Pad.ts

'use strict';
import {Database} from "ueberdb2";
import {AChangeSet, APool, AText} from "../types/PadType";
import {MapArrayType} from "../types/MapType";

/**
 * The pad object, defined with joose
 */

import AttributeMap from '../../static/js/AttributeMap';
import {applyToAText, checkRep, copyAText, deserializeOps, makeAText, makeSplice, opsFromAText, pack, unpack} from '../../static/js/Changeset';
import ChatMessage from '../../static/js/ChatMessage';
import AttributePool from '../../static/js/AttributePool';
const Stream = require('../utils/Stream');
const assert = require('assert').strict;
const db = require('./DB');
import settings from '../utils/Settings';
const authorManager = require('./AuthorManager');
const padDeletionManager = require('./PadDeletionManager');
const padManager = require('./PadManager');
const padMessageHandler = require('../handler/PadMessageHandler');
const groupManager = require('./GroupManager');
const CustomError = require('../utils/customError');
import readOnlyManager from './ReadOnlyManager';
import {HistoricalAuthorDataCache} from './HistoricalAuthorDataCache';
import log4js from 'log4js';
const padMessageLogger = log4js.getLogger('message');
import randomString from '../utils/randomstring';
const hooks = require('../../static/js/pluginfw/hooks');
import pad_utils from "../../static/js/pad_utils";
import {SmartOpAssembler} from "../../static/js/SmartOpAssembler";
import {timesLimit} from "async";

type PadViewSettings = {
  showAuthorColors: boolean;
  showLineNumbers: boolean;
  rtlIsTrue: boolean;
  padFontFamily: string;
  fadeInactiveAuthorColors: boolean;
};

type PadSettings = {
  enforceSettings: boolean;
  showChat: boolean;
  alwaysShowChat: boolean;
  chatAndUsers: boolean;
  lang: string | null;
  view: PadViewSettings;
  // Plugin-namespaced pad-wide options ride alongside the core keys.
  // Anything matching /^ep_[a-z0-9_]+$/ is preserved verbatim by
  // normalizePadSettings so plugins can use the existing padoptions
  // broadcast/persist rail without forking their own transport.
  [pluginKey: string]: any;
};

const PLUGIN_KEY_RE = /^ep_[a-z0-9_]+$/;
// Per-key serialized JSON size cap: ~64 KB. Pad-wide settings are persisted
// with the pad and broadcast to every connected client on every change, so
// plugins must keep their values small. A misbehaving plugin shouldn't bloat
// the pad payload or the broadcast.
const PLUGIN_KEY_MAX_BYTES = 64 * 1024;
// Combined ep_* size cap: ~256 KB. Same rationale, aggregated.
const PLUGIN_TOTAL_MAX_BYTES = 256 * 1024;

// Returns true iff `v` round-trips through JSON.stringify cleanly (no
// functions, symbols, BigInt, or circular references) and serializes to at
// most `maxBytes` UTF-8 bytes. Returns the serialized length on success so
// callers can enforce a cumulative cap without serializing twice.
const validatePluginValue = (
    key: string, value: unknown, maxBytes: number): {ok: true, bytes: number} | {ok: false, reason: string} => {
  let serialized: string;
  try {
    serialized = JSON.stringify(value);
  } catch (e: any) {
    return {ok: false, reason: `JSON.stringify failed: ${e && e.message || e}`};
  }
  if (serialized === undefined) {
    // JSON.stringify returns undefined for top-level functions/undefined.
    return {ok: false, reason: 'value is not JSON-serializable (function/undefined)'};
  }
  const bytes = Buffer.byteLength(serialized, 'utf8');
  if (bytes > maxBytes) {
    return {ok: false, reason: `serialized size ${bytes}B exceeds per-key cap ${maxBytes}B`};
  }
  return {ok: true, bytes};
};

