import 'dart:async';
import 'dart:convert';

import 'package:drift/drift.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter_secure_storage/flutter_secure_storage.dart';
import 'package:http/http.dart' as http;
import 'package:sentry_flutter/sentry_flutter.dart';

import '../database/app_database.dart';
import '../models/payment_method.dart';
import '../models/remote_command.dart';
import '../utils/app_config.dart';
import 'bar_tab_service.dart';

class RemoteSyncService {
  final AppDatabase database;
  final BarTabService barTabService;
  final FlutterSecureStorage secureStorage;

  RemoteSyncService({
    required this.database,
    required this.barTabService,
    FlutterSecureStorage? secureStorage,
  }) : secureStorage = secureStorage ?? const FlutterSecureStorage();

  static const _deviceIdKey = 'remote_device_id';
  static const _authTokenKey = 'remote_auth_token';
  static const _serverUrlKey = 'remote_server_url';
  static const _venueIdKey = 'remote_venue_id';

  final _eventController = StreamController<RemoteSyncEvent>.broadcast();

  Stream<RemoteSyncEvent> get events => _eventController.stream;

  bool _isSyncing = false;
  bool get isSyncing => _isSyncing;

  Timer? _syncTimer;
  int _consecutiveFailures = 0;
  bool _paused = false;

  Future<String?> get deviceId async =>
      await secureStorage.read(key: _deviceIdKey);

  Future<String?> get authToken async =>
      await secureStorage.read(key: _authTokenKey);

  Future<String?> get venueId async =>
      await secureStorage.read(key: _venueIdKey);

  Future<bool> get isConfigured async {
    final token = await authToken;
    final vid = await venueId;
    return token != null && token.isNotEmpty && vid != null && vid.isNotEmpty;
  }

  String get _baseUrl => kRemoteServerUrl;

  void startPeriodicSync({int intervalSeconds = 90}) {
    _syncTimer?.cancel();
    _syncTimer = Timer.periodic(
      Duration(seconds: intervalSeconds),
      (_) => _onTick(),
    );
  }

  void stopPeriodicSync() {
    _syncTimer?.cancel();
    _syncTimer = null;
  }

  void pause() {
    _paused = true;
  }

  void resume() {
    _paused = false;
  }

  Future<void> _onTick() async {
    if (_isSyncing || _paused) return;
    await sync();
  }

  Future<void> sync() async {
    if (_isSyncing) return;

    final configured = await isConfigured;
    if (!configured) return;

    _isSyncing = true;

    try {
      await _doSync();
      _consecutiveFailures = 0;
      _eventController.add(const RemoteSyncEvent(
        type: RemoteSyncEventType.syncCompleted,
      ));
    } catch (e, stack) {
      _consecutiveFailures++;
      debugPrint('RemoteSyncService: sync failed: $e');
      Sentry.captureException(e, stackTrace: stack);
      _eventController.add(RemoteSyncEvent(
        type: RemoteSyncEventType.syncFailed,
        message: e.toString(),
      ));
      _applyBackoff();
    } finally {
      _isSyncing = false;
    }
  }

  Future<void> _doSync() async {
    final token = await authToken;
    if (token == null) return;

    final deviceId = await this.deviceId;
    if (deviceId == null) return;

    final state = await _getSyncState();
    final openTabs = await _buildSnapshot();

    final request = SyncRequest(
      deviceId: deviceId,
      cursor: state?.serverCursor,
      openTabs: openTabs,
    );

    final response = await _httpPost(
      '$_baseUrl/devices/$deviceId/sync',
      body: request.toJson(),
      token: token,
    );

    if (response == null) return;

    final syncResponse = SyncResponse.fromJson(response);

    for (final command in syncResponse.commands) {
      await _processCommand(command);
    }

    for (final name in syncResponse.plannedTabNames) {
      final hasOpenTab = openTabs.any((t) => t.customerName == name);
      if (!hasOpenTab) {
        await barTabService.createTab(customerName: name);
      }
    }

    if (syncResponse.cursor != null) {
      await _saveCursor(syncResponse.cursor!);
    }

    await _updateSyncState(success: true);
  }

  Future<List<SnapshotTab>> _buildSnapshot() async {
    final openTabs = await barTabService.getOpenTabs();
    return openTabs.map((tab) => SnapshotTab(
      id: tab.id,
      customerName: tab.customerName,
      version: tab.version,
      totalInCents: tab.totalInCents,
      itemCount: tab.itemCount,
    )).toList();
  }

