@atlaskit/editor-plugin-collab-edit/dist/esm/pm-plugins/collapseStreamingSteps.js

Collab Edit plugin for @atlaskit/editor-core

function _createForOfIteratorHelper(r, e) { var t = "undefined" != typeof Symbol && r[Symbol.iterator] || r["@@iterator"]; if (!t) { if (Array.isArray(r) || (t = _unsupportedIterableToArray(r)) || e && r && "number" == typeof r.length) { t && (r = t); var _n = 0, F = function F() {}; return { s: F, n: function n() { return _n >= r.length ? { done: !0 } : { done: !1, value: r[_n++] }; }, e: function e(r) { throw r; }, f: F }; } throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); } var o, a = !0, u = !1; return { s: function s() { t = t.call(r); }, n: function n() { var r = t.next(); return a = r.done, r; }, e: function e(r) { u = !0, o = r; }, f: function f() { try { a || null == t.return || t.return(); } finally { if (u) throw o; } } }; }
function _unsupportedIterableToArray(r, a) { if (r) { if ("string" == typeof r) return _arrayLikeToArray(r, a); var t = {}.toString.call(r).slice(8, -1); return "Object" === t && r.constructor && (t = r.constructor.name), "Map" === t || "Set" === t ? Array.from(r) : "Arguments" === t || /^(?:Ui|I)nt(?:8|16|32)(?:Clamped)?Array$/.test(t) ? _arrayLikeToArray(r, a) : void 0; } }
function _arrayLikeToArray(r, a) { (null == a || a > r.length) && (a = r.length); for (var e = 0, n = Array(a); e < a; e++) n[e] = r[e]; return n; }
import { STREAMING_COLLAPSIBLE_STEPS } from '@atlaskit/editor-common/collab-streaming-step-collapse';
import { Transaction } from '@atlaskit/editor-prosemirror/state';
import { Rebaseable } from '@atlaskit/prosemirror-collab';
import { mergeOverlappingSteps } from './mergeOverlappingSteps';

/**
 * Is this step an intermediate frame that its producer has marked as collapsible, and is it still
 * free to be composed?
 */
var isCollapsibleFrame = function isCollapsibleFrame(rebaseable) {
  var origin = rebaseable.origin;
  if (!(origin instanceof Transaction) || origin.getMeta(STREAMING_COLLAPSIBLE_STEPS) !== true) {
    return false;
  }

  // Already sent to (or queued for) the collab service — composing it now would change a step the
  // backend has already seen. Mirrors the `mergeIsLocked` contract in `mergeUnconfirmedSteps`.
  return !origin.getMeta('mergeIsLocked');
};

/**
 * Starting document of each composed step this module has produced.
 *
 * A composed step is synthesised rather than taken from a transaction, so it cannot be found in
 * `origin.steps` and its starting document cannot be recovered the way an original frame's can.
 * `transformUnconfirmed` runs once per transaction and is handed back the steps it returned last
 * time, so the composed step needs to carry its document forward to keep composing against later
 * frames.
 *
 * Keyed on the step rather than its Rebaseable wrapper. `mergeUnconfirmedSteps` runs immediately
 * after this module in `transformUnconfirmed` and rebuilds every wrapper it is given — merging
 * enabled or not — so a wrapper-keyed entry would be unreachable by the very next pass. The step
 * survives that rebuild untouched, and is still replaced whenever the association genuinely
 * becomes stale: `rebaseSteps` maps steps into new objects, and a real merge composes a new one.
 */
var composedStepDocs = new WeakMap();

/**
 * The document this step was applied to.
 *
 * `transformUnconfirmed` is handed steps and nothing else, but a Rebaseable keeps a reference to
 * the transaction that produced it, and a transaction records the document before each of its
 * steps. That is enough for `mergeOverlappingSteps` to resolve merges it cannot derive from the
 * steps alone — notably a frame that replaces more than just what the previous frame inserted.
 *
 * Rebasing maps a step into a new object while keeping the original transaction, so a rebased step
 * is not found in `origin.steps` and correctly yields no document. `mergeOverlappingSteps` then
 * falls back to the merges it can prove without one.
 */
var docBeforeStep = function docBeforeStep(rebaseable) {
  var origin = rebaseable.origin,
    step = rebaseable.step;
  var composed = composedStepDocs.get(step);
  if (composed) {
    return composed;
  }
  var index = origin.steps.indexOf(step);
  return index >= 0 ? origin.docs[index] : undefined;
};

/**
 * Compose adjacent streaming frames in the unconfirmed queue so the collab service receives one
 * step per flush instead of one step per rendered chunk.
 *
 * This runs in the collab plugin's `transformUnconfirmed` hook, which fires *after* each frame has
 * already been applied to the document. Collapsing therefore has no effect on what the local user
 * sees, on undo history, or on any other plugin state — it only changes what is sent to the collab
 * service, and what is used as the rebase buffer when remote steps arrive.
 *
 * Because the unconfirmed steps double as the rebase buffer (`rebaseSteps` applies their inverses
 * to the live document), the composition must be exact. `mergeOverlappingSteps` only returns a
 * merge it can prove exact, and this function degrades to a no-op whenever it declines.
 *
 * @param steps Rebaseable steps
 * @returns Rebaseable steps, with adjacent streaming frames composed
 */
export function collapseStreamingSteps(steps) {
  // Fast path: nothing to do unless at least two frames could possibly compose.
  if (steps.length < 2) {
    return steps;
  }
  var collapsed = [];
  // The document the run currently at the tail of `collapsed` started from. A composed step
  // still applies to the document its first frame applied to, so this survives each merge.
  var runDocBefore;
  var _iterator = _createForOfIteratorHelper(steps),
    _step;
  try {
    for (_iterator.s(); !(_step = _iterator.n()).done;) {
      var rebaseable = _step.value;
      var previous = collapsed[collapsed.length - 1];
      if (!previous || !isCollapsibleFrame(previous) || !isCollapsibleFrame(rebaseable)) {
        collapsed.push(rebaseable);
        runDocBefore = docBeforeStep(rebaseable);
        continue;
      }
      var merged = mergeOverlappingSteps(previous, rebaseable, runDocBefore);
      if (!merged) {
        collapsed.push(rebaseable);
        runDocBefore = docBeforeStep(rebaseable);
        continue;
      }

      // Keep the earliest origin, matching `mergeUnconfirmedSteps`. `commitUnconfirmedSteps` in
      // the collab provider tracks completion by origin identity, so keeping the earliest means
      // the composed step is not considered confirmed until the whole run has been acknowledged.
      var composed = new Rebaseable(merged.step, merged.inverted, previous.origin);
      if (runDocBefore) {
        composedStepDocs.set(composed.step, runDocBefore);
      }
      collapsed[collapsed.length - 1] = composed;
    }
  } catch (err) {
    _iterator.e(err);
  } finally {
    _iterator.f();
  }
  return collapsed;
}