDoc(this.req, this.res, this.next)
+    })
+
+    it('should process the updates', function () {
+      return this.UpdatesManager.processUncompressedUpdatesWithLock
+        .calledWith(this.project_id, this.doc_id)
+        .should.equal(true)
+    })
+
+    return it('should return a success code', function () {
+      return this.res.sendStatus.calledWith(204).should.equal(true)
+    })
+  })
+
+  describe('flushProject', function () {
+    beforeEach(function () {
+      this.req = {
+        params: {
+          project_id: this.project_id,
+        },
+      }
+      this.res = { sendStatus: sinon.stub() }
+      this.UpdatesManager.processUncompressedUpdatesForProject = sinon
+        .stub()
+        .callsArg(1)
+      return this.HttpController.flushProject(this.req, this.res, this.next)
+    })
+
+    it('should process the updates', function () {
+      return this.UpdatesManager.processUncompressedUpdatesForProject
+        .calledWith(this.project_id)
+        .should.equal(true)
+    })
+
+    return it('should return a success code', function () {
+      return this.res.sendStatus.calledWith(204).should.equal(true)
+    })
+  })
+
+  describe('getDiff', function () {
+    beforeEach(function () {
+      this.from = 42
+      this.to = 45
+      this.req = {
+        params: {
+          doc_id: this.doc_id,
+          project_id: this.project_id,
+        },
+        query: {
+          from: this.from.toString(),
+          to: this.to.toString(),
+        },
+      }
+      this.res = { json: sinon.stub() }
+      this.diff = [{ u: 'mock-diff' }]
+      this.DiffManager.getDiff = sinon.stub().callsArgWith(4, null, this.diff)
+      return this.HttpController.getDiff(this.req, this.res, this.next)
+    })
+
+    it('should get the diff', function () {
+      return this.DiffManager.getDiff
+        .calledWith(
+          this.project_id,
+          this.doc_id,
+          parseInt(this.from, 10),
+          parseInt(this.to, 10)
+        )
+        .should.equal(true)
+    })
+
+    return it('should return the diff', function () {
+      return this.res.json.calledWith({ diff: this.diff }).should.equal(true)
+    })
+  })
+
+  describe('getUpdates', function () {
+    beforeEach(function () {
+      this.before = Date.now()
+      this.nextBeforeTimestamp = this.before - 100
+      this.min_count = 10
+      this.req = {
+        params: {
+          project_id: this.project_id,
+        },
+        query: {
+          before: this.before.toString(),
+          min_count: this.min_count.toString(),
+        },
+      }
+      this.res = { json: sinon.stub() }
+      this.updates = ['mock-summarized-updates']
+      this.UpdatesManager.getSummarizedProjectUpdates = sinon
+        .stub()
+        .callsArgWith(2, null, this.updates, this.nextBeforeTimestamp)
+      return this.HttpController.getUpdates(this.req, this.res, this.next)
+    })
+
+    it('should get the updates', function () {
+      return this.UpdatesManager.getSummarizedProjectUpdates
+        .calledWith(this.project_id, {
+          before: this.before,
+          min_count: this.min_count,
+        })
+        .should.equal(true)
+    })
+
+    return it('should return the formatted updates', function () {
+      return this.res.json
+        .calledWith({
+          updates: this.updates,
+          nextBeforeTimestamp: this.nextBeforeTimestamp,
+        })
+        .should.equal(true)
+    })
+  })
+
+  return describe('RestoreManager', function () {
+    beforeEach(function () {
+      this.version = '42'
+      this.req = {
+        params: {
+          doc_id: this.doc_id,
+          project_id: this.project_id,
+          version: this.version,
+        },
+        headers: {
+          'x-user-id': this.user_id,
+        },
+      }
+      this.res = { sendStatus: sinon.stub() }
+
+      this.RestoreManager.restoreToBeforeVersion = sinon.stub().callsArg(4)
+      return this.HttpController.restore(this.req, this.res, this.next)
+    })
+
+    it('should restore the document', function () {
+      return this.RestoreManager.restoreToBeforeVersion
+        .calledWith(
+          this.project_id,
+          this.doc_id,
+          parseInt(this.version, 10),
+          this.user_id
+        )
+        .should.equal(true)
+    })
+
+    return it('should return a success code', function () {
+      return this.res.sendStatus.calledWith(204).should.equal(true)
+    })
+  })
+})

services/track-changes/test/unit/js/LockManager/LockManagerTests.js

@@ -0,0 +1,317 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    mocha/no-nested-tests,
+    no-return-assign,
+    no-undef,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/LockManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('LockManager', function () {
+  beforeEach(function () {
+    this.Settings = {
+      redis: {
+        lock: {},
+      },
+    }
+    this.LockManager = SandboxedModule.require(modulePath, {
+      requires: {
+        '@overleaf/redis-wrapper': {
+          createClient: () => {
+            return (this.rclient = { auth: sinon.stub() })
+          },
+        },
+        '@overleaf/settings': this.Settings,
+      },
+    })
+
+    this.key = 'lock-key'
+    return (this.callback = sinon.stub())
+  })
+
+  describe('checkLock', function () {
+    describe('when the lock is taken', function () {
+      beforeEach(function () {
+        this.rclient.exists = sinon.stub().callsArgWith(1, null, '1')
+        return this.LockManager.checkLock(this.key, this.callback)
+      })
+
+      it('should check the lock in redis', function () {
+        return this.rclient.exists.calledWith(this.key).should.equal(true)
+      })
+
+      return it('should return the callback with false', function () {
+        return this.callback.calledWith(null, false).should.equal(true)
+      })
+    })
+
+    return describe('when the lock is free', function () {
+      beforeEach(function () {
+        this.rclient.exists = sinon.stub().callsArgWith(1, null, '0')
+        return this.LockManager.checkLock(this.key, this.callback)
+      })
+
+      return it('should return the callback with true', function () {
+        return this.callback.calledWith(null, true).should.equal(true)
+      })
+    })
+  })
+
+  describe('tryLock', function () {
+    describe('when the lock is taken', function () {
+      beforeEach(function () {
+        this.rclient.set = sinon.stub().callsArgWith(5, null, null)
+        this.LockManager.randomLock = sinon
+          .stub()
+          .returns('locked-random-value')
+        return this.LockManager.tryLock(this.key, this.callback)
+      })
+
+      it('should check the lock in redis', function () {
+        return this.rclient.set
+          .calledWith(
+            this.key,
+            'locked-random-value',
+            'EX',
+            this.LockManager.LOCK_TTL,
+            'NX'
+          )
+          .should.equal(true)
+      })
+
+      return it('should return the callback with false', function () {
+        return this.callback.calledWith(null, false).should.equal(true)
+      })
+    })
+
+    return describe('when the lock is free', function () {
+      beforeEach(function () {
+        this.rclient.set = sinon.stub().callsArgWith(5, null, 'OK')
+        return this.LockManager.tryLock(this.key, this.callback)
+      })
+
+      return it('should return the callback with true', function () {
+        return this.callback.calledWith(null, true).should.equal(true)
+      })
+    })
+  })
+
+  describe('deleteLock', function () {
+    return beforeEach(function () {
+      beforeEach(function () {
+        this.rclient.del = sinon.stub().callsArg(1)
+        return this.LockManager.deleteLock(this.key, this.callback)
+      })
+
+      it('should delete the lock in redis', function () {
+        return this.rclient.del.calledWith(key).should.equal(true)
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+  })
+
+  describe('getLock', function () {
+    describe('when the lock is not taken', function () {
+      beforeEach(function (done) {
+        this.LockManager.tryLock = sinon.stub().callsArgWith(1, null, true)
+        return this.LockManager.getLock(this.key, (...args) => {
+          this.callback(...Array.from(args || []))
+          return done()
+        })
+      })
+
+      it('should try to get the lock', function () {
+        return this.LockManager.tryLock.calledWith(this.key).should.equal(true)
+      })
+
+      it('should only need to try once', function () {
+        return this.LockManager.tryLock.callCount.should.equal(1)
+      })
+
+      return it('should return the callback', function () {
+        return this.callback.calledWith(null).should.equal(true)
+      })
+    })
+
+    describe('when the lock is initially set', function () {
+      beforeEach(function (done) {
+        const startTime = Date.now()
+        this.LockManager.LOCK_TEST_INTERVAL = 5
+        this.LockManager.tryLock = function (doc_id, callback) {
+          if (callback == null) {
+            callback = function (error, isFree) {}
+          }
+          if (Date.now() - startTime < 100) {
+            return callback(null, false)
+          } else {
+            return callback(null, true)
+          }
+        }
+        sinon.spy(this.LockManager, 'tryLock')
+
+        return this.LockManager.getLock(this.key, (...args) => {
+          this.callback(...Array.from(args || []))
+          return done()
+        })
+      })
+
+      it('should call tryLock multiple times until free', function () {
+        return (this.LockManager.tryLock.callCount > 1).should.equal(true)
+      })
+
+      return it('should return the callback', function () {
+        return this.callback.calledWith(null).should.equal(true)
+      })
+    })
+
+    return describe('when the lock times out', function () {
+      beforeEach(function (done) {
+        const time = Date.now()
+        this.LockManager.MAX_LOCK_WAIT_TIME = 5
+        this.LockManager.tryLock = sinon.stub().callsArgWith(1, null, false)
+        return this.LockManager.getLock(this.key, (...args) => {
+          this.callback(...Array.from(args || []))
+          return done()
+        })
+      })
+
+      return it('should return the callback with an error', function () {
+        return this.callback
+          .calledWith(sinon.match.instanceOf(Error))
+          .should.equal(true)
+      })
+    })
+  })
+
+  return describe('runWithLock', function () {
+    describe('with successful run', function () {
+      beforeEach(function () {
+        this.runner = function (releaseLock) {
+          if (releaseLock == null) {
+            releaseLock = function (error) {}
+          }
+          return releaseLock()
+        }
+        sinon.spy(this, 'runner')
+        this.LockManager.getLock = sinon.stub().callsArg(1)
+        this.LockManager.releaseLock = sinon.stub().callsArg(2)
+        return this.LockManager.runWithLock(
+          this.key,
+          this.runner,
+          this.callback
+        )
+      })
+
+      it('should get the lock', function () {
+        return this.LockManager.getLock.calledWith(this.key).should.equal(true)
+      })
+
+      it('should run the passed function', function () {
+        return this.runner.called.should.equal(true)
+      })
+
+      it('should release the lock', function () {
+        return this.LockManager.releaseLock
+          .calledWith(this.key)
+          .should.equal(true)
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+
+    describe('when the runner function returns an error', function () {
+      beforeEach(function () {
+        this.error = new Error('oops')
+        this.runner = releaseLock => {
+          if (releaseLock == null) {
+            releaseLock = function (error) {}
+          }
+          return releaseLock(this.error)
+        }
+        sinon.spy(this, 'runner')
+        this.LockManager.getLock = sinon.stub().callsArg(1)
+        this.LockManager.releaseLock = sinon.stub().callsArg(2)
+        return this.LockManager.runWithLock(
+          this.key,
+          this.runner,
+          this.callback
+        )
+      })
+
+      it('should release the lock', function () {
+        return this.LockManager.releaseLock
+          .calledWith(this.key)
+          .should.equal(true)
+      })
+
+      return it('should call the callback with the error', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+
+    return describe('releaseLock', function () {
+      describe('when the lock is current', function () {
+        beforeEach(function () {
+          this.rclient.eval = sinon.stub().yields(null, 1)
+          return this.LockManager.releaseLock(
+            this.key,
+            this.lockValue,
+            this.callback
+          )
+        })
+
+        it('should clear the data from redis', function () {
+          return this.rclient.eval
+            .calledWith(
+              this.LockManager.unlockScript,
+              1,
+              this.key,
+              this.lockValue
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+
+      return describe('when the lock has expired', function () {
+        beforeEach(function () {
+          this.rclient.eval = sinon.stub().yields(null, 0)
+          return this.LockManager.releaseLock(
+            this.key,
+            this.lockValue,
+            this.callback
+          )
+        })
+
+        return it('should return an error if the lock has expired', function () {
+          return this.callback
+            .calledWith(
+              sinon.match.has('message', 'tried to release timed out lock')
+            )
+            .should.equal(true)
+        })
+      })
+    })
+  })
+})

