/*
Copyright 2024 New Vector Ltd.
Copyright 2019-2021 The Matrix.org Foundation C.I.C.

SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only
Please see LICENSE files in the repository root for full details.
*/

import { EventEmitter } from "events";
import {
    RoomMember,
    Room,
    RoomEvent,
    RoomState,
    RoomStateEvent,
    MatrixEvent,
    Direction,
    EventTimeline,
    EventTimelineSet,
    IRoomTimelineData,
    EventType,
    ClientEvent,
    MatrixClient,
    HTTPError,
    IEventWithRoomId,
    IMatrixProfile,
    IResultRoomEvents,
    SyncStateData,
    SyncState,
    TimelineIndex,
    TimelineWindow,
} from "matrix-js-sdk/src/matrix";
import { KnownMembership } from "matrix-js-sdk/src/types";
import { sleep } from "matrix-js-sdk/src/utils";
import { logger } from "matrix-js-sdk/src/logger";

import PlatformPeg from "../PlatformPeg";
import { MatrixClientPeg } from "../MatrixClientPeg";
import SettingsStore from "../settings/SettingsStore";
import { SettingLevel } from "../settings/SettingLevel";
import { ICrawlerCheckpoint, IEventAndProfile, IIndexStats, ILoadArgs, ISearchArgs } from "./BaseEventIndexManager";

// The time in ms that the crawler will wait loop iterations if there
// have not been any checkpoints to consume in the last iteration.
const CRAWLER_IDLE_TIME = 5000;

// The maximum number of events our crawler should fetch in a single crawl.
const EVENTS_PER_CRAWL = 100;

interface ICrawler {
    cancel(): void;
}

/*
 * Event indexing class that wraps the platform specific event indexing.
 */
export default class EventIndex extends EventEmitter {
    private crawlerCheckpoints: ICrawlerCheckpoint[] = [];
    private crawler: ICrawler | null = null;
    private currentCheckpoint: ICrawlerCheckpoint | null = null;

    public async init(): Promise<void> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return;

        this.crawlerCheckpoints = await indexManager.loadCheckpoints();
        logger.log("EventIndex: Loaded checkpoints", this.crawlerCheckpoints);

        this.registerListeners();
    }

    /**
     * Register event listeners that are necessary for the event index to work.
     */
    public registerListeners(): void {
        const client = MatrixClientPeg.safeGet();

        client.on(ClientEvent.Sync, this.onSync);
        client.on(RoomEvent.Timeline, this.onRoomTimeline);
        client.on(RoomEvent.TimelineReset, this.onTimelineReset);
        client.on(RoomStateEvent.Events, this.onRoomStateEvent);
    }

    /**
     * Remove the event index specific event listeners.
     */
    public removeListeners(): void {
        const client = MatrixClientPeg.get();
        if (client === null) return;

        client.removeListener(ClientEvent.Sync, this.onSync);
        client.removeListener(RoomEvent.Timeline, this.onRoomTimeline);
        client.removeListener(RoomEvent.TimelineReset, this.onTimelineReset);
        client.removeListener(RoomStateEvent.Events, this.onRoomStateEvent);
    }

    /**
     * Get crawler checkpoints for the encrypted rooms and store them in the index.
     */
    public async addInitialCheckpoints(): Promise<void> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return;
        const client = MatrixClientPeg.safeGet();
        const rooms = client.getRooms();

        const isRoomEncrypted = (room: Room): boolean => {
            return client.isRoomEncrypted(room.roomId);
        };

        // We only care to crawl the encrypted rooms, non-encrypted
        // rooms can use the search provided by the homeserver.
        const encryptedRooms = rooms.filter(isRoomEncrypted);

        logger.log("EventIndex: Adding initial crawler checkpoints");

        // Gather the prev_batch tokens and create checkpoints for
        // our message crawler.
        await Promise.all(
            encryptedRooms.map(async (room): Promise<void> => {
                const timeline = room.getLiveTimeline();
                const token = timeline.getPaginationToken(Direction.Backward);

                const backCheckpoint: ICrawlerCheckpoint = {
                    roomId: room.roomId,
                    token: token,
                    direction: Direction.Backward,
                    fullCrawl: true,
                };

                const forwardCheckpoint: ICrawlerCheckpoint = {
                    roomId: room.roomId,
                    token: token,
                    direction: Direction.Forward,
                };

                try {
                    if (backCheckpoint.token) {
                        await indexManager.addCrawlerCheckpoint(backCheckpoint);
                        this.crawlerCheckpoints.push(backCheckpoint);
                    }

                    if (forwardCheckpoint.token) {
                        await indexManager.addCrawlerCheckpoint(forwardCheckpoint);
                        this.crawlerCheckpoints.push(forwardCheckpoint);
                    }
                } catch (e) {
                    logger.log(
                        "EventIndex: Error adding initial checkpoints for room",
                        room.roomId,
                        backCheckpoint,
                        forwardCheckpoint,
                        e,
                    );
                }
            }),
        );
    }

