Overleaf/libraries/overleaf-editor-core/lib/operation/text_operation.js

// @ts-check
/**
 * The text operation from OT.js with some minor cosmetic changes.
 *
 * Specifically, this is based on
 * https://github.com/Operational-Transformation/ot.js/
 * blob/298825f58fb51fefb352e7df5ddbc668f4d5646f/lib/text-operation.js
 * from 18 Mar 2013.
 */

'use strict'
const containsNonBmpChars = require('../util').containsNonBmpChars
const EditOperation = require('./edit_operation')
const {
  RetainOp,
  InsertOp,
  RemoveOp,
  isRetain,
  isInsert,
  isRemove,
} = require('./scan_op')
const {
  UnprocessableError,
  ApplyError,
  InvalidInsertionError,
  TooLongError,
} = require('../errors')
const Range = require('../range')
const ClearTrackingProps = require('../file_data/clear_tracking_props')
const TrackingProps = require('../file_data/tracking_props')

/**
 * @typedef {import('../file_data/string_file_data')} StringFileData
 * @typedef {import('../types').RawTextOperation} RawTextOperation
 * @typedef {import('../operation/scan_op').ScanOp} ScanOp
 * @typedef {import('../file_data/tracked_change_list')} TrackedChangeList
 * @typedef {import('../types').TrackingDirective} TrackingDirective
 * @typedef {{tracking?: TrackingProps, commentIds?: string[]}} InsertOptions
 */

/**
 * Create an empty text operation.
 * @extends EditOperation
 */
class TextOperation extends EditOperation {
  /**
   * Length of the longest file that we'll attempt to edit, in characters.
   *
   * This number used to be 2M characters, but it didn't include tracked
   * deletes. Now that it includes tracked deletes, we raise the limit to the
   * Mongo document size limit. It would have been impossible to store more
   * tracked deletes in a single document.
   */
  static MAX_STRING_LENGTH = 16 * Math.pow(1024, 2)

  /**
   * Max editable file length, excluding tracked deletes.
   */
  static MAX_STRING_LENGTH_EXCLUDING_TRACKED_DELETES = 2 * Math.pow(1024, 2)

  static UnprocessableError = UnprocessableError
  static ApplyError = ApplyError
  static InvalidInsertionError = InvalidInsertionError
  static TooLongError = TooLongError

  constructor() {
    super()
    // When an operation is applied to an input string, you can think of this as
    // if an imaginary cursor runs over the entire string and skips over some
    // parts, removes some parts and inserts characters at some positions. These
    // actions (skip/remove/insert) are stored as an array in the "ops" property.
    /** @type {ScanOp[]} */
    this.ops = []
    // An operation's baseLength is the length of every string the operation
    // can be applied to.
    this.baseLength = 0
    // The targetLength is the length of every string that results from applying
    // the operation on a valid input string.
    this.targetLength = 0
  }

  /**
   * @param {TextOperation} other
   * @return {boolean}
   */
  equals(other) {
    if (this.baseLength !== other.baseLength) {
      return false
    }
    if (this.targetLength !== other.targetLength) {
      return false
    }
    if (this.ops.length !== other.ops.length) {
      return false
    }
    for (let i = 0; i < this.ops.length; i++) {
      if (!this.ops[i].equals(other.ops[i])) {
        return false
      }
    }
    return true
  }

  // After an operation is constructed, the user of the library can specify the
  // actions of an operation (skip/insert/remove) with these three builder
  // methods. They all return the operation for convenient chaining.