/**
 * Copied from the Etherpad source code. It converts Windows line breaks to Unix
 * line breaks and convert Tabs to spaces
 * @param {String} txt The text to clean
 * @returns {String} The cleaned text
 */
exports.cleanText = (txt:string): string => txt.replace(/\r\n/g, '\n')
    .replace(/\r/g, '\n')
    .replace(/\t/g, '        ');

class Pad {
  private db: Database;
  private atext: AText;
  private pool: AttributePool;
  private head: number;
    private chatHead: number;
    private publicStatus: boolean;
    private id: string;
    private savedRevisions: any[];
    private padSettings: PadSettings;
    // Per-pad cache for handleClientReady's historicalAuthorData map. Lazily
    // initialised on first call so we don't touch authorManager during pad
    // construction. See HistoricalAuthorDataCache for the rationale (#7756).
    private historicalAuthorDataCache: HistoricalAuthorDataCache | null = null;
  /**
   * @param id
   * @param [database] - Database object to access this pad's records (and only this pad's records;
   *     the shared global Etherpad database object is still used for all other pad accesses, such
   *     as copying the pad). Defaults to the shared global Etherpad database object. This parameter
   *     can be used to shard pad storage across multiple database backends, to put each pad in its
   *     own database table, or to validate imported pad data before it is written to the database.
   */
  constructor(id:string, database = db) {
    this.db = database;
    this.atext = makeAText('\n');
    this.pool = new AttributePool();
    this.head = -1;
    this.chatHead = -1;
    this.publicStatus = false;
    this.id = id;
    this.savedRevisions = [];
    this.padSettings = Pad.normalizePadSettings();
  }

  static normalizePadSettings(rawPadSettings: any = {}): PadSettings {
    const rawView = rawPadSettings.view ?? {};
    const result: PadSettings = {
      enforceSettings: !!rawPadSettings.enforceSettings,
      showChat: rawPadSettings.showChat == null ? settings.padOptions.showChat !== false :
        !!rawPadSettings.showChat,
      alwaysShowChat: !!rawPadSettings.alwaysShowChat,
      chatAndUsers: !!rawPadSettings.chatAndUsers,
      // Default to null (not 'en') so the client's l10n auto-detect chain
      // (cookie -> navigator.language -> 'en' fallback) runs. Hardcoding 'en'
      // forces English on every pad regardless of the browser's Accept-Language
      // and broke #7586 (German system saw English pad UI in v2.7.0).
      lang: typeof rawPadSettings.lang === 'string' ? rawPadSettings.lang : null,
      view: {
        showAuthorColors: rawView.showAuthorColors == null ? true : !!rawView.showAuthorColors,
        showLineNumbers: rawView.showLineNumbers == null ?
          settings.padOptions.showLineNumbers !== false : !!rawView.showLineNumbers,
        rtlIsTrue: !!rawView.rtlIsTrue,
        padFontFamily: typeof rawView.padFontFamily === 'string' ? rawView.padFontFamily : '',
        fadeInactiveAuthorColors: rawView.fadeInactiveAuthorColors == null ?
          settings.padOptions.fadeInactiveAuthorColors !== false :
          !!rawView.fadeInactiveAuthorColors,
      },
    };
    if (settings.enablePluginPadOptions) {
      let totalBytes = 0;
      for (const [k, v] of Object.entries(rawPadSettings)) {
        if (!PLUGIN_KEY_RE.test(k)) continue;
        const check = validatePluginValue(k, v, PLUGIN_KEY_MAX_BYTES);
        if (!check.ok) {
          // Drop and log. Persistence/broadcast still rejects the value, but
          // the rest of the settings round-trip cleanly.
          console.warn(`[normalizePadSettings] dropping ${k}: ${check.reason}`);
          continue;
        }
        if (totalBytes + check.bytes > PLUGIN_TOTAL_MAX_BYTES) {
          console.warn(
              `[normalizePadSettings] dropping ${k}: combined ep_* size ` +
              `would exceed cap ${PLUGIN_TOTAL_MAX_BYTES}B`);
          continue;
        }
        totalBytes += check.bytes;
        result[k] = v;
      }
    }
    return result;
  }

  apool() {
    return this.pool;
  }

  getHeadRevisionNumber() {
    return this.head;
  }

  getSavedRevisionsNumber() {
    return this.savedRevisions.length;
  }

  getSavedRevisionsList() {
    const savedRev = this.savedRevisions.map((rev) => rev.revNum);
    savedRev.sort((a, b) => a - b);
    return savedRev;
  }

  getPublicStatus() {
    return this.publicStatus;
  }

  getPadSettings() {
    return Pad.normalizePadSettings(this.padSettings);
  }

  setPadSettings(rawPadSettings: any) {
    const nextPadSettings = {
      ...this.getPadSettings(),
      ...rawPadSettings,
      view: {
        ...this.getPadSettings().view,
        ...(rawPadSettings?.view ?? {}),
      },
    };
    this.padSettings = Pad.normalizePadSettings(nextPadSettings);
  }

