import React, { useCallback, useEffect, useMemo, useRef } from 'react';
import { MatrixEvent, Room } from 'matrix-js-sdk';
import { useMatrixClient } from '../../hooks/useMatrixClient';
import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
import { useRoomMediaTimeline } from '../../hooks/useRoomMediaTimeline';
import { useRoomNavigate } from '../../hooks/useRoomNavigate';
import { Lightbox, toLightboxItems } from './MediaGallery';

// How many media pages to walk back looking for the clicked event before
// settling for a single-item viewer.
const MAX_SEARCH_PAGES = 6;

type RoomMediaLightboxProps = {
  room: Room;
  eventId: string;
  onClose: () => void;
};

/**
 * [Gitea #219] The room timeline's image viewer is the gallery lightbox,
 * opened at the clicked event: same dark backdrop, sender + date, 1/N counter,
 * ←/→ across the room's media, zoom keys, download and "jump to message".
 *
 * Items come from the same detached media timeline the gallery uses (#163).
 * It starts at the live end, so an older image may not be loaded yet: we page
 * back a bounded number of times looking for it and meanwhile show the clicked
 * image on its own, so the viewer never waits on the network to open.
 */
export function RoomMediaLightbox({ room, eventId, onClose }: RoomMediaLightboxProps) {
  const mx = useMatrixClient();
  const useAuthentication = useMediaAuthentication();
  const { navigateRoom } = useRoomNavigate();
  const { events, loadMore, loading, canLoadMore } = useRoomMediaTimeline(mx, room);

  const items = useMemo(() => toLightboxItems(room, events), [room, events]);
  const index = items.findIndex((it) => it.eventId === eventId);

  const pagesRef = useRef(0);
  useEffect(() => {
    if (index !== -1 || loading || !canLoadMore || pagesRef.current >= MAX_SEARCH_PAGES) return;
    pagesRef.current += 1;
    loadMore();
  }, [index, loading, canLoadMore, loadMore]);

  // Until the event is in the loaded window, show just the clicked media.
  const fallbackItems = useMemo(() => {
    const ev: MatrixEvent | undefined = room.findEventById(eventId) ?? undefined;
    return ev ? toLightboxItems(room, [ev]) : [];
  }, [room, eventId]);

  const handleJump = useCallback(
    (id: string) => {
      onClose();
      navigateRoom(room.roomId, id);
    },
    [onClose, navigateRoom, room.roomId],
  );

  const found = index !== -1;
  const shownItems = found ? items : fallbackItems;
  if (shownItems.length === 0) return null;
  return (
    <Lightbox
      // Remount when the full list arrives so the index and zoom reset cleanly.
      key={found ? 'room' : 'single'}
      items={shownItems}
      initialIndex={found ? index : 0}
      useAuthentication={useAuthentication}
      onClose={onClose}
      onJump={handleJump}
    />
  );
}