function urlBase64ToUint8Array(base64String) {
  const padding = '='.repeat((4 - (base64String.length % 4)) % 4);
  const base64 = (base64String + padding).replace(/-/g, '+').replace(/_/g, '/');
  const rawData = atob(base64);
  return Uint8Array.from([...rawData].map((c) => c.charCodeAt(0)));
}

function isIOS() {
  return /iPad|iPhone|iPod/.test(navigator.userAgent) ||
    (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1);
}

function isStandalone() {
  return window.matchMedia('(display-mode: standalone)').matches || navigator.standalone === true;
}

const notificationsMessage = document.getElementById('notificationsMessage');
const notificationsBtn = document.getElementById('notificationsBtn');

function showMessage(text) {
  notificationsMessage.textContent = text;
  notificationsMessage.style.display = 'block';
  notificationsBtn.style.display = 'none';
}

function showButton(label, onClick) {
  notificationsMessage.style.display = 'none';
  notificationsBtn.textContent = label;
  notificationsBtn.style.display = 'inline-block';
  notificationsBtn.onclick = onClick;
}

let cachedPublicKey = null;

async function subscribe() {
  const reg = await navigator.serviceWorker.ready;
  const permission = await Notification.requestPermission();
  if (permission !== 'granted') {
    return initNotifications();
  }
  const sub = await reg.pushManager.subscribe({
    userVisibleOnly: true,
    applicationServerKey: urlBase64ToUint8Array(cachedPublicKey),
  });
  await api.post('/api/push/subscribe', { subscription: sub.toJSON() });
  initNotifications();
}

async function unsubscribe() {
  const reg = await navigator.serviceWorker.ready;
  const sub = await reg.pushManager.getSubscription();
  if (sub) {
    const endpoint = sub.endpoint;
    await sub.unsubscribe();
    await api.del('/api/push/subscribe', { endpoint });
  }
  initNotifications();
}

async function initNotifications() {
  if (!notificationsMessage) return;

  if (!('serviceWorker' in navigator) || !('PushManager' in window)) {
    return showMessage('Push notifications aren\'t supported in this browser.');
  }

  if (!window.isSecureContext) {
    return showMessage('Notifications require HTTPS. Set up a reverse proxy with a real certificate to use this.');
  }

  let vapid;
  try {
    vapid = await api.get('/api/push/vapid-public-key');
  } catch {
    return showMessage('Could not check notification status.');
  }
  if (!vapid.enabled) {
    return showMessage('Push notifications aren\'t configured on this server yet.');
  }
  cachedPublicKey = vapid.publicKey;

  if (isIOS() && !isStandalone()) {
    return showMessage('On iPhone/iPad: tap Share → Add to Home Screen, then open the app icon from your Home Screen and come back here to enable notifications.');
  }

  if (Notification.permission === 'denied') {
    return showMessage('Notifications are blocked for this site in your browser settings.');
  }

  const reg = await navigator.serviceWorker.register('/sw.js');
  await navigator.serviceWorker.ready;
  const existingSub = await reg.pushManager.getSubscription();

  if (existingSub) {
    showButton('Disable notifications on this device', unsubscribe);
  } else {
    showButton('Enable notifications on this device', subscribe);
  }
}

if (notificationsMessage) {
  initNotifications();
}