  /**
   * Appends a new revision
   * @param {Object} aChangeset The changeset to append to the pad
   * @param {String} authorId The id of the author
   * @return {Promise<number|string>}
   */
  async appendRevision(aChangeset:string, authorId = '') {
    const newAText = applyToAText(aChangeset, this.atext, this.pool);
    if (newAText.text === this.atext.text && newAText.attribs === this.atext.attribs &&
        this.head !== -1) {
      return this.head;
    }
    copyAText(newAText, this.atext);

    const newRev = ++this.head;

    // ex. getNumForAuthor
    if (authorId !== '') this.pool.putAttrib(['author', authorId]);

    const hook = this.head === 0 ? 'padCreate' : 'padUpdate';
    await Promise.all([
      // @ts-ignore
      this.db.set(`pad:${this.id}:revs:${newRev}`, {
        changeset: aChangeset,
        meta: {
          author: authorId,
          timestamp: Date.now(),
          ...newRev === this.getKeyRevisionNumber(newRev) ? {
            pool: this.pool,
            atext: this.atext,
          } : {},
        },
      }),
      this.saveToDatabase(),
      authorId && authorManager.addPad(authorId, this.id),
      hooks.aCallAll(hook, {
        pad: this,
        padId: this.id,
        authorId,
        get author() {
          pad_utils.warnDeprecated(`${hook} hook author context is deprecated; use authorId instead`);
          return this.authorId;
        },
        set author(authorId) {
          pad_utils.warnDeprecated(`${hook} hook author context is deprecated; use authorId instead`);
          this.authorId = authorId;
        },
        ...this.head === 0 ? {} : {
          revs: newRev,
          changeset: aChangeset,
        },
      }),
    ]);
    return newRev;
  }

  toJSON() {
    const o:Pad = {...this, pool: this.pool.toJsonable()};
    // @ts-ignore
    delete o.db;
    // @ts-ignore
    delete o.id;
    return o;
  }

  // save all attributes to the database
  async saveToDatabase() {
    // @ts-ignore
    await this.db.set(`pad:${this.id}`, this);
  }

  // get time of last edit (changeset application)
  async getLastEdit() {
    const revNum = this.getHeadRevisionNumber();
    // @ts-ignore
    return await this.db.getSub(`pad:${this.id}:revs:${revNum}`, ['meta', 'timestamp']);
  }

  async getRevisionChangeset(revNum: number) {
    // @ts-ignore
    return await this.db.getSub(`pad:${this.id}:revs:${revNum}`, ['changeset']);
  }

  async getRevisionAuthor(revNum: number) {
    // @ts-ignore
    return await this.db.getSub(`pad:${this.id}:revs:${revNum}`, ['meta', 'author']) ?? '';
  }

  async getRevisionDate(revNum: number) {
    // @ts-ignore
    return await this.db.getSub(`pad:${this.id}:revs:${revNum}`, ['meta', 'timestamp']);
  }

  /**
   * @param {number} revNum - Must be a key revision number (see `getKeyRevisionNumber`).
   * @returns The attribute text stored at `revNum`.
   */
  async _getKeyRevisionAText(revNum: number) {
    // @ts-ignore
    return await this.db.getSub(`pad:${this.id}:revs:${revNum}`, ['meta', 'atext']);
  }

  /**
   * Returns all authors that worked on this pad
   * @return {[String]} The id of authors who contributed to this pad
   */
  getAllAuthors() {
    const authorIds = [];

    for (const key in this.pool.numToAttrib) {
      if (this.pool.numToAttrib[key][0] === 'author' && this.pool.numToAttrib[key][1] !== '') {
        authorIds.push(this.pool.numToAttrib[key][1]);
      }
    }