  /**
   * Skip over a given number of characters.
   * @param {number | {r: number}} n
   * @param {{tracking?: TrackingDirective}} opts
   * @returns {TextOperation}
   */
  retain(n, opts = {}) {
    if (n === 0) {
      return this
    }

    if (!isRetain(n)) {
      throw new Error('retain expects an integer or a retain object')
    }
    const newOp = RetainOp.fromJSON(n)
    newOp.tracking = opts.tracking

    if (newOp.length === 0) {
      return this
    }

    this.baseLength += newOp.length
    this.targetLength += newOp.length

    const lastOperation = this.ops[this.ops.length - 1]
    if (lastOperation?.canMergeWith(newOp)) {
      // The last op is a retain op => we can merge them into one op.
      lastOperation.mergeWith(newOp)
    } else {
      // Create a new op.
      this.ops.push(newOp)
    }
    return this
  }

  /**
   * Insert a string at the current position.
   * @param {string | {i: string}} insertValue
   * @param {InsertOptions} opts
   * @returns {TextOperation}
   */
  insert(insertValue, opts = {}) {
    if (!isInsert(insertValue)) {
      throw new Error('insert expects a string or an insert object')
    }
    const newOp = InsertOp.fromJSON(insertValue)
    newOp.tracking = opts.tracking
    newOp.commentIds = opts.commentIds
    if (newOp.insertion === '') {
      return this
    }
    this.targetLength += newOp.insertion.length
    const ops = this.ops
    const lastOp = this.ops[this.ops.length - 1]
    if (lastOp?.canMergeWith(newOp)) {
      // Merge insert op.
      lastOp.mergeWith(newOp)
    } else if (lastOp instanceof RemoveOp) {
      // It doesn't matter when an operation is applied whether the operation
      // is remove(3), insert("something") or insert("something"), remove(3).
      // Here we enforce that in this case, the insert op always comes first.
      // This makes all operations that have the same effect when applied to
      // a document of the right length equal in respect to the `equals` method.
      const secondToLastOp = ops[ops.length - 2]
      if (secondToLastOp?.canMergeWith(newOp)) {
        secondToLastOp.mergeWith(newOp)
      } else {
        ops[ops.length] = ops[ops.length - 1]
        ops[ops.length - 2] = newOp
      }
    } else {
      ops.push(newOp)
    }
    return this
  }

  /**
   * Remove a string at the current position.
   * @param {number | string} n
   * @returns {TextOperation}
   */
  remove(n) {
    if (typeof n === 'string') {
      n = n.length
    }
    if (typeof n !== 'number') {
      throw new Error('remove expects an integer or a string')
    }
    if (n === 0) {
      return this
    }
    if (n > 0) {
      n = -n
    }
    const newOp = RemoveOp.fromJSON(n)
    this.baseLength -= n
    const lastOp = this.ops[this.ops.length - 1]
    if (lastOp?.canMergeWith(newOp)) {
      lastOp.mergeWith(newOp)
    } else {
      this.ops.push(newOp)
    }
    return this
  }

  /**
   * Tests whether this operation has no effect.
   */
  isNoop() {
    return (
      this.ops.length === 0 ||
      (this.ops.length === 1 && this.ops[0] instanceof RetainOp)
    )
  }

  /**
   * Pretty printing.
   */
  toString() {
    return this.ops.map(op => op.toString()).join(', ')
  }

  /**
   * @inheritdoc
   * @returns {RawTextOperation}
   */
  toJSON() {
    return { textOperation: this.ops.map(op => op.toJSON()) }
  }

  /**
   * Converts a plain JS object into an operation and validates it.
   * @param {RawTextOperation} obj
   * @returns {TextOperation}
   */
  static fromJSON = function ({ textOperation: ops }) {
    const o = new TextOperation()
    for (const op of ops) {
      if (isRetain(op)) {
        const retain = RetainOp.fromJSON(op)
        o.retain(retain.length, { tracking: retain.tracking })
      } else if (isInsert(op)) {
        const insert = InsertOp.fromJSON(op)
        o.insert(insert.insertion, {
          commentIds: insert.commentIds,
          tracking: insert.tracking,
        })
      } else if (isRemove(op)) {
        const remove = RemoveOp.fromJSON(op)
        o.remove(-remove.length)
      } else {
        throw new UnprocessableError('unknown operation: ' + JSON.stringify(op))
      }
    }
    return o
  }

