/**
 * Pure decisions for the `/player/[id]` route: which player surface to render,
 * and whether a load can be skipped because the backend is already playing the
 * requested item.
 *
 * Kept free of Svelte so both can be unit-tested without mounting the route.
 *
 * TRACES: UR-005 | DR-100 | UT-092, UT-093
 */

/** Which player component the route should render. */
export type PlayerSurface = "video" | "audio" | "pending";

export interface ReuseActivePlaybackInput {
  /** Item id the route was asked to play. */
  requestedId: string;
  /** Id of the media the backend currently reports as loaded, if any. */
  activeMediaId: string | null | undefined;
  /** Whether the requested item is video content. */
  isVideo: boolean;
  /** Explicit start position, if the caller asked for one. */
  startPosition?: number;
  /** Advancing to a next episode always restarts from the beginning. */
  forceRestart: boolean;
}

/**
 * Whether the route can show its UI over the backend's existing playback
 * instead of reloading the item (e.g. expanding the audio mini player).
 *
 * Never for video. The shortcut returns before a stream URL is fetched, which
 * is fine for audio (the backend owns the stream and the UI only mirrors it)
 * but leaves `<VideoPlayer>` with nothing to render. Leaving a webview-rendered
 * video does not clear the Rust controller's media — closing the route emits no
 * `stopped` state by design — so re-entering the same movie/episode hit this
 * shortcut and rendered the audio player instead.
 */
export function shouldReuseActivePlayback(input: ReuseActivePlaybackInput): boolean {
  return (
    !input.isVideo &&
    input.activeMediaId === input.requestedId &&
    !input.startPosition &&
    !input.forceRestart
  );
}

export interface PlayerSurfaceInput {
  isVideo: boolean;
  streamUrl: string | null;
}

/**
 * Which surface to render for the loaded item.
 *
 * Video without a stream URL is `pending`, never `audio` — falling through to
 * the audio player is how a movie/episode ended up in it.
 */
export function resolvePlayerSurface(input: PlayerSurfaceInput): PlayerSurface {
  if (input.isVideo) {
    return input.streamUrl ? "video" : "pending";
  }
  return "audio";
}