feat(wip): implement trip persistence through a local repository. Include loaded trips in the start page UI

frontend/lib/presentation/providers/trip_provider.dart

@@ -1,16 +1,86 @@
+import 'dart:async';
+
 import 'package:anyway/domain/entities/preferences.dart';
 import 'package:anyway/domain/entities/trip.dart';
+import 'package:anyway/domain/repositories/trip_repository.dart';
 import 'package:anyway/presentation/providers/landmark_providers.dart';
-
-import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:anyway/presentation/providers/core_providers.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 // Provides a function that creates a trip given preferences.
 final createTripProvider = Provider<Future<Trip> Function(Preferences)>((ref) {
-	return (Preferences prefs) async {
-		final repo = ref.read(tripRepositoryProvider);
-		final landmarks = await repo.searchLandmarks(prefs);
-		ref.read(intermediateLandmarksProvider.notifier).setLandmarks(landmarks);
-		return repo.getTrip(preferences: prefs, landmarks: landmarks);
-	};
+  return (Preferences prefs) async {
+    final repo = ref.read(tripRepositoryProvider);
+    final landmarks = await repo.searchLandmarks(prefs);
+    ref.read(intermediateLandmarksProvider.notifier).setLandmarks(landmarks);
+    final trip = await repo.getTrip(preferences: prefs, landmarks: landmarks);
+    await ref.read(currentTripsProvider.notifier).saveTrip(trip);
+    return trip;
+  };
 });
+
+class CurrentTripsNotifier extends AsyncNotifier<List<Trip>> {
+  TripRepository get _repository => ref.read(tripRepositoryProvider);
+  Future<List<Trip>>? _pendingLoad;
+
+  List<Trip> _currentTrips() => state.asData?.value ?? const <Trip>[];
+
+  @override
+  Future<List<Trip>> build() async {
+    final load = _repository.getSavedTrips();
+    _pendingLoad = load;
+    try {
+      final trips = await load;
+      return List.unmodifiable(trips);
+    } finally {
+      if (identical(_pendingLoad, load)) {
+        _pendingLoad = null;
+      }
+    }
+  }
+
+  Future<void> refresh() async {
+    state = const AsyncValue.loading();
+    final load = _repository.getSavedTrips();
+    _pendingLoad = load;
+    state = await AsyncValue.guard(() async {
+      final trips = await load;
+      return List.unmodifiable(trips);
+    });
+    if (identical(_pendingLoad, load)) {
+      _pendingLoad = null;
+    }
+  }
+
+  Future<void> saveTrip(Trip trip) async {
+    final previous = state;
+    final updatedTrips = [..._currentTrips()]
+      ..removeWhere((t) => t.uuid == trip.uuid)
+      ..insert(0, trip);
+    state = AsyncValue.data(List.unmodifiable(updatedTrips));
+
+    try {
+      await _repository.saveTrip(trip);
+    } catch (error) {
+      state = previous;
+      rethrow;
+    }
+  }
+
+  Future<void> deleteTrip(String uuid) async {
+    final previous = state;
+    final updatedTrips = _currentTrips()
+        .where((trip) => trip.uuid != uuid)
+        .toList(growable: false);
+    state = AsyncValue.data(List.unmodifiable(updatedTrips));
+
+    try {
+      await _repository.deleteSavedTrip(uuid);
+    } catch (error) {
+      state = previous;
+      rethrow;
+    }
+  }
+}
+
+final currentTripsProvider = AsyncNotifierProvider<CurrentTripsNotifier, List<Trip>>(CurrentTripsNotifier.new);