services/track-changes/test/unit/js/MongoManager/MongoManagerTests.js

@@ -0,0 +1,239 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/MongoManager.js'
+const packModulePath = '../../../../app/js/PackManager.js'
+const SandboxedModule = require('sandboxed-module')
+const { ObjectId } = require('mongodb')
+const tk = require('timekeeper')
+
+describe('MongoManager', function () {
+  beforeEach(function () {
+    tk.freeze(new Date())
+    this.MongoManager = SandboxedModule.require(modulePath, {
+      requires: {
+        './mongodb': { db: (this.db = {}), ObjectId },
+        './PackManager': (this.PackManager = {}),
+        '@overleaf/metrics': { timeAsyncMethod() {} },
+      },
+    })
+    this.callback = sinon.stub()
+    this.doc_id = ObjectId().toString()
+    return (this.project_id = ObjectId().toString())
+  })
+
+  afterEach(function () {
+    return tk.reset()
+  })
+
+  describe('getLastCompressedUpdate', function () {
+    beforeEach(function () {
+      this.update = 'mock-update'
+      this.db.docHistory = {}
+      this.db.docHistory.find = sinon.stub().returns(this.db.docHistory)
+      this.db.docHistory.findOne = sinon.stub().returns(this.db.docHistory)
+      this.db.docHistory.sort = sinon.stub().returns(this.db.docHistory)
+      this.db.docHistory.limit = sinon.stub().returns(this.db.docHistory)
+      this.db.docHistory.toArray = sinon
+        .stub()
+        .callsArgWith(0, null, [this.update])
+
+      return this.MongoManager.getLastCompressedUpdate(
+        this.doc_id,
+        this.callback
+      )
+    })
+
+    it('should find the updates for the doc', function () {
+      return this.db.docHistory.find
+        .calledWith({ doc_id: ObjectId(this.doc_id) })
+        .should.equal(true)
+    })
+
+    it('should limit to one result', function () {
+      return this.db.docHistory.limit.calledWith(1).should.equal(true)
+    })
+
+    it('should sort in descending version order', function () {
+      return this.db.docHistory.sort.calledWith({ v: -1 }).should.equal(true)
+    })
+
+    return it('should call the call back with the update', function () {
+      return this.callback.calledWith(null, this.update).should.equal(true)
+    })
+  })
+
+  describe('peekLastCompressedUpdate', function () {
+    describe('when there is no last update', function () {
+      beforeEach(function () {
+        this.PackManager.getLastPackFromIndex = sinon
+          .stub()
+          .callsArgWith(1, null, null)
+        this.MongoManager.getLastCompressedUpdate = sinon
+          .stub()
+          .callsArgWith(1, null, null)
+        return this.MongoManager.peekLastCompressedUpdate(
+          this.doc_id,
+          this.callback
+        )
+      })
+
+      it('should get the last update', function () {
+        return this.MongoManager.getLastCompressedUpdate
+          .calledWith(this.doc_id)
+          .should.equal(true)
+      })
+
+      return it('should call the callback with no update', function () {
+        return this.callback.calledWith(null, null).should.equal(true)
+      })
+    })
+
+    describe('when there is an update', function () {
+      beforeEach(function () {
+        this.update = { _id: Object() }
+        this.MongoManager.getLastCompressedUpdate = sinon
+          .stub()
+          .callsArgWith(1, null, this.update)
+        return this.MongoManager.peekLastCompressedUpdate(
+          this.doc_id,
+          this.callback
+        )
+      })
+
+      it('should get the last update', function () {
+        return this.MongoManager.getLastCompressedUpdate
+          .calledWith(this.doc_id)
+          .should.equal(true)
+      })
+
+      return it('should call the callback with the update', function () {
+        return this.callback.calledWith(null, this.update).should.equal(true)
+      })
+    })
+
+    return describe('when there is a last update in S3', function () {
+      beforeEach(function () {
+        this.update = { _id: Object(), v: 12345, v_end: 12345, inS3: true }
+        this.PackManager.getLastPackFromIndex = sinon
+          .stub()
+          .callsArgWith(1, null, this.update)
+        this.MongoManager.getLastCompressedUpdate = sinon
+          .stub()
+          .callsArgWith(1, null)
+        return this.MongoManager.peekLastCompressedUpdate(
+          this.doc_id,
+          this.callback
+        )
+      })
+
+      it('should get the last update', function () {
+        return this.MongoManager.getLastCompressedUpdate
+          .calledWith(this.doc_id)
+          .should.equal(true)
+      })
+
+      return it('should call the callback with a null update and the correct version', function () {
+        return this.callback
+          .calledWith(null, null, this.update.v_end)
+          .should.equal(true)
+      })
+    })
+  })
+
+  describe('backportProjectId', function () {
+    beforeEach(function () {
+      this.db.docHistory = { updateMany: sinon.stub().yields() }
+      return this.MongoManager.backportProjectId(
+        this.project_id,
+        this.doc_id,
+        this.callback
+      )
+    })
+
+    it("should insert the project_id into all entries for the doc_id which don't have it set", function () {
+      return this.db.docHistory.updateMany
+        .calledWith(
+          {
+            doc_id: ObjectId(this.doc_id),
+            project_id: { $exists: false },
+          },
+          {
+            $set: { project_id: ObjectId(this.project_id) },
+          }
+        )
+        .should.equal(true)
+    })
+
+    return it('should call the callback', function () {
+      return this.callback.called.should.equal(true)
+    })
+  })
+
+  describe('getProjectMetaData', function () {
+    beforeEach(function () {
+      this.metadata = { mock: 'metadata' }
+      this.db.projectHistoryMetaData = {
+        findOne: sinon.stub().callsArgWith(1, null, this.metadata),
+      }
+      return this.MongoManager.getProjectMetaData(
+        this.project_id,
+        this.callback
+      )
+    })
+
+    it('should look up the meta data in the db', function () {
+      return this.db.projectHistoryMetaData.findOne
+        .calledWith({ project_id: ObjectId(this.project_id) })
+        .should.equal(true)
+    })
+
+    return it('should return the metadata', function () {
+      return this.callback.calledWith(null, this.metadata).should.equal(true)
+    })
+  })
+
+  return describe('setProjectMetaData', function () {
+    beforeEach(function () {
+      this.metadata = { mock: 'metadata' }
+      this.db.projectHistoryMetaData = {
+        updateOne: sinon.stub().yields(),
+      }
+      return this.MongoManager.setProjectMetaData(
+        this.project_id,
+        this.metadata,
+        this.callback
+      )
+    })
+
+    it('should upsert the metadata into the DB', function () {
+      return this.db.projectHistoryMetaData.updateOne
+        .calledWith(
+          {
+            project_id: ObjectId(this.project_id),
+          },
+          {
+            $set: this.metadata,
+          },
+          {
+            upsert: true,
+          }
+        )
+        .should.equal(true)
+    })
+
+    return it('should call the callback', function () {
+      return this.callback.called.should.equal(true)
+    })
+  })
+})

