Push Notifications — Firebase FCM

npx expo install expo-notifications expo-device expo-constants @react-native-firebase/app @react-native-firebase/messaging
# Config plugins in app.config.ts:
# plugins: [['expo-notifications', { ... }], '@react-native-firebase/app', '@react-native-firebase/messaging']

import * as Notifications from 'expo-notifications';
import * as Device from 'expo-device';
import messaging from '@react-native-firebase/messaging';
import Constants from 'expo-constants';

// ---- How notifications behave when app is foregrounded ----
Notifications.setNotificationHandler({
  handleNotification: async () => ({
    shouldShowAlert: true,
    shouldPlaySound: true,
    shouldSetBadge: true,
  }),
});

// ---- Register device and get push token ----
export async function registerForPushNotifications(): Promise<string | null> {
  if (!Device.isDevice) {
    console.warn('Push notifications only work on physical devices');
    return null;
  }

  // 1. Request permission (iOS only — Android grants automatically)
  const { status: existingStatus } = await Notifications.getPermissionsAsync();
  let finalStatus = existingStatus;

  if (existingStatus !== 'granted') {
    const { status } = await Notifications.requestPermissionsAsync({
      ios: { allowAlert: true, allowBadge: true, allowSound: true },
    });
    finalStatus = status;
  }

  if (finalStatus !== 'granted') return null;

  // 2. Set Android notification channel (required for Android 8+)
  await Notifications.setNotificationChannelAsync('default', {
    name: 'Default',
    importance: Notifications.AndroidImportance.MAX,
    vibrationPattern: [0, 250, 250, 250],
    lightColor: '#6366f1',
    sound: 'default',
    showBadge: true,
  });

  // 3. Get FCM token (raw Firebase token — use for server-side send)
  const fcmToken = await messaging().getToken();

  // 4. Get Expo push token (use with Expo's send API)
  const expoPushToken = await Notifications.getExpoPushTokenAsync({
    projectId: Constants.expoConfig?.extra?.eas?.projectId,
  });

  console.log('FCM Token:', fcmToken);
  console.log('Expo Push Token:', expoPushToken.data);

  // 5. Send token to your backend
  await apiClient.post('/users/me/push-token', { fcmToken, expoPushToken: expoPushToken.data });

  return fcmToken;
}

// ---- Handle notifications in-app ----
export function usePushNotifications() {
  const navigationRef = React.useRef<NavigationContainerRef<RootStackParamList>>(null);

  useEffect(() => {
    // Register on mount
    registerForPushNotifications();

    // App in foreground — notification received
    const foregroundSub = Notifications.addNotificationReceivedListener(notification => {
      console.log('Foreground notification:', notification);
      // Show in-app banner or update badge
    });

    // User tapped notification (foreground or background)
    const responseSub = Notifications.addNotificationResponseReceivedListener(response => {
      const data = response.notification.request.content.data;
      // Navigate to relevant screen
      if (data.type === 'POST_LIKE' && data.postId) {
        navigationRef.current?.navigate('PostDetail', { postId: data.postId as string });
      }
    });

    // App was CLOSED — opened by notification tap (check initial notification)
    Notifications.getLastNotificationResponseAsync().then(response => {
      if (response?.notification.request.content.data.type === 'CHAT_MESSAGE') {
        // Navigate to chat
      }
    });

    // Background FCM (data-only messages — no UI, run JS)
    messaging().setBackgroundMessageHandler(async remoteMessage => {
      console.log('Background FCM:', remoteMessage);
      // Update badge, download data, etc.
    });

    return () => {
      foregroundSub.remove();
      responseSub.remove();
    };
  }, []);

  return { navigationRef };
}