/**
 * This code is mostly from the old Etherpad. Please help us to comment this code.
 * This helps other people to understand this code better and helps them to improve it.
 * TL;DR COMMENTS ON THIS FILE ARE HIGHLY APPRECIATED
 */

/**
 * Copyright 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS-IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
// revision info is a skip list whos entries represent a particular revision
// of the document.  These revisions are connected together by various
// changesets,  or deltas, between any two revisions.

function loadBroadcastRevisionsJS() {
  function Revision(revNum) {
    this.rev = revNum;
    this.changesets = [];
  }

  Revision.prototype.addChangeset = function (destIndex, changeset, timeDelta) {
    const changesetWrapper = {
      deltaRev: destIndex - this.rev,
      deltaTime: timeDelta,
      getValue() {
        return changeset;
      },
    };
    this.changesets.push(changesetWrapper);
    this.changesets.sort((a, b) => (b.deltaRev - a.deltaRev));
  };

  revisionInfo = {};
  revisionInfo.addChangeset = function (fromIndex, toIndex, changeset, backChangeset, timeDelta) {
    const startRevision = revisionInfo[fromIndex] || revisionInfo.createNew(fromIndex);
    const endRevision = revisionInfo[toIndex] || revisionInfo.createNew(toIndex);
    startRevision.addChangeset(toIndex, changeset, timeDelta);
    endRevision.addChangeset(fromIndex, backChangeset, -1 * timeDelta);
  };

  revisionInfo.latest = clientVars.collab_client_vars.rev || -1;

  revisionInfo.createNew = function (index) {
    revisionInfo[index] = new Revision(index);
    if (index > revisionInfo.latest) {
      revisionInfo.latest = index;
    }

    return revisionInfo[index];
  };

  // assuming that there is a path from fromIndex to toIndex, and that the links
  // are laid out in a skip-list format
  revisionInfo.getPath = function (fromIndex, toIndex) {
    const changesets = [];
    const spans = [];
    const times = [];
    let elem = revisionInfo[fromIndex] || revisionInfo.createNew(fromIndex);
    if (elem.changesets.length != 0 && fromIndex != toIndex) {
      const reverse = !(fromIndex < toIndex);
      while (((elem.rev < toIndex) && !reverse) || ((elem.rev > toIndex) && reverse)) {
        let couldNotContinue = false;
        const oldRev = elem.rev;

        for (let i = reverse ? elem.changesets.length - 1 : 0;
          reverse ? i >= 0 : i < elem.changesets.length;
          i += reverse ? -1 : 1) {
          if (((elem.changesets[i].deltaRev < 0) && !reverse) || ((elem.changesets[i].deltaRev > 0) && reverse)) {
            couldNotContinue = true;
            break;
          }

          if (((elem.rev + elem.changesets[i].deltaRev <= toIndex) && !reverse) || ((elem.rev + elem.changesets[i].deltaRev >= toIndex) && reverse)) {
            const topush = elem.changesets[i];
            changesets.push(topush.getValue());
            spans.push(elem.changesets[i].deltaRev);
            times.push(topush.deltaTime);
            elem = revisionInfo[elem.rev + elem.changesets[i].deltaRev];
            break;
          }
        }

        if (couldNotContinue || oldRev == elem.rev) break;
      }
    }

    let status = 'partial';
    if (elem.rev == toIndex) status = 'complete';

    return {
      fromRev: fromIndex,
      rev: elem.rev,
      status,
      changesets,
      spans,
      times,
    };
  };
}

exports.loadBroadcastRevisionsJS = loadBroadcastRevisionsJS;