import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
import {
  EventTimelineSetHandlerMap,
  EventType,
  MatrixClient,
  MatrixEvent,
  MatrixEventEvent,
  MsgType,
  Room,
  RoomEvent,
  RoomEventHandlerMap,
  ThreadEvent,
} from 'matrix-js-sdk';

import {
  collectTimelineEvents,
  createDetachedTimelineSet,
  createMediaFilter,
  DetachedTimelineSet,
} from '../utils/detachedTimeline';
import { decryptAllTimelineEvent } from '../utils/room';

export const MEDIA_MSGTYPES: ReadonlySet<string> = new Set<string>([
  MsgType.Image,
  MsgType.Video,
  MsgType.Audio,
  MsgType.File,
]);

export const isMediaMessage = (event: MatrixEvent): boolean =>
  event.getType() === EventType.RoomMessage &&
  !event.isRedacted() &&
  MEDIA_MSGTYPES.has(event.getContent().msgtype as string);

const PAGE_SIZE = 100;

export type RoomMediaTimeline = {
  /** Every loaded media message in the room and its threads, newest first. */
  events: MatrixEvent[];
  loadMore: () => Promise<void>;
  loading: boolean;
  loadError: boolean;
  canLoadMore: boolean;
  hasLoadedOnce: boolean;
};

/**
 * [Gitea #163] Media events for the gallery, paginated on a timeline set of
 * their own so the room's live timeline (and the message list rendering it)
 * is never mutated. Unencrypted rooms page through a server-side
 * `contains_url` filter (100 media per page); encrypted rooms page raw
 * history into a private set and filter after decrypting, exactly what the
 * gallery used to do on the live timeline.
 */
export const useRoomMediaTimeline = (mx: MatrixClient, room: Room): RoomMediaTimeline => {
  const detached = useMemo<DetachedTimelineSet>(
    () => createDetachedTimelineSet(mx, room, { filter: createMediaFilter(mx.getSafeUserId()) }),
    [mx, room],
  );

  // [Gitea #165] The SDK routes thread replies out of every room timeline set
  // (ours included) into the room's Thread objects, so media posted in a
  // thread only shows up if we read the loaded threads too.
  const readEvents = useCallback((): MatrixEvent[] => {
    const seen = new Set<string>();
    return [
      ...collectTimelineEvents(detached.set.getLiveTimeline()),
      ...room.getThreads().flatMap((thread) => thread.timeline),
    ]
      .filter((event) => {
        const id = event.getId();
        if (!id || seen.has(id) || !isMediaMessage(event)) return false;
        seen.add(id);
        return true;
      })
      .sort((a, b) => b.getTs() - a.getTs());
  }, [detached, room]);

  const [events, setEvents] = useState<MatrixEvent[]>(readEvents);
  const [loading, setLoading] = useState(false);
  const [loadError, setLoadError] = useState(false);
  const [canLoadMore, setCanLoadMore] = useState(true);
  const [hasLoadedOnce, setHasLoadedOnce] = useState(false);
  const loadingRef = useRef(false);

  useEffect(() => {
    setEvents(readEvents());
    setCanLoadMore(true);
    setHasLoadedOnce(false);
    setLoadError(false);
  }, [readEvents]);

  // Live updates. The server-filtered set is registered with the room and
  // receives new events itself; the private set (encrypted rooms) is fed here
  // once the event has decrypted. Redactions are applied to both.
  useEffect(() => {
    const { set, serverFiltered } = detached;
    const refresh = () => setEvents(readEvents());

    const addIfMedia = (event: MatrixEvent) => {
      if (!isMediaMessage(event)) return;
      if (set.findEventById(event.getId() ?? '')) return;
      set.addLiveEvent(event, { addToState: false });
      refresh();
    };

    const onTimeline: EventTimelineSetHandlerMap[RoomEvent.Timeline] = (
      event,
      eventRoom,
      _toStart,
      _removed,
      data,
    ) => {
      if (eventRoom?.roomId !== room.roomId || !data.liveEvent) return;
      if (serverFiltered) {
        // The room already routed it into our set (client-side filtered).
        if (data.timeline.getTimelineSet() === set) refresh();
        return;
      }
      if (event.isBeingDecrypted() || event.shouldAttemptDecryption()) {
        event.once(MatrixEventEvent.Decrypted, () => addIfMedia(event));
        return;
      }
      addIfMedia(event);
    };

    const onRedaction: RoomEventHandlerMap[RoomEvent.Redaction] = (event, eventRoom) => {
      if (eventRoom?.roomId !== room.roomId) return;
      const redactedId = event.event.redacts;
      if (!redactedId) return;
      if (!serverFiltered) set.removeEvent(redactedId);
      refresh();
    };

    const onThreadReply = (_thread: unknown, event: MatrixEvent) => {
      if (event.isBeingDecrypted() || event.shouldAttemptDecryption()) {
        event.once(MatrixEventEvent.Decrypted, () => {
          if (isMediaMessage(event)) refresh();
        });
        return;
      }
      if (isMediaMessage(event)) refresh();
    };

    room.on(RoomEvent.Timeline, onTimeline);
    room.on(RoomEvent.Redaction, onRedaction);
    room.on(ThreadEvent.NewReply, onThreadReply);
    return () => {
      room.removeListener(RoomEvent.Timeline, onTimeline);
      room.removeListener(RoomEvent.Redaction, onRedaction);
      room.removeListener(ThreadEvent.NewReply, onThreadReply);
    };
  }, [detached, room, readEvents]);

  const loadMore = useCallback(async () => {
    if (loadingRef.current || !canLoadMore) return;
    loadingRef.current = true;
    setLoading(true);
    setLoadError(false);
    try {
      const timeline = detached.set.getLiveTimeline();
      const hasMore = await mx.paginateEventTimeline(timeline, {
        backwards: true,
        limit: PAGE_SIZE,
      });
      if (room.hasEncryptionStateEvent()) {
        await decryptAllTimelineEvent(mx, timeline);
      }
      setEvents(readEvents());
      setCanLoadMore(hasMore);
      setHasLoadedOnce(true);
    } catch {
      // Stop auto-retry: the sentinel would keep firing on every render otherwise.
      // The user can retry manually via the button shown in the error state.
      setLoadError(true);
    } finally {
      loadingRef.current = false;
      setLoading(false);
    }
  }, [mx, room, detached, canLoadMore, readEvents]);

  return { events, loadMore, loading, loadError, canLoadMore, hasLoadedOnce };
};