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 'cloud/cloud_storage_provider.dart';
import 'cloud/dropbox_provider.dart';
import 'cloud/google_drive_provider.dart';
import 'cloud/onedrive_provider.dart';
import 'cloud/webdav_provider.dart';
import 'cloud_sync_service.dart';
import 'database_service.dart';

const _prefsKeyActiveProviderId = 'active_cloud_provider_id';
const _prefsKeyCloudFolderId = 'cloud_folder_id';
const _prefsKeyCloudFolderPath = 'cloud_folder_path';
const _prefsKeyKeepReceiptPhotosLocally = 'keep_receipt_photos_locally';
const _prefsKeyStaleLockMinutes = 'stale_lock_minutes';
const _prefsKeyKeepMaxQualityReceiptPhotos = 'keep_max_quality_receipt_photos';

const defaultStaleLockMinutes = 10;
const minStaleLockMinutes = 1;
const maxStaleLockMinutes = 60;

/// Thrown by [AppState.addVehicle] when the given VIN already belongs to
/// an active vehicle — VIN is the primary/unique identifier, so adding a
/// duplicate should be rejected rather than silently overwriting it.
class DuplicateVinException implements Exception {
  final String vin;
  DuplicateVinException(this.vin);

  @override
  String toString() => 'A vehicle with VIN "$vin" already exists.';
}

/// Single source of truth for the app's in-memory data (vehicles + fuel
/// entries), backed by [DatabaseService] (local SQLite) for persistence and
/// a [CloudSyncService] for pushing/pulling the shared copy on whichever
/// [CloudStorageProvider] the user has connected. Screens read from this
/// via Provider and call its mutating methods, which write through to the
/// local database immediately and kick off a best-effort background sync.
///
/// The `vehicles`/`fuelEntries` lists are an in-memory read cache of the
/// database, refreshed after every mutation and after every sync (since
/// sync's merge happens as SQL directly against the database, not by
/// handing back updated Dart objects).
class AppState extends ChangeNotifier {
  final DatabaseService database = DatabaseService();

  /// Every storage backend the user can choose from in Settings.
  final List<CloudStorageProvider> availableProviders = [
    GoogleDriveProvider(),
    DropboxProvider(),
    OneDriveProvider(),
    WebDavProvider(),
  ];

  CloudStorageProvider? activeProvider;
  CloudSyncService? cloudSync;

  final _uuid = const Uuid();

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

  String? cloudFolderPath;
  bool isSyncing = false;
  DateTime? lastSyncedAt;
  Object? lastSyncError;

  bool keepReceiptPhotosLocally = false;
  int staleLockMinutes = defaultStaleLockMinutes;

  /// When false (default), a newly captured receipt photo is downscaled
  /// and re-compressed to [receiptImageMaxDimension]/[receiptImageQuality]
  /// before it's stored — receipts are just photos of small printed text,
  /// so a full-resolution original (often several MB on a modern phone
  /// camera) buys nothing but cloud storage and sync bandwidth. When true,
  /// the original camera/gallery image is kept as-is.
  bool keepMaxQualityReceiptPhotos = false;

  /// Set if [init] fails. The UI shows this (with a retry option) instead
  /// of spinning forever — an unhandled exception here previously left
  /// `isLoading` stuck at true with no feedback at all.
  Object? initError;

  bool get isCloudConnected => activeProvider?.isSignedIn ?? false;
  String? get cloudAccountLabel => activeProvider?.accountLabel;

  StreamSubscription<List<ConnectivityResult>>? _connectivitySubscription;

  Future<void> init() async {
    isLoading = true;
    initError = null;
    notifyListeners();

    try {
      await database.init();
      await _refreshFromDatabase();

      final prefs = await SharedPreferences.getInstance();
      keepReceiptPhotosLocally = prefs.getBool(_prefsKeyKeepReceiptPhotosLocally) ?? false;
      staleLockMinutes = prefs.getInt(_prefsKeyStaleLockMinutes) ?? defaultStaleLockMinutes;
      keepMaxQualityReceiptPhotos =
          prefs.getBool(_prefsKeyKeepMaxQualityReceiptPhotos) ?? false;
    } catch (e) {
      initError = e;
      isLoading = false;
      notifyListeners();
      return;
    }

    isLoading = false;
    notifyListeners();

