import 'dart:async';
import 'dart:io';

import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:uuid/uuid.dart';

import '../models/fuel_entry.dart';
import '../models/vehicle.dart';
import 'drive_auth_service.dart';
import 'drive_sync_service.dart';
import 'storage_service.dart';

const _prefsKeyDriveFolderId = 'drive_app_folder_id';
const _prefsKeyDriveFolderPath = 'drive_app_folder_path';

/// Single source of truth for the app's in-memory data (vehicles + fuel
/// entries), backed by [StorageService] for local persistence and
/// [DriveSyncService] for pushing/pulling the shared Drive copy. Screens
/// read from this via Provider and call its mutating methods, which write
/// through to local disk immediately and kick off a best-effort background
/// sync to Drive.
class AppState extends ChangeNotifier {
  final StorageService storage = StorageService();
  final DriveAuthService driveAuth = DriveAuthService();
  late final DriveSyncService driveSync =
      DriveSyncService(authService: driveAuth, storageService: storage);
  final _uuid = const Uuid();

  List<Vehicle> vehicles = [];
  List<FuelEntry> fuelEntries = [];
  bool isLoading = true;

  bool isDriveConnected = false;
  String? driveAccountEmail;
  String? driveFolderPath;
  bool isSyncing = false;
  DateTime? lastSyncedAt;
  Object? lastSyncError;

  StreamSubscription<List<ConnectivityResult>>? _connectivitySubscription;

  Future<void> init() async {
    await storage.init();
    final data = await storage.loadData();
    vehicles = data.vehicles;
    fuelEntries = data.entries;
    isLoading = false;
    notifyListeners();

    _connectivitySubscription = Connectivity().onConnectivityChanged.listen((results) {
      if (results.any((r) => r != ConnectivityResult.none)) {
        unawaited(syncNow());
      }
    });

    unawaited(_restoreDriveConnection());
  }

  @override
  void dispose() {
    _connectivitySubscription?.cancel();
    super.dispose();
  }

  Future<void> _restoreDriveConnection() async {
    final signedIn = await driveAuth.attemptSilentSignIn();
    if (!signedIn) return;

    isDriveConnected = true;
    driveAccountEmail = driveAuth.currentAccountEmail;

    final prefs = await SharedPreferences.getInstance();
    final folderId = prefs.getString(_prefsKeyDriveFolderId);
    driveFolderPath = prefs.getString(_prefsKeyDriveFolderPath);
    if (folderId != null) {
      driveSync.configure(folderId);
    }
    notifyListeners();

    if (folderId != null) {
      unawaited(syncNow());
    }
  }

  Future<void> connectDrive() async {
    final email = await driveAuth.signIn();
    isDriveConnected = true;
    driveAccountEmail = email;
    notifyListeners();
  }

  Future<void> disconnectDrive() async {
    await driveAuth.signOut();
    driveSync.clearConfiguration();
    isDriveConnected = false;
    driveAccountEmail = null;
    driveFolderPath = null;

    final prefs = await SharedPreferences.getInstance();
    await prefs.remove(_prefsKeyDriveFolderId);
    await prefs.remove(_prefsKeyDriveFolderPath);
    notifyListeners();
  }

  Future<void> chooseDriveFolder({
    required String parentId,
    required String breadcrumbPath,
  }) async {
    final folderId = await driveSync.selectAppFolder(parentId);
    driveFolderPath = breadcrumbPath;

    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_prefsKeyDriveFolderId, folderId);
    await prefs.setString(_prefsKeyDriveFolderPath, breadcrumbPath);
    notifyListeners();

    unawaited(syncNow());
  }

  Future<void> syncNow() async {
    if (isSyncing || !driveSync.isConfigured) return;

    isSyncing = true;
    notifyListeners();

    final result = await driveSync.syncNow(
      localVehicles: vehicles,
      localFuelEntries: fuelEntries,
    );

    if (result.ranSync) {
      vehicles = result.vehicles!;
      fuelEntries = result.fuelEntries!;
      await storage.saveData(vehicles: vehicles, entries: fuelEntries);
      lastSyncedAt = DateTime.now();
      lastSyncError = null;
    } else if (result.error != null) {
      lastSyncError = result.error;
    }

    isSyncing = false;
    notifyListeners();
  }

  Future<void> addVehicle({
    required String make,
    required String model,
    required String color,
    required String licensePlate,
  }) async {
    vehicles.add(Vehicle(
      id: _uuid.v4(),
      make: make,
      model: model,
      color: color,
      licensePlate: licensePlate,
      updatedAt: DateTime.now().toUtc(),
    ));
    await _persist();
  }

  Future<void> updateVehicle(Vehicle updated) async {
    final index = vehicles.indexWhere((v) => v.id == updated.id);
    if (index != -1) {
      vehicles[index] = updated.copyWith(updatedAt: DateTime.now().toUtc());
      await _persist();
    }
  }

  Future<void> deleteVehicle(String vehicleId) async {
    for (final entry in fuelEntries.where((e) => e.vehicleId == vehicleId)) {
      await storage.deleteReceiptImage(entry.receiptImagePath);
    }
    fuelEntries.removeWhere((e) => e.vehicleId == vehicleId);
    vehicles.removeWhere((v) => v.id == vehicleId);
    await _persist();
  }

  Future<FuelEntry> addFuelEntry({
    required String vehicleId,
    required DateTime date,
    required double gallons,
    required double pricePerGallon,
    required double totalCost,
    File? receiptImage,
  }) async {
    final id = _uuid.v4();
    String? storedImagePath;
    if (receiptImage != null) {
      storedImagePath = await storage.storeReceiptImage(receiptImage, id);
    }

    final entry = FuelEntry(
      id: id,
      vehicleId: vehicleId,
      date: date,
      gallons: gallons,
      pricePerGallon: pricePerGallon,
      totalCost: totalCost,
      receiptImagePath: storedImagePath,
      updatedAt: DateTime.now().toUtc(),
    );
    fuelEntries.add(entry);
    await _persist();
    return entry;
  }

  Future<void> deleteFuelEntry(String entryId) async {
    final entry = fuelEntries.firstWhere((e) => e.id == entryId);
    await storage.deleteReceiptImage(entry.receiptImagePath);
    fuelEntries.removeWhere((e) => e.id == entryId);
    await _persist();
  }

  List<FuelEntry> entriesForVehicle(String vehicleId) {
    final list = fuelEntries.where((e) => e.vehicleId == vehicleId).toList();
    list.sort((a, b) => b.date.compareTo(a.date));
    return list;
  }

  double totalGallonsForVehicle(String vehicleId) => fuelEntries
      .where((e) => e.vehicleId == vehicleId)
      .fold(0.0, (sum, e) => sum + e.gallons);

  double get totalGallonsAllVehicles =>
      fuelEntries.fold(0.0, (sum, e) => sum + e.gallons);

  Vehicle? vehicleById(String id) {
    try {
      return vehicles.firstWhere((v) => v.id == id);
    } catch (_) {
      return null;
    }
  }

  Future<void> _persist() async {
    await storage.saveData(vehicles: vehicles, entries: fuelEntries);
    notifyListeners();
    unawaited(syncNow());
  }
}