added categories, import export, settings

lib/services/app_settings.dart

@@ -0,0 +1,89 @@
+/// App-wide settings: dark mode and the user supermarket list.
+library;
+
+import 'package:flutter/material.dart';
+
+import '../models/supermarket.dart';
+import '../utils/supermarkets.dart';
+import 'product_repository.dart';
+
+class AppSettings extends ChangeNotifier {
+  AppSettings(this.repository);
+
+  final ProductRepository repository;
+
+  bool darkMode = false;
+  List<Supermarket> supermarkets = List<Supermarket>.from(kDefaultSupermarkets);
+  int catalogGeneration = 0;
+
+  Future<void> load() async {
+    try {
+      darkMode = await repository.getDarkMode();
+      supermarkets = await repository.getSupermarkets();
+      notifyListeners();
+    } catch (_) {
+      // Widget tests and first-run without a plugin keep the defaults.
+    }
+  }
+
+  Future<void> setDarkMode(bool enabled) async {
+    darkMode = enabled;
+    notifyListeners();
+    try {
+      await repository.setDarkMode(enabled);
+    } catch (_) {}
+  }
+
+  Future<void> addSupermarket(String name, int colorValue) async {
+    final trimmed = name.trim();
+    if (trimmed.isEmpty) return;
+    final store = await repository.addSupermarket(
+      name: trimmed,
+      colorValue: colorValue,
+    );
+    supermarkets = [...supermarkets, store];
+    notifyListeners();
+  }
+
+  Future<void> updateSupermarket(Supermarket store) async {
+    await repository.updateSupermarket(store);
+    supermarkets = [
+      for (final item in supermarkets)
+        if (item.id == store.id) store else item,
+    ];
+    notifyListeners();
+  }
+
+  Future<void> deleteSupermarket(int id) async {
+    await repository.deleteSupermarket(id);
+    supermarkets = [
+      for (final item in supermarkets)
+        if (item.id != id) item,
+    ];
+    notifyListeners();
+  }
+
+  Future<void> reload() async {
+    await load();
+    catalogGeneration++;
+    notifyListeners();
+  }
+}
+
+class SettingsScope extends InheritedNotifier<AppSettings> {
+  const SettingsScope({
+    super.key,
+    required AppSettings settings,
+    required super.child,
+  }) : super(notifier: settings);
+
+  static AppSettings of(BuildContext context) {
+    final scope = context.dependOnInheritedWidgetOfExactType<SettingsScope>();
+    assert(scope != null, 'SettingsScope not found');
+    return scope!.notifier!;
+  }
+
+  static AppSettings? maybeOf(BuildContext context) {
+    return context.dependOnInheritedWidgetOfExactType<SettingsScope>()?.notifier;
+  }
+}