  /**
   * Apply an operation to a string, returning a new string. Throws an error if
   * there's a mismatch between the input string and the operation.
   * @override
   * @inheritdoc
   * @param {StringFileData} file
   */
  apply(file) {
    const str = file.getContent()
    const operation = this
    if (containsNonBmpChars(str)) {
      throw new TextOperation.ApplyError(
        'The string contains non BMP characters.',
        operation,
        str
      )
    }
    if (str.length !== operation.baseLength) {
      throw new TextOperation.ApplyError(
        "The operation's base length must be equal to the string's length.",
        operation,
        str
      )
    }

    const ops = this.ops
    let inputCursor = 0
    let result = ''
    for (const op of ops) {
      if (op instanceof RetainOp) {
        if (inputCursor + op.length > str.length) {
          throw new ApplyError(
            "Operation can't retain more chars than are left in the string.",
            op.toJSON(),
            str
          )
        }
        file.trackedChanges.applyRetain(result.length, op.length, {
          tracking: op.tracking,
        })
        result += str.slice(inputCursor, inputCursor + op.length)
        inputCursor += op.length
      } else if (op instanceof InsertOp) {
        if (containsNonBmpChars(op.insertion)) {
          throw new InvalidInsertionError(str, op.toJSON())
        }
        file.trackedChanges.applyInsert(result.length, op.insertion, {
          tracking: op.tracking,
        })
        file.comments.applyInsert(
          new Range(result.length, op.insertion.length),
          { commentIds: op.commentIds }
        )
        result += op.insertion
      } else if (op instanceof RemoveOp) {
        file.trackedChanges.applyDelete(result.length, op.length)
        file.comments.applyDelete(new Range(result.length, op.length))
        inputCursor += op.length
      } else {
        throw new UnprocessableError('Unknown ScanOp type during apply')
      }
    }

    if (inputCursor !== str.length) {
      throw new TextOperation.ApplyError(
        "The operation didn't operate on the whole string.",
        operation,
        str
      )
    }

    if (result.length > TextOperation.MAX_STRING_LENGTH) {
      // We're over the hard limit, with or without tracked deletes
      throw new TextOperation.TooLongError(operation, result.length)
    }

    if (
      result.length > TextOperation.MAX_STRING_LENGTH_EXCLUDING_TRACKED_DELETES
    ) {
      // We might be over the limit, but we need to check how much of the
      // length is tracked deletes.
      let trackedDeletesLength = 0
      for (const change of file.trackedChanges) {
        if (change.tracking.type === 'delete') {
          trackedDeletesLength += change.range.length
        }
      }

      if (
        result.length - trackedDeletesLength >
        TextOperation.MAX_STRING_LENGTH_EXCLUDING_TRACKED_DELETES
      ) {
        throw new TextOperation.TooLongError(operation, result.length)
      }
    }

    file.content = result
  }

  /**
   * @inheritdoc
   * @param {number} length of the original string; non-negative
   * @return {number} length of the new string; non-negative
   */
  applyToLength(length) {
    const operation = this
    if (length !== operation.baseLength) {
      throw new TextOperation.ApplyError(
        "The operation's base length must be equal to the string's length.",
        operation,
        length
      )
    }

    const { length: newLength, inputCursor } = this.ops.reduce(
      (intermediate, op) => op.applyToLength(intermediate),
      { length: 0, inputCursor: 0, inputLength: length }
    )

    if (inputCursor !== length) {
      throw new TextOperation.ApplyError(
        "The operation didn't operate on the whole string.",
        operation,
        length
      )
    }
    if (newLength > TextOperation.MAX_STRING_LENGTH) {
      throw new TextOperation.TooLongError(operation, newLength)
    }
    return newLength
  }

