using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;

namespace Server
{
    class Program
    {
        static byte[] _buffer = new byte[1024];
        static Socket _server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        static List<Socket> _list = new List<Socket>();
        static void Main(string[] args)
        {
            Console.WriteLine("Server's port ?");
            string port = Console.ReadLine();
            Setup(port);
            Console.WriteLine("Waiting for connexions...");
            Console.WriteLine(GetLocalIP());
            Console.ReadLine();
        }

        private static void Setup(string port)
        {
            int Port = int.Parse(port);
            _server.Bind(new IPEndPoint(IPAddress.Any ,Port));
            _server.Listen(5);
            _server.BeginAccept(new AsyncCallback(AcceptCallback), _server);
        }

        private static void AcceptCallback(IAsyncResult AR)
        {
            Socket socket = _server.EndAccept(AR);
            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
            _list.Add(socket);
            Console.WriteLine("Client connected !");
            socket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), socket);

        }

        private static void ReceiveCallback(IAsyncResult AR)
        {
            Socket socket = (Socket)AR.AsyncState;
            try
            {
                int received = socket.EndReceive(AR);
                byte[] _buff = new byte[received];
                Array.Copy(_buffer, _buff, received);
                string Text = Encoding.UTF8.GetString(_buff);
                Console.WriteLine("Text received : " + Text);
                string sendingtext = "All is OK !";
                byte[] _send = null;
                _send = Encoding.UTF8.GetBytes(sendingtext);
                socket.BeginSend(_send, 0, _send.Length, SocketFlags.None, new AsyncCallback(SendCallback), socket);
                socket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), socket);
            }
            catch(SocketException)
            {
                Console.WriteLine("Client not connected !");
            }
        }

       private static void SendCallback(IAsyncResult AR)
        {
            Socket socket = (Socket)AR.AsyncState;
            socket.EndSend(AR);

        }

        private static string GetLocalIP()
        {
            IPHostEntry host;
            host = Dns.GetHostEntry(Dns.GetHostName());
            foreach (IPAddress ip in host.AddressList)
            {
                if (ip.AddressFamily == AddressFamily.InterNetwork)
                {
                    return ip.ToString();
                }
            }
            return "127.0.0.1";
        }

    }
}