    /*
     * The sync event listener.
     *
     * The listener has two cases:
     *     - First sync after start up, check if the index is empty, add
     *         initial checkpoints, if so. Start the crawler background task.
     *     - Every other sync, tell the event index to commit all the queued up
     *         live events
     */
    private onSync = async (state: SyncState, prevState: SyncState | null, data?: SyncStateData): Promise<void> => {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return;

        if (prevState === "PREPARED" && state === "SYNCING") {
            // If our indexer is empty we're most likely running Element the
            // first time with indexing support or running it with an
            // initial sync. Add checkpoints to crawl our encrypted rooms.
            const eventIndexWasEmpty = await indexManager.isEventIndexEmpty();
            if (eventIndexWasEmpty) await this.addInitialCheckpoints();

            this.startCrawler();
            return;
        }

        if (prevState === "SYNCING" && state === "SYNCING") {
            // A sync was done, presumably we queued up some live events,
            // commit them now.
            await indexManager.commitLiveEvents();
        }
    };

    /*
     * The Room.timeline listener.
     *
     * This listener waits for live events in encrypted rooms, if they are
     * decrypted or unencrypted we queue them to be added to the index,
     * otherwise we save their event id and wait for them in the Event.decrypted
     * listener.
     */
    private onRoomTimeline = async (
        ev: MatrixEvent,
        room: Room | undefined,
        toStartOfTimeline: boolean | undefined,
        removed: boolean,
        data: IRoomTimelineData,
    ): Promise<void> => {
        if (!room) return; // notification timeline, we'll get this event again with a room specific timeline

        const client = MatrixClientPeg.safeGet();

        // We only index encrypted rooms locally.
        if (!client.isRoomEncrypted(ev.getRoomId()!)) return;

        if (ev.isRedaction()) {
            return this.redactEvent(ev);
        }

        // If it isn't a live event or if it's redacted there's nothing to do.
        if (toStartOfTimeline || !data || !data.liveEvent || ev.isRedacted()) {
            return;
        }

        await client.decryptEventIfNeeded(ev);

        await this.addLiveEventToIndex(ev);
    };

    private onRoomStateEvent = async (ev: MatrixEvent, state: RoomState): Promise<void> => {
        if (!MatrixClientPeg.safeGet().isRoomEncrypted(state.roomId)) return;

        if (ev.getType() === EventType.RoomEncryption && !(await this.isRoomIndexed(state.roomId))) {
            logger.log("EventIndex: Adding a checkpoint for a newly encrypted room", state.roomId);
            this.addRoomCheckpoint(state.roomId, true);
        }
    };

    /*
     * Removes a redacted event from our event index.
     * We cannot rely on Room.redaction as this only fires if the redaction applied to an event the js-sdk has loaded.
     */
    private redactEvent = async (ev: MatrixEvent): Promise<void> => {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return;

        const associatedId = ev.getAssociatedId();
        if (!associatedId) return;

        try {
            await indexManager.deleteEvent(associatedId);
        } catch (e) {
            logger.log("EventIndex: Error deleting event from index", e);
        }
    };

    /*
     * The Room.timelineReset listener.
     *
     * Listens for timeline resets that are caused by a limited timeline to
     * re-add checkpoints for rooms that need to be crawled again.
     */
    private onTimelineReset = async (room: Room | undefined): Promise<void> => {
        if (!room) return;
        if (!MatrixClientPeg.safeGet().isRoomEncrypted(room.roomId)) return;

        logger.log("EventIndex: Adding a checkpoint because of a limited timeline", room.roomId);

        this.addRoomCheckpoint(room.roomId, false);
    };

