import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/foundation.dart';

class NotificationService {
  static final NotificationService _instance = NotificationService._internal();
  factory NotificationService() => _instance;
  NotificationService._internal();

  FirebaseMessaging? _messaging;
  
  static const String vapidKey = 'BKrFSFm2cb2DNtEpTNmEy3acpi2ziRA5DhzKSyjshqAWANaoydztUTa0Cn3jwh1v7KN6pHUQfsODFXUWrKG6aSU';
  
  static const List<String> topics = [
    'all',
    'newposts',
    'newinvites',
    'invitesfollowup',
    'appnews',
  ];

  Future<void> initialize() async {
    if (!kIsWeb) {
      print('Notifications are only supported on web platform');
      return;
    }

    _messaging = FirebaseMessaging.instance;
    
    await _requestPermission();
    await _subscribeToTopics();
    await _setupMessageHandlers();
  }

  Future<void> _requestPermission() async {
    if (_messaging == null) return;

    NotificationSettings settings = await _messaging!.requestPermission(
      alert: true,
      announcement: false,
      badge: true,
      carPlay: false,
      criticalAlert: false,
      provisional: false,
      sound: true,
    );

    print('User granted permission: ${settings.authorizationStatus}');
    
    if (settings.authorizationStatus == AuthorizationStatus.authorized) {
      print('User granted permission for notifications');
    } else if (settings.authorizationStatus == AuthorizationStatus.provisional) {
      print('User granted provisional permission for notifications');
    } else {
      print('User declined or has not accepted permission for notifications');
    }
  }

  Future<void> _subscribeToTopics() async {
    if (_messaging == null) return;

    for (String topic in topics) {
      try {
        await _messaging!.subscribeToTopic(topic);
        print('Subscribed to topic: $topic');
      } catch (e) {
        print('Error subscribing to topic $topic: $e');
      }
    }
  }

  Future<void> _setupMessageHandlers() async {
    if (_messaging == null) return;

    // Handle foreground messages
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      print('Got a message whilst in the foreground!');
      print('Message data: ${message.data}');

      if (message.notification != null) {
        print('Message also contained a notification: ${message.notification}');
        _showNotification(message.notification!);
      }
    });

    // Handle background messages
    FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);

    // Handle notification taps
    FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
      print('A new onMessageOpenedApp event was published!');
      print('Message data: ${message.data}');
      _handleNotificationTap(message);
    });

    // Get the initial message if the app was opened from a notification
    RemoteMessage? initialMessage = await _messaging!.getInitialMessage();
    if (initialMessage != null) {
      print('App opened from notification: ${initialMessage.data}');
      _handleNotificationTap(initialMessage);
    }

    // Get the FCM token for this device
    String? token = await _messaging!.getToken(vapidKey: vapidKey);
    print('FCM Token: $token');
  }

  void _showNotification(RemoteNotification notification) {
    // For web, we rely on the service worker to show notifications
    // This is mainly for logging and debugging
    print('Notification Title: ${notification.title}');
    print('Notification Body: ${notification.body}');
  }

  void _handleNotificationTap(RemoteMessage message) {
    // Handle notification tap actions here
    print('Notification tapped: ${message.data}');
    
    // You can navigate to specific screens based on the notification data
    // For example:
    // if (message.data['type'] == 'newpost') {
    //   // Navigate to posts screen
    // } else if (message.data['type'] == 'newinvite') {
    //   // Navigate to invitations screen
    // }
  }

  Future<void> unsubscribeFromTopic(String topic) async {
    if (_messaging == null) return;
    
    try {
      await _messaging!.unsubscribeFromTopic(topic);
      print('Unsubscribed from topic: $topic');
    } catch (e) {
      print('Error unsubscribing from topic $topic: $e');
    }
  }

  Future<void> subscribeToTopic(String topic) async {
    if (_messaging == null) return;
    
    try {
      await _messaging!.subscribeToTopic(topic);
      print('Subscribed to topic: $topic');
    } catch (e) {
      print('Error subscribing to topic $topic: $e');
    }
  }

  Future<String?> getToken() async {
    if (_messaging == null) return null;
    return await _messaging!.getToken(vapidKey: vapidKey);
  }
}

// Background message handler must be a top-level function
Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  print('Handling a background message: ${message.messageId}');
  print('Message data: ${message.data}');
  
  if (message.notification != null) {
    print('Background message contained a notification: ${message.notification}');
  }
}