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

    unawaited(_restoreCloudConnection());
  }

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

  Future<void> _refreshFromDatabase() async {
    vehicles = await database.getVehicles();
    fuelEntries = await database.getFuelEntries();
  }

  CloudStorageProvider? _providerById(CloudProviderId id) {
    for (final provider in availableProviders) {
      if (provider.id == id) return provider;
    }
    return null;
  }

  Future<void> _restoreCloudConnection() async {
    final prefs = await SharedPreferences.getInstance();
    final storedProviderName = prefs.getString(_prefsKeyActiveProviderId);
    if (storedProviderName == null) return;

    final matchingId = CloudProviderId.values
        .where((id) => id.name == storedProviderName)
        .firstOrNull;
    final provider = matchingId == null ? null : _providerById(matchingId);
    if (provider == null) return;

    final signedIn = await provider.attemptSilentSignIn();
    if (!signedIn) return;

    activeProvider = provider;
    cloudSync = CloudSyncService(provider: provider, databaseService: database);

    final folderId = prefs.getString(_prefsKeyCloudFolderId);
    cloudFolderPath = prefs.getString(_prefsKeyCloudFolderPath);
    if (folderId != null) {
      cloudSync!.configure(folderId);
    }
    notifyListeners();

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

  Future<void> connectProvider(CloudProviderId id) async {
    final provider = _providerById(id);
    if (provider == null) return;

    await provider.signIn();
    activeProvider = provider;
    cloudSync = CloudSyncService(provider: provider, databaseService: database);

    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_prefsKeyActiveProviderId, id.name);
    notifyListeners();
  }

  /// Like [connectProvider], but for a [ManualCredentialCloudStorageProvider]
  /// (currently just WebDAV) that needs a server URL/username/password
  /// instead of an OAuth browser flow. The caller (Settings) is responsible
  /// for collecting those from the user first.
  Future<void> connectProviderWithCredentials(
    CloudProviderId id, {
    required String serverUrl,
    required String username,
    required String password,
  }) async {
    final provider = _providerById(id);
    if (provider == null || provider is! ManualCredentialCloudStorageProvider) return;

    await (provider as ManualCredentialCloudStorageProvider).signInWithCredentials(
      serverUrl: serverUrl,
      username: username,
      password: password,
    );
    activeProvider = provider;
    cloudSync = CloudSyncService(provider: provider, databaseService: database);

    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_prefsKeyActiveProviderId, id.name);
    notifyListeners();
  }

  Future<void> disconnectCloud() async {
    final provider = activeProvider;
    if (provider == null) return;

    await provider.signOut();
    cloudSync?.clearConfiguration();
    activeProvider = null;
    cloudSync = null;
    cloudFolderPath = null;

    final prefs = await SharedPreferences.getInstance();
    await prefs.remove(_prefsKeyActiveProviderId);
    await prefs.remove(_prefsKeyCloudFolderId);
    await prefs.remove(_prefsKeyCloudFolderPath);
    notifyListeners();
  }

  Future<void> chooseCloudFolder({
    required String parentId,
    required String breadcrumbPath,
    String? currentFolderName,
  }) async {
    final sync = cloudSync;
    if (sync == null) return;

    final folderId =
        await sync.selectAppFolder(parentId, currentFolderName: currentFolderName);
    cloudFolderPath = breadcrumbPath;

    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_prefsKeyCloudFolderId, folderId);
    await prefs.setString(_prefsKeyCloudFolderPath, breadcrumbPath);
    notifyListeners();

    unawaited(syncNow());
  }

  Future<void> syncNow() async {
    final sync = cloudSync;
    if (isSyncing || sync == null || !sync.isConfigured) return;

    isSyncing = true;
    notifyListeners();

    final result = await sync.syncNow(
      keepLocalReceiptCopies: keepReceiptPhotosLocally,
      staleLockAge: Duration(minutes: staleLockMinutes),
    );

    if (result.ranSync) {
      await _refreshFromDatabase();
      lastSyncedAt = DateTime.now();
      lastSyncError = null;
    } else if (result.error != null) {
      lastSyncError = result.error;
    }

    isSyncing = false;
    notifyListeners();
  }

  Future<void> setKeepReceiptPhotosLocally(bool value) async {
    keepReceiptPhotosLocally = value;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setBool(_prefsKeyKeepReceiptPhotosLocally, value);
    notifyListeners();
  }

