/**
 * Client-side push notification helpers.
 * All functions are safe to call in the browser only.
 */

export function isNotificationSupported(): boolean {
  return (
    typeof window !== 'undefined' &&
    'serviceWorker' in navigator &&
    'PushManager' in window &&
    'Notification' in window
  );
}

export function getNotificationPermission(): NotificationPermission | 'unsupported' {
  if (!isNotificationSupported()) return 'unsupported';
  return Notification.permission;
}

export async function requestNotificationPermission(): Promise<NotificationPermission> {
  return Notification.requestPermission();
}

export async function registerServiceWorker(): Promise<ServiceWorkerRegistration | null> {
  if (!('serviceWorker' in navigator)) return null;
  try {
    const registration = await navigator.serviceWorker.register('/sw.js');
    return registration;
  } catch (err) {
    console.error('[Push] Service worker registration failed:', err);
    return null;
  }
}

function urlBase64ToUint8Array(base64String: string): Uint8Array {
  const padding = '='.repeat((4 - (base64String.length % 4)) % 4);
  const base64 = (base64String + padding).replace(/-/g, '+').replace(/_/g, '/');
  const rawData = window.atob(base64);
  const outputArray = new Uint8Array(rawData.length);
  for (let i = 0; i < rawData.length; ++i) {
    outputArray[i] = rawData.charCodeAt(i);
  }
  return outputArray;
}

export async function subscribeToPush(
  registration: ServiceWorkerRegistration
): Promise<PushSubscription | null> {
  const vapidPublicKey = process.env.NEXT_PUBLIC_VAPID_PUBLIC_KEY;
  if (!vapidPublicKey) {
    console.error('[Push] VAPID public key not configured');
    return null;
  }

  try {
    const subscription = await registration.pushManager.subscribe({
      userVisibleOnly: true,
      applicationServerKey: urlBase64ToUint8Array(vapidPublicKey),
    });
    return subscription;
  } catch (err) {
    console.error('[Push] Subscribe failed:', err);
    return null;
  }
}

export async function sendSubscriptionToServer(
  subscription: PushSubscription
): Promise<boolean> {
  try {
    const res = await fetch('/api/push/subscribe', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        endpoint: subscription.endpoint,
        keys: {
          p256dh: btoa(String.fromCharCode(...new Uint8Array(subscription.getKey('p256dh')!))),
          auth: btoa(String.fromCharCode(...new Uint8Array(subscription.getKey('auth')!))),
        },
      }),
    });
    return res.ok;
  } catch (err) {
    console.error('[Push] Failed to send subscription to server:', err);
    return false;
  }
}

export async function unsubscribeFromPush(
  registration: ServiceWorkerRegistration
): Promise<boolean> {
  try {
    const subscription = await registration.pushManager.getSubscription();
    if (!subscription) return true;

    // Delete from server
    await fetch('/api/push/subscribe', {
      method: 'DELETE',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ endpoint: subscription.endpoint }),
    });

    // Unsubscribe locally
    await subscription.unsubscribe();
    return true;
  } catch (err) {
    console.error('[Push] Unsubscribe failed:', err);
    return false;
  }
}

export async function isCurrentlySubscribed(): Promise<boolean> {
  if (!isNotificationSupported()) return false;
  try {
    const registration = await navigator.serviceWorker.ready;
    const subscription = await registration.pushManager.getSubscription();
    return !!subscription;
  } catch {
    return false;
  }
}