Function getChangesetInfo

src/node/handler/PadMessageHandler.ts:1551–1622

(pad: PadType, startNum: number, endNum:number, granularity: number)

 * https://github.com/ether/pad/blob/master/etherpad/src/etherpad/control/pad/pad_changeset_control.js#L144
 */
const getChangesetInfo = async (pad: PadType, startNum: number, endNum:number, granularity: number) => {
  const headRevision = pad.getHeadRevisionNumber();

  // calculate the last full endnum
  if (endNum > headRevision + 1) endNum = headRevision + 1;
  endNum = Math.floor(endNum / granularity) * granularity;

  const compositesChangesetNeeded = [];
  const revTimesNeeded = [];

  // figure out which composite Changeset and revTimes we need, to load them in bulk
  for (let start = startNum; start < endNum; start += granularity) {
    const end = start + granularity;

    // add the composite Changeset we needed
    compositesChangesetNeeded.push({start, end});

    // add the t1 time we need
    revTimesNeeded.push(start === 0 ? 0 : start - 1);

    // add the t2 time we need
    revTimesNeeded.push(end - 1);
  }

  // Get all needed db values in parallel.
  const composedChangesets:MapArrayType<any> = {};
  const revisionDate:number[] = [];
  const [lines] = await Promise.all([
    getPadLines(pad, startNum - 1),
    // Get all needed composite Changesets.
    ...compositesChangesetNeeded.map(async (item) => {
      const changeset = await exports.composePadChangesets(pad, item.start, item.end);
      composedChangesets[`${item.start}/${item.end}`] = changeset;
    }),
    // Get all needed revision Dates.
    ...revTimesNeeded.map(async (revNum) => {
      const revDate = await pad.getRevisionDate(revNum);
      revisionDate[revNum] = revDate;
    }),
  ]);

  // doesn't know what happens here exactly :/
  const timeDeltas = [];
  const forwardsChangesets = [];
  const backwardsChangesets = [];
  const apool = new AttributePool();

  for (let compositeStart = startNum; compositeStart < endNum; compositeStart += granularity) {
    const compositeEnd = compositeStart + granularity;
    if (compositeEnd > endNum || compositeEnd > headRevision + 1) break;

    const forwards = composedChangesets[`${compositeStart}/${compositeEnd}`];
    const backwards = inverse(forwards, lines.textlines, lines.alines, pad.apool());

    mutateAttributionLines(forwards, lines.alines, pad.apool());
    mutateTextLines(forwards, lines.textlines);

    const forwards2 = moveOpsToNewPool(forwards, pad.apool(), apool);