services/track-changes/test/unit/js/PackManager/PackManagerTests.js

@@ -0,0 +1,704 @@
+/* eslint-disable
+    mocha/no-identical-title,
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { assert, expect } = require('chai')
+const modulePath = '../../../../app/js/PackManager.js'
+const SandboxedModule = require('sandboxed-module')
+const { ObjectId } = require('mongodb')
+const _ = require('underscore')
+
+const tk = require('timekeeper')
+
+describe('PackManager', function () {
+  beforeEach(function () {
+    tk.freeze(new Date())
+    this.PackManager = SandboxedModule.require(modulePath, {
+      requires: {
+        bson: require('bson'),
+        './mongodb': { db: (this.db = {}), ObjectId },
+        './LockManager': {},
+        './MongoAWS': {},
+        '@overleaf/metrics': { inc() {} },
+        './ProjectIterator': require('../../../../app/js/ProjectIterator.js'), // Cache for speed
+        '@overleaf/settings': {
+          redis: { lock: { key_schema: {} } },
+        },
+      },
+    })
+    this.callback = sinon.stub()
+    this.doc_id = ObjectId().toString()
+    this.project_id = ObjectId().toString()
+    return (this.PackManager.MAX_COUNT = 512)
+  })
+
+  afterEach(function () {
+    return tk.reset()
+  })
+
+  describe('insertCompressedUpdates', function () {
+    beforeEach(function () {
+      this.lastUpdate = {
+        _id: '12345',
+        pack: [
+          { op: 'op-1', meta: 'meta-1', v: 1 },
+          { op: 'op-2', meta: 'meta-2', v: 2 },
+        ],
+        n: 2,
+        sz: 100,
+      }
+      this.newUpdates = [
+        { op: 'op-3', meta: 'meta-3', v: 3 },
+        { op: 'op-4', meta: 'meta-4', v: 4 },
+      ]
+      return (this.db.docHistory = {
+        insertOne: sinon.stub().yields(),
+        insert: sinon.stub().callsArg(1),
+        updateOne: sinon.stub().yields(),
+        findAndModify: sinon.stub().callsArg(1),
+      })
+    })
+
+    describe('with no last update', function () {
+      beforeEach(function () {
+        this.PackManager.insertUpdatesIntoNewPack = sinon.stub().callsArg(4)
+        return this.PackManager.insertCompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          null,
+          this.newUpdates,
+          true,
+          this.callback
+        )
+      })
+
+      describe('for a small update', function () {
+        it('should insert the update into a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(this.project_id, this.doc_id, this.newUpdates, true)
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+
+      return describe('for many small updates', function () {
+        beforeEach(function () {
+          this.newUpdates = __range__(0, 2048, true).map(i => ({
+            op: `op-${i}`,
+            meta: `meta-${i}`,
+            v: i,
+          }))
+          return this.PackManager.insertCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            null,
+            this.newUpdates,
+            false,
+            this.callback
+          )
+        })
+
+        it('should append the initial updates to the existing pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(0, 512),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the first set remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(512, 1024),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the second set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(1024, 1536),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the third set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(1536, 2048),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the final set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(2048, 2049),
+              false
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+    })
+
+    describe('with an existing pack as the last update', function () {
+      beforeEach(function () {
+        this.PackManager.appendUpdatesToExistingPack = sinon.stub().callsArg(5)
+        this.PackManager.insertUpdatesIntoNewPack = sinon.stub().callsArg(4)
+        return this.PackManager.insertCompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          this.lastUpdate,
+          this.newUpdates,
+          false,
+          this.callback
+        )
+      })
+
+      describe('for a small update', function () {
+        it('should append the update to the existing pack', function () {
+          return this.PackManager.appendUpdatesToExistingPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.lastUpdate,
+              this.newUpdates,
+              false
+            )
+            .should.equal(true)
+        })
+        it('should not insert any new packs', function () {
+          return this.PackManager.insertUpdatesIntoNewPack.called.should.equal(
+            false
+          )
+        })
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+
+      describe('for many small updates', function () {
+        beforeEach(function () {
+          this.newUpdates = __range__(0, 2048, true).map(i => ({
+            op: `op-${i}`,
+            meta: `meta-${i}`,
+            v: i,
+          }))
+          return this.PackManager.insertCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            this.lastUpdate,
+            this.newUpdates,
+            false,
+            this.callback
+          )
+        })
+
+        it('should append the initial updates to the existing pack', function () {
+          return this.PackManager.appendUpdatesToExistingPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.lastUpdate,
+              this.newUpdates.slice(0, 510),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the first set remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(510, 1022),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the second set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(1022, 1534),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the third set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(1534, 2046),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the final set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(2046, 2049),
+              false
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+
+      return describe('for many big updates', function () {
+        beforeEach(function () {
+          const longString = __range__(
+            0,
+            0.75 * this.PackManager.MAX_SIZE,
+            true
+          )
+            .map(j => 'a')
+            .join('')
+          this.newUpdates = [0, 1, 2, 3, 4].map(i => ({
+            op: `op-${i}-${longString}`,
+            meta: `meta-${i}`,
+            v: i,
+          }))
+          return this.PackManager.insertCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            this.lastUpdate,
+            this.newUpdates,
+            false,
+            this.callback
+          )
+        })
+
+        it('should append the initial updates to the existing pack', function () {
+          return this.PackManager.appendUpdatesToExistingPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.lastUpdate,
+              this.newUpdates.slice(0, 1),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the first set remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(1, 2),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the second set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(2, 3),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the third set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(3, 4),
+              false
+            )
+            .should.equal(true)
+        })
+
+        it('should insert the final set of remaining updates as a new pack', function () {
+          return this.PackManager.insertUpdatesIntoNewPack
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.newUpdates.slice(4, 5),
+              false
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+    })
+
+    describe('flushCompressedUpdates', function () {
+      return describe('when there is no previous update', function () {
+        beforeEach(function () {
+          return this.PackManager.flushCompressedUpdates(
+            this.project_id,
+            this.doc_id,
+            null,
+            this.newUpdates,
+            true,
+            this.callback
+          )
+        })
+
+        return describe('for a small update  that will expire', function () {
+          it('should insert the update into mongo', function () {
+            return this.db.docHistory.insertOne
+              .calledWithMatch({
+                pack: this.newUpdates,
+                project_id: ObjectId(this.project_id),
+                doc_id: ObjectId(this.doc_id),
+                n: this.newUpdates.length,
+                v: this.newUpdates[0].v,
+                v_end: this.newUpdates[this.newUpdates.length - 1].v,
+              })
+              .should.equal(true)
+          })
+
+          it('should set an expiry time in the future', function () {
+            return this.db.docHistory.insertOne
+              .calledWithMatch({
+                expiresAt: new Date(Date.now() + 7 * 24 * 3600 * 1000),
+              })
+              .should.equal(true)
+          })
+
+          return it('should call the callback', function () {
+            return this.callback.called.should.equal(true)
+          })
+        })
+      })
+    })
+
+    describe('when there is a recent previous update in mongo that expires', function () {
+      beforeEach(function () {
+        this.lastUpdate = {
+          _id: '12345',
+          pack: [
+            { op: 'op-1', meta: 'meta-1', v: 1 },
+            { op: 'op-2', meta: 'meta-2', v: 2 },
+          ],
+          n: 2,
+          sz: 100,
+          meta: { start_ts: Date.now() - 6 * 3600 * 1000 },
+          expiresAt: new Date(Date.now()),
+        }
+
+        return this.PackManager.flushCompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          this.lastUpdate,
+          this.newUpdates,
+          true,
+          this.callback
+        )
+      })
+
+      return describe('for a small update that will expire', function () {
+        it('should append the update in mongo', function () {
+          return this.db.docHistory.updateOne
+            .calledWithMatch(
+              { _id: this.lastUpdate._id },
+              {
+                $push: { pack: { $each: this.newUpdates } },
+                $set: { v_end: this.newUpdates[this.newUpdates.length - 1].v },
+              }
+            )
+            .should.equal(true)
+        })
+
+        it('should set an expiry time in the future', function () {
+          return this.db.docHistory.updateOne
+            .calledWithMatch(sinon.match.any, {
+              $set: { expiresAt: new Date(Date.now() + 7 * 24 * 3600 * 1000) },
+            })
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+    })
+
+    describe('when there is a recent previous update in mongo that expires', function () {
+      beforeEach(function () {
+        this.PackManager.updateIndex = sinon.stub().callsArg(2)
+
+        this.lastUpdate = {
+          _id: '12345',
+          pack: [
+            { op: 'op-1', meta: 'meta-1', v: 1 },
+            { op: 'op-2', meta: 'meta-2', v: 2 },
+          ],
+          n: 2,
+          sz: 100,
+          meta: { start_ts: Date.now() - 6 * 3600 * 1000 },
+          expiresAt: new Date(Date.now()),
+        }
+
+        return this.PackManager.flushCompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          this.lastUpdate,
+          this.newUpdates,
+          false,
+          this.callback
+        )
+      })
+
+      return describe('for a small update that will not expire', function () {
+        it('should insert the update into mongo', function () {
+          return this.db.docHistory.insertOne
+            .calledWithMatch({
+              pack: this.newUpdates,
+              project_id: ObjectId(this.project_id),
+              doc_id: ObjectId(this.doc_id),
+              n: this.newUpdates.length,
+              v: this.newUpdates[0].v,
+              v_end: this.newUpdates[this.newUpdates.length - 1].v,
+            })
+            .should.equal(true)
+        })
+
+        it('should not set any expiry time', function () {
+          return this.db.docHistory.insertOne
+            .neverCalledWithMatch(sinon.match.has('expiresAt'))
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+    })
+
+    return describe('when there is an old previous update in mongo', function () {
+      beforeEach(function () {
+        this.lastUpdate = {
+          _id: '12345',
+          pack: [
+            { op: 'op-1', meta: 'meta-1', v: 1 },
+            { op: 'op-2', meta: 'meta-2', v: 2 },
+          ],
+          n: 2,
+          sz: 100,
+          meta: { start_ts: Date.now() - 30 * 24 * 3600 * 1000 },
+          expiresAt: new Date(Date.now() - 30 * 24 * 3600 * 1000),
+        }
+
+        return this.PackManager.flushCompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          this.lastUpdate,
+          this.newUpdates,
+          true,
+          this.callback
+        )
+      })
+
+      return describe('for a small update that will expire', function () {
+        it('should insert the update into mongo', function () {
+          return this.db.docHistory.insertOne
+            .calledWithMatch({
+              pack: this.newUpdates,
+              project_id: ObjectId(this.project_id),
+              doc_id: ObjectId(this.doc_id),
+              n: this.newUpdates.length,
+              v: this.newUpdates[0].v,
+              v_end: this.newUpdates[this.newUpdates.length - 1].v,
+            })
+            .should.equal(true)
+        })
+
+        it('should set an expiry time in the future', function () {
+          return this.db.docHistory.insertOne
+            .calledWithMatch({
+              expiresAt: new Date(Date.now() + 7 * 24 * 3600 * 1000),
+            })
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+    })
+  })
+
+  describe('getOpsByVersionRange', function () {})
+
+  describe('loadPacksByVersionRange', function () {})
+
+  describe('fetchPacksIfNeeded', function () {})
+
+  describe('makeProjectIterator', function () {})
+
+  describe('getPackById', function () {})
+
+  describe('increaseTTL', function () {})
+
+  describe('getIndex', function () {})
+
+  describe('getPackFromIndex', function () {})
+  // getLastPackFromIndex:
+  // getIndexWithKeys
+  // initialiseIndex
+  // updateIndex
+  // findCompletedPacks
+  // findUnindexedPacks
+  // insertPacksIntoIndexWithLock
+  // _insertPacksIntoIndex
+  // archivePack
+  // checkArchivedPack
+  // processOldPack
+  // 	updateIndexIfNeeded
+  // 	findUnarchivedPacks
+
+  return describe('checkArchiveNotInProgress', function () {
+    describe('when an archive is in progress', function () {
+      beforeEach(function () {
+        this.db.docHistoryIndex = {
+          findOne: sinon.stub().callsArgWith(2, null, { inS3: false }),
+        }
+        return this.PackManager.checkArchiveNotInProgress(
+          this.project_id,
+          this.doc_id,
+          this.pack_id,
+          this.callback
+        )
+      })
+      it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+      return it('should return an error', function () {
+        return this.callback
+          .calledWith(sinon.match.has('message'))
+          .should.equal(true)
+      })
+    })
+
+    describe('when an archive is completed', function () {
+      beforeEach(function () {
+        this.db.docHistoryIndex = {
+          findOne: sinon.stub().callsArgWith(2, null, { inS3: true }),
+        }
+        return this.PackManager.checkArchiveNotInProgress(
+          this.project_id,
+          this.doc_id,
+          this.pack_id,
+          this.callback
+        )
+      })
+      it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+      return it('should return an error', function () {
+        return this.callback
+          .calledWith(sinon.match.has('message'))
+          .should.equal(true)
+      })
+    })
+
+    return describe('when the archive has not started or completed', function () {
+      beforeEach(function () {
+        this.db.docHistoryIndex = {
+          findOne: sinon.stub().callsArgWith(2, null, {}),
+        }
+        return this.PackManager.checkArchiveNotInProgress(
+          this.project_id,
+          this.doc_id,
+          this.pack_id,
+          this.callback
+        )
+      })
+      it('should call the callback with no error', function () {
+        return this.callback.called.should.equal(true)
+      })
+      return it('should return with no error', function () {
+        return (typeof this.callback.lastCall.args[0]).should.equal('undefined')
+      })
+    })
+  })
+})
+
+// describe "setTTLOnArchivedPack", ->
+// 	beforeEach ->
+// 		@pack_id = "somepackid"
+// 		@onedayinms = 86400000
+// 		@db.docHistory =
+// 			findAndModify : sinon.stub().callsArgWith(1)
+
+// 	it "should set expires to 1 day", (done)->
+// 		#@PackManager._getOneDayInFutureWithRandomDelay = sinon.stub().returns(@onedayinms)
+// 		@PackManager.setTTLOnArchivedPack @project_id, @doc_id, @pack_id, =>
+// 			args = @db.docHistory.findAndModify.args[0][0]
+// 			args.query._id.should.equal @pack_id
+// 			args.update['$set'].expiresAt.should.equal @onedayinms
+// 			done()
+
+// describe "_getOneDayInFutureWithRandomDelay", ->
+// 	beforeEach ->
+// 		@onedayinms = 86400000
+// 		@thirtyMins = 1000 * 60 * 30
+
+// 	it "should give 1 day + 30 mins random time", (done)->
+// 		loops = 10000
+// 		while --loops > 0
+// 			randomDelay = @PackManager._getOneDayInFutureWithRandomDelay() - new Date(Date.now() + @onedayinms)
+// 			randomDelay.should.be.above(0)
+// 			randomDelay.should.be.below(@thirtyMins + 1)
+// 		done()
+
+function __range__(left, right, inclusive) {
+  const range = []
+  const ascending = left < right
+  const end = !inclusive ? right : ascending ? right + 1 : right - 1
+  for (let i = left; ascending ? i < end : i > end; ascending ? i++ : i--) {
+    range.push(i)
+  }
+  return range
+}