  Future<void> _processCommand(RemoteCommand command) async {
    final alreadyProcessed = await _isCommandProcessed(command.id);
    if (alreadyProcessed) return;

    if (command.isExpired) {
      await _ackCommand(command.id, 'expired', 'Command expired');
      await _recordProcessed(command.id, command.type, 'expired');
      return;
    }

    if (command.type != 'close_tab') {
      await _ackCommand(command.id, 'failed', 'Unknown command type: ${command.type}');
      await _recordProcessed(command.id, command.type, 'failed');
      return;
    }

    try {
      final tab = await barTabService.getTabById(command.tabId);

      if (tab == null) {
        await _ackCommand(command.id, 'conflict', 'Tab not found');
        await _recordProcessed(command.id, command.type, 'conflict');
        _eventController.add(const RemoteSyncEvent(
          type: RemoteSyncEventType.conflict,
          message: 'Tab not found',
        ));
        return;
      }

      if (!tab.isOpen) {
        await _ackCommand(command.id, 'conflict', 'Tab already closed');
        await _recordProcessed(command.id, command.type, 'conflict');
        _eventController.add(const RemoteSyncEvent(
          type: RemoteSyncEventType.conflict,
          message: 'Tab already closed',
        ));
        return;
      }

      if (tab.version != command.expectedVersion) {
        await _ackCommand(command.id, 'conflict', 'Version mismatch');
        await _recordProcessed(command.id, command.type, 'conflict');
        _eventController.add(const RemoteSyncEvent(
          type: RemoteSyncEventType.conflict,
          message: 'Tab was modified since the request',
        ));
        return;
      }

      final method = PaymentMethod.fromValue(command.paymentMethod);
      await barTabService.closeTab(command.tabId, paymentMethod: method);

      await _ackCommand(command.id, 'completed');
      await _recordProcessed(command.id, command.type, 'completed');

      _eventController.add(RemoteSyncEvent(
        type: RemoteSyncEventType.tabClosedRemotely,
        tabCustomerName: tab.customerName,
        requestedBy: command.requestedBy,
      ));
    } catch (e, stack) {
      debugPrint('RemoteSyncService: command processing failed: $e');
      Sentry.captureException(e, stackTrace: stack);
      await _ackCommand(command.id, 'failed', e.toString());
      await _recordProcessed(command.id, command.type, 'failed');
    }
  }

  Future<Map<String, dynamic>?> _httpPost(
    String url, {
    required Map<String, dynamic> body,
    required String token,
  }) async {
    final response = await http.post(
      Uri.parse(url),
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer $token',
      },
      body: jsonEncode(body),
    ).timeout(const Duration(seconds: 15));

    if (response.statusCode == 401) {
      await secureStorage.delete(key: _authTokenKey);
      debugPrint('RemoteSyncService: token revoked');
      return null;
    }

    if (response.statusCode == 429) {
      final retryAfter = response.headers['retry-after'];
      if (retryAfter != null) {
        final seconds = int.tryParse(retryAfter) ?? 60;
        _applyBackoff(forcedDelay: seconds);
      }
      return null;
    }

    if (response.statusCode < 200 || response.statusCode >= 300) {
      debugPrint('RemoteSyncService: HTTP ${response.statusCode}: ${response.body}');
      return null;
    }

    if (response.body.isEmpty) return {};

    return jsonDecode(response.body) as Map<String, dynamic>;
  }

  Future<void> _ackCommand(
    String commandId,
    String status, [
    String? result,
  ]) async {
    final token = await authToken;
    final deviceId = await this.deviceId;
    if (token == null || deviceId == null) return;

    try {
      final ack = CommandAck(commandId: commandId, status: status, result: result);
      await _httpPost(
        '$_baseUrl/devices/$deviceId/commands/$commandId/ack',
        body: ack.toJson(),
        token: token,
      );
    } catch (e) {
      debugPrint('RemoteSyncService: ack failed: $e');
    }
  }

