using System;
using System.Net;
using System.Net.Sockets;

namespace chat100_sharp
{
    class Session
    {
        public Session(Socket socket)
        {
            _socket = socket;
        }

        public IAsyncResult DoRead()
        {
            return _socket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, HandleRead, null);
        }

        public void HandleRead(IAsyncResult result)
        {
            var size = _socket.EndReceive(result);
            if (size > 0)
            {
                DoWrite(_buffer, 0, size);
            }
            else
            {
                _socket.Close();
            }
        }

        public IAsyncResult DoWrite(byte[] buffer, int offset, int size)
        {
            return _socket.BeginSend(buffer, offset, size, SocketFlags.None, HandleWrite, size);
        }

        public void HandleWrite(IAsyncResult result)
        {
            var sizeToWrite = (int)result.AsyncState;
            var written = _socket.EndSend(result);
            if (sizeToWrite > written)
            {
                DoWrite(_buffer, written, sizeToWrite - written);
            }
            else
            {
                DoRead();
            }
        }

        private readonly Socket _socket;
        private readonly byte[] _buffer = new byte[4096];
    }

    class Program
    {
        static void Main(string[] args)
        {
            var socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
            socket.Bind(new IPEndPoint(IPAddress.Any, 12345));
            socket.Listen(100);

            try
            {
                while (true)
                {
                    var client = socket.Accept();
                    new Session(client).DoRead();
                }
            }
            catch (Exception e) { Console.WriteLine(e.Message); }
            socket.Close();
        }
    }
}