created viewmodel and multiple tests

compass_app/app/lib/common/utils/response.dart

@@ -1,17 +0,0 @@
-sealed class Response<T> {
-  const Response();
-  factory Response.ok(T value) => Ok(value);
-  factory Response.error(Exception error) => Error(error);
-  Ok<T> get asOk => this as Ok<T>;
-  Error get asError => this as Error<T>;
-}
-
-final class Ok<T> extends Response<T> {
-  const Ok(this.value);
-  final T value;
-}
-
-final class Error<T> extends Response<T> {
-  const Error(this.error);
-  final Exception error;
-}

compass_app/app/lib/common/utils/result.dart

@@ -0,0 +1,23 @@
+sealed class Result<T> {
+  const Result();
+  factory Result.ok(T value) => Ok(value);
+  factory Result.error(Exception error) => Error(error);
+  Ok<T> get asOk => this as Ok<T>;
+  Error get asError => this as Error<T>;
+}
+
+final class Ok<T> extends Result<T> {
+  const Ok(this.value);
+  final T value;
+
+  @override
+  String toString() => 'Result<$T>.ok($value)';
+}
+
+final class Error<T> extends Result<T> {
+  const Error(this.error);
+  final Exception error;
+
+  @override
+  String toString() => 'Result<$T>.error($error)';
+}

compass_app/app/lib/features/results/business/model/destination.dart

@@ -29,4 +29,9 @@ class Destination {
 
   /// e.g. 'https://storage.googleapis.com/tripedia-images/destinations/alaska.jpg'
   final String imageUrl;
+
+  @override
+  String toString() {
+    return 'Destination{ref: $ref, name: $name, country: $country, continent: $continent, knownFor: $knownFor, tags: $tags, imageUrl: $imageUrl}';
+  }
 }

compass_app/app/lib/features/results/business/usecases/search_destination_usecase.dart

@@ -1,22 +1,25 @@
-import 'package:compass_app/common/utils/response.dart';
+import 'package:compass_app/common/utils/result.dart';
 import 'package:compass_app/features/results/business/model/destination.dart';
 import 'package:compass_app/features/results/data/destination_repository.dart';
 
 /// Perform search over possible destinations
 class SearchDestinationUsecase {
-  SearchDestinationUsecase({required this.repository});
+  SearchDestinationUsecase({
+    required DestinationRepository repository,
+  }) : _repository = repository;
 
-  final DestinationRepository repository;
+  final DestinationRepository _repository;
 
-  Future<Response<List<Destination>>> search({ String? continent }) async {
+  Future<Result<List<Destination>>> search({String? continent}) async {
     bool filter(Destination destination) {
       return (continent == null || destination.continent == continent);
     }
 
-    final response = await repository.getDestinations();
-    return switch (response) {
-      Ok() => Response.ok(response.value.where(filter).toList()),
-      Error() => response,
+    final result = await _repository.getDestinations();
+    print('Result: $result');
+    return switch (result) {
+      Ok() => Result.ok(result.value.where(filter).toList()),
+      Error() => result,
     };
   }
-}
+}

compass_app/app/lib/features/results/data/destination_repository.dart

@@ -1,12 +1,12 @@
-import 'package:compass_app/common/utils/response.dart';
+import 'package:compass_app/common/utils/result.dart';
 import 'package:compass_app/features/results/business/model/destination.dart';
 
 /// Data source with all possible destinations
 class DestinationRepository {
 
   /// Get complete list of destinations
-  Future<Response<List<Destination>>> getDestinations() {
+  Future<Result<List<Destination>>> getDestinations() {
     // TODO: Load some data
-    return Future.value(Response.ok([]));
+    return Future.value(Result.ok([]));
   }
 }

compass_app/app/lib/features/results/presentation/results_screen.dart

@@ -0,0 +1,26 @@
+import 'package:compass_app/features/results/presentation/results_viewmodel.dart';
+import 'package:flutter/material.dart';
+
+class ResultsScreen extends StatelessWidget {
+  const ResultsScreen({
+    super.key,
+    required this.resultsViewModel,
+  });
+
+  final ResultsViewModel resultsViewModel;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: ListenableBuilder(
+        listenable: resultsViewModel,
+        builder: (BuildContext context, Widget? child) {
+          if (resultsViewModel.loading) {
+            return const CircularProgressIndicator();
+          }
+          return const Placeholder();
+        },
+      ),
+    );
+  }
+}

