export type WakeStatus = "off" | "waiting" | "requesting" | "active" | "unavailable" | "unsupported";
type Sentinel = Pick<WakeLockSentinel, "released" | "release" | "addEventListener">;

// Browser access is injected so asynchronous acquisition and release can be tested.
export function createScreenWakeLock(options: {
  request?: () => Promise<Sentinel>;
  visible: () => boolean;
  status: (value: WakeStatus) => void;
}) {
  let desired = false;
  let disposed = false;
  let pending = false;
  let generation = 0;
  let lock: Sentinel | null = null;
  const report = (value: WakeStatus) => { if (!disposed) options.status(value); };
  const wanted = () => desired && !disposed && options.visible();
  function release() {
    generation++;
    const old = lock;
    lock = null;
    if (old) void old.release().catch(() => {});
  }
  async function sync() {
    if (!wanted()) {
      release();
      report(desired ? "waiting" : "off");
      return;
    }
    if (!options.request) { report("unsupported"); return; }
    if (lock && !lock.released) { report("active"); return; }
    if (pending) return;
    pending = true;
    const version = generation;
    report("requesting");
    try {
      const acquired = await options.request();
      if (version !== generation || !wanted()) {
        await acquired.release();
        return;
      }
      lock = acquired;
      acquired.addEventListener("release", () => {
        if (lock !== acquired) return;
        lock = null;
        // Do not repeatedly fight a system/battery decision to revoke the lock.
        report(wanted() ? "unavailable" : desired ? "waiting" : "off");
      }, { once: true });
      report(acquired.released ? "unavailable" : "active");
    } catch {
      if (version === generation && wanted()) report("unavailable");
    } finally {
      pending = false;
      // An off/on or hidden/visible transition may have invalidated a pending request.
      if (version !== generation && wanted()) void sync();
    }
  }
  return {
    update(enabled: boolean) { desired = enabled; void sync(); },
    refresh() { void sync(); },
    dispose() { disposed = true; desired = false; release(); },
  };
}