Compass app (#2446)

compass_app/app/lib/ui/results/view_models/results_viewmodel.dart

@@ -0,0 +1,111 @@
+// Copyright 2024 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:logging/logging.dart';
+
+import '../../../data/repositories/destination/destination_repository.dart';
+import '../../../data/repositories/itinerary_config/itinerary_config_repository.dart';
+import '../../../domain/models/destination/destination.dart';
+import '../../../domain/models/itinerary_config/itinerary_config.dart';
+import '../../../utils/command.dart';
+import '../../../utils/result.dart';
+import 'package:flutter/cupertino.dart';
+
+/// Results screen view model
+/// Based on https://docs.flutter.dev/get-started/fwe/state-management#using-mvvm-for-your-applications-architecture
+class ResultsViewModel extends ChangeNotifier {
+  ResultsViewModel({
+    required DestinationRepository destinationRepository,
+    required ItineraryConfigRepository itineraryConfigRepository,
+  })  : _destinationRepository = destinationRepository,
+        _itineraryConfigRepository = itineraryConfigRepository {
+    updateItineraryConfig = Command1<void, String>(_updateItineraryConfig);
+    search = Command0(_search)..execute();
+  }
+
+  final _log = Logger('ResultsViewModel');
+
+  final DestinationRepository _destinationRepository;
+
+  final ItineraryConfigRepository _itineraryConfigRepository;
+
+  // Setters are private
+  List<Destination> _destinations = [];
+
+  /// List of destinations, may be empty but never null
+  List<Destination> get destinations => _destinations;
+
+  ItineraryConfig? _itineraryConfig;
+
+  /// Filter options to display on search bar
+  ItineraryConfig get config => _itineraryConfig ?? const ItineraryConfig();
+
+  /// Perform search
+  late final Command0 search;
+
+  /// Store ViewModel data into [ItineraryConfigRepository] before navigating.
+  late final Command1<void, String> updateItineraryConfig;
+
+  Future<Result<void>> _search() async {
+    // Load current itinerary config
+    final resultConfig = await _itineraryConfigRepository.getItineraryConfig();
+    if (resultConfig is Error) {
+      _log.warning(
+        'Failed to load stored ItineraryConfig',
+        resultConfig.asError.error,
+      );
+      return resultConfig;
+    }
+    _itineraryConfig = resultConfig.asOk.value;
+    notifyListeners();
+
+    final result = await _destinationRepository.getDestinations();
+    switch (result) {
+      case Ok():
+        {
+          // If the result is Ok, update the list of destinations
+          _destinations = result.value
+              .where((destination) =>
+                  destination.continent == _itineraryConfig!.continent)
+              .toList();
+          _log.fine('Destinations (${_destinations.length}) loaded');
+        }
+      case Error():
+        {
+          _log.warning('Failed to load destinations', result.error);
+        }
+    }
+
+    // After finish loading results, notify the view
+    notifyListeners();
+    return result;
+  }
+
+  Future<Result<void>> _updateItineraryConfig(String destinationRef) async {
+    assert(destinationRef.isNotEmpty, "destinationRef should not be empty");
+
+    final resultConfig = await _itineraryConfigRepository.getItineraryConfig();
+    if (resultConfig is Error) {
+      _log.warning(
+        'Failed to load stored ItineraryConfig',
+        resultConfig.asError.error,
+      );
+      return resultConfig;
+    }
+
+    final itineraryConfig = resultConfig.asOk.value;
+    final result = await _itineraryConfigRepository
+        .setItineraryConfig(itineraryConfig.copyWith(
+      destination: destinationRef,
+      activities: [],
+    ));
+    if (result is Error) {
+      _log.warning(
+        'Failed to store ItineraryConfig',
+        result.asError.error,
+      );
+    }
+    return result;
+  }
+}