services/track-changes/test/unit/js/RedisManager/RedisManagerTests.js

@@ -0,0 +1,164 @@
+/* eslint-disable
+    camelcase,
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/RedisManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('RedisManager', function () {
+  beforeEach(function () {
+    this.RedisManager = SandboxedModule.require(modulePath, {
+      requires: {
+        '@overleaf/redis-wrapper': {
+          createClient: () => {
+            return (this.rclient = {
+              auth: sinon.stub(),
+              multi: () => this.rclient,
+            })
+          },
+        },
+        '@overleaf/settings': {
+          redis: {
+            history: {
+              key_schema: {
+                uncompressedHistoryOps({ doc_id }) {
+                  return `UncompressedHistoryOps:${doc_id}`
+                },
+                docsWithHistoryOps({ project_id }) {
+                  return `DocsWithHistoryOps:${project_id}`
+                },
+              },
+            },
+          },
+        },
+      },
+    })
+    this.doc_id = 'doc-id-123'
+    this.project_id = 'project-id-123'
+    this.batchSize = 100
+    return (this.callback = sinon.stub())
+  })
+
+  describe('getOldestDocUpdates', function () {
+    beforeEach(function () {
+      this.rawUpdates = [
+        { v: 42, op: 'mock-op-42' },
+        { v: 45, op: 'mock-op-45' },
+      ]
+      this.jsonUpdates = Array.from(this.rawUpdates).map(update =>
+        JSON.stringify(update)
+      )
+      this.rclient.lrange = sinon.stub().callsArgWith(3, null, this.jsonUpdates)
+      return this.RedisManager.getOldestDocUpdates(
+        this.doc_id,
+        this.batchSize,
+        this.callback
+      )
+    })
+
+    it('should read the updates from redis', function () {
+      return this.rclient.lrange
+        .calledWith(
+          `UncompressedHistoryOps:${this.doc_id}`,
+          0,
+          this.batchSize - 1
+        )
+        .should.equal(true)
+    })
+
+    it('should call the callback with the unparsed ops', function () {
+      return this.callback.calledWith(null, this.jsonUpdates).should.equal(true)
+    })
+
+    describe('expandDocUpdates', function () {
+      beforeEach(function () {
+        return this.RedisManager.expandDocUpdates(
+          this.jsonUpdates,
+          this.callback
+        )
+      })
+
+      return it('should call the callback with the parsed ops', function () {
+        return this.callback
+          .calledWith(null, this.rawUpdates)
+          .should.equal(true)
+      })
+    })
+
+    return describe('deleteAppliedDocUpdates', function () {
+      beforeEach(function () {
+        this.rclient.lrem = sinon.stub()
+        this.rclient.srem = sinon.stub()
+        this.rclient.exec = sinon.stub().callsArgWith(0)
+        return this.RedisManager.deleteAppliedDocUpdates(
+          this.project_id,
+          this.doc_id,
+          this.jsonUpdates,
+          this.callback
+        )
+      })
+
+      it('should delete the first update from redis', function () {
+        return this.rclient.lrem
+          .calledWith(
+            `UncompressedHistoryOps:${this.doc_id}`,
+            1,
+            this.jsonUpdates[0]
+          )
+          .should.equal(true)
+      })
+
+      it('should delete the second update from redis', function () {
+        return this.rclient.lrem
+          .calledWith(
+            `UncompressedHistoryOps:${this.doc_id}`,
+            1,
+            this.jsonUpdates[1]
+          )
+          .should.equal(true)
+      })
+
+      it('should delete the doc from the set of docs with history ops', function () {
+        return this.rclient.srem
+          .calledWith(`DocsWithHistoryOps:${this.project_id}`, this.doc_id)
+          .should.equal(true)
+      })
+
+      return it('should call the callback ', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+  })
+
+  return describe('getDocIdsWithHistoryOps', function () {
+    beforeEach(function () {
+      this.doc_ids = ['mock-id-1', 'mock-id-2']
+      this.rclient.smembers = sinon.stub().callsArgWith(1, null, this.doc_ids)
+      return this.RedisManager.getDocIdsWithHistoryOps(
+        this.project_id,
+        this.callback
+      )
+    })
+
+    it('should read the doc_ids from redis', function () {
+      return this.rclient.smembers
+        .calledWith(`DocsWithHistoryOps:${this.project_id}`)
+        .should.equal(true)
+    })
+
+    return it('should call the callback with the doc_ids', function () {
+      return this.callback.calledWith(null, this.doc_ids).should.equal(true)
+    })
+  })
+})

services/track-changes/test/unit/js/RestoreManager/RestoreManagerTests.js

@@ -0,0 +1,64 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/RestoreManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('RestoreManager', function () {
+  beforeEach(function () {
+    this.RestoreManager = SandboxedModule.require(modulePath, {
+      requires: {
+        './DocumentUpdaterManager': (this.DocumentUpdaterManager = {}),
+        './DiffManager': (this.DiffManager = {}),
+      },
+    })
+    this.callback = sinon.stub()
+    this.project_id = 'mock-project-id'
+    this.doc_id = 'mock-doc-id'
+    this.user_id = 'mock-user-id'
+    return (this.version = 42)
+  })
+
+  return describe('restoreToBeforeVersion', function () {
+    beforeEach(function () {
+      this.content = 'mock content'
+      this.DocumentUpdaterManager.setDocument = sinon.stub().callsArg(4)
+      this.DiffManager.getDocumentBeforeVersion = sinon
+        .stub()
+        .callsArgWith(3, null, this.content)
+      return this.RestoreManager.restoreToBeforeVersion(
+        this.project_id,
+        this.doc_id,
+        this.version,
+        this.user_id,
+        this.callback
+      )
+    })
+
+    it('should get the content before the requested version', function () {
+      return this.DiffManager.getDocumentBeforeVersion
+        .calledWith(this.project_id, this.doc_id, this.version)
+        .should.equal(true)
+    })
+
+    it('should set the document in the document updater', function () {
+      return this.DocumentUpdaterManager.setDocument
+        .calledWith(this.project_id, this.doc_id, this.content, this.user_id)
+        .should.equal(true)
+    })
+
+    return it('should call the callback', function () {
+      return this.callback.called.should.equal(true)
+    })
+  })
+})

services/track-changes/test/unit/js/UpdateCompressor/UpdateCompressorTests.js

@@ -0,0 +1,848 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/UpdateCompressor.js'
+const SandboxedModule = require('sandboxed-module')
+
+const bigstring = __range__(0, 2 * 1024 * 1024, true)
+  .map(i => 'a')
+  .join('')
+const mediumstring = __range__(0, 1024 * 1024, true)
+  .map(j => 'a')
+  .join('')
+
+describe('UpdateCompressor', function () {
+  beforeEach(function () {
+    this.UpdateCompressor = SandboxedModule.require(modulePath, {
+      requires: {
+        '../lib/diff_match_patch': require('../../../../app/lib/diff_match_patch'),
+      },
+    })
+    this.user_id = 'user-id-1'
+    this.other_user_id = 'user-id-2'
+    this.ts1 = Date.now()
+    return (this.ts2 = Date.now() + 1000)
+  })
+
+  describe('convertToSingleOpUpdates', function () {
+    it('should split grouped updates into individual updates', function () {
+      return expect(
+        this.UpdateCompressor.convertToSingleOpUpdates([
+          {
+            op: [
+              (this.op1 = { p: 0, i: 'Foo' }),
+              (this.op2 = { p: 6, i: 'bar' }),
+            ],
+            meta: { ts: this.ts1, user_id: this.user_id },
+            v: 42,
+          },
+          {
+            op: [(this.op3 = { p: 10, i: 'baz' })],
+            meta: { ts: this.ts2, user_id: this.other_user_id },
+            v: 43,
+          },
+        ])
+      ).to.deep.equal([
+        {
+          op: this.op1,
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+        {
+          op: this.op2,
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+        {
+          op: this.op3,
+          meta: {
+            start_ts: this.ts2,
+            end_ts: this.ts2,
+            user_id: this.other_user_id,
+          },
+          v: 43,
+        },
+      ])
+    })
+
+    it('should return no-op updates when the op list is empty', function () {
+      return expect(
+        this.UpdateCompressor.convertToSingleOpUpdates([
+          {
+            op: [],
+            meta: { ts: this.ts1, user_id: this.user_id },
+            v: 42,
+          },
+        ])
+      ).to.deep.equal([
+        {
+          op: this.UpdateCompressor.NOOP,
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+      ])
+    })
+
+    return it('should ignore comment ops', function () {
+      return expect(
+        this.UpdateCompressor.convertToSingleOpUpdates([
+          {
+            op: [
+              (this.op1 = { p: 0, i: 'Foo' }),
+              (this.op2 = { p: 9, c: 'baz' }),
+              (this.op3 = { p: 6, i: 'bar' }),
+            ],
+            meta: { ts: this.ts1, user_id: this.user_id },
+            v: 42,
+          },
+        ])
+      ).to.deep.equal([
+        {
+          op: this.op1,
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+        {
+          op: this.op3,
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+      ])
+    })
+  })
+
+  describe('concatUpdatesWithSameVersion', function () {
+    it('should concat updates with the same version', function () {
+      return expect(
+        this.UpdateCompressor.concatUpdatesWithSameVersion([
+          {
+            op: (this.op1 = { p: 0, i: 'Foo' }),
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: (this.op2 = { p: 6, i: 'bar' }),
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: (this.op3 = { p: 10, i: 'baz' }),
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.other_user_id,
+            },
+            v: 43,
+          },
+        ])
+      ).to.deep.equal([
+        {
+          op: [this.op1, this.op2],
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+        {
+          op: [this.op3],
+          meta: {
+            start_ts: this.ts2,
+            end_ts: this.ts2,
+            user_id: this.other_user_id,
+          },
+          v: 43,
+        },
+      ])
+    })
+
+    return it('should turn a noop into an empty op', function () {
+      return expect(
+        this.UpdateCompressor.concatUpdatesWithSameVersion([
+          {
+            op: this.UpdateCompressor.NOOP,
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+        ])
+      ).to.deep.equal([
+        {
+          op: [],
+          meta: { start_ts: this.ts1, end_ts: this.ts1, user_id: this.user_id },
+          v: 42,
+        },
+      ])
+    })
+  })
+
+  describe('compress', function () {
+    describe('insert - insert', function () {
+      it('should append one insert to the other', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 6, i: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'foobar' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should insert one insert inside the other', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 5, i: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'fobaro' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should not append separated inserts', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 9, i: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'foo' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 9, i: 'bar' },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should not append inserts that are too big (second op)', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 6, i: bigstring },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'foo' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 6, i: bigstring },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should not append inserts that are too big (first op)', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: bigstring },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 3 + bigstring.length, i: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: bigstring },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 3 + bigstring.length, i: 'bar' },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      return it('should not append inserts that are too big (first and second op)', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: mediumstring },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 3 + mediumstring.length, i: mediumstring },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: mediumstring },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 3 + mediumstring.length, i: mediumstring },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+
+    describe('delete - delete', function () {
+      it('should append one delete to the other', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, d: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 3, d: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, d: 'foobar' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should insert one delete inside the other', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, d: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 1, d: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 1, d: 'bafoor' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      return it('should not append separated deletes', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, d: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 9, d: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, d: 'foo' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 9, d: 'bar' },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+
+    describe('insert - delete', function () {
+      it('should undo a previous insert', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 5, d: 'o' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'fo' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should remove part of an insert from the middle', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'fobaro' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 5, d: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'foo' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should cancel out two opposite updates', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 3, d: 'foo' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: '' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      it('should not combine separated updates', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foo' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 9, d: 'bar' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'foo' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 9, d: 'bar' },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      return it('should not combine updates with overlap beyond the end', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, i: 'foobar' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 6, d: 'bardle' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: 'foobar' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 6, d: 'bardle' },
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+
+    describe('delete - insert', function () {
+      it('should do a diff of the content', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, d: 'one two three four five six seven eight' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 3, i: 'one 2 three four five six seven eight' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 7, d: 'two' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+          {
+            op: { p: 7, i: '2' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+
+      return it('should return a no-op if the delete and insert are the same', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: { p: 3, d: 'one two three four five six seven eight' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 3, i: 'one two three four five six seven eight' },
+              meta: { ts: this.ts2, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: { p: 3, i: '' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+
+    describe('noop - insert', function () {
+      return it('should leave them untouched', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: this.UpdateCompressor.NOOP,
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 6, i: 'bar' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: this.UpdateCompressor.NOOP,
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 6, i: 'bar' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+
+    return describe('noop - delete', function () {
+      return it('should leave them untouched', function () {
+        return expect(
+          this.UpdateCompressor.compressUpdates([
+            {
+              op: this.UpdateCompressor.NOOP,
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 42,
+            },
+            {
+              op: { p: 6, d: 'bar' },
+              meta: { ts: this.ts1, user_id: this.user_id },
+              v: 43,
+            },
+          ])
+        ).to.deep.equal([
+          {
+            op: this.UpdateCompressor.NOOP,
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: { p: 6, d: 'bar' },
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+  })
+
+  return describe('compressRawUpdates', function () {
+    return describe('merging in-place with an array op', function () {
+      return it('should not change the existing last updates', function () {
+        return expect(
+          this.UpdateCompressor.compressRawUpdates(
+            {
+              op: [
+                { p: 1000, d: 'hello' },
+                { p: 1000, i: 'HELLO()' },
+              ],
+              meta: {
+                start_ts: this.ts1,
+                end_ts: this.ts1,
+                user_id: this.user_id,
+              },
+              v: 42,
+            },
+            [
+              {
+                op: [{ p: 1006, i: 'WORLD' }],
+                meta: { ts: this.ts2, user_id: this.user_id },
+                v: 43,
+              },
+            ]
+          )
+        ).to.deep.equal([
+          {
+            op: [
+              { p: 1000, d: 'hello' },
+              { p: 1000, i: 'HELLO()' },
+            ],
+            meta: {
+              start_ts: this.ts1,
+              end_ts: this.ts1,
+              user_id: this.user_id,
+            },
+            v: 42,
+          },
+          {
+            op: [{ p: 1006, i: 'WORLD' }],
+            meta: {
+              start_ts: this.ts2,
+              end_ts: this.ts2,
+              user_id: this.user_id,
+            },
+            v: 43,
+          },
+        ])
+      })
+    })
+  })
+})
+
+function __range__(left, right, inclusive) {
+  const range = []
+  const ascending = left < right
+  const end = !inclusive ? right : ascending ? right + 1 : right - 1
+  for (let i = left; ascending ? i < end : i > end; ascending ? i++ : i--) {
+    range.push(i)
+  }
+  return range
+}