    return authorIds;
  }

  /**
   * Returns the `{authorId -> {name, colorId}}` map used by handleClientReady
   * to populate clientVars.collab_client_vars.historicalAuthorData. Cached
   * per pad with a short TTL so a burst of simultaneous joins share one
   * computation. Writes from `authorManager.setAuthorName` /
   * `setAuthorColorId` become visible within at most the cache TTL (5s).
   */
  async getHistoricalAuthorData(): Promise<{[authorId: string]: {name: string; colorId: string}}> {
    if (this.historicalAuthorDataCache == null) {
      this.historicalAuthorDataCache = new HistoricalAuthorDataCache(
        () => this.getAllAuthors(),
        (id: string) => authorManager.getAuthor(id),
        5_000,
        Date.now,
        (id: string) => {
          // Preserves the explicit error log emitted by the previous inline
          // Promise.all loop in handleClientReady before this cache landed.
          // Don't drop missing-author logs silently — they point at
          // https://github.com/ether/etherpad-lite/issues/2802.
          padMessageLogger.error(
            `There is no author for authorId: ${id}. ` +
            'This is possibly related to https://github.com/ether/etherpad-lite/issues/2802');
        },
      );
    }
    return this.historicalAuthorDataCache.get();
  }

  async getInternalRevisionAText(targetRev: number) {
    const keyRev = this.getKeyRevisionNumber(targetRev);
    const headRev = this.getHeadRevisionNumber();
    if (targetRev > headRev) targetRev = headRev;
    const [keyAText, changesets] = await Promise.all([
      this._getKeyRevisionAText(keyRev),
      Promise.all(
          Stream.range(keyRev + 1, targetRev + 1).map(this.getRevisionChangeset.bind(this))),
    ]);
    const apool = this.apool();
    let atext = keyAText;
    for (const cs of changesets) atext = applyToAText(cs, atext, apool);
    return atext;
  }

  async getRevision(revNum: number) {
    return await this.db.get(`pad:${this.id}:revs:${revNum}`);
  }

  async getAllAuthorColors() {
    const authorIds = this.getAllAuthors();
    const returnTable:MapArrayType<string> = {};
    const colorPalette = authorManager.getColorPalette();

    await Promise.all(
        authorIds.map((authorId) => authorManager.getAuthorColorId(authorId).then((colorId:string) => {
          // colorId might be a hex color or an number out of the palette
          returnTable[authorId] = colorPalette[colorId] || colorId;
        })));

    return returnTable;
  }

  getValidRevisionRange(startRev: any, endRev:any) {
    startRev = parseInt(startRev, 10);
    const head = this.getHeadRevisionNumber();
    endRev = endRev ? parseInt(endRev, 10) : head;

    if (isNaN(startRev) || startRev < 0 || startRev > head) {
      startRev = null;
    }

    if (isNaN(endRev) || endRev < startRev) {
      endRev = null;
    } else if (endRev > head) {
      endRev = head;
    }

    if (startRev != null && endRev != null) {
      return {startRev, endRev};
    }
    return null;
  }

  getKeyRevisionNumber(revNum: number) {
    return Math.floor(revNum / 100) * 100;
  }

  /**
   * @returns {string} The pad's text.
   */
  text(): string {
    return this.atext.text;
  }

  /**
   * Splices text into the pad. If the result of the splice does not end with a newline, one will be
   * automatically appended.
   *
   * @param {number} start - Location in pad text to start removing and inserting characters. Must
   *     be a non-negative integer less than or equal to `this.text().length`.
   * @param {number} ndel - Number of characters to remove starting at `start`. Must be a
   *     non-negative integer less than or equal to `this.text().length - start`.
   * @param {string} ins - New text to insert at `start` (after the `ndel` characters are deleted).
   * @param {string} [authorId] - Author ID of the user making the change (if applicable).
   */
  async spliceText(start:number, ndel:number, ins: string, authorId: string = '') {
    if (start < 0) throw new RangeError(`start index must be non-negative (is ${start})`);
    if (ndel < 0) throw new RangeError(`characters to delete must be non-negative (is ${ndel})`);
    const orig = this.text();
    assert(orig.endsWith('\n'));
    if (start + ndel > orig.length) throw new RangeError('start/delete past the end of the text');
    ins = exports.cleanText(ins);
    const willEndWithNewline =
        start + ndel < orig.length || // Keeping last char (which is guaranteed to be a newline).
        ins.endsWith('\n') ||
        (!ins && start > 0 && orig[start - 1] === '\n');
    if (!willEndWithNewline) ins += '\n';
    if (ndel === 0 && ins.length === 0) return;
    const attribs = authorId ? [['author', authorId] as [string, string]] : undefined;
    const changeset = makeSplice(orig, start, ndel, ins, attribs, this.pool);
    await this.appendRevision(changeset, authorId);
  }

