// Optional PWA notifications for the whole-corpus sweep — a long run can finish
// or pause (e.g. on a usage limit) while the user has stepped away, so a system
// notification is a welcome nudge. Strictly best-effort and a graceful no-op
// everywhere it doesn't apply:
//   • no Notification API              → no-op;
//   • permission not granted           → no-op (firing never prompts);
//   • the tab is focused               → no-op (don't nag someone who's watching);
//   • not an installed/opt-in PWA      → no permission is ever requested (the
//     request is gated on a registered service worker, which only PWA-shipping
//     sites have — see export/app/lib/mode.ts shipsPwa()).

function supported(): boolean {
  return typeof window !== "undefined" && "Notification" in window;
}

// Fire a sweep notification IF permission is granted and the tab is hidden (the
// user has stepped away). Never prompts; never throws.
export function notifySweep(title: string, body: string): void {
  if (!supported() || Notification.permission !== "granted") return;
  // Only nudge when the user isn't already looking at the tab.
  if (typeof document !== "undefined" && document.visibilityState === "visible") {
    return;
  }
  try {
    new Notification(title, { body });
  } catch {
    /* some engines require notifications go through the SW registration; ignore */
  }
}

// Ask for notification permission once, at the start of a sweep (a user gesture),
// but ONLY on a PWA-shipping site — proxied by a registered service worker, which
// a dumb (non-PWA) site never has. No-op if already decided or unsupported.
export async function ensureSweepNotifyPermission(): Promise<void> {
  if (!supported() || Notification.permission !== "default") return;
  try {
    const reg = await navigator.serviceWorker?.getRegistration?.();
    if (!reg) return; // not an installed/opt-in PWA — don't prompt
    await Notification.requestPermission();
  } catch {
    /* permission flow unavailable — no-op */
  }
}