// http://msdn.microsoft.com/en-us/library/fx6588te(v=vs.80).aspx 
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;

namespace echo
{
    // State object for reading client data asynchronously
    public class StateObject {
        // Client  socket.
        public Socket workSocket = null;
        // Size of receive buffer.
        public const int BufferSize = 64 * 1024;
        // Receive buffer.
        public byte[] buffer = new byte[BufferSize];
        // Received data string.
        public StringBuilder sb = new StringBuilder();  
    }

    public class AsynchronousSocketListener {
        // Thread signal.
        public static ManualResetEvent allDone = new ManualResetEvent(false);

        public AsynchronousSocketListener() {
        }

        public static void StartListening() {
            UInt16 port = 11000;
            UInt16 maxConnections = 100;

            // Establish the local endpoint for the socket.
            // The DNS name of the computer
            // running the listener is "host.contoso.com".
            IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
            IPAddress ipAddress = ipHostInfo.AddressList[0];
            IPEndPoint localEndPoint = new IPEndPoint(ipAddress, port);

            // Create a TCP/IP socket.
            Socket listener = new Socket(AddressFamily.InterNetwork,
                SocketType.Stream, ProtocolType.Tcp );

            // Bind the socket to the local endpoint and listen for incoming connections.
            try {
                listener.Bind(localEndPoint);
                listener.Listen(maxConnections);

                Console.WriteLine("Listening on {0}:{1}", ipAddress, port);

                while (true) {
                    // Set the event to nonsignaled state.
                    allDone.Reset();

                    // Start an asynchronous socket to listen for connections.
                    Console.WriteLine("Waiting for a connection...");
                    listener.BeginAccept( 
                        new AsyncCallback(AcceptCallback),
                        listener );

                    // Wait until a connection is made before continuing.
                    allDone.WaitOne();
                }

            } catch (Exception e) {
                Console.WriteLine(e.ToString());
            }

            Console.WriteLine("\nPress ENTER to continue...");
            Console.Read();
        }

        public static void AcceptCallback(IAsyncResult ar) {
            // Signal the main thread to continue.
            allDone.Set();

            // Get the socket that handles the client request.
            Socket listener = (Socket) ar.AsyncState;
            Socket handler = listener.EndAccept(ar);

            // Create the state object.
            StateObject state = new StateObject();
            state.workSocket = handler;
            try {
            handler.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,
                new AsyncCallback(ReadCallback), state);
            } catch(Exception e) {
                Console.WriteLine ("oh dear");
                Console.WriteLine(e.ToString());
            }
        }

        public static void ReadCallback(IAsyncResult ar) {
            String content = String.Empty;
            
            // Retrieve the state object and the handler socket
            // from the asynchronous state object.
            StateObject state = (StateObject) ar.AsyncState;
            Socket handler = state.workSocket;

            // Read data from the client socket.
            int bytesRead;
            try {
                bytesRead = handler.EndReceive(ar);
            } catch (Exception e) {
                Console.WriteLine ("Client already disconnected " + e.ToString());
                return;
            }

            if (bytesRead > 0) {
                Console.WriteLine ("some bytes read");
                // There  might be more data, so store the data received so far.
                state.sb.Append(Encoding.ASCII.GetString(
                    state.buffer,0,bytesRead));

                // Check for end-of-file tag. If it is not there, read 
                // more data.
                content = state.sb.ToString();
                if (content.IndexOf("<EOF>") > -1) {
                    // All the data has been read from the 
                    // client. Display it on the console.
                    Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",
                        content.Length, content );
                    // Echo the data back to the client.
                    Send(handler, content);
                } else {
                    // Not all data received. Get more.
                    handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                    new AsyncCallback(ReadCallback), state);
                }
            } else {
                Console.WriteLine ("0 bytes read");
            }
        }
        
        private static void Send(Socket handler, String data) {
            // Convert the string data to byte data using ASCII encoding.
            byte[] byteData = Encoding.ASCII.GetBytes(data);

            // Begin sending the data to the remote device.
            handler.BeginSend(byteData, 0, byteData.Length, 0,
                new AsyncCallback(SendCallback), handler);
        }

        private static void SendCallback(IAsyncResult ar) {
            try {
                // Retrieve the socket from the state object.
                Socket handler = (Socket) ar.AsyncState;

                // Complete sending the data to the remote device.
                int bytesSent = handler.EndSend(ar);
                Console.WriteLine("Sent {0} bytes to client.", bytesSent);

                handler.Shutdown(SocketShutdown.Both);
                handler.Close();

            } catch (Exception e) {
                Console.WriteLine(e.ToString());
            }
        }


        public static int Main(String[] args) {
            StartListening();
            return 0;
        }
    }
}