  /**
   * Replaces the pad's text with new text.
   *
   * @param {string} newText - The pad's new text. If this string does not end with a newline, one
   *     will be automatically appended.
   * @param {string} [authorId] - The author ID of the user that initiated the change, if
   *     applicable.
   */
  async setText(newText: string, authorId = '') {
    await this.spliceText(0, this.text().length, newText, authorId);
  }

  /**
   * Appends text to the pad.
   *
   * @param {string} newText - Text to insert just BEFORE the pad's existing terminating newline.
   * @param {string} [authorId] - The author ID of the user that initiated the change, if
   *     applicable.
   */
  async appendText(newText:string, authorId = '') {
    await this.spliceText(this.text().length - 1, 0, newText, authorId);
  }

  /**
   * Adds a chat message to the pad, including saving it to the database.
   *
   * @param {(ChatMessage|string)} msgOrText - Either a chat message object (recommended) or a
   *     string containing the raw text of the user's chat message (deprecated).
   * @param {?string} [authorId] - The user's author ID. Deprecated; use `msgOrText.authorId`
   *     instead.
   * @param {?number} [time] - Message timestamp (milliseconds since epoch). Deprecated; use
   *     `msgOrText.time` instead.
   */
  async appendChatMessage(msgOrText: string| ChatMessage, authorId = null, time = null) {
    const msg =
          msgOrText instanceof ChatMessage ? msgOrText : new ChatMessage(msgOrText, authorId, time);
    this.chatHead++;
    await Promise.all([
      // Don't save the display name in the database because the user can change it at any time. The
      // `displayName` property will be populated with the current value when the message is read
      // from the database.
      this.db.set(`pad:${this.id}:chat:${this.chatHead}`, {...msg, displayName: undefined}),
      this.saveToDatabase(),
    ]);
  }

  /**
   * @param {number} entryNum - ID of the desired chat message.
   * @returns {?ChatMessage}
   */
  async getChatMessage(entryNum: number) {
    const entry = await this.db.get(`pad:${this.id}:chat:${entryNum}`);
    if (entry == null) return null;
    const message = ChatMessage.fromObject(entry);
    message.displayName = await authorManager.getAuthorName(message.authorId);
    return message;
  }

  /**
   * @param {number} start - ID of the first desired chat message.
   * @param {number} end - ID of the last desired chat message.
   * @returns {ChatMessage[]} Any existing messages with IDs between `start` (inclusive) and `end`
   *     (inclusive), in order. Note: `start` and `end` form a closed interval, not a half-open
   *     interval as is typical in code.
   */
  async getChatMessages(start: string, end: number) {
    const entries =
        await Promise.all(Stream.range(start, end + 1).map(this.getChatMessage.bind(this)));

    // sort out broken chat entries
    // it looks like in happened in the past that the chat head was
    // incremented, but the chat message wasn't added
    return entries.filter((entry) => {
      const pass = (entry != null);
      if (!pass) {
        console.warn(`WARNING: Found broken chat entry in pad ${this.id}`);
      }
      return pass;
    });
  }

  async init(text:string, authorId = '') {
    // try to load the pad
    const value = await this.db.get(`pad:${this.id}`);

    // if this pad exists, load it
    if (value != null) {
      Object.assign(this, value);
      if ('pool' in value) this.pool = new AttributePool().fromJsonable(value.pool);
    } else {
      if (text == null) {
        const context = {pad: this, authorId, type: 'text', content: settings.defaultPadText};
        await hooks.aCallAll('padDefaultContent', context);
        if (context.type !== 'text') throw new Error(`unsupported content type: ${context.type}`);
        text = exports.cleanText(context.content);
      }
      const firstAttribs = authorId ? [['author', authorId] as [string, string]] : undefined;
      const firstChangeset = makeSplice('\n', 0, 0, text, firstAttribs, this.pool);
      await this.appendRevision(firstChangeset, authorId);
    }
    this.padSettings = Pad.normalizePadSettings(this.padSettings);
    await hooks.aCallAll('padLoad', {pad: this});
  }

  async copy(destinationID: string, force: boolean) {
    // Kick everyone from this pad.
    // This was commented due to https://github.com/ether/etherpad-lite/issues/3183.
    // Do we really need to kick everyone out?
    // padMessageHandler.kickSessionsFromPad(sourceID);

