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

frontend/lib/presentation/utils/trip_location_utils.dart

@@ -0,0 +1,78 @@
+import 'package:anyway/domain/entities/trip.dart';
+import 'package:geocoding/geocoding.dart';
+
+class TripLocationUtils {
+  const TripLocationUtils._();
+
+  static List<double>? startCoordinates(Trip trip) {
+    if (trip.landmarks.isEmpty) {
+      return null;
+    }
+    final coords = trip.landmarks.first.location;
+    if (coords.length < 2) {
+      return null;
+    }
+    return coords;
+  }
+
+  static Future<TripLocaleInfo> resolveLocaleInfo(Trip trip) async {
+    final coords = startCoordinates(trip);
+    if (coords == null) {
+      return const TripLocaleInfo();
+    }
+
+    if (GeocodingPlatform.instance == null) {
+      final fallbackCity = '${coords[0].toStringAsFixed(2)}, ${coords[1].toStringAsFixed(2)}';
+      return TripLocaleInfo(cityName: fallbackCity, coordinates: coords);
+    }
+
+    try {
+      final placemarks = await placemarkFromCoordinates(coords[0], coords[1]);
+      if (placemarks.isEmpty) {
+        return TripLocaleInfo(coordinates: coords);
+      }
+      final placemark = placemarks.first;
+      final city = placemark.locality ?? placemark.subAdministrativeArea;
+      final country = placemark.country;
+      final isoCountryCode = placemark.isoCountryCode;
+      return TripLocaleInfo(cityName: city, countryName: country, countryCode: isoCountryCode, flagEmoji: _flagEmoji(isoCountryCode), coordinates: coords);
+    } catch (_) {
+      return TripLocaleInfo(coordinates: coords);
+    }
+  }
+
+  static Future<String> resolveCityName(Trip trip) async {
+    final localeInfo = await resolveLocaleInfo(trip);
+    return localeInfo.cityName ?? 'Unknown';
+  }
+
+  static String? _flagEmoji(String? countryCode) {
+    if (countryCode == null || countryCode.length != 2) {
+      return null;
+    }
+    final upper = countryCode.toUpperCase();
+    final first = upper.codeUnitAt(0);
+    final second = upper.codeUnitAt(1);
+    if (!_isAsciiLetter(first) || !_isAsciiLetter(second)) {
+      return null;
+    }
+    const base = 0x1F1E6;
+    final firstFlag = base + (first - 0x41);
+    final secondFlag = base + (second - 0x41);
+    return String.fromCharCodes([firstFlag, secondFlag]);
+  }
+
+  static bool _isAsciiLetter(int codeUnit) => codeUnit >= 0x41 && codeUnit <= 0x5A;
+}
+
+class TripLocaleInfo {
+  const TripLocaleInfo({this.cityName, this.countryName, this.countryCode, this.flagEmoji, this.coordinates});
+
+  final String? cityName;
+  final String? countryName;
+  final String? countryCode;
+  final String? flagEmoji;
+  final List<double>? coordinates;
+
+  bool get hasResolvedCity => cityName != null && cityName!.trim().isNotEmpty && cityName != 'Unknown';
+}