    /**
     * Check if an event should be added to the event index.
     *
     * Most notably we filter events for which decryption failed, are redacted
     * or aren't of a type that we know how to index.
     *
     * @param {MatrixEvent} ev The event that should be checked.
     * @returns {bool} Returns true if the event can be indexed, false
     * otherwise.
     */
    private isValidEvent(ev: MatrixEvent): boolean {
        const isUsefulType = [EventType.RoomMessage, EventType.RoomName, EventType.RoomTopic].includes(
            ev.getType() as EventType,
        );
        const validEventType = isUsefulType && !ev.isRedacted() && !ev.isDecryptionFailure();

        let validMsgType = true;
        let hasContentValue = true;

        if (ev.getType() === EventType.RoomMessage && !ev.isRedacted()) {
            // Expand this if there are more invalid msgtypes.
            const msgtype = ev.getContent().msgtype;

            if (!msgtype) validMsgType = false;
            else validMsgType = !msgtype.startsWith("m.key.verification");

            if (!ev.getContent().body) hasContentValue = false;
        } else if (ev.getType() === EventType.RoomTopic && !ev.isRedacted()) {
            if (!ev.getContent().topic) hasContentValue = false;
        } else if (ev.getType() === EventType.RoomName && !ev.isRedacted()) {
            if (!ev.getContent().name) hasContentValue = false;
        }

        return validEventType && validMsgType && hasContentValue;
    }

    private eventToJson(ev: MatrixEvent): IEventWithRoomId {
        const e = ev.getEffectiveEvent() as any;

        if (ev.isEncrypted()) {
            // Let us store some additional data so we can re-verify the event.
            // The js-sdk checks if an event is encrypted using the algorithm,
            // the sender key and ed25519 signing key are used to find the
            // correct device that sent the event which allows us to check the
            // verification state of the event, either directly or using cross
            // signing.
            e.curve25519Key = ev.getSenderKey();
            e.ed25519Key = ev.getClaimedEd25519Key();
            e.algorithm = ev.getWireContent().algorithm;
            e.forwardingCurve25519KeyChain = ev.getForwardingCurve25519KeyChain();
        } else {
            // Make sure that unencrypted events don't contain any of that data,
            // despite what the server might give to us.
            delete e.curve25519Key;
            delete e.ed25519Key;
            delete e.algorithm;
            delete e.forwardingCurve25519KeyChain;
        }

        return e;
    }

    /**
     * Queue up live events to be added to the event index.
     *
     * @param {MatrixEvent} ev The event that should be added to the index.
     */
    private async addLiveEventToIndex(ev: MatrixEvent): Promise<void> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();

        if (!indexManager || !this.isValidEvent(ev)) return;

        const e = this.eventToJson(ev);

        const profile = {
            displayname: ev.sender?.rawDisplayName,
            avatar_url: ev.sender?.getMxcAvatarUrl(),
        };

        await indexManager.addEventToIndex(e, profile);
    }

    /**
     * Emmit that the crawler has changed the checkpoint that it's currently
     * handling.
     */
    private emitNewCheckpoint(): void {
        this.emit("changedCheckpoint", this.currentRoom());
    }

    private async addEventsFromLiveTimeline(timeline: EventTimeline): Promise<void> {
        const events = timeline.getEvents();

        for (let i = 0; i < events.length; i++) {
            const ev = events[i];
            await this.addLiveEventToIndex(ev);
        }
    }

    private async addRoomCheckpoint(roomId: string, fullCrawl = false): Promise<void> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return;
        const client = MatrixClientPeg.safeGet();
        const room = client.getRoom(roomId);

        if (!room) return;

        const timeline = room.getLiveTimeline();
        const token = timeline.getPaginationToken(Direction.Backward);

        if (!token) {
            // The room doesn't contain any tokens, meaning the live timeline
            // contains all the events, add those to the index.
            await this.addEventsFromLiveTimeline(timeline);
            return;
        }

        const checkpoint = {
            roomId: room.roomId,
            token: token,
            fullCrawl: fullCrawl,
            direction: Direction.Backward,
        };

        logger.log("EventIndex: Adding checkpoint", checkpoint);

        try {
            await indexManager.addCrawlerCheckpoint(checkpoint);
        } catch (e) {
            logger.log("EventIndex: Error adding new checkpoint for room", room.roomId, checkpoint, e);
        }

        this.crawlerCheckpoints.push(checkpoint);
    }

    /**
     * The main crawler loop.
     *
     * Goes through crawlerCheckpoints and fetches events from the server to be
     * added to the EventIndex.
     *
     * If a /room/{roomId}/messages request doesn't contain any events, stop the
     * crawl, otherwise create a new checkpoint and push it to the
     * crawlerCheckpoints queue, so we go through them in a round-robin way.
     */
    private async crawlerFunc(): Promise<void> {
        let cancelled = false;

        const client = MatrixClientPeg.safeGet();
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return;

        this.crawler = {
            cancel: () => {
                cancelled = true;
            },
        };

        let idle = false;

        while (!cancelled) {
            let sleepTime = SettingsStore.getValueAt(SettingLevel.DEVICE, "crawlerSleepTime");