    // flush the source pad:
    await this.saveToDatabase();

    // if it's a group pad, let's make sure the group exists.
    const destGroupID = await this.checkIfGroupExistAndReturnIt(destinationID);

    // if force is true and already exists a Pad with the same id, remove that Pad
    await this.removePadIfForceIsTrueAndAlreadyExist(destinationID, force);

    const copyRecord = async (keySuffix: string) => {
      const val = await this.db.get(`pad:${this.id}${keySuffix}`);
      await db.set(`pad:${destinationID}${keySuffix}`, val);
    };

    const promises = (function* () {
      yield copyRecord('');
      // @ts-ignore
      yield* Stream.range(0, this.head + 1).map((i) => copyRecord(`:revs:${i}`));
      // @ts-ignore
      yield* Stream.range(0, this.chatHead + 1).map((i) => copyRecord(`:chat:${i}`));
      // @ts-ignore
      yield this.copyAuthorInfoToDestinationPad(destinationID);
      if (destGroupID) yield db.setSub(`group:${destGroupID}`, ['pads', destinationID], 1);
    }).call(this);
    for (const p of new Stream(promises).batch(100).buffer(99)) await p;

    // Initialize the new pad (will update the listAllPads cache)
    const dstPad = await padManager.getPad(destinationID, null);

    // let the plugins know the pad was copied
    await hooks.aCallAll('padCopy', {
      get originalPad() {
        pad_utils.warnDeprecated('padCopy originalPad context property is deprecated; use srcPad instead');
        return this.srcPad;
      },
      get destinationID() {
        pad_utils.warnDeprecated(
            'padCopy destinationID context property is deprecated; use dstPad.id instead');
        return this.dstPad.id;
      },
      srcPad: this,
      dstPad,
    });

    return {padID: destinationID};
  }

  async checkIfGroupExistAndReturnIt(destinationID: string) {
    let destGroupID:false|string = false;

    if (destinationID.indexOf('$') >= 0) {
      destGroupID = destinationID.split('$')[0];
      const groupExists = await groupManager.doesGroupExist(destGroupID);

      // group does not exist
      if (!groupExists) {
        throw new CustomError('groupID does not exist for destinationID', 'apierror');
      }
    }
    return destGroupID;
  }

  async removePadIfForceIsTrueAndAlreadyExist(destinationID: string, force: boolean|string) {
    // if the pad exists, we should abort, unless forced.
    const exists = await padManager.doesPadExist(destinationID);

    // allow force to be a string
    if (typeof force === 'string') {
      force = (force.toLowerCase() === 'true');
    } else {
      force = !!force;
    }

    if (exists) {
      if (!force) {
        console.error('erroring out without force');
        throw new CustomError('destinationID already exists', 'apierror');
      }

      // exists and forcing
      const pad = await padManager.getPad(destinationID);
      await pad.remove();
    }
  }

  async copyAuthorInfoToDestinationPad(destinationID: string) {
    // add the new sourcePad to all authors who contributed to the old one
    await Promise.all(this.getAllAuthors().map(
        (authorID) => authorManager.addPad(authorID, destinationID)));
  }

  async copyPadWithoutHistory(destinationID: string, force: string|boolean, authorId = '') {
    // flush the source pad
    this.saveToDatabase();

    // if it's a group pad, let's make sure the group exists.
    const destGroupID = await this.checkIfGroupExistAndReturnIt(destinationID);

    // if force is true and already exists a Pad with the same id, remove that Pad
    await this.removePadIfForceIsTrueAndAlreadyExist(destinationID, force);

    await this.copyAuthorInfoToDestinationPad(destinationID);

    // Group pad? Add it to the group's list
    if (destGroupID) {
      await db.setSub(`group:${destGroupID}`, ['pads', destinationID], 1);
    }

