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lib/shared/services/billing_service.dart

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+import 'package:shared_preferences/shared_preferences.dart';
+import '../models/user_model.dart';
+
+abstract class BillingService {
+  Future<bool> purchasePro();
+  Future<bool> restorePurchases();
+  Future<UserPlan> getCurrentPlan();
+}
+
+class MockBillingService implements BillingService {
+  static const _key = 'user_plan';
+  final SharedPreferences _prefs;
+
+  MockBillingService(this._prefs);
+
+  @override
+  Future<bool> purchasePro() async {
+    await Future.delayed(const Duration(seconds: 1));
+    await _prefs.setString(_key, 'vip');
+    return true;
+  }
+
+  @override
+  Future<bool> restorePurchases() async {
+    await Future.delayed(const Duration(seconds: 1));
+    return false;
+  }
+
+  @override
+  Future<UserPlan> getCurrentPlan() async {
+    final value = _prefs.getString(_key);
+    return value == 'vip' ? UserPlan.vip : UserPlan.free;
+  }
+}