  Future<void> setKeepMaxQualityReceiptPhotos(bool value) async {
    keepMaxQualityReceiptPhotos = value;
    final prefs = await SharedPreferences.getInstance();
    await prefs.setBool(_prefsKeyKeepMaxQualityReceiptPhotos, value);
    notifyListeners();
  }

  /// Clamped to [minStaleLockMinutes, maxStaleLockMinutes] — see the
  /// Settings "Advanced" section, which restricts the picker to that range
  /// anyway; this is a defensive backstop for any other caller.
  Future<void> setStaleLockMinutes(int minutes) async {
    staleLockMinutes = minutes.clamp(minStaleLockMinutes, maxStaleLockMinutes);
    final prefs = await SharedPreferences.getInstance();
    await prefs.setInt(_prefsKeyStaleLockMinutes, staleLockMinutes);
    notifyListeners();
  }

  /// Throws [DuplicateVinException] if [vin] already belongs to another
  /// active vehicle — VIN must stay unique even though it's editable, so
  /// silently letting a duplicate through would be a real correctness bug,
  /// not just a UX wrinkle.
  Future<void> addVehicle({
    required String vin,
    String? nickname,
  }) async {
    if (await database.vinExists(vin)) {
      throw DuplicateVinException(vin);
    }
    final vehicle = Vehicle(
      id: _uuid.v4(),
      vin: vin,
      nickname: nickname,
      updatedAt: DateTime.now().toUtc(),
    );
    await database.saveVehicle(vehicle);
    await _persist();
  }

  /// Throws [DuplicateVinException] if [updated]'s VIN now collides with
  /// another active vehicle's — this is the check [addVehicle] does for a
  /// new vehicle, but here it also has to exclude the vehicle being edited
  /// itself (its VIN obviously still matches its own prior value if it
  /// wasn't changed).
  Future<void> updateVehicle(Vehicle updated) async {
    if (await database.vinExists(updated.vin, excludeId: updated.id)) {
      throw DuplicateVinException(updated.vin);
    }
    await database.saveVehicle(updated.copyWith(updatedAt: DateTime.now().toUtc()));
    await _persist();
  }

  Future<void> deleteVehicle(String id) async {
    final now = DateTime.now().toUtc();
    final orphanedLocalPaths = await database.softDeleteFuelEntriesForVehicle(id, now);
    for (final path in orphanedLocalPaths) {
      await database.deleteReceiptImageFile(path);
    }
    await database.softDeleteVehicle(id, now);
    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) {
      final vin = vehicles.firstWhere((v) => v.id == vehicleId).vin;
      storedImagePath = await database.storeReceiptImage(receiptImage, id, vin, date);
    }

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

  Future<void> deleteFuelEntry(String entryId) async {
    final entry = fuelEntries.firstWhere((e) => e.id == entryId);
    await database.deleteReceiptImageFile(entry.receiptImagePath);
    await database.softDeleteFuelEntry(entryId, DateTime.now().toUtc());
    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;
    }
  }

  /// Exact match against an active vehicle's VIN — same comparison
  /// [DatabaseService.vinExists] does, not case-insensitive, since VIN
  /// isn't normalized to any particular case on manual entry (only OCR
  /// scanning uppercases it).
  Vehicle? vehicleByVin(String vin) {
    try {
      return vehicles.firstWhere((v) => v.vin == vin);
    } catch (_) {
      return null;
    }
  }

  Future<void> _persist() async {
    await _refreshFromDatabase();
    notifyListeners();
    unawaited(syncNow());
  }
}

extension _FirstOrNull<T> on Iterable<T> {
  T? get firstOrNull => isEmpty ? null : first;
}