    // initialize the pad with a new line to avoid getting the defaultText
    const dstPad = await padManager.getPad(destinationID, '\n', authorId);
    dstPad.pool = this.pool.clone();

    const oldAText = this.atext;

    // based on Changeset.makeSplice
    const assem = new SmartOpAssembler();
    for (const op of opsFromAText(oldAText)) assem.append(op);
    assem.endDocument();

    // although we have instantiated the dstPad with '\n', an additional '\n' is
    // added internally, so the pad text on the revision 0 is "\n\n"
    const oldLength = 2;

    const newLength = assem.getLengthChange();
    const newText = oldAText.text;

    // create a changeset that removes the previous text and add the newText with
    // all atributes present on the source pad
    const changeset = pack(oldLength, newLength, assem.toString(), newText);
    dstPad.appendRevision(changeset, authorId);

    await hooks.aCallAll('padCopy', {
      get originalPad() {
        pad_utils.warnDeprecated('padCopy originalPad context property is deprecated; use srcPad instead');
        return this.srcPad;
      },
      get destinationID() {
        pad_utils.warnDeprecated(
            'padCopy destinationID context property is deprecated; use dstPad.id instead');
        return this.dstPad.id;
      },
      srcPad: this,
      dstPad,
    });

    return {padID: destinationID};
  }

  async remove() {
    const padID = this.id;
    const p = [];

    // kick everyone from this pad
    padMessageHandler.kickSessionsFromPad(padID);

    // delete all relations - the original code used async.parallel but
    // none of the operations except getting the group depended on callbacks
    // so the database operations here are just started and then left to
    // run to completion

    // is it a group pad? -> delete the entry of this pad in the group
    if (padID.indexOf('$') >= 0) {
      // it is a group pad
      const groupID = padID.substring(0, padID.indexOf('$'));
      const group = await db.get(`group:${groupID}`);

      // remove the pad entry
      delete group.pads[padID];

      // set the new value
      p.push(db.set(`group:${groupID}`, group));
    }

    // remove the readonly entries
    p.push(readOnlyManager.getReadOnlyId(padID).then(async (readonlyID: string) => {
      await db.remove(`readonly2pad:${readonlyID}`);
    }));
    p.push(db.remove(`pad2readonly:${padID}`));

    // delete all chat messages
    // @ts-ignore
    p.push(timesLimit(this.chatHead + 1, 500, async (i: string) => {
      await this.db.remove(`pad:${this.id}:chat:${i}`, null);
    }));

    // delete all revisions
    // @ts-ignore
    p.push(timesLimit(this.head + 1, 500, async (i: string) => {
      await this.db.remove(`pad:${this.id}:revs:${i}`, null);
    }));

    // remove pad from all authors who contributed
    this.getAllAuthors().forEach((authorId) => {
      p.push(authorManager.removePad(authorId, padID));
    });

    // delete the pad entry and delete pad from padManager
    p.push(padManager.removePad(padID));
    p.push(padDeletionManager.removeDeletionToken(padID));
    p.push(hooks.aCallAll('padRemove', {
      get padID() {
        pad_utils.warnDeprecated('padRemove padID context property is deprecated; use pad.id instead');
        return this.pad.id;
      },
      pad: this,
    }));
    await Promise.all(p);
  }

  // set in db
  async setPublicStatus(publicStatus: boolean) {
    this.publicStatus = publicStatus;
    await this.saveToDatabase();
  }

  async addSavedRevision(revNum: string, savedById: string, label: string) {
    // if this revision is already saved, return silently
    for (const i in this.savedRevisions) {
      if (this.savedRevisions[i] && this.savedRevisions[i].revNum === revNum) {
        return;
      }
    }

    // build the saved revision object
    const savedRevision:MapArrayType<any> = {};
    savedRevision.revNum = revNum;
    savedRevision.savedById = savedById;
    savedRevision.label = label || `Revision ${revNum}`;
    savedRevision.timestamp = Date.now();
    savedRevision.id = randomString(10);