  Future<RemoteSyncStateRow?> _getSyncState() async {
    final query = database.select(database.remoteSyncState)
      ..where((row) => row.deviceId.equals('default'));
    return query.getSingleOrNull();
  }

  Future<void> _saveCursor(String cursor) async {
    await database
        .into(database.remoteSyncState)
        .insertOnConflictUpdate(
          RemoteSyncStateCompanion(
            deviceId: const Value('default'),
            serverCursor: Value(cursor),
          ),
        );
  }

  Future<void> _updateSyncState({required bool success}) async {
    final now = DateTime.now();
    final existing = await _getSyncState();

    if (existing == null) {
      await database.into(database.remoteSyncState).insert(
        RemoteSyncStateCompanion.insert(
          deviceId: 'default',
          lastSuccessfulSyncAt: Value(success ? now : null),
          lastAttemptedSyncAt: Value(now),
          consecutiveFailureCount: Value(success ? 0 : 1),
        ),
      );
    } else {
      await (database.update(database.remoteSyncState)
            ..where((row) => row.deviceId.equals('default')))
          .write(RemoteSyncStateCompanion(
        lastSuccessfulSyncAt: Value(success ? now : existing.lastSuccessfulSyncAt),
        lastAttemptedSyncAt: Value(now),
        consecutiveFailureCount: Value(
          success ? 0 : existing.consecutiveFailureCount + 1,
        ),
      ));
    }
  }

  Future<bool> _isCommandProcessed(String commandId) async {
    final query = database.select(database.processedRemoteCommands)
      ..where((row) => row.commandId.equals(commandId));
    final result = await query.getSingleOrNull();
    return result != null;
  }

  Future<void> _recordProcessed(
    String commandId,
    String commandType,
    String result,
  ) async {
    await database
        .into(database.processedRemoteCommands)
        .insertOnConflictUpdate(
          ProcessedRemoteCommandsCompanion.insert(
            commandId: commandId,
            commandType: commandType,
            processedAt: DateTime.now(),
            result: result,
          ),
        );
  }

  void _applyBackoff({int? forcedDelay}) {
    final delay = forcedDelay ?? _calculateBackoff();
    _syncTimer?.cancel();
    _syncTimer = Timer(Duration(seconds: delay), () => _onTick());
  }

  int _calculateBackoff() {
    if (_consecutiveFailures <= 1) return 90;
    final backoff = 90 * (1 << (_consecutiveFailures - 1).clamp(0, 3));
    return backoff.clamp(90, 600);
  }

  Future<void> setCredentials({
    required String deviceId,
    required String token,
    required String venueId,
    String? serverUrl,
  }) async {
    await secureStorage.write(key: _deviceIdKey, value: deviceId);
    await secureStorage.write(key: _authTokenKey, value: token);
    await secureStorage.write(key: _venueIdKey, value: venueId);
    if (serverUrl != null) {
      await secureStorage.write(key: _serverUrlKey, value: serverUrl);
    }
  }

  Future<void> clearCredentials() async {
    await secureStorage.delete(key: _deviceIdKey);
    await secureStorage.delete(key: _authTokenKey);
    await secureStorage.delete(key: _serverUrlKey);
    await secureStorage.delete(key: _venueIdKey);
  }

  Future<DateTime?> get lastSuccessfulSyncAt async {
    final state = await _getSyncState();
    return state?.lastSuccessfulSyncAt;
  }

  Future<int> get lastFailureCount async {
    final state = await _getSyncState();
    return state?.consecutiveFailureCount ?? 0;
  }

  Future<List<ProcessedRemoteCommandRow>> getRecentActivity() async {
    final query = database.select(database.processedRemoteCommands)
      ..orderBy([(row) => OrderingTerm.desc(row.processedAt)])
      ..limit(50);
    return query.get();
  }

  void dispose() {
    _syncTimer?.cancel();
    _eventController.close();
  }
}