overleaf/libraries/overleaf-editor-core/test/text_operation.test.js

// @ts-check
//
// These tests are based on the OT.js tests:
// https://github.com/Operational-Transformation/ot.js/blob/
//   8873b7e28e83f9adbf6c3a28ec639c9151a838ae/test/lib/test-text-operation.js
//
'use strict'

const { expect } = require('chai')
const random = require('./support/random')
const randomOperation = require('./support/random_text_operation')

const ot = require('..')
const TextOperation = ot.TextOperation
const StringFileData = require('../lib/file_data/string_file_data')
const { RetainOp, InsertOp, RemoveOp } = require('../lib/operation/scan_op')

describe('TextOperation', function () {
  const numTrials = 500

  it('tracks base and target lengths', function () {
    const o = new TextOperation()
    expect(o.baseLength).to.equal(0)
    expect(o.targetLength).to.equal(0)
    o.retain(5)
    expect(o.baseLength).to.equal(5)
    expect(o.targetLength).to.equal(5)
    o.insert('abc')
    expect(o.baseLength).to.equal(5)
    expect(o.targetLength).to.equal(8)
    o.retain(2)
    expect(o.baseLength).to.equal(7)
    expect(o.targetLength).to.equal(10)
    o.remove(2)
    expect(o.baseLength).to.equal(9)
    expect(o.targetLength).to.equal(10)
  })

  it('supports chaining', function () {
    const o = new TextOperation()
      .retain(5)
      .retain(0)
      .insert('lorem')
      .insert('')
      .remove('abc')
      .remove(3)
      .remove(0)
      .remove('')
    expect(o.ops.length).to.equal(3)
  })

  it('ignores empty operations', function () {
    const o = new TextOperation()
    o.retain(0)
    o.insert('')
    o.remove('')
    expect(o.ops.length).to.equal(0)
  })

  it('checks for equality', function () {
    const op1 = new TextOperation().remove(1).insert('lo').retain(2).retain(3)
    const op2 = new TextOperation().remove(-1).insert('l').insert('o').retain(5)
    expect(op1.equals(op2)).to.be.true
    op1.remove(1)
    op2.retain(1)
    expect(op1.equals(op2)).to.be.false
  })

  it('merges ops', function () {
    function last(arr) {
      return arr[arr.length - 1]
    }
    const o = new TextOperation()
    expect(o.ops.length).to.equal(0)
    o.retain(2)
    expect(o.ops.length).to.equal(1)
    expect(last(o.ops).equals(new RetainOp(2))).to.be.true
    o.retain(3)
    expect(o.ops.length).to.equal(1)
    expect(last(o.ops).equals(new RetainOp(5))).to.be.true
    o.insert('abc')
    expect(o.ops.length).to.equal(2)
    expect(last(o.ops).equals(new InsertOp('abc'))).to.be.true
    o.insert('xyz')
    expect(o.ops.length).to.equal(2)
    expect(last(o.ops).equals(new InsertOp('abcxyz'))).to.be.true
    o.remove('d')
    expect(o.ops.length).to.equal(3)
    expect(last(o.ops).equals(new RemoveOp(1))).to.be.true
    o.remove('d')
    expect(o.ops.length).to.equal(3)
    expect(last(o.ops).equals(new RemoveOp(2))).to.be.true
  })

  it('checks for no-ops', function () {
    const o = new TextOperation()
    expect(o.isNoop()).to.be.true
    o.retain(5)
    expect(o.isNoop()).to.be.true
    o.retain(3)
    expect(o.isNoop()).to.be.true
    o.insert('lorem')
    expect(o.isNoop()).to.be.false
  })

  it('converts to string', function () {
    const o = new TextOperation()
    o.retain(2)
    o.insert('lorem')
    o.remove('ipsum')
    o.retain(5)
    expect(o.toString()).to.equal(
      "retain 2, insert 'lorem', remove 5, retain 5"
    )
  })

  it('converts from JSON', function () {
    const ops = [2, -1, -1, 'cde']
    const o = TextOperation.fromJSON({ textOperation: ops })
    expect(o.ops.length).to.equal(3)
    expect(o.baseLength).to.equal(4)
    expect(o.targetLength).to.equal(5)