            // Don't let the user configure a lower sleep time than 100 ms.
            sleepTime = Math.max(sleepTime, 100);

            if (idle) {
                sleepTime = CRAWLER_IDLE_TIME;
            }

            if (this.currentCheckpoint !== null) {
                this.currentCheckpoint = null;
                this.emitNewCheckpoint();
            }

            await sleep(sleepTime);

            if (cancelled) {
                break;
            }

            const checkpoint = this.crawlerCheckpoints.shift();

            /// There is no checkpoint available currently, one may appear if
            // a sync with limited room timelines happens, so go back to sleep.
            if (checkpoint === undefined) {
                idle = true;
                continue;
            }

            this.currentCheckpoint = checkpoint;
            this.emitNewCheckpoint();

            idle = false;

            // We have a checkpoint, let us fetch some messages, again, very
            // conservatively to not bother our homeserver too much.
            const eventMapper = client.getEventMapper({ preventReEmit: true });
            // TODO we need to ensure to use member lazy loading with this
            // request so we get the correct profiles.
            let res: Awaited<ReturnType<MatrixClient["createMessagesRequest"]>>;

            try {
                res = await client.createMessagesRequest(
                    checkpoint.roomId,
                    checkpoint.token,
                    EVENTS_PER_CRAWL,
                    checkpoint.direction,
                );
            } catch (e) {
                if (e instanceof HTTPError && e.httpStatus === 403) {
                    logger.log(
                        "EventIndex: Removing checkpoint as we don't have ",
                        "permissions to fetch messages from this room.",
                        checkpoint,
                    );
                    try {
                        await indexManager.removeCrawlerCheckpoint(checkpoint);
                    } catch (e) {
                        logger.log("EventIndex: Error removing checkpoint", checkpoint, e);
                        // We don't push the checkpoint here back, it will
                        // hopefully be removed after a restart. But let us
                        // ignore it for now as we don't want to hammer the
                        // endpoint.
                    }
                    continue;
                }

                logger.log("EventIndex: Error crawling using checkpoint:", checkpoint, ",", e);
                this.crawlerCheckpoints.push(checkpoint);
                continue;
            }

            if (cancelled) {
                this.crawlerCheckpoints.push(checkpoint);
                break;
            }

            if (res.chunk.length === 0) {
                logger.log("EventIndex: Done with the checkpoint", checkpoint);
                // We got to the start/end of our timeline, lets just
                // delete our checkpoint and go back to sleep.
                try {
                    await indexManager.removeCrawlerCheckpoint(checkpoint);
                } catch (e) {
                    logger.log("EventIndex: Error removing checkpoint", checkpoint, e);
                }
                continue;
            }

            // Convert the plain JSON events into Matrix events so they get
            // decrypted if necessary.
            const matrixEvents = res.chunk.map(eventMapper);
            let stateEvents: MatrixEvent[] = [];
            if (res.state !== undefined) {
                stateEvents = res.state.map(eventMapper);
            }

            const profiles: Record<string, IMatrixProfile> = {};

            stateEvents.forEach((ev) => {
                if (ev.getContent().membership === KnownMembership.Join) {
                    profiles[ev.getSender()!] = {
                        displayname: ev.getContent().displayname,
                        avatar_url: ev.getContent().avatar_url,
                    };
                }
            });

            const decryptionPromises = matrixEvents
                .filter((event) => event.isEncrypted())
                .map((event) => {
                    return client.decryptEventIfNeeded(event, { emit: false });
                });

            // Let us wait for all the events to get decrypted.
            await Promise.all(decryptionPromises);

            // TODO if there are no events at this point we're missing a lot
            // decryption keys, do we want to retry this checkpoint at a later
            // stage?
            const filteredEvents = matrixEvents.filter(this.isValidEvent);

            // Collect the redaction events, so we can delete the redacted events from the index.
            const redactionEvents = matrixEvents.filter((ev) => ev.isRedaction());

