import 'package:shared_preferences/shared_preferences.dart';
import 'package:travel_mate/models/transport_segment.dart';

/// Service that stores per-trip transport segments locally for offline access.
///
/// Uses `SharedPreferences` keyed by `trip_transport_<tripId>` to keep
/// creation/edit quick without round-trips. Real-time status can later be
/// updated by a background job hitting external APIs.
class TransportService {
  /// Loads stored transport segments for [tripId].
  Future<List<TransportSegment>> loadSegments(String tripId) async {
    final prefs = await SharedPreferences.getInstance();
    final raw = prefs.getString(_key(tripId));
    if (raw == null) return const [];
    try {
      return TransportSegment.decodeList(raw);
    } catch (_) {
      await prefs.remove(_key(tripId));
      return const [];
    }
  }

  /// Persists the full list of segments for [tripId].
  Future<void> saveSegments(
    String tripId,
    List<TransportSegment> segments,
  ) async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_key(tripId), TransportSegment.encodeList(segments));
  }

  /// Adds a segment entry.
  Future<List<TransportSegment>> addSegment(
    String tripId,
    TransportSegment segment,
  ) async {
    final current = await loadSegments(tripId);
    final updated = [...current, segment];
    await saveSegments(tripId, updated);
    return updated;
  }

  /// Deletes a segment by [segmentId].
  Future<List<TransportSegment>> deleteSegment(
    String tripId,
    String segmentId,
  ) async {
    final current = await loadSegments(tripId);
    final updated = current.where((s) => s.id != segmentId).toList();
    await saveSegments(tripId, updated);
    return updated;
  }

  /// Updates the status of a segment (e.g., delayed/boarding/in_air).
  Future<List<TransportSegment>> updateStatus(
    String tripId,
    String segmentId,
    String status,
  ) async {
    final current = await loadSegments(tripId);
    final updated = current
        .map((s) {
          if (s.id != segmentId) return s;
          return s.copyWith(status: status);
        })
        .toList(growable: false);
    await saveSegments(tripId, updated);
    return updated;
  }

  String _key(String tripId) => 'trip_transport_$tripId';
}