services/track-changes/test/unit/js/UpdateTrimmer/UpdateTrimmerTests.js

@@ -0,0 +1,182 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/UpdateTrimmer.js'
+const SandboxedModule = require('sandboxed-module')
+const tk = require('timekeeper')
+
+describe('UpdateTrimmer', function () {
+  beforeEach(function () {
+    this.now = new Date()
+    tk.freeze(this.now)
+
+    this.UpdateTrimmer = SandboxedModule.require(modulePath, {
+      requires: {
+        './WebApiManager': (this.WebApiManager = {}),
+        './MongoManager': (this.MongoManager = {}),
+      },
+    })
+
+    this.callback = sinon.stub()
+    return (this.project_id = 'mock-project-id')
+  })
+
+  afterEach(function () {
+    return tk.reset()
+  })
+
+  return describe('shouldTrimUpdates', function () {
+    beforeEach(function () {
+      this.metadata = {}
+      this.details = { features: {} }
+      this.MongoManager.getProjectMetaData = sinon
+        .stub()
+        .callsArgWith(1, null, this.metadata)
+      this.MongoManager.setProjectMetaData = sinon.stub().callsArgWith(2)
+      this.MongoManager.upgradeHistory = sinon.stub().callsArgWith(1)
+      return (this.WebApiManager.getProjectDetails = sinon
+        .stub()
+        .callsArgWith(1, null, this.details))
+    })
+
+    describe('with preserveHistory set in the project meta data', function () {
+      beforeEach(function () {
+        this.metadata.preserveHistory = true
+        return this.UpdateTrimmer.shouldTrimUpdates(
+          this.project_id,
+          this.callback
+        )
+      })
+
+      it('should look up the meta data', function () {
+        return this.MongoManager.getProjectMetaData
+          .calledWith(this.project_id)
+          .should.equal(true)
+      })
+
+      it('should not look up the project details', function () {
+        return this.WebApiManager.getProjectDetails.called.should.equal(false)
+      })
+
+      return it('should return false', function () {
+        return this.callback.calledWith(null, false).should.equal(true)
+      })
+    })
+
+    describe('without preserveHistory set in the project meta data', function () {
+      beforeEach(function () {
+        return (this.metadata.preserveHistory = false)
+      })
+
+      describe('when the project has the versioning feature', function () {
+        beforeEach(function () {
+          this.details.features.versioning = true
+          return this.UpdateTrimmer.shouldTrimUpdates(
+            this.project_id,
+            this.callback
+          )
+        })
+
+        it('should look up the meta data', function () {
+          return this.MongoManager.getProjectMetaData
+            .calledWith(this.project_id)
+            .should.equal(true)
+        })
+
+        it('should look up the project details', function () {
+          return this.WebApiManager.getProjectDetails
+            .calledWith(this.project_id)
+            .should.equal(true)
+        })
+
+        it('should insert preserveHistory into the metadata', function () {
+          return this.MongoManager.setProjectMetaData
+            .calledWith(this.project_id, { preserveHistory: true })
+            .should.equal(true)
+        })
+
+        it('should upgrade any existing history', function () {
+          return this.MongoManager.upgradeHistory
+            .calledWith(this.project_id)
+            .should.equal(true)
+        })
+
+        return it('should return false', function () {
+          return this.callback.calledWith(null, false).should.equal(true)
+        })
+      })
+
+      return describe('when the project does not have the versioning feature', function () {
+        beforeEach(function () {
+          this.details.features.versioning = false
+          return this.UpdateTrimmer.shouldTrimUpdates(
+            this.project_id,
+            this.callback
+          )
+        })
+
+        return it('should return true', function () {
+          return this.callback.calledWith(null, true).should.equal(true)
+        })
+      })
+    })
+
+    return describe('without any meta data', function () {
+      beforeEach(function () {
+        return (this.MongoManager.getProjectMetaData = sinon
+          .stub()
+          .callsArgWith(1, null, null))
+      })
+
+      describe('when the project has the versioning feature', function () {
+        beforeEach(function () {
+          this.details.features.versioning = true
+          return this.UpdateTrimmer.shouldTrimUpdates(
+            this.project_id,
+            this.callback
+          )
+        })
+
+        it('should insert preserveHistory into the metadata', function () {
+          return this.MongoManager.setProjectMetaData
+            .calledWith(this.project_id, { preserveHistory: true })
+            .should.equal(true)
+        })
+
+        it('should upgrade any existing history', function () {
+          return this.MongoManager.upgradeHistory
+            .calledWith(this.project_id)
+            .should.equal(true)
+        })
+
+        return it('should return false', function () {
+          return this.callback.calledWith(null, false).should.equal(true)
+        })
+      })
+
+      return describe('when the project does not have the versioning feature', function () {
+        beforeEach(function () {
+          this.details.features.versioning = false
+          return this.UpdateTrimmer.shouldTrimUpdates(
+            this.project_id,
+            this.callback
+          )
+        })
+
+        return it('should return true', function () {
+          return this.callback.calledWith(null, true).should.equal(true)
+        })
+      })
+    })
+  })
+})

