import 'dart:async';
import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:supabase_flutter/supabase_flutter.dart';

class OfflineQueueService {
  static final OfflineQueueService _instance = OfflineQueueService._internal();
  factory OfflineQueueService() => _instance;
  OfflineQueueService._internal();

  final SupabaseClient _supabase = Supabase.instance.client;
  final Connectivity _connectivity = Connectivity();
  List<Map<String, dynamic>> _queue = [];
  bool _isOnline = true;
  bool _syncing = false;

  static const Duration _timeout = Duration(seconds: 30);

  Future<T> _withTimeout<T>(Future<T> future, [String? operation]) async {
    try {
      return await future.timeout(
        _timeout,
        onTimeout: () => throw TimeoutException('${operation ?? 'Operasi'} timeout setelah $_timeout'),
      );
    } on TimeoutException catch (e) {
      debugPrint('OfflineQueue timeout: $e');
      rethrow;
    }
  }

  List<Map<String, dynamic>> get queue => List.unmodifiable(_queue);
  bool get isOnline => _isOnline;
  bool get hasPendingItems => _queue.isNotEmpty;

  Future<void> init() async {
    await _loadQueue();
    _connectivity.onConnectivityChanged.listen(_updateConnectionStatus);
    await _checkConnection();
    if (_isOnline) await _processQueue();
  }

  Future<void> _loadQueue() async {
    final prefs = await SharedPreferences.getInstance();
    final queueJson = prefs.getString('offline_queue');
    if (queueJson != null) {
      final List<dynamic> decoded = json.decode(queueJson);
      _queue = decoded.cast<Map<String, dynamic>>();
    }
  }

  Future<void> _saveQueue() async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString('offline_queue', json.encode(_queue));
  }

  Future<void> _checkConnection() async {
    final result = await _connectivity.checkConnectivity();
    _updateConnectionStatus(result);
  }

  void _updateConnectionStatus(List<ConnectivityResult> result) {
    _isOnline = result.any((r) => r != ConnectivityResult.none);
    if (_isOnline && _queue.isNotEmpty) {
      _processQueue();
    }
  }

  Future<void> addToQueue(Map<String, dynamic> transaction) async {
    _queue.add(transaction);
    await _saveQueue();
    if (_isOnline) {
      await _processQueue();
    }
  }

  Future<void> _processQueue() async {
    if (_syncing || !_isOnline || _queue.isEmpty) return;
    _syncing = true;

    while (_queue.isNotEmpty && _isOnline) {
      final item = _queue.first;
      try {
        await _processTransaction(item);
        _queue.removeAt(0);
        await _saveQueue();
      } catch (e) {
        _syncing = false;
        return;
      }
    }
    _syncing = false;
  }

  Future<void> _processTransaction(Map<String, dynamic> transaction) async {
    final sale = transaction['sale'] as Map<String, dynamic>;
    final items = (transaction['items'] as List?) ?? [];

    final saleId = sale['id'] as String;
    final storeId = sale['store_id'] as String?;
    final existing = await _withTimeout(
      _supabase
          .from('sales')
          .select('id, total_cost')
          .eq('id', saleId)
          .eq('store_id', storeId ?? '00000000-0000-0000-0000-000000000000')
          .maybeSingle(),
      'Check existing sale',
    );

    if (existing == null) {
      await _withTimeout(
        _supabase.from('sales').insert(sale),
        'Insert queued sale',
      );
    } else {
      final existingTotalCost = (existing['total_cost'] as num?)?.toDouble() ?? 0;
      if (existingTotalCost <= 0 && sale['total_cost'] != null) {
        await _withTimeout(
          _supabase
              .from('sales')
              .update({'total_cost': sale['total_cost']})
              .eq('id', saleId)
              .eq('store_id', storeId ?? '00000000-0000-0000-0000-000000000000'),
          'Update sale total_cost',
        );
      }
    }

    for (final it in items) {
      final productId = it['product_id'] as String;
      final qty = (it['qty'] as num).toInt();
      final product = await _withTimeout(
        _supabase
            .from('products')
            .select()
            .eq('id', productId)
            .eq('store_id', storeId ?? '00000000-0000-0000-0000-000000000000')
            .maybeSingle(),
        'Load product for stock update',
      );
      if (product != null) {
        final currentStock = (product['stock'] as num).toInt();
        final newStock = (currentStock - qty).clamp(0, 1 << 62);
        await _withTimeout(
          _supabase
              .from('products')
              .update({'stock': newStock})
              .eq('id', productId)
              .eq('store_id', storeId ?? '00000000-0000-0000-0000-000000000000'),
          'Update product stock',
        );
      }
    }
  }

  Future<void> clearQueue() async {
    _queue.clear();
    await _saveQueue();
  }
}