    function assertIncorrectAfter(fn) {
      const ops2 = ops.slice(0)
      fn(ops2)
      expect(() => {
        TextOperation.fromJSON({ textOperation: ops2 })
      }).to.throw
    }

    assertIncorrectAfter(ops2 => {
      ops2.push({ insert: 'x' })
    })
    assertIncorrectAfter(ops2 => {
      ops2.push(null)
    })
  })

  it(
    'applies (randomised)',
    random.test(numTrials, () => {
      const str = random.string(50)
      const o = randomOperation(str)
      expect(str.length).to.equal(o.baseLength)
      const file = new StringFileData(str)
      o.apply(file)
      const result = file.getContent()
      expect(result.length).to.equal(o.targetLength)
    })
  )

  it(
    'inverts (randomised)',
    random.test(numTrials, () => {
      const str = random.string(50)
      const o = randomOperation(str)
      const p = o.invert(new StringFileData(str))
      expect(o.baseLength).to.equal(p.targetLength)
      expect(o.targetLength).to.equal(p.baseLength)
      const file = new StringFileData(str)
      o.apply(file)
      p.apply(file)
      const result = file.getContent()
      expect(result).to.equal(str)
    })
  )

  it(
    'converts to/from JSON (randomised)',
    random.test(numTrials, () => {
      const doc = random.string(50)
      const operation = randomOperation(doc)
      const roundTripOperation = TextOperation.fromJSON(operation.toJSON())
      expect(operation.equals(roundTripOperation)).to.be.true
    })
  )

  it(
    'composes (randomised)',
    random.test(numTrials, () => {
      // invariant: apply(str, compose(a, b)) === apply(apply(str, a), b)
      const str = random.string(20)
      const a = randomOperation(str)
      const file = new StringFileData(str)
      a.apply(file)
      const afterA = file.getContent()
      expect(afterA.length).to.equal(a.targetLength)
      const b = randomOperation(afterA)
      b.apply(file)
      const afterB = file.getContent()
      expect(afterB.length).to.equal(b.targetLength)
      const ab = a.compose(b)
      expect(ab.targetLength).to.equal(b.targetLength)
      ab.apply(new StringFileData(str))
      const afterAB = file.getContent()
      expect(afterAB).to.equal(afterB)
    })
  )

  it(
    'transforms (randomised)',
    random.test(numTrials, () => {
      // invariant: compose(a, b') = compose(b, a')
      // where (a', b') = transform(a, b)
      const str = random.string(20)
      const a = randomOperation(str)
      const b = randomOperation(str)
      const primes = TextOperation.transform(a, b)
      const aPrime = primes[0]
      const bPrime = primes[1]
      const abPrime = a.compose(bPrime)
      const baPrime = b.compose(aPrime)
      const abFile = new StringFileData(str)
      const baFile = new StringFileData(str)
      abPrime.apply(abFile)
      baPrime.apply(baFile)
      expect(abPrime.equals(baPrime)).to.be.true
      expect(abFile.getContent()).to.equal(baFile.getContent())
    })
  )

  it('throws when invalid operations are applied', function () {
    const operation = new TextOperation().retain(1)
    expect(() => {
      operation.apply(new StringFileData(''))
    }).to.throw(TextOperation.ApplyError)
    expect(() => {
      operation.apply(new StringFileData(' '))
    }).not.to.throw
  })

  it('throws when insert text contains non BMP chars', function () {
    const operation = new TextOperation()
    const str = '𝌆\n'
    expect(() => {
      operation.insert(str)
    }).to.throw(
      TextOperation.UnprocessableError,
      /inserted text contains non BMP characters/
    )
  })

  it('throws when base string contains non BMP chars', function () {
    const operation = new TextOperation()
    const str = '𝌆\n'
    expect(() => {
      operation.apply(new StringFileData(str))
    }).to.throw(
      TextOperation.UnprocessableError,
      /string contains non BMP characters/
    )
  })

  it('throws at from JSON when it contains non BMP chars', function () {
    const operation = ['𝌆\n']
    expect(() => {
      TextOperation.fromJSON({ textOperation: operation })
    }).to.throw(
      TextOperation.UnprocessableError,
      /inserted text contains non BMP characters/
    )
  })
})