services/track-changes/test/unit/js/UpdatesManager/UpdatesManagerTests.js

@@ -0,0 +1,1333 @@
+/* eslint-disable
+    camelcase,
+    handle-callback-err,
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS101: Remove unnecessary use of Array.from
+ * DS102: Remove unnecessary code created because of implicit returns
+ * DS207: Consider shorter variations of null checks
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const { ObjectId } = require('mongodb')
+const modulePath = '../../../../app/js/UpdatesManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('UpdatesManager', function () {
+  beforeEach(function () {
+    this.UpdatesManager = SandboxedModule.require(modulePath, {
+      singleOnly: true,
+      requires: {
+        './UpdateCompressor': (this.UpdateCompressor = {}),
+        './MongoManager': (this.MongoManager = {}),
+        './PackManager': (this.PackManager = {}),
+        './RedisManager': (this.RedisManager = {}),
+        './LockManager': (this.LockManager = {}),
+        './WebApiManager': (this.WebApiManager = {}),
+        './UpdateTrimmer': (this.UpdateTrimmer = {}),
+        './DocArchiveManager': (this.DocArchiveManager = {}),
+        '@overleaf/settings': {
+          redis: {
+            lock: {
+              key_schema: {
+                historyLock({ doc_id }) {
+                  return `HistoryLock:${doc_id}`
+                },
+              },
+            },
+          },
+        },
+      },
+    })
+    this.doc_id = 'doc-id-123'
+    this.project_id = 'project-id-123'
+    this.callback = sinon.stub()
+    return (this.temporary = 'temp-mock')
+  })
+
+  describe('compressAndSaveRawUpdates', function () {
+    describe('when there are no raw ops', function () {
+      beforeEach(function () {
+        this.MongoManager.peekLastCompressedUpdate = sinon.stub()
+        return this.UpdatesManager.compressAndSaveRawUpdates(
+          this.project_id,
+          this.doc_id,
+          [],
+          this.temporary,
+          this.callback
+        )
+      })
+
+      it('should not need to access the database', function () {
+        return this.MongoManager.peekLastCompressedUpdate.called.should.equal(
+          false
+        )
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+
+    describe('when there is no compressed history to begin with', function () {
+      beforeEach(function () {
+        this.rawUpdates = [
+          { v: 12, op: 'mock-op-12' },
+          { v: 13, op: 'mock-op-13' },
+        ]
+        this.compressedUpdates = [{ v: 13, op: 'compressed-op-12' }]
+
+        this.MongoManager.peekLastCompressedUpdate = sinon
+          .stub()
+          .callsArgWith(1, null, null)
+        this.PackManager.insertCompressedUpdates = sinon.stub().callsArg(5)
+        this.UpdateCompressor.compressRawUpdates = sinon
+          .stub()
+          .returns(this.compressedUpdates)
+        return this.UpdatesManager.compressAndSaveRawUpdates(
+          this.project_id,
+          this.doc_id,
+          this.rawUpdates,
+          this.temporary,
+          this.callback
+        )
+      })
+
+      it('should look at the last compressed op', function () {
+        return this.MongoManager.peekLastCompressedUpdate
+          .calledWith(this.doc_id)
+          .should.equal(true)
+      })
+
+      it('should save the compressed ops as a pack', function () {
+        return this.PackManager.insertCompressedUpdates
+          .calledWith(
+            this.project_id,
+            this.doc_id,
+            null,
+            this.compressedUpdates,
+            this.temporary
+          )
+          .should.equal(true)
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+
+    describe('when the raw ops need appending to existing history', function () {
+      beforeEach(function () {
+        this.lastCompressedUpdate = { v: 11, op: 'compressed-op-11' }
+        this.compressedUpdates = [
+          { v: 12, op: 'compressed-op-11+12' },
+          { v: 13, op: 'compressed-op-12' },
+        ]
+
+        this.MongoManager.peekLastCompressedUpdate = sinon
+          .stub()
+          .callsArgWith(
+            1,
+            null,
+            this.lastCompressedUpdate,
+            this.lastCompressedUpdate.v
+          )
+        this.PackManager.insertCompressedUpdates = sinon.stub().callsArg(5)
+        return (this.UpdateCompressor.compressRawUpdates = sinon
+          .stub()
+          .returns(this.compressedUpdates))
+      })
+
+      describe('when the raw ops start where the existing history ends', function () {
+        beforeEach(function () {
+          this.rawUpdates = [
+            { v: 12, op: 'mock-op-12' },
+            { v: 13, op: 'mock-op-13' },
+          ]
+          return this.UpdatesManager.compressAndSaveRawUpdates(
+            this.project_id,
+            this.doc_id,
+            this.rawUpdates,
+            this.temporary,
+            this.callback
+          )
+        })
+
+        it('should look at the last compressed op', function () {
+          return this.MongoManager.peekLastCompressedUpdate
+            .calledWith(this.doc_id)
+            .should.equal(true)
+        })
+
+        it('should compress the raw ops', function () {
+          return this.UpdateCompressor.compressRawUpdates
+            .calledWith(null, this.rawUpdates)
+            .should.equal(true)
+        })
+
+        it('should save the new compressed ops into a pack', function () {
+          return this.PackManager.insertCompressedUpdates
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.lastCompressedUpdate,
+              this.compressedUpdates,
+              this.temporary
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+
+      describe('when the raw ops start where the existing history ends and the history is in a pack', function () {
+        beforeEach(function () {
+          this.lastCompressedUpdate = {
+            pack: [{ v: 11, op: 'compressed-op-11' }],
+            v: 11,
+          }
+          this.rawUpdates = [
+            { v: 12, op: 'mock-op-12' },
+            { v: 13, op: 'mock-op-13' },
+          ]
+          this.MongoManager.peekLastCompressedUpdate = sinon
+            .stub()
+            .callsArgWith(
+              1,
+              null,
+              this.lastCompressedUpdate,
+              this.lastCompressedUpdate.v
+            )
+          return this.UpdatesManager.compressAndSaveRawUpdates(
+            this.project_id,
+            this.doc_id,
+            this.rawUpdates,
+            this.temporary,
+            this.callback
+          )
+        })
+
+        it('should look at the last compressed op', function () {
+          return this.MongoManager.peekLastCompressedUpdate
+            .calledWith(this.doc_id)
+            .should.equal(true)
+        })
+
+        it('should compress the raw ops', function () {
+          return this.UpdateCompressor.compressRawUpdates
+            .calledWith(null, this.rawUpdates)
+            .should.equal(true)
+        })
+
+        it('should save the new compressed ops into a pack', function () {
+          return this.PackManager.insertCompressedUpdates
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              this.lastCompressedUpdate,
+              this.compressedUpdates,
+              this.temporary
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+
+      describe('when some raw ops are passed that have already been compressed', function () {
+        beforeEach(function () {
+          this.rawUpdates = [
+            { v: 10, op: 'mock-op-10' },
+            { v: 11, op: 'mock-op-11' },
+            { v: 12, op: 'mock-op-12' },
+            { v: 13, op: 'mock-op-13' },
+          ]
+
+          return this.UpdatesManager.compressAndSaveRawUpdates(
+            this.project_id,
+            this.doc_id,
+            this.rawUpdates,
+            this.temporary,
+            this.callback
+          )
+        })
+
+        return it('should only compress the more recent raw ops', function () {
+          return this.UpdateCompressor.compressRawUpdates
+            .calledWith(null, this.rawUpdates.slice(-2))
+            .should.equal(true)
+        })
+      })
+
+      describe('when the raw ops do not follow from the last compressed op version', function () {
+        beforeEach(function () {
+          this.rawUpdates = [{ v: 13, op: 'mock-op-13' }]
+          return this.UpdatesManager.compressAndSaveRawUpdates(
+            this.project_id,
+            this.doc_id,
+            this.rawUpdates,
+            this.temporary,
+            this.callback
+          )
+        })
+
+        it('should call the callback with an error', function () {
+          return this.callback
+            .calledWith(
+              sinon.match.has(
+                'message',
+                'Tried to apply raw op at version 13 to last compressed update with version 11 from unknown time'
+              )
+            )
+            .should.equal(true)
+        })
+
+        return it('should not insert any update into mongo', function () {
+          return this.PackManager.insertCompressedUpdates.called.should.equal(
+            false
+          )
+        })
+      })
+
+      return describe('when the raw ops are out of order', function () {
+        beforeEach(function () {
+          this.rawUpdates = [
+            { v: 13, op: 'mock-op-13' },
+            { v: 12, op: 'mock-op-12' },
+          ]
+          return this.UpdatesManager.compressAndSaveRawUpdates(
+            this.project_id,
+            this.doc_id,
+            this.rawUpdates,
+            this.temporary,
+            this.callback
+          )
+        })
+
+        it('should call the callback with an error', function () {
+          return this.callback
+            .calledWith(sinon.match.has('message'))
+            .should.equal(true)
+        })
+
+        return it('should not insert any update into mongo', function () {
+          return this.PackManager.insertCompressedUpdates.called.should.equal(
+            false
+          )
+        })
+      })
+    })
+
+    return describe('when the raw ops need appending to existing history which is in S3', function () {
+      beforeEach(function () {
+        this.lastCompressedUpdate = null
+        this.lastVersion = 11
+        this.compressedUpdates = [{ v: 13, op: 'compressed-op-12' }]
+
+        this.MongoManager.peekLastCompressedUpdate = sinon
+          .stub()
+          .callsArgWith(1, null, null, this.lastVersion)
+        this.PackManager.insertCompressedUpdates = sinon.stub().callsArg(5)
+        return (this.UpdateCompressor.compressRawUpdates = sinon
+          .stub()
+          .returns(this.compressedUpdates))
+      })
+
+      return describe('when the raw ops start where the existing history ends', function () {
+        beforeEach(function () {
+          this.rawUpdates = [
+            { v: 12, op: 'mock-op-12' },
+            { v: 13, op: 'mock-op-13' },
+          ]
+          return this.UpdatesManager.compressAndSaveRawUpdates(
+            this.project_id,
+            this.doc_id,
+            this.rawUpdates,
+            this.temporary,
+            this.callback
+          )
+        })
+
+        it('should try to look at the last compressed op', function () {
+          return this.MongoManager.peekLastCompressedUpdate
+            .calledWith(this.doc_id)
+            .should.equal(true)
+        })
+
+        it('should compress the last compressed op and the raw ops', function () {
+          return this.UpdateCompressor.compressRawUpdates
+            .calledWith(this.lastCompressedUpdate, this.rawUpdates)
+            .should.equal(true)
+        })
+
+        it('should save the compressed ops', function () {
+          return this.PackManager.insertCompressedUpdates
+            .calledWith(
+              this.project_id,
+              this.doc_id,
+              null,
+              this.compressedUpdates,
+              this.temporary
+            )
+            .should.equal(true)
+        })
+
+        return it('should call the callback', function () {
+          return this.callback.called.should.equal(true)
+        })
+      })
+    })
+  })
+
+  describe('processUncompressedUpdates', function () {
+    beforeEach(function () {
+      this.UpdatesManager.compressAndSaveRawUpdates = sinon
+        .stub()
+        .callsArgWith(4)
+      this.RedisManager.deleteAppliedDocUpdates = sinon.stub().callsArg(3)
+      this.MongoManager.backportProjectId = sinon.stub().callsArg(2)
+      return (this.UpdateTrimmer.shouldTrimUpdates = sinon
+        .stub()
+        .callsArgWith(1, null, (this.temporary = 'temp mock')))
+    })
+
+    describe('when there is fewer than one batch to send', function () {
+      beforeEach(function () {
+        this.updates = ['mock-update']
+        this.RedisManager.getOldestDocUpdates = sinon
+          .stub()
+          .callsArgWith(2, null, this.updates)
+        this.RedisManager.expandDocUpdates = sinon
+          .stub()
+          .callsArgWith(1, null, this.updates)
+        return this.UpdatesManager.processUncompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          this.temporary,
+          this.callback
+        )
+      })
+
+      it('should get the oldest updates', function () {
+        return this.RedisManager.getOldestDocUpdates
+          .calledWith(this.doc_id, this.UpdatesManager.REDIS_READ_BATCH_SIZE)
+          .should.equal(true)
+      })
+
+      it('should compress and save the updates', function () {
+        return this.UpdatesManager.compressAndSaveRawUpdates
+          .calledWith(
+            this.project_id,
+            this.doc_id,
+            this.updates,
+            this.temporary
+          )
+          .should.equal(true)
+      })
+
+      it('should delete the batch of uncompressed updates that was just processed', function () {
+        return this.RedisManager.deleteAppliedDocUpdates
+          .calledWith(this.project_id, this.doc_id, this.updates)
+          .should.equal(true)
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+
+    return describe('when there are multiple batches to send', function () {
+      beforeEach(function (done) {
+        this.UpdatesManager.REDIS_READ_BATCH_SIZE = 2
+        this.updates = [
+          'mock-update-0',
+          'mock-update-1',
+          'mock-update-2',
+          'mock-update-3',
+          'mock-update-4',
+        ]
+        this.redisArray = this.updates.slice()
+        this.RedisManager.getOldestDocUpdates = (
+          doc_id,
+          batchSize,
+          callback
+        ) => {
+          if (callback == null) {
+            callback = function (error, updates) {}
+          }
+          const updates = this.redisArray.slice(0, batchSize)
+          this.redisArray = this.redisArray.slice(batchSize)
+          return callback(null, updates)
+        }
+        sinon.spy(this.RedisManager, 'getOldestDocUpdates')
+        this.RedisManager.expandDocUpdates = (jsonUpdates, callback) => {
+          return callback(null, jsonUpdates)
+        }
+        sinon.spy(this.RedisManager, 'expandDocUpdates')
+        return this.UpdatesManager.processUncompressedUpdates(
+          this.project_id,
+          this.doc_id,
+          this.temporary,
+          (...args) => {
+            this.callback(...Array.from(args || []))
+            return done()
+          }
+        )
+      })
+
+      it('should get the oldest updates in three batches ', function () {
+        return this.RedisManager.getOldestDocUpdates.callCount.should.equal(3)
+      })
+
+      it('should compress and save the updates in batches', function () {
+        this.UpdatesManager.compressAndSaveRawUpdates
+          .calledWith(
+            this.project_id,
+            this.doc_id,
+            this.updates.slice(0, 2),
+            this.temporary
+          )
+          .should.equal(true)
+        this.UpdatesManager.compressAndSaveRawUpdates
+          .calledWith(
+            this.project_id,
+            this.doc_id,
+            this.updates.slice(2, 4),
+            this.temporary
+          )
+          .should.equal(true)
+        return this.UpdatesManager.compressAndSaveRawUpdates
+          .calledWith(
+            this.project_id,
+            this.doc_id,
+            this.updates.slice(4, 5),
+            this.temporary
+          )
+          .should.equal(true)
+      })
+
+      it('should delete the batches of uncompressed updates', function () {
+        return this.RedisManager.deleteAppliedDocUpdates.callCount.should.equal(
+          3
+        )
+      })
+
+      return it('should call the callback', function () {
+        return this.callback.called.should.equal(true)
+      })
+    })
+  })
+
+  describe('processCompressedUpdatesWithLock', function () {
+    beforeEach(function () {
+      this.UpdateTrimmer.shouldTrimUpdates = sinon
+        .stub()
+        .callsArgWith(1, null, (this.temporary = 'temp mock'))
+      this.MongoManager.backportProjectId = sinon.stub().callsArg(2)
+      this.UpdatesManager._processUncompressedUpdates = sinon.stub().callsArg(3)
+      this.LockManager.runWithLock = sinon.stub().callsArg(2)
+      return this.UpdatesManager.processUncompressedUpdatesWithLock(
+        this.project_id,
+        this.doc_id,
+        this.callback
+      )
+    })
+
+    it('should check if the updates are temporary', function () {
+      return this.UpdateTrimmer.shouldTrimUpdates
+        .calledWith(this.project_id)
+        .should.equal(true)
+    })
+
+    it('should backport the project id', function () {
+      return this.MongoManager.backportProjectId
+        .calledWith(this.project_id, this.doc_id)
+        .should.equal(true)
+    })
+
+    it('should run processUncompressedUpdates with the lock', function () {
+      return this.LockManager.runWithLock
+        .calledWith(`HistoryLock:${this.doc_id}`)
+        .should.equal(true)
+    })
+
+    return it('should call the callback', function () {
+      return this.callback.called.should.equal(true)
+    })
+  })
+
+  describe('getDocUpdates', function () {
+    beforeEach(function () {
+      this.updates = ['mock-updates']
+      this.options = { to: 'mock-to', limit: 'mock-limit' }
+      this.PackManager.getOpsByVersionRange = sinon
+        .stub()
+        .callsArgWith(4, null, this.updates)
+      this.UpdatesManager.processUncompressedUpdatesWithLock = sinon
+        .stub()
+        .callsArg(2)
+      return this.UpdatesManager.getDocUpdates(
+        this.project_id,
+        this.doc_id,
+        this.options,
+        this.callback
+      )
+    })
+
+    it('should process outstanding updates', function () {
+      return this.UpdatesManager.processUncompressedUpdatesWithLock
+        .calledWith(this.project_id, this.doc_id)
+        .should.equal(true)
+    })
+
+    it('should get the updates from the database', function () {
+      return this.PackManager.getOpsByVersionRange
+        .calledWith(
+          this.project_id,
+          this.doc_id,
+          this.options.from,
+          this.options.to
+        )
+        .should.equal(true)
+    })
+
+    return it('should return the updates', function () {
+      return this.callback.calledWith(null, this.updates).should.equal(true)
+    })
+  })
+
+  describe('getDocUpdatesWithUserInfo', function () {
+    beforeEach(function () {
+      this.updates = ['mock-updates']
+      this.options = { to: 'mock-to', limit: 'mock-limit' }
+      this.updatesWithUserInfo = ['updates-with-user-info']
+      this.UpdatesManager.getDocUpdates = sinon
+        .stub()
+        .callsArgWith(3, null, this.updates)
+      this.UpdatesManager.fillUserInfo = sinon
+        .stub()
+        .callsArgWith(1, null, this.updatesWithUserInfo)
+      return this.UpdatesManager.getDocUpdatesWithUserInfo(
+        this.project_id,
+        this.doc_id,
+        this.options,
+        this.callback
+      )
+    })
+
+    it('should get the updates', function () {
+      return this.UpdatesManager.getDocUpdates
+        .calledWith(this.project_id, this.doc_id, this.options)
+        .should.equal(true)
+    })
+
