KC-APP/client/app/lib/chat_socket.dart

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

import 'package:web_socket_channel/web_socket_channel.dart';

import 'api.dart';

/// Thin wrapper over the raw `ws` chat gateway. The NestJS `WsAdapter`
/// expects `{"event": ..., "data": ...}` frames in both directions.
class ChatSocket {
  ChatSocket(this._uri);
  final Uri _uri;

  WebSocketChannel? _channel;
  final _messages = StreamController<ChatMessage>.broadcast();
  final _status = StreamController<String>.broadcast();

  /// Incoming `chat:message` frames.
  Stream<ChatMessage> get messages => _messages.stream;

  /// "connected" / "closed" / "error: ..." for a small status line.
  Stream<String> get status => _status.stream;

  void connect(String channelId) {
    _channel = WebSocketChannel.connect(_uri);
    _channel!.stream.listen(
      (raw) {
        _status.add('connected');
        try {
          final frame = jsonDecode(raw as String) as Map<String, dynamic>;
          if (frame['event'] == 'chat:message') {
            _messages.add(ChatMessage.fromJson(frame['data'] as Map<String, dynamic>));
          }
        } catch (_) {
          // ignore frames we don't model
        }
      },
      onError: (Object e) => _status.add('error: $e'),
      onDone: () => _status.add('closed'),
    );
    _send('chat:join', {'channelId': channelId});
  }

  void sendMessage(String channelId, String body) {
    _send('chat:send', {'channelId': channelId, 'body': body});
  }

  void _send(String event, Map<String, dynamic> data) {
    _channel?.sink.add(jsonEncode({'event': event, 'data': data}));
  }

  void dispose() {
    _channel?.sink.close();
    _messages.close();
    _status.close();
  }
}