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

/// Persists dated reminders/to-dos per trip locally for offline use.
class ReminderService {
  /// Loads reminders for [tripId].
  Future<List<ReminderItem>> loadReminders(String tripId) async {
    final prefs = await SharedPreferences.getInstance();
    final raw = prefs.getString(_key(tripId));
    if (raw == null) return const [];
    try {
      return ReminderItem.decodeList(raw);
    } catch (_) {
      await prefs.remove(_key(tripId));
      return const [];
    }
  }

  /// Saves full list.
  Future<void> saveReminders(
    String tripId,
    List<ReminderItem> reminders,
  ) async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(_key(tripId), ReminderItem.encodeList(reminders));
  }

  /// Adds a reminder.
  Future<List<ReminderItem>> addReminder(
    String tripId,
    ReminderItem reminder,
  ) async {
    final current = await loadReminders(tripId);
    final updated = [...current, reminder];
    await saveReminders(tripId, updated);
    return updated;
  }

  /// Toggles done state.
  Future<List<ReminderItem>> toggleReminder(
    String tripId,
    String reminderId,
  ) async {
    final current = await loadReminders(tripId);
    final updated = current
        .map((r) => r.id == reminderId ? r.copyWith(isDone: !r.isDone) : r)
        .toList(growable: false);
    await saveReminders(tripId, updated);
    return updated;
  }

  /// Deletes a reminder.
  Future<List<ReminderItem>> deleteReminder(
    String tripId,
    String reminderId,
  ) async {
    final current = await loadReminders(tripId);
    final updated = current.where((r) => r.id != reminderId).toList();
    await saveReminders(tripId, updated);
    return updated;
  }

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