            // Let us convert the events back into a format that EventIndex can
            // consume.
            const events = filteredEvents.map((ev) => {
                const e = this.eventToJson(ev);

                let profile: IMatrixProfile = {};
                if (e.sender in profiles) profile = profiles[e.sender];
                const object = {
                    event: e,
                    profile: profile,
                };
                return object;
            });

            let newCheckpoint: ICrawlerCheckpoint | null = null;

            // The token can be null for some reason. Don't create a checkpoint
            // in that case since adding it to the db will fail.
            if (res.end) {
                // Create a new checkpoint so we can continue crawling the room
                // for messages.
                newCheckpoint = {
                    roomId: checkpoint.roomId,
                    token: res.end,
                    fullCrawl: checkpoint.fullCrawl,
                    direction: checkpoint.direction,
                };
            }

            try {
                for (let i = 0; i < redactionEvents.length; i++) {
                    const ev = redactionEvents[i];
                    const eventId = ev.getAssociatedId();

                    if (eventId) {
                        await indexManager.deleteEvent(eventId);
                    } else {
                        logger.warn("EventIndex: Redaction event doesn't contain a valid associated event id", ev);
                    }
                }

                const eventsAlreadyAdded = await indexManager.addHistoricEvents(events, newCheckpoint, checkpoint);

                // We didn't get a valid new checkpoint from the server, nothing
                // to do here anymore.
                if (!newCheckpoint) {
                    logger.log(
                        "EventIndex: The server didn't return a valid ",
                        "new checkpoint, not continuing the crawl.",
                        checkpoint,
                    );
                    continue;
                }

                // If all events were already indexed we assume that we caught
                // up with our index and don't need to crawl the room further.
                // Let us delete the checkpoint in that case, otherwise push
                // the new checkpoint to be used by the crawler.
                if (eventsAlreadyAdded === true && newCheckpoint.fullCrawl !== true) {
                    logger.log(
                        "EventIndex: Checkpoint had already all events",
                        "added, stopping the crawl",
                        checkpoint,
                    );
                    await indexManager.removeCrawlerCheckpoint(newCheckpoint);
                } else {
                    if (eventsAlreadyAdded === true) {
                        logger.log(
                            "EventIndex: Checkpoint had already all events",
                            "added, but continuing due to a full crawl",
                            checkpoint,
                        );
                    }
                    this.crawlerCheckpoints.push(newCheckpoint);
                }
            } catch (e) {
                logger.log("EventIndex: Error during a crawl", e);
                // An error occurred, put the checkpoint back so we
                // can retry.
                this.crawlerCheckpoints.push(checkpoint);
            }
        }

        this.crawler = null;
    }

    /**
     * Start the crawler background task.
     */
    public startCrawler(): void {
        if (this.crawler !== null) return;
        this.crawlerFunc();
    }

    /**
     * Stop the crawler background task.
     */
    public stopCrawler(): void {
        if (this.crawler === null) return;
        this.crawler.cancel();
    }

    /**
     * Close the event index.
     *
     * This removes all the MatrixClient event listeners, stops the crawler
     * task, and closes the index.
     */
    public async close(): Promise<void> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        this.removeListeners();
        this.stopCrawler();
        await indexManager?.closeEventIndex();
    }

    /**
     * Search the event index using the given term for matching events.
     *
     * @param {ISearchArgs} searchArgs The search configuration for the search,
     * sets the search term and determines the search result contents.
     *
     * @return {Promise<IResultRoomEvents[]>} A promise that will resolve to an array
     * of search results once the search is done.
     */
    public async search(searchArgs: ISearchArgs): Promise<IResultRoomEvents | undefined> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        return indexManager?.searchEventIndex(searchArgs);
    }

    /**
     * Load events that contain URLs from the event index.
     *
     * @param {Room} room The room for which we should fetch events containing
     * URLs
     *
     * @param {number} limit The maximum number of events to fetch.
     *
     * @param {string} fromEvent From which event should we continue fetching
     * events from the index. This is only needed if we're continuing to fill
     * the timeline, e.g. if we're paginating. This needs to be set to a event
     * id of an event that was previously fetched with this function.
     *
     * @param {string} direction The direction in which we will continue
     * fetching events. EventTimeline.BACKWARDS to continue fetching events that
     * are older than the event given in fromEvent, EventTimeline.FORWARDS to
     * fetch newer events.
     *
     * @returns {Promise<MatrixEvent[]>} Resolves to an array of events that
     * contain URLs.
     */
    public async loadFileEvents(
        room: Room,
        limit = 10,
        fromEvent?: string,
        direction: string = EventTimeline.BACKWARDS,
    ): Promise<MatrixEvent[]> {
        const client = MatrixClientPeg.safeGet();
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        if (!indexManager) return [];

        const loadArgs: ILoadArgs = {
            roomId: room.roomId,
            limit: limit,
        };

        if (fromEvent) {
            loadArgs.fromEvent = fromEvent;
            loadArgs.direction = direction;
        }

        let events: IEventAndProfile[];