  /**
   * @inheritdoc
   * @param {StringFileData} previousState
   */
  invert(previousState) {
    const str = previousState.getContent()
    let strIndex = 0
    const inverse = new TextOperation()
    const ops = this.ops
    for (let i = 0, l = ops.length; i < l; i++) {
      const op = ops[i]
      if (op instanceof RetainOp) {
        // Where we need to end up after the retains
        const target = strIndex + op.length
        // A previous retain could have overriden some tracking info. Now we
        // need to restore it.
        const previousRanges = previousState.trackedChanges.inRange(
          new Range(strIndex, op.length)
        )

        let removeTrackingInfoIfNeeded
        if (op.tracking) {
          removeTrackingInfoIfNeeded = new ClearTrackingProps()
        }

        for (const trackedChange of previousRanges) {
          if (strIndex < trackedChange.range.start) {
            inverse.retain(trackedChange.range.start - strIndex, {
              tracking: removeTrackingInfoIfNeeded,
            })
            strIndex = trackedChange.range.start
          }
          if (trackedChange.range.end < strIndex + op.length) {
            inverse.retain(trackedChange.range.length, {
              tracking: trackedChange.tracking,
            })
            strIndex = trackedChange.range.end
          }
          if (trackedChange.range.end !== strIndex) {
            // No need to split the range at the end
            const [left] = trackedChange.range.splitAt(strIndex)
            inverse.retain(left.length, { tracking: trackedChange.tracking })
            strIndex = left.end
          }
        }
        if (strIndex < target) {
          inverse.retain(target - strIndex, {
            tracking: removeTrackingInfoIfNeeded,
          })
          strIndex = target
        }
      } else if (op instanceof InsertOp) {
        inverse.remove(op.insertion.length)
      } else if (op instanceof RemoveOp) {
        const segments = calculateTrackingCommentSegments(
          strIndex,
          op.length,
          previousState.comments,
          previousState.trackedChanges
        )
        for (const segment of segments) {
          inverse.insert(str.slice(strIndex, strIndex + segment.length), {
            tracking: segment.tracking,
            commentIds: segment.commentIds,
          })
          strIndex += segment.length
        }
      } else {
        throw new UnprocessableError('unknown scanop during inversion')
      }
    }
    return inverse
  }

  /**
   * @inheritdoc
   * @param {EditOperation} other
   */
  canBeComposedWithForUndo(other) {
    if (!(other instanceof TextOperation)) {
      return false
    }

    if (this.isNoop() || other.isNoop()) {
      return true
    }

    const startA = getStartIndex(this)
    const startB = getStartIndex(other)
    const simpleA = getSimpleOp(this)
    const simpleB = getSimpleOp(other)
    if (!simpleA || !simpleB) {
      return false
    }

    if (simpleA instanceof InsertOp && simpleB instanceof InsertOp) {
      return startA + simpleA.insertion.length === startB
    }

    if (simpleA instanceof RemoveOp && simpleB instanceof RemoveOp) {
      // there are two possibilities to delete: with backspace and with the
      // delete key.
      return startB + simpleB.length === startA || startA === startB
    }

    return false
  }

  /**
   * @inheritdoc
   * @param {EditOperation} other
   */
  canBeComposedWith(other) {
    if (!(other instanceof TextOperation)) {
      return false
    }
    return this.targetLength === other.baseLength
  }

  /**
   * @inheritdoc
   * @param {EditOperation} operation2
   */
  compose(operation2) {
    if (!(operation2 instanceof TextOperation)) {
      throw new Error(
        `Trying to compose TextOperation with ${operation2?.constructor?.name}.`
      )
    }
    const operation1 = this
    if (operation1.targetLength !== operation2.baseLength) {
      throw new Error(
        'The base length of the second operation has to be the ' +
          'target length of the first operation'
      )
    }

    const operation = new TextOperation() // the combined operation
    const ops1 = operation1.ops
    const ops2 = operation2.ops // for fast access
    let i1 = 0
    let i2 = 0 // current index into ops1 respectively ops2
    let op1 = ops1[i1++]
    let op2 = ops2[i2++] // current ops
    for (;;) {
      // Dispatch on the type of op1 and op2
      if (typeof op1 === 'undefined' && typeof op2 === 'undefined') {
        // end condition: both ops1 and ops2 have been processed
        break
      }

