simplify tikzexternalize checks

services/clsi/app/coffee/CompileManager.coffee

@@ -62,10 +62,12 @@ module.exports = CompileManager =
 					callback()
 
 			createTikzFileIfRequired = (callback) ->
-				if TikzManager.needsOutputFile(request.rootResourcePath, resourceList)
-					TikzManager.injectOutputFile compileDir, request.rootResourcePath, callback
-				else
-					callback()
+				TikzManager.checkMainFile compileDir, request.rootResourcePath, resourceList, (error, usesTikzExternalize) ->
+					return callback(error) if error?
+					if usesTikzExternalize
+						TikzManager.injectOutputFile compileDir, request.rootResourcePath, callback
+					else
+						callback()
 
 			# set up environment variables for chktex
 			env = {}

services/clsi/app/coffee/TikzManager.coffee

@@ -1,6 +1,7 @@
 fs = require "fs"
 Path = require "path"
 ResourceWriter = require "./ResourceWriter"
+SafeReader = require "./SafeReader"
 logger = require "logger-sharelatex"
 
 # for \tikzexternalize to work the main file needs to match the
@@ -8,25 +9,21 @@ logger = require "logger-sharelatex"
 # copy of the main file as 'output.tex'.
 
 module.exports = TikzManager =
-	needsOutputFile: (rootResourcePath, resources) ->
+
+	checkMainFile: (compileDir, mainFile, resources, callback = (error, usesTikzExternalize) ->) ->
 		# if there's already an output.tex file, we don't want to touch it
 		for resource in resources
 			if resource.path is "output.tex"
-				return false
+				logger.log compileDir: compileDir, mainFile: mainFile, "output.tex already in resources"
+				return callback(null, false)
 		# if there's no output.tex, see if we are using tikz/pgf in the main file
-		for resource in resources
-			if resource.path is rootResourcePath
-				return TikzManager._includesTikz (resource)
-		# otherwise false
-		return false
-
-	_includesTikz: (resource) ->
-		# check if we are using tikz externalize
-		content = resource.content?.slice(0,65536)
-		if content?.indexOf("\\tikzexternalize") >= 0
-			return true
-		else
-			return false
+		ResourceWriter.checkPath compileDir, mainFile, (error, path) ->
+			return callback(error) if error?
+			SafeReader.readFile path, 65536, "utf8", (error, content) ->
+				return callback(error) if error?
+				usesTikzExternalize = content?.indexOf("\\tikzexternalize") >= 0
+				logger.log compileDir: compileDir, mainFile: mainFile, usesTikzExternalize:usesTikzExternalize, "checked for tikzexternalize"
+				callback null, usesTikzExternalize
 
 	injectOutputFile: (compileDir, mainFile, callback = (error) ->) ->
 		ResourceWriter.checkPath compileDir, mainFile, (error, path) ->

services/clsi/test/unit/coffee/CompileManagerTests.coffee

@@ -108,7 +108,7 @@ describe "CompileManager", ->
 			@OutputFileFinder.findOutputFiles = sinon.stub().callsArgWith(2, null, @output_files)
 			@OutputCacheManager.saveOutputFiles = sinon.stub().callsArgWith(2, null, @build_files)
 			@DraftModeManager.injectDraftMode = sinon.stub().callsArg(1)
-			@TikzManager.needsOutputFile = sinon.stub().returns(false)
+			@TikzManager.checkMainFile = sinon.stub().callsArg(3, false)
 		
 		describe "normally", ->
 			beforeEach ->

services/clsi/test/unit/coffee/TikzManager.coffee

@@ -7,34 +7,63 @@ describe 'TikzManager', ->
 	beforeEach ->
 		@TikzManager = SandboxedModule.require modulePath, requires:
 			"./ResourceWriter": @ResourceWriter = {}
+			"./SafeReader": @SafeReader = {}
 			"fs": @fs = {}
 			"logger-sharelatex": @logger = {log: () ->}
 
-	describe "needsOutputFile", ->
-		it "should return true if there is a \\tikzexternalize", ->
-			@TikzManager.needsOutputFile("main.tex", [
-				{ path: 'foo.tex' },
-				{ path: 'main.tex', content:'foo \\usepackage{tikz} \\tikzexternalize' }
-			]).should.equal true
-
-		it "should return false if there is no \\tikzexternalize", ->
-			@TikzManager.needsOutputFile("main.tex", [
-				{ path: 'foo.tex' },
-				{ path: 'main.tex', content:'foo \\usepackage{tikz}' }
-			]).should.equal false
-
-		it "should return false if there is already an output.tex file", ->
-			@TikzManager.needsOutputFile("main.tex", [
-				{ path: 'foo.tex' },
-				{ path: 'main.tex', content:'foo \\usepackage{tikz} \\tikzexternalize' },
-				{ path: 'output.tex' }
-			]).should.equal false
-
-		it "should return false if the file has no content", ->
-			@TikzManager.needsOutputFile("main.tex", [
-				{ path: 'foo.tex' },
-				{ path: 'main.tex' }
-			]).should.equal false
+	describe "checkMainFile", ->
+		beforeEach ->
+				@compileDir = "compile-dir"
+				@mainFile = "main.tex"
+				@callback = sinon.stub()
+
+		describe "if there is already an output.tex file in the resources", ->
+			beforeEach ->
+				@resources = [{path:"main.tex"},{path:"output.tex"}]
+				@TikzManager.checkMainFile @compileDir, @mainFile, @resources, @callback
+
+			it "should call the callback with false ", ->
+				@callback.calledWithExactly(null, false)
+				.should.equal true
+
+		describe "if there is no output.tex file in the resources", ->
+			beforeEach ->
+				@resources = [{path:"main.tex"}]
+				@ResourceWriter.checkPath = sinon.stub()
+					.withArgs(@compileDir, @mainFile)
+					.callsArgWith(2, null, "#{@compileDir}/#{@mainFile}")
+
+			describe "and the main file contains tikzexternalize", ->
+				beforeEach ->
+					@SafeReader.readFile = sinon.stub()
+						.withArgs("#{@compileDir}/#{@mainFile}")
+						.callsArgWith(3, null, "hello \\tikzexternalize")
+					@TikzManager.checkMainFile @compileDir, @mainFile, @resources, @callback
+
+				it "should look at the file on disk", ->
+					@SafeReader.readFile
+					.calledWith("#{@compileDir}/#{@mainFile}")
+					.should.equal true
+
+				it "should call the callback with true ", ->
+					@callback.calledWithExactly(null, true)
+					.should.equal true
+
+			describe "and the main file does not contain tikzexternalize", ->
+				beforeEach ->
+					@SafeReader.readFile = sinon.stub()
+						.withArgs("#{@compileDir}/#{@mainFile}")
+						.callsArgWith(3, null, "hello")
+					@TikzManager.checkMainFile @compileDir, @mainFile, @resources, @callback
+
+				it "should look at the file on disk", ->
+					@SafeReader.readFile
+					.calledWith("#{@compileDir}/#{@mainFile}")
+					.should.equal true
+
+				it "should call the callback with false", ->
+					@callback.calledWithExactly(null, false)
+					.should.equal true
 
 	describe "injectOutputFile", ->
 		beforeEach ->