hub/frontend/lib/backend.dart

import 'package:http/http.dart' as http;
import 'dart:html';
import 'dart:convert';
import 'dart:async';

class ChatInfo {
  int id;
  String name;

  ChatInfo({required this.id, required this.name});
}

class Backend {
  static WebSocket? _socket;
  static String? _url;
  static Map<int, Completer> _pendingActions = {};
  static Map<int, StreamController<Map<String, dynamic>>> _chatControllers = {};
  static int _nextNonce = 0; // Tracking nonce for each action
  static StreamController<Map<String, dynamic>> _packetStreamController = StreamController.broadcast();

  // Cached Data
  static List<ChatInfo>? _chats;
  
  // Authentication
  static ({String username, String password})? _credentials;
  static Completer<bool>? _loginCompleter;
  static Completer? _credentialsCompleter;

  static void setup(String url) {
    _url = url;
    connect();
  }

  static Future<void> signup(String username, String email, String password) async {
    final response = await http.post(Uri.parse("$_url/user/signup"),
      headers: {
        'Content-Type': 'application/json',
      },
      body: jsonEncode({
        'username': username,
        'email': email,
        'password': password,
      })
    );

    if (response.statusCode < 200 || response.statusCode >= 300) {
      throw Exception("Signup Status Code ${response.statusCode}");
    }
  }

  static Future<bool> auth(String username, String password) {
    if (_credentials != null) {
      print("Cannot authenticate twice");
      return Future.value(false);
    }
    _credentials = (username: username, password: password);
    if (_credentialsCompleter != null) {
      _credentialsCompleter!.complete(_credentials);
      _credentialsCompleter = null;
    }
    _loginCompleter = Completer();
    return _loginCompleter!.future;
  }

  static void connect() {
    _socket = WebSocket(_url! + "/ws");
    _socket!.onOpen.listen((event) async {
      print('Connected to the WebSocket server');
      Backend.invalidateCache(chat: true);

      print('Logging in...');
      // secure the listener for the response before sending credentials
      var responseFuture = nextIncomingMessage();
      if (_credentials != null) {
        _socket!.send(json.encode({'username': _credentials!.username, 'password': _credentials!.password}));
      } else {
        _credentialsCompleter = Completer();
        _credentialsCompleter!.future.then((credentials) {
          _socket!.send(json.encode({'username': credentials.username, 'password': credentials.password}));
        });
      }
      var response = await responseFuture;
      if (response['error'] == null) {
        _loginCompleter?.complete(true);
      } else {
        _loginCompleter?.complete(false);
        _socket!.close(); // Retry
      }
      _loginCompleter = null;
    });
    _socket!.onError.listen((event) {
      print('Error: $event');
      _reconnect();
    });
    _socket!.onClose.listen((event) {
      print('Disconnected. Attempting to reconnect...');
      _reconnect();
    });
    _socket!.onMessage.listen((event) {
      _handleIncomingMessage(event.data);
    });
  }

  static void disconnect() {
    _socket?.close();
  }

  static void _reconnect() {
    Future.delayed(Duration(seconds: 1), () {
      connect();
    });
  }

  static Future<dynamic> sendAction(String action, Map<String, dynamic> body) {
    int nonce = _nextNonce++;
    Completer completer = Completer();
    _pendingActions[nonce] = completer;

    final packet = {
      'action': action,
      'nonce': nonce,
      'body': body,
    };
    _socket!.send(json.encode(packet));

    return completer.future.then((response) {
      _pendingActions.remove(nonce); // Clean up the mapping
      return response;
    });
  }

  static void _handleIncomingMessage(String data) {
    var jsonData = json.decode(data);
    print("Incoming Packet: $jsonData");
    
    if (jsonData['nonce'] != null) {
      int nonce = jsonData['nonce'];
      if (_pendingActions.containsKey(nonce)) {
        // Complete the response
        _pendingActions[nonce]!.complete(jsonData);
      } else {
        print("Orphan response for action nonce $nonce");
      }
    } else if (jsonData['action'] == 'chat-message') {
      int chatId = jsonData['chatId'];
      final controller = _chatControllers[chatId];
      if (controller != null && !controller.isClosed) {
        controller.add(jsonData);
      } else {
        print("No active listeners for chatId $chatId");
      }
    } else {
      if (jsonData['error'] != null) {
        print("Error: ${jsonData['error']}");
      }
      _packetStreamController.add(jsonData);
    }
  }

  static Future<Map<String, dynamic>> nextIncomingMessage() {
    return _packetStreamController.stream.first;
  }

  static Stream<Map<String, dynamic>> chatMessages(int chatId) {
    if (!_chatControllers.containsKey(chatId) || _chatControllers[chatId]!.isClosed) {
      _chatControllers[chatId] = StreamController<Map<String, dynamic>>.broadcast();
    }
    return _chatControllers[chatId]!.stream;
  }

  static void removeChatListener(int chatId) {
    final controller = _chatControllers.remove(chatId);
    if (controller != null && !controller.isClosed) {
      controller.close();
    }
  }

  static Future<List<ChatInfo>> getChats () async {
    if (_chats == null) {
      final response = await Backend.sendAction("get-chats", {});
      List<dynamic> chatObjects = response['chats'];
      _chats = chatObjects
          .map((msg) => ChatInfo(
                id: msg['id'],
                name: msg['name']?.isNotEmpty == true ? msg['name'] : '[Chat ${msg['id']}]',
              ))
          .toList();
    }
    return _chats!;
  }

  static Future<ChatInfo?> getChat (int chatId) async {
    final chats = await getChats();
    try {
      return chats.firstWhere((chat) => chat.id == chatId);
    } on StateError {
      return null;
    }
  }

  static void invalidateCache ({bool chat = false}) {
    if (chat) { _chats = null; }
  }

  static void ping() {
    if (_socket!= null && _socket!.readyState == WebSocket.OPEN) {
      final data = json.encode({'path': 'ping'});
      _socket!.send(data);
      print('Ping sent: $data');
    }
  }
}