      if (op1 instanceof RemoveOp) {
        operation.remove(-op1.length)
        op1 = ops1[i1++]
        continue
      }

      if (op2 instanceof InsertOp) {
        operation.insert(op2.insertion, {
          tracking: op2.tracking,
          commentIds: op2.commentIds,
        })
        op2 = ops2[i2++]
        continue
      }

      if (typeof op1 === 'undefined') {
        throw new Error(
          'Cannot compose operations: first operation is too short.'
        )
      }
      if (typeof op2 === 'undefined') {
        throw new Error(
          'Cannot compose operations: first operation is too long.'
        )
      }

      if (op1 instanceof RetainOp && op2 instanceof RetainOp) {
        // If both have tracking info, use the latter one. Otherwise use the
        // tracking info from the former.
        const tracking = op2.tracking ?? op1.tracking
        if (op1.length > op2.length) {
          operation.retain(op2.length, {
            tracking,
          })
          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
          op2 = ops2[i2++]
        } else if (op1.length === op2.length) {
          operation.retain(op1.length, {
            tracking,
          })
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          operation.retain(op1.length, {
            tracking,
          })
          op2 = new RetainOp(op2.length - op1.length, op2.tracking)
          op1 = ops1[i1++]
        }
      } else if (op1 instanceof InsertOp && op2 instanceof RemoveOp) {
        if (op1.insertion.length > op2.length) {
          op1 = new InsertOp(
            op1.insertion.slice(op2.length),
            op1.tracking,
            op1.commentIds
          )
          op2 = ops2[i2++]
        } else if (op1.insertion.length === op2.length) {
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          op2 = RemoveOp.fromJSON(op1.insertion.length - op2.length)
          op1 = ops1[i1++]
        }
      } else if (op1 instanceof InsertOp && op2 instanceof RetainOp) {
        /** @type InsertOptions */
        const opts = {
          commentIds: op1.commentIds,
        }
        if (op2.tracking instanceof TrackingProps) {
          // Prefer the tracking info on the second operation
          opts.tracking = op2.tracking
        } else if (!(op2.tracking instanceof ClearTrackingProps)) {
          // The second operation does not cancel the first operation's tracking
          opts.tracking = op1.tracking
        }
        if (op1.insertion.length > op2.length) {
          operation.insert(op1.insertion.slice(0, op2.length), opts)
          op1 = new InsertOp(
            op1.insertion.slice(op2.length),
            op1.tracking,
            op1.commentIds
          )
          op2 = ops2[i2++]
        } else if (op1.insertion.length === op2.length) {
          operation.insert(op1.insertion, opts)
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          operation.insert(op1.insertion, opts)
          op2 = new RetainOp(op2.length - op1.insertion.length, op2.tracking)
          op1 = ops1[i1++]
        }
      } else if (op1 instanceof RetainOp && op2 instanceof RemoveOp) {
        if (op1.length > op2.length) {
          operation.remove(-op2.length)
          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
          op2 = ops2[i2++]
        } else if (op1.length === op2.length) {
          operation.remove(-op2.length)
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          operation.remove(op1.length)
          op2 = RemoveOp.fromJSON(op1.length - op2.length)
          op1 = ops1[i1++]
        }
      } else {
        throw new Error(
          "This shouldn't happen: op1: " +
            JSON.stringify(op1) +
            ', op2: ' +
            JSON.stringify(op2)
        )
      }
    }
    return operation
  }

