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lib/services/app_state.dart

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+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:uuid/uuid.dart';
+
+import '../models/fuel_entry.dart';
+import '../models/vehicle.dart';
+import 'storage_service.dart';
+
+/// Single source of truth for the app's in-memory data (vehicles + fuel
+/// entries), backed by [StorageService] for persistence. Screens read from
+/// this via Provider and call its mutating methods, which take care of
+/// writing through to disk and notifying listeners.
+class AppState extends ChangeNotifier {
+  final StorageService storage = StorageService();
+  final _uuid = const Uuid();
+
+  List<Vehicle> vehicles = [];
+  List<FuelEntry> fuelEntries = [];
+  bool isLoading = true;
+
+  Future<void> init() async {
+    await storage.init();
+    final data = await storage.loadData();
+    vehicles = data.vehicles;
+    fuelEntries = data.entries;
+    isLoading = 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,
+    ));
+    await _persist();
+  }
+
+  Future<void> updateVehicle(Vehicle updated) async {
+    final index = vehicles.indexWhere((v) => v.id == updated.id);
+    if (index != -1) {
+      vehicles[index] = updated;
+      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,
+    );
+    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> changeSaveDirectory(String newPath) async {
+    await storage.setSaveDirectory(newPath);
+    notifyListeners();
+  }
+
+  Future<void> _persist() async {
+    await storage.saveData(vehicles: vehicles, entries: fuelEntries);
+    notifyListeners();
+  }
+}