import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_timezone/flutter_timezone.dart';

import '../../../core/firebase/firebase_providers.dart';

/// Registriert das Gerät für Push-Erinnerungen und hält die
/// Erinnerungs-Einstellungen im Nutzer-Dokument aktuell.
///
/// Abstrakte Basis, damit Tests eine No-Op-Variante einsetzen können.
abstract class PushRegistrationService {
  Future<void> registerDevice(User user);
  Future<void> syncReminderTime(TimeOfDay time);
}

class FirebasePushRegistrationService implements PushRegistrationService {
  FirebasePushRegistrationService(this._firestore, this._auth);

  final FirebaseFirestore _firestore;
  final FirebaseAuth _auth;
  bool _tokenListenerAttached = false;

  @override
  Future<void> registerDevice(User user) async {
    final messaging = FirebaseMessaging.instance;

    // Fragt beim ersten Mal die Push-Berechtigung ab (iOS-Dialog,
    // Android 13+ Systemdialog); danach ist der Aufruf ein No-Op.
    final settings = await messaging.requestPermission();
    if (settings.authorizationStatus == AuthorizationStatus.denied) return;

    final token = await messaging.getToken();
    if (token != null) {
      await _saveToken(user.uid, token);
    }
    if (!_tokenListenerAttached) {
      _tokenListenerAttached = true;
      messaging.onTokenRefresh.listen((newToken) {
        final current = _auth.currentUser;
        if (current != null) _saveToken(current.uid, newToken);
      });
    }
  }

  Future<void> _saveToken(String uid, String token) async {
    final timezone = await FlutterTimezone.getLocalTimezone();
    await _firestore.collection('users').doc(uid).set({
      'fcmTokens': FieldValue.arrayUnion([token]),
      'timezone': timezone,
    }, SetOptions(merge: true));
  }

  @override
  Future<void> syncReminderTime(TimeOfDay time) async {
    final user = _auth.currentUser;
    if (user == null) return;
    final formatted =
        '${time.hour.toString().padLeft(2, '0')}:${time.minute.toString().padLeft(2, '0')}';
    await _firestore.collection('users').doc(user.uid).set({
      'reminderTime': formatted,
    }, SetOptions(merge: true));
  }
}

final pushRegistrationServiceProvider = Provider<PushRegistrationService>((ref) {
  return FirebasePushRegistrationService(
    ref.watch(firestoreProvider),
    ref.watch(firebaseAuthProvider),
  );
});