/**
 * Decides which of a playlist's dumps a viewer may see. The playlist service
 * filters its listings with it, and the WebSocket service filters each
 * client's `playlist_dumps_updated` message the same way.
 *
 * @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);
}