compass_app/app/lib/features/results/presentation/results_viewmodel.dart

@@ -0,0 +1,48 @@
+import 'package:compass_app/common/utils/result.dart';
+import 'package:compass_app/features/results/business/model/destination.dart';
+import 'package:compass_app/features/results/business/usecases/search_destination_usecase.dart';
+import 'package:flutter/cupertino.dart';
+
+/// Based on https://docs.flutter.dev/get-started/fwe/state-management#using-mvvm-for-your-applications-architecture
+class ResultsViewModel extends ChangeNotifier {
+  ResultsViewModel({
+    required SearchDestinationUsecase searchDestinationUsecase,
+  }) : _searchDestinationUsecase = searchDestinationUsecase;
+
+  final SearchDestinationUsecase _searchDestinationUsecase;
+
+  // Expose values in ViewModel using getters, hide setters
+  List<Destination> _destinations = [];
+  bool _loading = false;
+
+  /// List of destinations, may be empty but never null
+  List<Destination> get destinations => _destinations;
+
+  /// Loading state
+  bool get loading => _loading;
+
+  /// Perform search
+  Future<void> search({String? continent}) async {
+    // Set loading state and notify the view
+    _loading = true;
+    notifyListeners();
+
+    // Call the search usecase and request data
+    final result = await _searchDestinationUsecase.search(continent: continent);
+    // Set loading state to false
+    _loading = false;
+    switch (result) {
+      case Ok(): {
+        // If the result is Ok, update the list of destinations
+        _destinations = result.value;
+      }
+      case Error(): {
+        // TODO: Handle error
+        print(result.error);
+      }
+    }
+
+    // After finish loading results, notify the view
+    notifyListeners();
+  }
+}

compass_app/app/test/features/results/business/usecases/search_destination_usecase_test.dart

@@ -1,4 +1,4 @@
-import 'package:compass_app/common/utils/response.dart';
+import 'package:compass_app/common/utils/result.dart';
 import 'package:compass_app/features/results/business/model/destination.dart';
 import 'package:compass_app/features/results/business/usecases/search_destination_usecase.dart';
 import 'package:compass_app/features/results/data/destination_repository.dart';
@@ -24,13 +24,24 @@ void main() {
       expect(result.asOk.value.first.name, 'name1');
     });
   });
+
+  group('SearchDestinationUsecase errors', () {
+    final errorRepository = _ErrorRepository();
+    final usecase = SearchDestinationUsecase(repository: errorRepository);
+
+    test('should return error', () async {
+      final result = await usecase.search();
+      expect(result, isA<Error>());
+      expect(result.asError.error, isNotNull);
+    });
+  });
 }
 
 class _FakeRepository implements DestinationRepository {
   @override
-  Future<Response<List<Destination>>> getDestinations() {
+  Future<Result<List<Destination>>> getDestinations() {
     return Future.value(
-      Response.ok(
+      Result.ok(
         [
           Destination(
             ref: 'ref1',
@@ -55,3 +66,10 @@ class _FakeRepository implements DestinationRepository {
     );
   }
 }
+
+class _ErrorRepository implements DestinationRepository {
+  @override
+  Future<Result<List<Destination>>> getDestinations() {
+    return Future.value(Result<List<Destination>>.error(Exception('Invalid')));
+  }
+}

compass_app/app/test/features/results/presentation/results_viewmodel_test.dart

@@ -0,0 +1,38 @@
+import 'package:compass_app/common/utils/result.dart';
+import 'package:compass_app/features/results/business/model/destination.dart';
+import 'package:compass_app/features/results/business/usecases/search_destination_usecase.dart';
+import 'package:compass_app/features/results/presentation/results_viewmodel.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('ResultsViewModel tests', () {
+    final fakeUsecase = _FakeUsecase();
+    final viewModel = ResultsViewModel(searchDestinationUsecase: fakeUsecase);
+
+    // perform a simple test
+    // verifies that the list of items is properly loaded
+    // TODO: Verify loading state and calls to search method
+    test('should load items', () async {
+      expect(viewModel.destinations.length, 0);
+      await viewModel.search();
+      expect(viewModel.destinations.length, 1);
+    });
+  });
+}
+
+class _FakeUsecase implements SearchDestinationUsecase {
+  @override
+  Future<Result<List<Destination>>> search({String? continent}) async {
+    return Result.ok([
+      Destination(
+        ref: 'ref1',
+        name: 'name1',
+        country: 'country1',
+        continent: 'continent1',
+        knownFor: 'knownFor1',
+        tags: ['tags1'],
+        imageUrl: 'imageUrl1',
+      ),
+    ]);
+  }
+}