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

/// Service that persists per-trip documents metadata locally.
///
/// Documents are stored as JSON in `SharedPreferences` to keep the UI
/// responsive offline. Each trip key is `trip_docs_<tripId>`. The service is
/// tolerant to corrupted payloads and resets gracefully to an empty list.
class TripDocumentService {
  /// Loads documents for the given [tripId]. Returns an empty list when none.
  Future<List<TripDocument>> loadDocuments(String tripId) async {
    final prefs = await SharedPreferences.getInstance();
    final raw = prefs.getString(_key(tripId));
    if (raw == null) return const [];
    try {
      return TripDocument.decodeList(raw);
    } catch (_) {
      await prefs.remove(_key(tripId));
      return const [];
    }
  }

  /// Saves the full document list for [tripId].
  Future<void> saveDocuments(String tripId, List<TripDocument> docs) async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_key(tripId), TripDocument.encodeList(docs));
  }

  /// Adds a new document entry and persists the updated list.
  Future<List<TripDocument>> addDocument(
    String tripId,
    TripDocument doc,
  ) async {
    final current = await loadDocuments(tripId);
    final updated = [...current, doc];
    await saveDocuments(tripId, updated);
    return updated;
  }

  /// Deletes a document by [docId] and persists the change.
  Future<List<TripDocument>> deleteDocument(String tripId, String docId) async {
    final current = await loadDocuments(tripId);
    final updated = current.where((d) => d.id != docId).toList();
    await saveDocuments(tripId, updated);
    return updated;
  }

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