        // Get our events from the event index.
        try {
            events = await indexManager.loadFileEvents(loadArgs);
        } catch (e) {
            logger.log("EventIndex: Error getting file events", e);
            return [];
        }

        const eventMapper = client.getEventMapper();

        // Turn the events into MatrixEvent objects.
        const matrixEvents = events.map((e) => {
            const matrixEvent = eventMapper(e.event);

            const member = new RoomMember(room.roomId, matrixEvent.getSender()!);

            // We can't really reconstruct the whole room state from our
            // EventIndex to calculate the correct display name. Use the
            // disambiguated form always instead.
            member.name = e.profile.displayname + " (" + matrixEvent.getSender() + ")";

            // This is sets the avatar URL.
            const memberEvent = eventMapper({
                content: {
                    membership: KnownMembership.Join,
                    avatar_url: e.profile.avatar_url,
                    displayname: e.profile.displayname,
                },
                type: EventType.RoomMember,
                event_id: matrixEvent.getId() + ":eventIndex",
                room_id: matrixEvent.getRoomId(),
                sender: matrixEvent.getSender(),
                origin_server_ts: matrixEvent.getTs(),
                state_key: matrixEvent.getSender(),
            });

            // We set this manually to avoid emitting RoomMember.membership and
            // RoomMember.name events.
            member.events.member = memberEvent;
            matrixEvent.sender = member;

            return matrixEvent;
        });

        return matrixEvents;
    }

    /**
     * Fill a timeline with events that contain URLs.
     *
     * @param {TimelineSet} timelineSet The TimelineSet the Timeline belongs to,
     * used to check if we're adding duplicate events.
     *
     * @param {Timeline} timeline The Timeline which should be filed with
     * events.
     *
     * @param {Room} room The room for which we should fetch events containing
     * URLs
     *
     * @param {number} limit The maximum number of events to fetch.
     *
     * @param {string} fromEvent From which event should we continue fetching
     * events from the index. This is only needed if we're continuing to fill
     * the timeline, e.g. if we're paginating. This needs to be set to a event
     * id of an event that was previously fetched with this function.
     *
     * @param {string} direction The direction in which we will continue
     * fetching events. EventTimeline.BACKWARDS to continue fetching events that
     * are older than the event given in fromEvent, EventTimeline.FORWARDS to
     * fetch newer events.
     *
     * @returns {Promise<boolean>} Resolves to true if events were added to the
     * timeline, false otherwise.
     */
    public async populateFileTimeline(
        timelineSet: EventTimelineSet,
        timeline: EventTimeline,
        room: Room,
        limit = 10,
        fromEvent?: string,
        direction: string = EventTimeline.BACKWARDS,
    ): Promise<boolean> {
        const matrixEvents = await this.loadFileEvents(room, limit, fromEvent, direction);

        // If this is a normal fill request, not a pagination request, we need
        // to get our events in the BACKWARDS direction but populate them in the
        // forwards direction.
        // This needs to happen because a fill request might come with an
        // existing timeline e.g. if you close and re-open the FilePanel.
        if (fromEvent === null) {
            matrixEvents.reverse();
            direction = direction == EventTimeline.BACKWARDS ? EventTimeline.FORWARDS : EventTimeline.BACKWARDS;
        }

        // Add the events to the timeline of the file panel.
        matrixEvents.forEach((e) => {
            if (!timelineSet.eventIdToTimeline(e.getId()!)) {
                timelineSet.addEventToTimeline(e, timeline, direction == EventTimeline.BACKWARDS);
            }
        });

        let ret = false;
        let paginationToken = "";