  /**
   * Transform takes two operations A and B that happened concurrently and
   * produces two operations A' and B' (in an array) such that
   * `apply(apply(S, A), B') = apply(apply(S, B), A')`. This function is the
   * heart of OT.
   * @param {TextOperation} operation1
   * @param {TextOperation} operation2
   * @returns {[TextOperation, TextOperation]}
   */
  static transform(operation1, operation2) {
    if (operation1.baseLength !== operation2.baseLength) {
      throw new Error('Both operations have to have the same base length')
    }

    const operation1prime = new TextOperation()
    const operation2prime = new TextOperation()
    const ops1 = operation1.ops
    const ops2 = operation2.ops
    let i1 = 0
    let i2 = 0
    let op1 = ops1[i1++]
    let op2 = ops2[i2++]
    for (;;) {
      // At every iteration of the loop, the imaginary cursor that both
      // operation1 and operation2 have that operates on the input string must
      // have the same position in the input string.

      if (typeof op1 === 'undefined' && typeof op2 === 'undefined') {
        // end condition: both ops1 and ops2 have been processed
        break
      }

      // next two cases: one or both ops are insert ops
      // => insert the string in the corresponding prime operation, skip it in
      // the other one. If both op1 and op2 are insert ops, prefer op1.
      if (op1 instanceof InsertOp) {
        operation1prime.insert(op1.insertion, {
          tracking: op1.tracking,
          commentIds: op1.commentIds,
        })
        operation2prime.retain(op1.insertion.length)
        op1 = ops1[i1++]
        continue
      }
      if (op2 instanceof InsertOp) {
        operation1prime.retain(op2.insertion.length)
        operation2prime.insert(op2.insertion, {
          tracking: op2.tracking,
          commentIds: op2.commentIds,
        })
        op2 = ops2[i2++]
        continue
      }

      if (typeof op1 === 'undefined') {
        throw new Error(
          'Cannot compose operations: first operation is too short.'
        )
      }
      if (typeof op2 === 'undefined') {
        throw new Error(
          'Cannot compose operations: first operation is too long.'
        )
      }

      let minl
      if (op1 instanceof RetainOp && op2 instanceof RetainOp) {
        // Simple case: retain/retain

        // If both have tracking info, we use the one from op1
        /** @type {TrackingProps | ClearTrackingProps | undefined} */
        let operation1primeTracking
        /** @type {TrackingProps | ClearTrackingProps | undefined} */
        let operation2primeTracking
        if (op1.tracking) {
          operation1primeTracking = op1.tracking
        } else {
          operation2primeTracking = op2.tracking
        }

        if (op1.length > op2.length) {
          minl = op2.length
          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
          op2 = ops2[i2++]
        } else if (op1.length === op2.length) {
          minl = op2.length
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          minl = op1.length
          op2 = new RetainOp(op2.length - op1.length, op2.tracking)
          op1 = ops1[i1++]
        }
        operation1prime.retain(minl, { tracking: operation1primeTracking })
        operation2prime.retain(minl, { tracking: operation2primeTracking })
      } else if (op1 instanceof RemoveOp && op2 instanceof RemoveOp) {
        // Both operations remove the same string at the same position. We don't
        // need to produce any operations, we just skip over the remove ops and
        // handle the case that one operation removes more than the other.
        if (op1.length > op2.length) {
          op1 = RemoveOp.fromJSON(op2.length - op1.length)
          op2 = ops2[i2++]
        } else if (op1.length === op2.length) {
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          op2 = RemoveOp.fromJSON(op1.length - op2.length)
          op1 = ops1[i1++]
        }
        // next two cases: remove/retain and retain/remove
      } else if (op1 instanceof RemoveOp && op2 instanceof RetainOp) {
        if (op1.length > op2.length) {
          minl = op2.length
          op1 = RemoveOp.fromJSON(op2.length - op1.length)
          op2 = ops2[i2++]
        } else if (op1.length === op2.length) {
          minl = op2.length
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          minl = op1.length
          op2 = new RetainOp(op2.length - op1.length, op2.tracking)
          op1 = ops1[i1++]
        }
        operation1prime.remove(minl)
      } else if (op1 instanceof RetainOp && op2 instanceof RemoveOp) {
        if (op1.length > op2.length) {
          minl = op2.length
          op1 = new RetainOp(op1.length - op2.length, op1.tracking)
          op2 = ops2[i2++]
        } else if (op1.length === op2.length) {
          minl = op1.length
          op1 = ops1[i1++]
          op2 = ops2[i2++]
        } else {
          minl = op1.length
          op2 = RemoveOp.fromJSON(op1.length - op2.length)
          op1 = ops1[i1++]
        }
        operation2prime.remove(minl)
      } else {
        throw new Error("The two operations aren't compatible")
      }
    }

