import 'dart:async';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:chepuhagram/logic/auth_provider.dart';
import 'package:chepuhagram/logic/contact_provider.dart';
import 'package:chepuhagram/presentation/screens/login_screen.dart';
import 'package:chepuhagram/presentation/screens/contacts_screen.dart';
import 'package:chepuhagram/presentation/screens/account_setup_screen.dart';
import 'package:chepuhagram/presentation/screens/key_recovery_screen.dart';
import 'package:chepuhagram/presentation/screens/chat_screen.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:chepuhagram/main.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:convert';
import 'package:chepuhagram/domain/services/crypto_service.dart';
import 'package:cryptography/cryptography.dart';
import 'package:flutter/foundation.dart';
import 'package:chepuhagram/core/theme_manager.dart';
import 'dart:ui';
import 'dart:io';
import 'package:flutter_secure_storage/flutter_secure_storage.dart';

class SplashScreen extends StatefulWidget {
  const SplashScreen({super.key});

  @override
  State<SplashScreen> createState() => _SplashScreenState();
}

class _SplashScreenState extends State<SplashScreen>
    with TickerProviderStateMixin {
  int? _targetChatId;
  String? _statusMessage;

  late AnimationController _fadeController;
  late AnimationController _pulseController;
  late Animation<double> _fadeAnimation;
  late Animation<double> _pulseAnimation;

  static const String _notificationLaunchKey = 'notification_launch_data';
  static const String _contactPublicKey = 'contact_public_key_';
  static const String _contactSharedKey = 'contact_shared_key_';
  @override
  void initState() {
    super.initState();
    _fadeController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 800),
    );
    _pulseController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 1200),
    );

    _fadeAnimation = Tween<double>(
      begin: 0.0,
      end: 1.0,
    ).animate(CurvedAnimation(parent: _fadeController, curve: Curves.easeIn));

    _pulseAnimation = Tween<double>(begin: 1.0, end: 1.15).animate(
      CurvedAnimation(parent: _pulseController, curve: Curves.easeInOut),
    );

    _pulseController.repeat(reverse: true);
    _fadeController.forward();

    _setupNotificationHandler();
    _initializeApp();
  }

  void _setupNotificationHandler() {
    FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
      if (message.data['type'] == 'enc_message') {
        final senderId = int.tryParse(
          message.data['sender_id']?.toString() ?? '',
        );
        if (senderId != null) {
          setState(() => _targetChatId = senderId);
        }
      }
    });
  }

  Future<void> _initializeApp() async {
    if (!mounted) return;
    setState(() => _statusMessage = "Подключение...");

    final authProvider = context.read<AuthProvider>();
    bool? isLoggedIn;
    try {
      isLoggedIn = await authProvider.tryAutoLogin();
    } catch (e) {
      setState(
        () => _statusMessage =
            'Ошибка входа: ${e.toString().replaceAll('Exception: ', '')}',
      );
      await Future.delayed(const Duration(seconds: 3));
      if (mounted) _navigateTo(const LoginScreen());
      return;
    }

    if (!mounted) return;

    if (isLoggedIn) {
      setState(() => _statusMessage = "Аутентификация...");
      bool connected = false;
      int connectAttempt = 1;
      while (!connected) {
        try {
          await authProvider.initRealtime();
          connected = true;
        } catch (e) {
          setState(
            () => _statusMessage = 'Соединение... (попытка $connectAttempt)',
          );
          connectAttempt++;
          await Future.delayed(const Duration(seconds: 2));
        }
      }

      setState(() => _statusMessage = "Загрузка профиля...");
      await authProvider.refreshMe();

      if (authProvider.needsSetup) {
        _navigateTo(const AccountSetupScreen());
      } else if (authProvider.needsKeyRecovery) {
        _navigateTo(const KeyRecoveryScreen());
      } else {
        setState(() => _statusMessage = "Загрузка контактов...");
        _loadContactsAndNavigate(authProvider.currentUserId);
      }
    } else {
      _navigateTo(const LoginScreen());
    }
  }

  Future<void> _loadContactsAndNavigate(int? currentUserId) async {
    final contactProvider = context.read<ContactProvider>();
    final cryptoService = context.read<CryptoService>();

    final int? targetId = await _getTargetChatId();

    // Мгновенно уходим на экран контактов, показывая лоадеры "Дешифровка..."
    _navigateTo(ContactsScreen(targetChatId: targetId));

    try {
      contactProvider.setCurrentUserId(currentUserId);
      await contactProvider.loadContacts(enrichContacts: false);

      final storage = const FlutterSecureStorage();
      final myPrivKeyBase64 = await cryptoService.getPrivateKey();

      if (myPrivKeyBase64 != null) {
        final String privKeyFingerprint = myPrivKeyBase64.replaceAll(RegExp(r'[^a-zA-Z0-9]'), '');
        final String fingerprint = privKeyFingerprint.substring(
            0, privKeyFingerprint.length > 16 ? 16 : privKeyFingerprint.length);

