import 'dart:io';

import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';

/// Handles background FCM messages (must be top-level function)
@pragma('vm:entry-point')
Future<void> firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  // Firebase is already initialized in main — nothing to do here,
  // the OS will display the notification automatically.
}

class PushNotificationService {
  static final FlutterLocalNotificationsPlugin _localNotifications =
      FlutterLocalNotificationsPlugin();

  /// Notifier set when the user taps a notification (background or terminated).
  static final ValueNotifier<RemoteMessage?> tappedMessage = ValueNotifier(null);

  /// Call once after Firebase.initializeApp(), passing the instanceId.
  static Future<void> initialize(String instanceId) async {
    // Register background handler
    FirebaseMessaging.onBackgroundMessage(firebaseMessagingBackgroundHandler);

    // Request permission (iOS / Android 13+)
    await FirebaseMessaging.instance.requestPermission(
      alert: true,
      badge: true,
      sound: true,
    );

    // Configure local notifications for foreground display
    const androidSettings =
        AndroidInitializationSettings('@mipmap/ic_launcher');
    const iosSettings = DarwinInitializationSettings();
    await _localNotifications.initialize(
      const InitializationSettings(android: androidSettings, iOS: iosSettings),
    );

    // Subscribe to the instance topic
    await subscribeToInstance(instanceId);

    // Show local notification when app is in foreground
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      _showLocalNotification(message);
    });

    // App opened from background by tapping a notification
    FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
      tappedMessage.value = message;
    });

    // App launched from terminated state by tapping a notification
    final initial = await FirebaseMessaging.instance.getInitialMessage();
    if (initial != null) {
      Future.delayed(const Duration(milliseconds: 500), () {
        tappedMessage.value = initial;
      });
    }
  }

  static Future<void> subscribeToInstance(String instanceId) async {
    await FirebaseMessaging.instance
        .subscribeToTopic('instance_$instanceId');
  }

  static Future<void> unsubscribeFromInstance(String instanceId) async {
    await FirebaseMessaging.instance
        .unsubscribeFromTopic('instance_$instanceId');
  }

  static Future<void> _showLocalNotification(RemoteMessage message) async {
    final notification = message.notification;
    if (notification == null) return;

    const androidDetails = AndroidNotificationDetails(
      'push_notifications',
      'Push Notifications',
      channelDescription: 'Notifications from the museum',
      importance: Importance.high,
      priority: Priority.high,
    );
    const iosDetails = DarwinNotificationDetails();

    await _localNotifications.show(
      notification.hashCode,
      notification.title,
      notification.body,
      const NotificationDetails(android: androidDetails, iOS: iosDetails),
    );
  }
}