    return [operation1prime, operation2prime]
  }
}

// Operation are essentially lists of ops. There are three types of ops:
//
// * Retain ops: Advance the cursor position by a given number of characters.
//   Represented by positive ints.
// * Insert ops: Insert a given string at the current cursor position.
//   Represented by strings.
// * Remove ops: Remove the next n characters. Represented by negative ints.

/**
 *
 * @param {TextOperation} operation
 * @returns {ScanOp | null}
 */
function getSimpleOp(operation) {
  const ops = operation.ops
  switch (ops.length) {
    case 1:
      return ops[0]
    case 2:
      return ops[0] instanceof RetainOp
        ? ops[1]
        : ops[1] instanceof RetainOp
          ? ops[0]
          : null
    case 3:
      if (ops[0] instanceof RetainOp && ops[2] instanceof RetainOp) {
        return ops[1]
      }
  }
  return null
}

/**
 * @param {TextOperation} operation
 * @return {number}
 */
function getStartIndex(operation) {
  if (operation.ops[0] instanceof RetainOp) {
    return operation.ops[0].length
  }
  return 0
}

/**
 * Constructs the segments defined as each overlapping range of tracked
 * changes and comments. Each segment can have it's own tracking props and
 * attached comment ids.
 *
 *                  The quick brown fox jumps over the lazy dog
 * Tracked inserts            ----------               -----
 * Tracked deletes      ------
 * Comment 1               -------
 * Comment 2                    ----
 * Comment 3                           -----------------
 *
 * Approx. boundaries:  |  | | || |   |                |   |
 *
 * @param {number} cursor
 * @param {number} length
 * @param {import('../file_data/comment_list')} commentsList
 * @param {TrackedChangeList} trackedChangeList
 * @returns {{length: number, commentIds?: string[], tracking?: TrackingProps}[]}
 */
function calculateTrackingCommentSegments(
  cursor,
  length,
  commentsList,
  trackedChangeList
) {
  const breaks = new Set()
  const opStart = cursor
  const opEnd = cursor + length
  /**
   * Utility function to limit breaks to the boundary set by the operation range
   * @param {number} rangeBoundary
   */
  function addBreak(rangeBoundary) {
    if (rangeBoundary < opStart || rangeBoundary > opEnd) {
      return
    }
    breaks.add(rangeBoundary)
  }
  // Add comment boundaries
  for (const comment of commentsList.comments.values()) {
    for (const range of comment.ranges) {
      addBreak(range.end)
      addBreak(range.start)
    }
  }
  // Add tracked change boundaries
  for (const trackedChange of trackedChangeList.asSorted()) {
    addBreak(trackedChange.range.start)
    addBreak(trackedChange.range.end)
  }
  // Add operation boundaries
  addBreak(opStart)
  addBreak(opEnd)

  // Sort the boundaries so that we can construct ranges between them
  const sortedBreaks = Array.from(breaks).sort((a, b) => a - b)

  const separateRanges = []
  for (let i = 1; i < sortedBreaks.length; i++) {
    const start = sortedBreaks[i - 1]
    const end = sortedBreaks[i]
    const currentRange = new Range(start, end - start)
    // The comment ids that cover the current range is part of this sub-range
    const commentIds = commentsList.idsCoveringRange(currentRange)
    // The tracking info that covers the current range is part of this sub-range
    const tracking = trackedChangeList.propsAtRange(currentRange)
    separateRanges.push({
      length: currentRange.length,
      commentIds: commentIds.length > 0 ? commentIds : undefined,
      tracking,
    })
  }
  return separateRanges
}

module.exports = TextOperation