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

frontend/lib/data/datasources/trip_local_datasource.dart

@@ -0,0 +1,83 @@
+import 'dart:convert';
+
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// Defines the contract for persisting trip payloads locally.
+abstract class TripLocalDataSource {
+	/// Returns all saved trip JSON payloads, newest first.
+	Future<List<Map<String, dynamic>>> loadTrips();
+
+	/// Returns a single trip payload by uuid if present.
+  /// TODO - should directly return Trip?
+	Future<Map<String, dynamic>?> getTrip(String uuid);
+
+	/// Upserts the provided trip payload (also used for editing existing trips).
+	Future<void> upsertTrip(Map<String, dynamic> tripJson);
+
+	/// Removes the trip with the matching uuid.
+	Future<void> deleteTrip(String uuid);
+}
+
+class TripLocalDataSourceImpl implements TripLocalDataSource {
+	TripLocalDataSourceImpl({Future<SharedPreferences>? preferences})
+			: _prefsFuture = preferences ?? SharedPreferences.getInstance();
+
+	static const String _storageKey = 'savedTrips';
+	final Future<SharedPreferences> _prefsFuture;
+
+	@override
+	Future<List<Map<String, dynamic>>> loadTrips() async {
+		final prefs = await _prefsFuture;
+		final stored = prefs.getStringList(_storageKey);
+		if (stored == null) return [];
+		return stored.map(_decodeTrip).toList();
+	}
+
+	@override
+	Future<Map<String, dynamic>?> getTrip(String uuid) async {
+		final trips = await loadTrips();
+		for (final trip in trips) {
+			if (trip['uuid'] == uuid) {
+				return Map<String, dynamic>.from(trip);
+			}
+		}
+		return null;
+	}
+
+	@override
+	Future<void> upsertTrip(Map<String, dynamic> tripJson) async {
+		final uuid = tripJson['uuid'];
+		if (uuid is! String || uuid.isEmpty) {
+			throw ArgumentError('Trip JSON must contain a uuid string');
+		}
+
+		final trips = await loadTrips();
+		trips.removeWhere((trip) => trip['uuid'] == uuid);
+		trips.insert(0, Map<String, dynamic>.from(tripJson));
+		await _persistTrips(trips);
+	}
+
+	@override
+	Future<void> deleteTrip(String uuid) async {
+		final trips = await loadTrips();
+		final updated = trips.where((trip) => trip['uuid'] != uuid).toList();
+		if (updated.length == trips.length) {
+			return;
+		}
+		await _persistTrips(updated);
+	}
+
+	Future<void> _persistTrips(List<Map<String, dynamic>> trips) async {
+		final prefs = await _prefsFuture;
+		final payload = trips.map(jsonEncode).toList();
+		await prefs.setStringList(_storageKey, payload);
+	}
+
+	Map<String, dynamic> _decodeTrip(String raw) {
+		final decoded = jsonDecode(raw);
+		if (decoded is! Map<String, dynamic>) {
+			throw const FormatException('Saved trip entry is not a JSON object');
+		}
+		return Map<String, dynamic>.from(decoded);
+	}
+}

frontend/lib/data/repositories/backend_trip_repository.dart

@@ -1,13 +1,15 @@
+import 'package:anyway/data/datasources/trip_local_datasource.dart';
+import 'package:anyway/data/datasources/trip_remote_datasource.dart';
 import 'package:anyway/domain/entities/landmark.dart';
 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/data/datasources/trip_remote_datasource.dart';
 
 class BackendTripRepository implements TripRepository {
   final TripRemoteDataSource remote;
+  final TripLocalDataSource local;
 
-  BackendTripRepository({required this.remote});
+  BackendTripRepository({required this.remote, required this.local});
 
   @override
   Future<Trip> getTrip({Preferences? preferences, String? tripUUID, List<Landmark>? landmarks}) async {
@@ -86,4 +88,27 @@ class BackendTripRepository implements TripRepository {
     prefsPayload['max_time_minute'] = preferences.maxTimeMinutes;
     return prefsPayload;
   }
+
+  // TODO - should this be moved to a separate local repository?
+  @override
+  Future<List<Trip>> getSavedTrips() async {
+    final rawTrips = await local.loadTrips();
+    return rawTrips.map(Trip.fromJson).toList(growable: false);
+  }
+
+  @override
+  Future<Trip?> getSavedTrip(String uuid) async {
+    final json = await local.getTrip(uuid);
+    return json == null ? null : Trip.fromJson(json);
+  }
+
+  @override
+  Future<void> saveTrip(Trip trip) async {
+    await local.upsertTrip(trip.toJson());
+  }
+
+  @override
+  Future<void> deleteSavedTrip(String uuid) async {
+    await local.deleteTrip(uuid);
+  }
 }