/**
 * Decides which of a playlist's dumps a viewer may see. The playlist service
 * filters its listings with it, the WebSocket service filters each client's
 * `playlist_dumps_updated` message the same way, and the queries that list
 * playlists count their dumps by the same rule.
 *
 * @module
 */

import type { Playlist } from "../../shared/playlist.ts";

/**
 * The fields of a playlist's dump that {@link isMemberVisibleTo} needs. A
 * `Dump` has them. For its broadcasts, the playlist service reads only these.
 */
export interface PlaylistMember {
  id: string;
  isPrivate: boolean;
  /** The dump's poster, not the playlist's owner. */
  userId: string;
}

/**
 * Checks whether `viewerId` may see `member` in `playlist`. A public dump is
 * visible to all. A private dump is visible only to the playlist's owner, and
 * only if they posted it: moderators don't see it, and neither does the owner
 * once someone else's dump in their playlist goes private. A null or undefined
 * `viewerId` is a signed-out viewer.
 */
export function isMemberVisibleTo(
  member: PlaylistMember,
  playlist: Pick<Playlist, "userId">,
  viewerId: string | null | undefined,
): boolean {
  return !member.isPrivate ||
    (member.userId === viewerId && viewerId === playlist.userId);
}

/**
 * The `dump_count` column of a query on `playlists p`: how many of the
 * playlist's dumps the viewer may see, by {@link isMemberVisibleTo}'s rule.
 * Its `?` takes the viewer's id, or `""` for a signed-out one, and comes
 * before the query's other parameters, the column being in its select list.
 */
export const VISIBLE_DUMP_COUNT = `(SELECT COUNT(*) FROM playlist_dumps pd
     INNER JOIN dumps d ON d.id = pd.dump_id
    WHERE pd.playlist_id = p.id
      AND (d.is_private = 0 OR (d.user_id = p.user_id AND p.user_id = ?))
   ) as dump_count`;

/**
 * Returns how many of `members` the viewer may see in `playlist`, the
 * `dumpCount` the playlist has for them.
 */
export function countVisibleTo(
  members: PlaylistMember[],
  playlist: Pick<Playlist, "userId">,
  viewerId: string | null | undefined,
): number {
  return members.filter((m) => isMemberVisibleTo(m, playlist, viewerId))
    .length;
}