import 'dart:convert';
import 'dart:math';

import 'package:shared_preferences/shared_preferences.dart';

class OfflineQueue {
  static const _key = 'delivery_offline_events';

  Future<void> enqueue(Map<String, dynamic> event) async {
    final prefs = await SharedPreferences.getInstance();
    final items = prefs.getStringList(_key) ?? <String>[];
    final eventId = '${event['event_id'] ?? uuidV4()}';
    final alreadyQueued = items.any((item) {
      final decoded = jsonDecode(item);
      return decoded is Map && '${decoded['event_id']}' == eventId;
    });
    if (alreadyQueued) return;
    items.add(
      jsonEncode({
        ...event,
        'event_id': eventId,
      }),
    );
    await prefs.setStringList(_key, items);
  }

  static String uuidV4() {
    final bytes = List<int>.generate(16, (_) => Random.secure().nextInt(256));
    bytes[6] = (bytes[6] & 0x0f) | 0x40;
    bytes[8] = (bytes[8] & 0x3f) | 0x80;
    final hex = bytes.map((value) => value.toRadixString(16).padLeft(2, '0')).join();
    return '${hex.substring(0, 8)}-${hex.substring(8, 12)}-${hex.substring(12, 16)}-${hex.substring(16, 20)}-${hex.substring(20)}';
  }

  Future<List<Map<String, dynamic>>> pending() async {
    final prefs = await SharedPreferences.getInstance();
    return (prefs.getStringList(_key) ?? <String>[])
        .map((item) => jsonDecode(item) as Map<String, dynamic>)
        .toList();
  }

  Future<void> removeFirst() async {
    final prefs = await SharedPreferences.getInstance();
    final items = prefs.getStringList(_key) ?? <String>[];
    if (items.isEmpty) return;
    await prefs.setStringList(_key, items.sublist(1));
  }

  Future<int> count() async {
    final prefs = await SharedPreferences.getInstance();
    return (prefs.getStringList(_key) ?? <String>[]).length;
  }

  Future<void> clear() async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.remove(_key);
  }
}