    // save this new saved revision
    this.savedRevisions.push(savedRevision);
    await this.saveToDatabase();
  }

  getSavedRevisions() {
    return this.savedRevisions;
  }

  /**
   * Asserts that all pad data is consistent. Throws if inconsistent.
   */
  async check() {
    assert(this.id != null);
    assert.equal(typeof this.id, 'string');

    const head = this.getHeadRevisionNumber();
    assert(head != null);
    assert(Number.isInteger(head));
    assert(head >= -1);

    const savedRevisionsList = this.getSavedRevisionsList();
    assert(Array.isArray(savedRevisionsList));
    assert.equal(this.getSavedRevisionsNumber(), savedRevisionsList.length);
    let prevSavedRev = null;
    for (const rev of savedRevisionsList) {
      assert(rev != null);
      assert(Number.isInteger(rev));
      assert(rev >= 0);
      assert(rev <= head);
      assert(prevSavedRev == null || rev > prevSavedRev);
      prevSavedRev = rev;
    }
    const savedRevisions = this.getSavedRevisions();
    assert(Array.isArray(savedRevisions));
    assert.equal(savedRevisions.length, savedRevisionsList.length);
    const savedRevisionsIds = new Set();
    for (const savedRev of savedRevisions) {
      assert(savedRev != null);
      assert.equal(typeof savedRev, 'object');
      assert(savedRevisionsList.includes(savedRev.revNum));
      assert(savedRev.id != null);
      assert.equal(typeof savedRev.id, 'string');
      assert(!savedRevisionsIds.has(savedRev.id));
      savedRevisionsIds.add(savedRev.id);
    }

    const pool = this.apool();
    assert(pool instanceof AttributePool);
    await pool.check();

    const authorIds = new Set();
    pool.eachAttrib((k, v) => {
      if (k === 'author' && v) authorIds.add(v);
    });
    const revs = Stream.range(0, head + 1)
        .map(async (r: number) => {
          const isKeyRev = r === this.getKeyRevisionNumber(r);
          try {
            return await Promise.all([
              r,
              this.getRevisionChangeset(r),
              this.getRevisionAuthor(r),
              this.getRevisionDate(r),
              isKeyRev,
              isKeyRev ? this._getKeyRevisionAText(r) : null,
            ]);
          } catch (err:any) {
            err.message = `(pad ${this.id} revision ${r}) ${err.message}`;
            throw err;
          }
        })
        .batch(100).buffer(99);
    let atext = makeAText('\n');
    for await (const [r, changeset, authorId, timestamp, isKeyRev, keyAText] of revs) {
      try {
        assert(authorId != null);
        assert.equal(typeof authorId, 'string');
        if (authorId) authorIds.add(authorId);
        assert(timestamp != null);
        assert.equal(typeof timestamp, 'number');
        assert(timestamp > 0);
        assert(changeset != null);
        assert.equal(typeof changeset, 'string');
        checkRep(changeset);
        const unpacked = unpack(changeset);
        let text = atext.text;
        for (const op of deserializeOps(unpacked.ops)) {
          if (['=', '-'].includes(op.opcode)) {
            assert(text.length >= op.chars);
            const consumed = text.slice(0, op.chars);
            const nlines = (consumed.match(/\n/g) || []).length;
            assert.equal(op.lines, nlines);
            if (op.lines > 0) assert(consumed.endsWith('\n'));
            text = text.slice(op.chars);
          }
          assert.equal(op.attribs, AttributeMap.fromString(op.attribs, pool).toString());
        }
        atext = applyToAText(changeset, atext, pool);
        if (isKeyRev) assert.deepEqual(keyAText, atext);
      } catch (err:any) {
        err.message = `(pad ${this.id} revision ${r}) ${err.message}`;
        throw err;
      }
    }
    assert.equal(this.text(), atext.text);
    assert.deepEqual(this.atext, atext);
    assert.deepEqual(this.getAllAuthors().sort(), [...authorIds].sort());

    assert(this.chatHead != null);
    assert(Number.isInteger(this.chatHead));
    assert(this.chatHead >= -1);
    const chats = Stream.range(0, this.chatHead + 1)
        .map(async (c: number) => {
          try {
            const msg = await this.getChatMessage(c);
            assert(msg != null);
            assert(msg instanceof ChatMessage);
          } catch (err:any) {
            err.message = `(pad ${this.id} chat message ${c}) ${err.message}`;
            throw err;
          }
        })
        .batch(100).buffer(99);
    for (const p of chats) await p;

    await hooks.aCallAll('padCheck', {pad: this});
  }
}
exports.Pad = Pad;