        // Set the pagination token to the oldest event that we retrieved.
        if (matrixEvents.length > 0) {
            paginationToken = matrixEvents[matrixEvents.length - 1].getId()!;
            ret = true;
        }

        logger.log(
            "EventIndex: Populating file panel with",
            matrixEvents.length,
            "events and setting the pagination token to",
            paginationToken,
        );

        timeline.setPaginationToken(paginationToken, EventTimeline.BACKWARDS);
        return ret;
    }

    /**
     * Emulate a TimelineWindow pagination() request with the event index as the event source
     *
     * Might not fetch events from the index if the timeline already contains
     * events that the window isn't showing.
     *
     * @param {Room} room The room for which we should fetch events containing
     * URLs
     *
     * @param {TimelineWindow} timelineWindow The timeline window that should be
     * populated with new events.
     *
     * @param {string} direction The direction in which we should paginate.
     * EventTimeline.BACKWARDS to paginate back, EventTimeline.FORWARDS to
     * paginate forwards.
     *
     * @param {number} limit The maximum number of events to fetch while
     * paginating.
     *
     * @returns {Promise<boolean>} Resolves to a boolean which is true if more
     * events were successfully retrieved.
     */
    public paginateTimelineWindow(
        room: Room,
        timelineWindow: TimelineWindow,
        direction: Direction,
        limit: number,
    ): Promise<boolean> {
        const tl = timelineWindow.getTimelineIndex(direction);

        if (!tl) return Promise.resolve(false);
        if (tl.pendingPaginate) return tl.pendingPaginate;

        if (timelineWindow.extend(direction, limit)) {
            return Promise.resolve(true);
        }

        const paginationMethod = async (
            timelineWindow: TimelineWindow,
            timelineIndex: TimelineIndex,
            room: Room,
            direction: Direction,
            limit: number,
        ): Promise<boolean> => {
            const timeline = timelineIndex.timeline;
            const timelineSet = timeline.getTimelineSet();
            const token = timeline.getPaginationToken(direction) ?? undefined;

            const ret = await this.populateFileTimeline(timelineSet, timeline, room, limit, token, direction);

            timelineIndex.pendingPaginate = undefined;
            timelineWindow.extend(direction, limit);

            return ret;
        };

        const paginationPromise = paginationMethod(timelineWindow, tl, room, direction, limit);
        tl.pendingPaginate = paginationPromise;

        return paginationPromise;
    }

    /**
     * Get statistical information of the index.
     *
     * @return {Promise<IIndexStats>} A promise that will resolve to the index
     * statistics.
     */
    public async getStats(): Promise<IIndexStats | undefined> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        return indexManager?.getStats();
    }

    /**
     * Check if the room with the given id is already indexed.
     *
     * @param {string} roomId The ID of the room which we want to check if it
     * has been already indexed.
     *
     * @return {Promise<boolean>} Returns true if the index contains events for
     * the given room, false otherwise.
     */
    public async isRoomIndexed(roomId: string): Promise<boolean | undefined> {
        const indexManager = PlatformPeg.get()?.getEventIndexingManager();
        return indexManager?.isRoomIndexed(roomId);
    }

    /**
     * Get the room that we are currently crawling.
     *
     * @returns {Room} A MatrixRoom that is being currently crawled, null
     * if no room is currently being crawled.
     */
    public currentRoom(): Room | null {
        if (this.currentCheckpoint === null && this.crawlerCheckpoints.length === 0) {
            return null;
        }

        const client = MatrixClientPeg.safeGet();

        if (this.currentCheckpoint !== null) {
            return client.getRoom(this.currentCheckpoint.roomId);
        } else {
            return client.getRoom(this.crawlerCheckpoints[0].roomId);
        }
    }

    public crawlingRooms(): {
        crawlingRooms: Set<string>;
        totalRooms: Set<string>;
    } {
        const totalRooms = new Set<string>();
        const crawlingRooms = new Set<string>();

        this.crawlerCheckpoints.forEach((checkpoint, index) => {
            crawlingRooms.add(checkpoint.roomId);
        });

        if (this.currentCheckpoint !== null) {
            crawlingRooms.add(this.currentCheckpoint.roomId);
        }

        const client = MatrixClientPeg.safeGet();
        const rooms = client.getRooms();

        const isRoomEncrypted = (room: Room): boolean => {
            return client.isRoomEncrypted(room.roomId);
        };

        const encryptedRooms = rooms.filter(isRoomEncrypted);
        encryptedRooms.forEach((room, index) => {
            totalRooms.add(room.roomId);
        });

        return { crawlingRooms, totalRooms };
    }
}