import 'dart:convert';
import 'package:shared_preferences/shared_preferences.dart';

class BeaconCache {
  static const _keyBeaconData = 'beacon_cache_data';
  static const _keyBeaconTimestamp = 'beacon_cache_timestamp';
  static const _cacheDuration = Duration(hours: 24); // Cache for 24 hours

  /// Save beacon list to cache
  static Future<void> save(Map<String, int> beacons) async {
    final prefs = await SharedPreferences.getInstance();
    final json = jsonEncode(beacons);
    await prefs.setString(_keyBeaconData, json);
    await prefs.setInt(_keyBeaconTimestamp, DateTime.now().millisecondsSinceEpoch);
  }

  /// Load beacon list from cache (returns null if expired or not found)
  static Future<Map<String, int>?> load() async {
    final prefs = await SharedPreferences.getInstance();
    final timestamp = prefs.getInt(_keyBeaconTimestamp);
    final data = prefs.getString(_keyBeaconData);

    if (timestamp == null || data == null) {
      return null;
    }

    // Check if cache is expired
    final cachedTime = DateTime.fromMillisecondsSinceEpoch(timestamp);
    if (DateTime.now().difference(cachedTime) > _cacheDuration) {
      return null;
    }

    try {
      final decoded = jsonDecode(data) as Map<String, dynamic>;
      return decoded.map((k, v) => MapEntry(k, v as int));
    } catch (e) {
      return null;
    }
  }

  /// Clear the beacon cache
  static Future<void> clear() async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.remove(_keyBeaconData);
    await prefs.remove(_keyBeaconTimestamp);
  }
}