// How to use Sockets to create Servers in Java

import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class client_rec
{
  client_rec (int x, Socket s, DataOutputStream dos, DataInputStream di)
  {
    sock = s;
    clientnumber = x;
    dis = di;
    this.dos = dos;
  }
  int clientnumber;
  Socket sock;
  DataInputStream dis;
  DataOutputStream dos;
}

class client_monitor extends Thread
{
  server serv;
  client_rec cr;
  client_monitor (server s, client_rec x)
  {
    serv = s;
    cr = x;
    start();
  }
  public void run ()
  {
    String x = new String("");
    // output the current seed value
  stop:
    {
    while (true)
      {
	try
	  {
	    x = cr.dis.readUTF();
	    if (x.equalsIgnoreCase("stop"))
	      {
		cr.dos.writeUTF("Client stopped");
		break stop;
	      }
	    else
	      {
		int seed = (int) ( Math.random() * 1000);
		cr.dos.writeUTF("Value server is thinking of: ");
		cr.dos.writeInt(seed);
		serv.display.append("Client: " + cr.clientnumber + 
				    " Request satisfied\n");
	      }
	  }
	catch (IOException e) 
	  {
	    break stop;
	  }
      }
    }
    
    // close connection
    serv.display.append("Shutting down client: " + 
			cr.clientnumber + "\n");
    serv.remove_client(cr);
    try
      {
	cr.sock.close();
      }
    catch (IOException e)
      {
	serv.display.append("Error shutting down socket: " + e.toString());
      }
    stop();
    cr = null;
    serv.display.append("Client: " + cr.clientnumber + "  closed\n");
  }
}

public class server extends JFrame
{
  static int max_clients = 2;
  int client_count;
  client_rec clients[];
  JTextArea display;
  public server()
  {
    super("Number Server");
    display = new JTextArea(6, 25);
    display.setLineWrap(true);
    display.setEditable(false);
    display.setBackground(Color.yellow);
    JScrollPane jsp = new JScrollPane(display);
    jsp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);


    Container c = getContentPane();
    c.setLayout(new BorderLayout());
    c.add(jsp, BorderLayout.CENTER);

    setSize(300, 200);
    setVisible(true);
    addWindowListener(new WindowAdapter () 
		      {
			public void windowClosing (WindowEvent e)
			  {
			    System.exit(0);
			  }
		      });
  }
  public client_rec add_client 
  (int c, Socket s, DataOutputStream dos, DataInputStream di)
  {
    if (client_count < max_clients)
      {
	client_rec x = new client_rec(c, s, dos, di);
	clients[client_count] = x;
	client_count = client_count + 1;
	return x;
      }
    return null;
  }
  public void remove_client
  (client_rec x)
  {
    for (int i = 0; i < client_count; i++)
      {
	if (clients[i] == x)
	  {
	    for (int j = i+1; j < client_count; j++)
	      clients[j-1] = clients[j];
	    client_count = client_count - 1;
	    return;
	  }
      }
  }
  public void startServer()
  {
    ServerSocket s;
    Socket connection;
    DataOutputStream sos;
    DataInputStream sis;
    client_count = 0;
    try
      {
	// set up a socket listening to 5500 with client limit max_clients
	s = new ServerSocket(5500, max_clients);
	display.append("Server listening on port: 5500\n");
	clients = new client_rec[max_clients];
	while (true)
	  {
	    connection = s.accept();
	    display.append( "Connection: " + (client_count + 1) + 
			    "  received from: " + 
			    connection.getInetAddress().getHostName() 
			    + "\n");
	    // create input and output streams for socket...
	    sos = new DataOutputStream(connection.getOutputStream());
	    sis = new DataInputStream(connection.getInputStream());
	    client_rec cr = 
	      add_client(client_count + 1, connection, sos, sis);
	    if (cr == null)
	      {
		display.append("Client limit!! Connection refused...\n");
		sos.writeUTF("Refused");
	      }
	    else
	      {
		display.append("Connection granted..." + "\n");
		client_monitor cm = new client_monitor(this, cr);
		sos.writeUTF("Connected...");
	      }
	  }
      }
    catch (IOException e)
      {
	e.printStackTrace(); 
      }
  }

  public static void main (String args[])
  {
    server s = new server();
    s.startServer();
  }

}