import { useAtomValue } from 'jotai';
import { useMemo } from 'react';
import { useMatrixClient } from '../../../hooks/useMatrixClient';
import { mDirectAtom } from '../../../state/mDirectList';
import { allRoomsAtom } from '../../../state/room-list/roomList';
import { useDirects, useOrphanRooms } from '../../../state/hooks/roomList';
import { roomToParentsAtom } from '../../../state/room/roomToParents';

// After P3c the Direct tab is universal: every joined non-space «orphan»
// room renders here, regardless of `m.direct`. Implementation =
// `useOrphanRooms ∪ useDirects`:
//
//   - `useOrphanRooms` = `isRoom && !mDirects.has && !roomToParents.has` →
//     non-space rooms that don't live inside any space and aren't m.direct-
//     tagged. The formerly-Home tab.
//   - `useDirects` = `isRoom && mDirects.has` → every m.direct-tagged
//     non-space room. **No `roomToParents` filter** — a room that is BOTH a
//     space child AND m.direct-tagged appears here. This is intentional and
//     pre-dates P3c: the m.direct flag wins over the space-child membership
//     for routing purposes (user sees the DM in /direct/, opening it loses
//     space context). The same room is hidden from the parent space's child-
//     room navigation list (`useChildRoomScopeFactory` excludes m.direct);
//     it stays reachable from space message search via
//     `useRecursiveChildNonSpaceRoomScopeFactory` (post-P3c universal).
//
// Duplicates inside the union are deduped via Set semantics below. The
// product call (DM-tagged-space-child resolves to /direct/, not /space/{id}/)
// is open for revision — see desired_features §21 (Channels plan).
export const useDirectRooms = (): string[] => {
  const mx = useMatrixClient();
  const mDirects = useAtomValue(mDirectAtom);
  const roomToParents = useAtomValue(roomToParentsAtom);
  const orphanRooms = useOrphanRooms(mx, allRoomsAtom, mDirects, roomToParents);
  const directs = useDirects(mx, allRoomsAtom, mDirects);
  return useMemo(() => {
    const seen = new Set<string>();
    const out: string[] = [];
    orphanRooms.forEach((id) => {
      if (!seen.has(id)) {
        seen.add(id);
        out.push(id);
      }
    });
    directs.forEach((id) => {
      if (!seen.has(id)) {
        seen.add(id);
        out.push(id);
      }
    });
    return out;
  }, [orphanRooms, directs]);
};