        // Проходим по каждому контакту строго ПО ОЧЕРЕДИ
        for (var c in contactProvider.contacts) {
          final savedKeyHex = await storage.read(
            key: '${_contactSharedKey}${fingerprint}_${c.id}',
          );
          final savedPubKey = await storage.read(
            key: '${_contactPublicKey}${fingerprint}_${c.id}',
          );

          if (savedKeyHex != null && savedPubKey == c.publicKey) {
            // Состояние 1: Ключ уже был в локальном хранилище устройства.
            // Применяем его моментально без ожидания.
            final secretKey = SecretKey(base64Decode(savedKeyHex));
            contactProvider.setSharedKey(c.id, secretKey);
            CryptoService.cacheSharedKey(c.id, secretKey);
          } else if (c.publicKey != null) {
            // Состояние 2: Ключа нет на диске. Вычисляем Диффи-Хеллмана для ЭТОГО конкретного контакта.
            // Цикл приостановится (await), давая UI продышаться и показать анимацию для предыдущих контактов.
            final secretKey = await cryptoService.deriveSharedSecret(
              myPrivKeyBase64,
              c.publicKey!,
              contactId: c.id,
            );

            // Как только ключ готов — ТУТ ЖЕ обновляем провайдер и RAM-кэш для этой строки.
            // Виджет AnimatedSwitcher на экране контактов сразу поймает обновление и красиво проявит текст.
            contactProvider.setSharedKey(c.id, secretKey);
            CryptoService.cacheSharedKey(c.id, secretKey);

            // Извлекаем байты и сохраняем в SecureStorage.
            // Опускаем await для записи на диск, чтобы медленная файловая система не тормозила расчет следующего ключа.
            secretKey.extractBytes().then((bytes) {
              storage.write(
                key: '${_contactSharedKey}${fingerprint}_${c.id}',
                value: base64Encode(bytes),
              );
              storage.write(
                key: '${_contactPublicKey}${fingerprint}_${c.id}',
                value: c.publicKey!,
              );
            });
          }
        }
      }
    } catch (e) {
      print("Ошибка при фоновой загрузке контактов или ключей: $e");
    }
  }

  Future<int?> _getTargetChatId() async {
    int? targetChatId = _targetChatId;
    final prefs = await SharedPreferences.getInstance();

    if (targetChatId == null) {
      final savedData = prefs.getString(_notificationLaunchKey);
      if (savedData != null) {
        try {
          final data = jsonDecode(savedData) as Map<String, dynamic>;
          targetChatId = int.tryParse(data['sender_id']?.toString() ?? '');
        } catch (e) {
          print('Error parsing saved notification data: $e');
        }
      }
    }

    if (targetChatId == null && initialMessage != null) {
      if (initialMessage!.data['type'] == 'enc_message') {
        targetChatId = int.tryParse(
          initialMessage!.data['sender_id']?.toString() ?? '',
        );
      }
    }

    await prefs.remove(_notificationLaunchKey);
    return targetChatId;
  }

  void _navigateTo(Widget screen) {
    if (mounted) {
      Navigator.pushReplacement(
        context,
        MaterialPageRoute(builder: (_) => screen),
      );
    }
  }

  @override
  void dispose() {
    _fadeController.dispose();
    _pulseController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final colorScheme = Theme.of(context).colorScheme;

    return Scaffold(
      body: Stack(
        children: [
          Center(
            child: FadeTransition(
              opacity: _fadeAnimation,
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  const Spacer(),
                  const Spacer(),
                  ScaleTransition(
                    scale: _pulseAnimation,
                    child: Icon(
                      Icons.messenger_outline,
                      size: 80,
                      color: colorScheme.primary,
                    ),
                  ),
                  const SizedBox(height: 24),
                  Text(
                    "Chepuhagram",
                    style: TextStyle(
                      color: colorScheme.primary,
                      fontSize: 32,
                      fontWeight: FontWeight.bold,
                      letterSpacing: 1.2,
                    ),
                  ),
                  const SizedBox(height: 80),
                  SizedBox(
                    height: 40,
                    child: AnimatedSwitcher(
                      duration: const Duration(milliseconds: 300),
                      child: _statusMessage != null
                          ? Text(
                              _statusMessage!,
                              key: ValueKey(_statusMessage),
                              style: TextStyle(
                                color: colorScheme.outline,
                                fontSize: 14,
                              ),
                              textAlign: TextAlign.center,
                            )
                          : const SizedBox.shrink(),
                    ),
                  ),
                  const CircularProgressIndicator(),
                  const Spacer(),
                  Text(
                    'Made by ArturKarasevich',
                    style: TextStyle(color: colorScheme.outline, fontSize: 12),
                  ),
                  const Spacer(),
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }
}