applyChanges()

in backend/new.js [1756:1826]

• 60 lines of code
• 13 McCabe index (conditional complexity)

  applyChanges(changeBuffers, isLocal = false) {
    // decoded change has the form { actor, seq, startOp, time, message, deps, actorIds, hash, columns, buffer }
    let decodedChanges = changeBuffers.map(buffer => {
      const decoded = decodeChangeColumns(buffer)
      decoded.buffer = buffer
      return decoded
    })

    let patches = {_root: {objectId: '_root', type: 'map', props: {}}}
    let docState = {
      maxOp: this.maxOp,
      changeIndexByHash: this.changeIndexByHash,
      actorIds: this.actorIds,
      heads: this.heads,
      clock: this.clock,
      blocks: this.blocks.slice(),
      objectMeta: Object.assign({}, this.objectMeta)
    }
    let queue = (this.queue.length === 0) ? decodedChanges : decodedChanges.concat(this.queue)
    let allApplied = [], objectIds = new Set()

    while (true) {
      const [applied, enqueued] = applyChanges(patches, queue, docState, objectIds)
      queue = enqueued
      if (applied.length > 0) allApplied = allApplied.concat(applied)
      if (queue.length === 0) break

      // If we are missing a dependency, and we haven't computed the hash graph yet, first compute
      // the hashes to see if we actually have it already
      if (applied.length === 0) {
        if (!this.haveHashGraph) this.computeHashGraph(); else break
      }
    }

    setupPatches(patches, objectIds, docState)

    // Update the document state only if `applyChanges` does not throw an exception
    for (let change of allApplied) {
      this.changes.push(change.buffer)
      if (!this.hashesByActor[change.actor]) this.hashesByActor[change.actor] = []
      this.hashesByActor[change.actor][change.seq - 1] = change.hash
      this.changeIndexByHash[change.hash] = this.changes.length - 1
      this.dependenciesByHash[change.hash] = change.deps
      this.dependentsByHash[change.hash] = []
      for (let dep of change.deps) {
        if (!this.dependentsByHash[dep]) this.dependentsByHash[dep] = []
        this.dependentsByHash[dep].push(change.hash)
      }
      appendChange(this.changesEncoders, change, docState.actorIds, this.changeIndexByHash)
    }

    this.maxOp        = docState.maxOp
    this.actorIds     = docState.actorIds
    this.heads        = docState.heads
    this.clock        = docState.clock
    this.blocks       = docState.blocks
    this.objectMeta   = docState.objectMeta
    this.queue        = queue
    this.binaryDoc    = null
    this.initPatch    = null

    let patch = {
      maxOp: this.maxOp, clock: this.clock, deps: this.heads,
      pendingChanges: this.queue.length, diffs: patches._root
    }
    if (isLocal && decodedChanges.length === 1) {
      patch.actor = decodedChanges[0].actor
      patch.seq = decodedChanges[0].seq
    }
    return patch
  }