+    it('should file the updates with the user info', function () {
+      return this.UpdatesManager.fillUserInfo
+        .calledWith(this.updates)
+        .should.equal(true)
+    })
+
+    return it('should return the updates with the filled details', function () {
+      return this.callback
+        .calledWith(null, this.updatesWithUserInfo)
+        .should.equal(true)
+    })
+  })
+
+  describe('processUncompressedUpdatesForProject', function () {
+    beforeEach(function (done) {
+      this.doc_ids = ['mock-id-1', 'mock-id-2']
+      this.UpdateTrimmer.shouldTrimUpdates = sinon
+        .stub()
+        .callsArgWith(1, null, (this.temporary = 'temp mock'))
+      this.MongoManager.backportProjectId = sinon.stub().callsArg(2)
+      this.UpdatesManager._processUncompressedUpdatesForDocWithLock = sinon
+        .stub()
+        .callsArg(3)
+      this.RedisManager.getDocIdsWithHistoryOps = sinon
+        .stub()
+        .callsArgWith(1, null, this.doc_ids)
+      return this.UpdatesManager.processUncompressedUpdatesForProject(
+        this.project_id,
+        () => {
+          this.callback()
+          return done()
+        }
+      )
+    })
+
+    it('should get all the docs with history ops', function () {
+      return this.RedisManager.getDocIdsWithHistoryOps
+        .calledWith(this.project_id)
+        .should.equal(true)
+    })
+
+    it('should process the doc ops for the each doc_id', function () {
+      return Array.from(this.doc_ids).map(doc_id =>
+        this.UpdatesManager._processUncompressedUpdatesForDocWithLock
+          .calledWith(this.project_id, doc_id, this.temporary)
+          .should.equal(true)
+      )
+    })
+
+    return it('should call the callback', function () {
+      return this.callback.called.should.equal(true)
+    })
+  })
+
+  describe('getSummarizedProjectUpdates', function () {
+    beforeEach(function () {
+      this.updates = [
+        {
+          doc_id: 123,
+          v: 456,
+          op: 'mock-updates',
+          meta: { user_id: 123, start_ts: 1233, end_ts: 1234 },
+        },
+      ]
+      this.options = { before: 'mock-before', limit: 'mock-limit' }
+      this.summarizedUpdates = [
+        {
+          meta: { user_ids: [123], start_ts: 1233, end_ts: 1234 },
+          docs: { 123: { fromV: 456, toV: 456 } },
+        },
+      ]
+      this.updatesWithUserInfo = ['updates-with-user-info']
+      this.done_state = false
+      this.iterator = {
+        next: cb => {
+          this.done_state = true
+          return cb(null, this.updates)
+        },
+        done: () => {
+          return this.done_state
+        },
+      }
+      this.PackManager.makeProjectIterator = sinon
+        .stub()
+        .callsArgWith(2, null, this.iterator)
+      this.UpdatesManager.processUncompressedUpdatesForProject = sinon
+        .stub()
+        .callsArg(1)
+      this.UpdatesManager.fillSummarizedUserInfo = sinon
+        .stub()
+        .callsArgWith(1, null, this.updatesWithUserInfo)
+      return this.UpdatesManager.getSummarizedProjectUpdates(
+        this.project_id,
+        this.options,
+        this.callback
+      )
+    })
+
+    it('should process any outstanding updates', function () {
+      return this.UpdatesManager.processUncompressedUpdatesForProject
+        .calledWith(this.project_id)
+        .should.equal(true)
+    })
+
+    it('should get the updates', function () {
+      return this.PackManager.makeProjectIterator
+        .calledWith(this.project_id, this.options.before)
+        .should.equal(true)
+    })
+
+    it('should fill the updates with the user info', function () {
+      return this.UpdatesManager.fillSummarizedUserInfo
+        .calledWith(this.summarizedUpdates)
+        .should.equal(true)
+    })
+
+    return it('should return the updates with the filled details', function () {
+      return this.callback
+        .calledWith(null, this.updatesWithUserInfo)
+        .should.equal(true)
+    })
+  })
+
+  // describe "_extendBatchOfSummarizedUpdates", ->
+  // 	beforeEach ->
+  // 		@before = Date.now()
+  // 		@min_count = 2
+  // 		@existingSummarizedUpdates = ["summarized-updates-3"]
+  // 		@summarizedUpdates = ["summarized-updates-3", "summarized-update-2", "summarized-update-1"]
+
+  // 	describe "when there are updates to get", ->
+  // 		beforeEach ->
+  // 			@updates = [
+  // 				{op: "mock-op-1", meta: end_ts: @before - 10},
+  // 				{op: "mock-op-1", meta: end_ts: @nextBeforeTimestamp = @before - 20}
+  // 			]
+  // 			@existingSummarizedUpdates = ["summarized-updates-3"]
+  // 			@summarizedUpdates = ["summarized-updates-3", "summarized-update-2", "summarized-update-1"]
+  // 			@UpdatesManager._summarizeUpdates = sinon.stub().returns(@summarizedUpdates)
+  // 			@UpdatesManager.getProjectUpdatesWithUserInfo = sinon.stub().callsArgWith(2, null, @updates)
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates @project_id, @existingSummarizedUpdates, @before, @min_count, @callback
+
+  // 		it "should get the updates", ->
+  // 			@UpdatesManager.getProjectUpdatesWithUserInfo
+  // 				.calledWith(@project_id, { before: @before, limit: 3 * @min_count })
+  // 				.should.equal true
+
+  // 		it "should summarize the updates", ->
+  // 			@UpdatesManager._summarizeUpdates
+  // 				.calledWith(@updates, @existingSummarizedUpdates)
+  // 				.should.equal true
+
+  // 		it "should call the callback with the summarized updates and the next before timestamp", ->
+  // 			@callback.calledWith(null, @summarizedUpdates, @nextBeforeTimestamp).should.equal true
+
+  // 	describe "when there are no more updates", ->
+  // 		beforeEach ->
+  // 			@updates = []
+  // 			@UpdatesManager._summarizeUpdates = sinon.stub().returns(@summarizedUpdates)
+  // 			@UpdatesManager.getProjectUpdatesWithUserInfo = sinon.stub().callsArgWith(2, null, @updates)
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates @project_id, @existingSummarizedUpdates, @before, @min_count, @callback
+
+  // 		it "should call the callback with the summarized updates and null for nextBeforeTimestamp", ->
+  // 			@callback.calledWith(null, @summarizedUpdates, null).should.equal true
+
+  // describe "getSummarizedProjectUpdates", ->
+  // 	describe "when one batch of updates is enough to meet the limit", ->
+  // 		beforeEach ->
+  // 			@before = Date.now()
+  // 			@min_count = 2
+  // 			@updates = ["summarized-updates-3", "summarized-updates-2"]
+  // 			@nextBeforeTimestamp = @before - 100
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates = sinon.stub().callsArgWith(4, null, @updates, @nextBeforeTimestamp)
+  // 			@UpdatesManager.getSummarizedProjectUpdates @project_id, { before: @before, min_count: @min_count }, @callback
+
+  // 		it "should get the batch of summarized updates", ->
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates
+  // 				.calledWith(@project_id, [], @before, @min_count)
+  // 				.should.equal true
+
+  // 		it "should call the callback with the updates", ->
+  // 			@callback.calledWith(null, @updates, @nextBeforeTimestamp).should.equal true
+
+  // 	describe "when multiple batches are needed to meet the limit", ->
+  // 		beforeEach ->
+  // 			@before = Date.now()
+  // 			@min_count = 4
+  // 			@firstBatch =  [{ toV: 6, fromV: 6 }, { toV: 5, fromV: 5 }]
+  // 			@nextBeforeTimestamp = @before - 100
+  // 			@secondBatch = [{ toV: 4, fromV: 4 }, { toV: 3, fromV: 3 }]
+  // 			@nextNextBeforeTimestamp = @before - 200
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates = (project_id, existingUpdates, before, desiredLength, callback) =>
+  // 				if existingUpdates.length == 0
+  // 					callback null, @firstBatch, @nextBeforeTimestamp
+  // 				else
+  // 					callback null, @firstBatch.concat(@secondBatch), @nextNextBeforeTimestamp
+  // 			sinon.spy @UpdatesManager, "_extendBatchOfSummarizedUpdates"
+  // 			@UpdatesManager.getSummarizedProjectUpdates @project_id, { before: @before, min_count: @min_count }, @callback
+
+  // 		it "should get the first batch of summarized updates", ->
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates
+  // 				.calledWith(@project_id, [], @before, @min_count)
+  // 				.should.equal true
+
+  // 		it "should get the second batch of summarized updates", ->
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates
+  // 				.calledWith(@project_id, @firstBatch, @nextBeforeTimestamp, @min_count)
+  // 				.should.equal true
+
+  // 		it "should call the callback with all the updates", ->
+  // 			@callback.calledWith(null, @firstBatch.concat(@secondBatch), @nextNextBeforeTimestamp).should.equal true
+
+  // 	describe "when the end of the database is hit", ->
+  // 		beforeEach ->
+  // 			@before = Date.now()
+  // 			@min_count = 4
+  // 			@updates =  [{ toV: 6, fromV: 6 }, { toV: 5, fromV: 5 }]
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates = sinon.stub().callsArgWith(4, null, @updates, null)
+  // 			@UpdatesManager.getSummarizedProjectUpdates @project_id, { before: @before, min_count: @min_count }, @callback
+
+  // 		it "should get the batch of summarized updates", ->
+  // 			@UpdatesManager._extendBatchOfSummarizedUpdates
+  // 				.calledWith(@project_id, [], @before, @min_count)
+  // 				.should.equal true
+
+  // 		it "should call the callback with the updates", ->
+  // 			@callback.calledWith(null, @updates, null).should.equal true
+
+  describe('fillUserInfo', function () {
+    describe('with valid users', function () {
+      beforeEach(function (done) {
+        this.user_id_1 = ObjectId().toString()
+        this.user_id_2 = ObjectId().toString()
+        this.updates = [
+          {
+            meta: {
+              user_id: this.user_id_1,
+            },
+            op: 'mock-op-1',
+          },
+          {
+            meta: {
+              user_id: this.user_id_1,
+            },
+            op: 'mock-op-2',
+          },
+          {
+            meta: {
+              user_id: this.user_id_2,
+            },
+            op: 'mock-op-3',
+          },
+        ]
+        this.user_info = {}
+        this.user_info[this.user_id_1] = { email: 'user1@sharelatex.com' }
+        this.user_info[this.user_id_2] = { email: 'user2@sharelatex.com' }
+
+        this.WebApiManager.getUserInfo = (user_id, callback) => {
+          if (callback == null) {
+            callback = function (error, userInfo) {}
+          }
+          return callback(null, this.user_info[user_id])
+        }
+        sinon.spy(this.WebApiManager, 'getUserInfo')
+
+        return this.UpdatesManager.fillUserInfo(
+          this.updates,
+          (error, results) => {
+            this.results = results
+            return done()
+          }
+        )
+      })
+
+      it('should only call getUserInfo once for each user_id', function () {
+        this.WebApiManager.getUserInfo.calledTwice.should.equal(true)
+        this.WebApiManager.getUserInfo
+          .calledWith(this.user_id_1)
+          .should.equal(true)
+        return this.WebApiManager.getUserInfo
+          .calledWith(this.user_id_2)
+          .should.equal(true)
+      })
+
+      return it('should return the updates with the user info filled', function () {
+        return expect(this.results).to.deep.equal([
+          {
+            meta: {
+              user: {
+                email: 'user1@sharelatex.com',
+              },
+            },
+            op: 'mock-op-1',
+          },
+          {
+            meta: {
+              user: {
+                email: 'user1@sharelatex.com',
+              },
+            },
+            op: 'mock-op-2',
+          },
+          {
+            meta: {
+              user: {
+                email: 'user2@sharelatex.com',
+              },
+            },
+            op: 'mock-op-3',
+          },
+        ])
+      })
+    })
+
+    return describe('with invalid user ids', function () {
+      beforeEach(function (done) {
+        this.updates = [
+          {
+            meta: {
+              user_id: null,
+            },
+            op: 'mock-op-1',
+          },
+          {
+            meta: {
+              user_id: 'anonymous-user',
+            },
+            op: 'mock-op-2',
+          },
+        ]
+        this.WebApiManager.getUserInfo = (user_id, callback) => {
+          if (callback == null) {
+            callback = function (error, userInfo) {}
+          }
+          return callback(null, this.user_info[user_id])
+        }
+        sinon.spy(this.WebApiManager, 'getUserInfo')
+
+        return this.UpdatesManager.fillUserInfo(
+          this.updates,
+          (error, results) => {
+            this.results = results
+            return done()
+          }
+        )
+      })
+
+      it('should not call getUserInfo', function () {
+        return this.WebApiManager.getUserInfo.called.should.equal(false)
+      })
+
+      return it('should return the updates without the user info filled', function () {
+        return expect(this.results).to.deep.equal([
+          {
+            meta: {},
+            op: 'mock-op-1',
+          },
+          {
+            meta: {},
+            op: 'mock-op-2',
+          },
+        ])
+      })
+    })
+  })
+
+  return describe('_summarizeUpdates', function () {
+    beforeEach(function () {
+      this.now = Date.now()
+      this.user_1 = { id: 'mock-user-1' }
+      return (this.user_2 = { id: 'mock-user-2' })
+    })
+
+    it('should concat updates that are close in time', function () {
+      const result = this.UpdatesManager._summarizeUpdates([
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_1.id,
+            start_ts: this.now + 20,
+            end_ts: this.now + 30,
+          },
+          v: 5,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_2.id,
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+          v: 4,
+        },
+      ])
+
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 4,
+              toV: 5,
+            },
+          },
+          meta: {
+            user_ids: [this.user_1.id, this.user_2.id],
+            start_ts: this.now,
+            end_ts: this.now + 30,
+          },
+        },
+      ])
+    })
+
+    it('should leave updates that are far apart in time', function () {
+      const oneDay = 1000 * 60 * 60 * 24
+      const result = this.UpdatesManager._summarizeUpdates([
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_2.id,
+            start_ts: this.now + oneDay,
+            end_ts: this.now + oneDay + 10,
+          },
+          v: 5,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_1.id,
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+          v: 4,
+        },
+      ])
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 5,
+              toV: 5,
+            },
+          },
+          meta: {
+            user_ids: [this.user_2.id],
+            start_ts: this.now + oneDay,
+            end_ts: this.now + oneDay + 10,
+          },
+        },
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 4,
+              toV: 4,
+            },
+          },
+          meta: {
+            user_ids: [this.user_1.id],
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+        },
+      ])
+    })
+
+    it('should concat onto existing summarized updates', function () {
+      const result = this.UpdatesManager._summarizeUpdates(
+        [
+          {
+            doc_id: 'doc-id-2',
+            meta: {
+              user_id: this.user_1.id,
+              start_ts: this.now + 20,
+              end_ts: this.now + 30,
+            },
+            v: 5,
+          },
+          {
+            doc_id: 'doc-id-2',
+            meta: {
+              user_id: this.user_2.id,
+              start_ts: this.now,
+              end_ts: this.now + 10,
+            },
+            v: 4,
+          },
+        ],
+        [
+          {
+            docs: {
+              'doc-id-1': {
+                fromV: 6,
+                toV: 8,
+              },
+            },
+            meta: {
+              user_ids: [this.user_1.id],
+              start_ts: this.now + 40,
+              end_ts: this.now + 50,
+            },
+          },
+        ]
+      )
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              toV: 8,
+              fromV: 6,
+            },
+            'doc-id-2': {
+              toV: 5,
+              fromV: 4,
+            },
+          },
+          meta: {
+            user_ids: [this.user_1.id, this.user_2.id],
+            start_ts: this.now,
+            end_ts: this.now + 50,
+          },
+        },
+      ])
+    })
+
+    it('should include null user values', function () {
+      const result = this.UpdatesManager._summarizeUpdates([
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_1.id,
+            start_ts: this.now + 20,
+            end_ts: this.now + 30,
+          },
+          v: 5,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: null,
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+          v: 4,
+        },
+      ])
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 4,
+              toV: 5,
+            },
+          },
+          meta: {
+            user_ids: [this.user_1.id, null],
+            start_ts: this.now,
+            end_ts: this.now + 30,
+          },
+        },
+      ])
+    })
+
+    it('should include null user values, when the null is earlier in the updates list', function () {
+      const result = this.UpdatesManager._summarizeUpdates([
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: null,
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+          v: 4,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_1.id,
+            start_ts: this.now + 20,
+            end_ts: this.now + 30,
+          },
+          v: 5,
+        },
+      ])
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 4,
+              toV: 5,
+            },
+          },
+          meta: {
+            user_ids: [null, this.user_1.id],
+            start_ts: this.now,
+            end_ts: this.now + 30,
+          },
+        },
+      ])
+    })
+
+    it('should roll several null user values into one', function () {
+      const result = this.UpdatesManager._summarizeUpdates([
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_1.id,
+            start_ts: this.now + 20,
+            end_ts: this.now + 30,
+          },
+          v: 5,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: null,
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+          v: 4,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: null,
+            start_ts: this.now + 2,
+            end_ts: this.now + 4,
+          },
+          v: 4,
+        },
+      ])
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 4,
+              toV: 5,
+            },
+          },
+          meta: {
+            user_ids: [this.user_1.id, null],
+            start_ts: this.now,
+            end_ts: this.now + 30,
+          },
+        },
+      ])
+    })
+
+    return it('should split updates before a big delete', function () {
+      const result = this.UpdatesManager._summarizeUpdates([
+        {
+          doc_id: 'doc-id-1',
+          op: [{ d: 'this is a long long long long long delete', p: 34 }],
+          meta: {
+            user_id: this.user_1.id,
+            start_ts: this.now + 20,
+            end_ts: this.now + 30,
+          },
+          v: 5,
+        },
+        {
+          doc_id: 'doc-id-1',
+          meta: {
+            user_id: this.user_2.id,
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+          v: 4,
+        },
+      ])
+
+      return expect(result).to.deep.equal([
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 5,
+              toV: 5,
+            },
+          },
+          meta: {
+            user_ids: [this.user_1.id],
+            start_ts: this.now + 20,
+            end_ts: this.now + 30,
+          },
+        },
+        {
+          docs: {
+            'doc-id-1': {
+              fromV: 4,
+              toV: 4,
+            },
+          },
+          meta: {
+            user_ids: [this.user_2.id],
+            start_ts: this.now,
+            end_ts: this.now + 10,
+          },
+        },
+      ])
+    })
+  })
+})

