import { Room, RoomEvent } from 'matrix-js-sdk';
import { useEffect, useState } from 'react';
import { useMatrixClient } from './useMatrixClient';

function computePositions(room: Room, myUserId: string): Map<string, string[]> {
  const map = new Map<string, string[]>();
  for (const member of room.getJoinedMembers()) {
    if (member.userId === myUserId) continue;
    const evtId = room.getEventReadUpTo(member.userId);
    if (!evtId) continue;
    const arr = map.get(evtId);
    if (arr) arr.push(member.userId);
    else map.set(evtId, [member.userId]);
  }
  return map;
}

export function useRoomReadPositions(room: Room): Map<string, string[]> {
  const mx = useMatrixClient();
  const myUserId = mx.getUserId() ?? '';
  const [positions, setPositions] = useState(() => computePositions(room, myUserId));

  useEffect(() => {
    setPositions(computePositions(room, myUserId));
    const onReceipt = () => setPositions(computePositions(room, myUserId));
    room.on(RoomEvent.Receipt, onReceipt);
    return () => {
      room.removeListener(RoomEvent.Receipt, onReceipt);
    };
  }, [room, myUserId]);

  return positions;
}