// The YouTube player's address-bar keys. The player opens over any page (the feed, a channel page, Home,
// a playlist, a channel's watched videos), so its keys are the shell's: no module owns them, a page
// switch clears them, and the page under it keeps its own. The player names them in its own history
// entry (lib/history's `useBackToClose`), so Back lands on the page as it was, without the player.
// The list it plays from is the page's: the feed's filters, the open playlist (`pl`) — already named.
// No position: the player resumes from the server's (`video_states`), which is where it was left.
const PLAYER_WATCH_KEY = "watch"; // the item of the list playing now
const PLAYER_RELATED_KEY = "wrel"; // a related video played in place over it
const PLAYER_PANEL_KEY = "wtab"; // the wide panel's tab, when it is not the description
export const PLAYER_KEYS = [PLAYER_WATCH_KEY, PLAYER_RELATED_KEY, PLAYER_PANEL_KEY] as const;

export type PlayerPanelTab = "description" | "related";

export type PlayerUrlState = { watch: string; related: string | null; panel: PlayerPanelTab };

/** The player's keys for its entry. The panel's tab is written only when it is not the default: no
 *  browser remembers it, so a link without one opens the description as this one would. */
export function playerParamUpdates(state: PlayerUrlState): Record<string, string | null> {
  return {
    [PLAYER_WATCH_KEY]: state.watch,
    [PLAYER_RELATED_KEY]: state.related,
    [PLAYER_PANEL_KEY]: state.panel === "related" ? "related" : null,
  };
}

/** The player an address names, or null when it names none. */
function playerFrom(params: URLSearchParams): PlayerUrlState | null {
  const watch = params.get(PLAYER_WATCH_KEY);
  if (!watch) return null;
  return {
    watch,
    related: params.get(PLAYER_RELATED_KEY) || null,
    panel: params.get(PLAYER_PANEL_KEY) === "related" ? "related" : "description",
  };
}

/** The player the address names now: read by a host as it mounts (a reload, a bookmark), and by the
 *  player as it opens. No entry but the player's own carries these keys once the history has caught
 *  up, so a host mounted later (a page switch back) finds none. */
export function linkedPlayer(): PlayerUrlState | null {
  return playerFrom(new URLSearchParams(window.location.search));
}