services/track-changes/test/unit/js/WebApiManager/WebApiManagerTests.js

@@ -0,0 +1,208 @@
+/* eslint-disable
+    no-return-assign,
+    no-unused-vars,
+*/
+// TODO: This file was created by bulk-decaffeinate.
+// Fix any style issues and re-enable lint.
+/*
+ * decaffeinate suggestions:
+ * DS102: Remove unnecessary code created because of implicit returns
+ * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
+ */
+const sinon = require('sinon')
+const { expect } = require('chai')
+const modulePath = '../../../../app/js/WebApiManager.js'
+const SandboxedModule = require('sandboxed-module')
+
+describe('WebApiManager', function () {
+  beforeEach(function () {
+    this.WebApiManager = SandboxedModule.require(modulePath, {
+      requires: {
+        requestretry: (this.request = {}),
+        '@overleaf/settings': (this.settings = {
+          apis: {
+            web: {
+              url: 'http://example.com',
+              user: 'sharelatex',
+              pass: 'password',
+            },
+          },
+        }),
+      },
+    })
+    this.callback = sinon.stub()
+    this.user_id = 'mock-user-id'
+    this.project_id = 'mock-project-id'
+    this.user_info = {
+      email: 'leo@sharelatex.com',
+      id: this.user_id,
+      first_name: 'Leo',
+      last_nane: 'Lion',
+      extra_param: 'blah',
+    }
+    return (this.project = { features: 'mock-features' })
+  })
+
+  describe('getUserInfo', function () {
+    describe('successfully', function () {
+      beforeEach(function () {
+        this.body = JSON.stringify(this.user_info)
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 200 }, this.body)
+        return this.WebApiManager.getUserInfo(this.user_id, this.callback)
+      })
+
+      it('should get the user from the web api', function () {
+        return this.request.get
+          .calledWithMatch({
+            url: `${this.settings.apis.web.url}/user/${this.user_id}/personal_info`,
+            auth: {
+              user: this.settings.apis.web.user,
+              pass: this.settings.apis.web.pass,
+              sendImmediately: true,
+            },
+          })
+          .should.equal(true)
+      })
+
+      return it('should call the callback with only the email, id and names', function () {
+        return this.callback
+          .calledWith(null, {
+            id: this.user_id,
+            email: this.user_info.email,
+            first_name: this.user_info.first_name,
+            last_name: this.user_info.last_name,
+          })
+          .should.equal(true)
+      })
+    })
+
+    describe('when the web API returns an error', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(
+            1,
+            (this.error = new Error('something went wrong')),
+            null,
+            null
+          )
+        return this.WebApiManager.getUserInfo(this.user_id, this.callback)
+      })
+
+      return it('should return an error to the callback', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+
+    describe('when the web returns a failure error code', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 500, attempts: 42 }, '')
+        return this.WebApiManager.getUserInfo(this.user_id, this.callback)
+      })
+
+      return it('should return the callback with an error', function () {
+        return this.callback
+          .calledWith(
+            sinon.match.has(
+              'message',
+              'web returned a non-success status code: 500 (attempts: 42)'
+            )
+          )
+          .should.equal(true)
+      })
+    })
+
+    return describe('when the user cannot be found', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 404 }, 'nothing')
+        return this.WebApiManager.getUserInfo(this.user_id, this.callback)
+      })
+
+      return it('should return a null value', function () {
+        return this.callback.calledWith(null, null).should.equal(true)
+      })
+    })
+  })
+
+  return describe('getProjectDetails', function () {
+    describe('successfully', function () {
+      beforeEach(function () {
+        this.body = JSON.stringify(this.project)
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 200 }, this.body)
+        return this.WebApiManager.getProjectDetails(
+          this.project_id,
+          this.callback
+        )
+      })
+
+      it('should get the project from the web api', function () {
+        return this.request.get
+          .calledWithMatch({
+            url: `${this.settings.apis.web.url}/project/${this.project_id}/details`,
+            auth: {
+              user: this.settings.apis.web.user,
+              pass: this.settings.apis.web.pass,
+              sendImmediately: true,
+            },
+          })
+          .should.equal(true)
+      })
+
+      return it('should call the callback with the project', function () {
+        return this.callback.calledWith(null, this.project).should.equal(true)
+      })
+    })
+
+    describe('when the web API returns an error', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(
+            1,
+            (this.error = new Error('something went wrong')),
+            null,
+            null
+          )
+        return this.WebApiManager.getProjectDetails(
+          this.project_id,
+          this.callback
+        )
+      })
+
+      return it('should return an error to the callback', function () {
+        return this.callback.calledWith(this.error).should.equal(true)
+      })
+    })
+
+    return describe('when the web returns a failure error code', function () {
+      beforeEach(function () {
+        this.request.get = sinon
+          .stub()
+          .callsArgWith(1, null, { statusCode: 500, attempts: 42 }, '')
+        return this.WebApiManager.getProjectDetails(
+          this.project_id,
+          this.callback
+        )
+      })
+
+      return it('should return the callback with an error', function () {
+        return this.callback
+          .calledWith(
+            sinon.match.has(
+              'message',
+              'web returned a non-success status code: 500 (attempts: 42)'
+            )
+          )
+          .should.equal(true)
+      })
+    })
+  })
+})