package telnet;

import java.io.IOException;
import java.net.Socket;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Set;
import java.util.Iterator;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.spi.SelectorProvider;

public class TelnetServer {

    public static void main(String args[]) {
	serve();
    }

    private static void serve() {

	Selector selector;
        try {
            selector = SelectorProvider.provider().openSelector();
        }
        catch (IOException e) {
            System.err.println("could not create channel selector: " + e);
            return;
        }

        ServerSocketChannel channel;
        try {
            channel = ServerSocketChannel.open();
        }
        catch (IOException e) {
            System.err.println("could not create channel: " + e);
            return;
        }

        try {
            channel.configureBlocking(false);
        }
        catch (IOException e) {
            System.err.println("could not set channel non-blocking mode: " + e);
            return;
        }

	final String ANY_ADDR = "0.0.0.0";
        InetAddress anyAddr;
        try {
            anyAddr = InetAddress.getByName(ANY_ADDR);
        }
        catch (UnknownHostException e) {
            System.err.println("could not solve wildcard address: " + ANY_ADDR + ": " + e);
            return;
        }

	final int listenPort = 1234;
        InetSocketAddress sockAddr = new InetSocketAddress(anyAddr, listenPort);
        if (sockAddr == null) {
            System.err.println("could not create socket for wildcard address on port " + listenPort);
            return;
        }

        try {
            channel.socket().bind(sockAddr);
        }
        catch (IOException e) {
            System.err.println("could not bind to local address: " + anyAddr.getHostAddress() + ":" + listenPort + ": " + e);
            return;
        }

        SelectionKey acceptKey;
        try {
            acceptKey = channel.register(selector, SelectionKey.OP_ACCEPT);
        }
        catch (ClosedChannelException e) {
            System.err.println("could not register accept interest: " + e);
            return;
        }

	System.out.println("waiting for connections on " + listenPort);

	for (;;) {

            int addedKeys;
            try {
                addedKeys = selector.select();
            }
            catch (IOException e) {
                System.err.println("channel selection failed: " + e);
                continue;
            }
	    if (addedKeys <= 0) {
		System.err.println("no key selected");
		break;
	    }

	    System.out.println("selected keys: " + addedKeys);

	    Set readyKeys = selector.selectedKeys();

	    for (Iterator i = readyKeys.iterator(); i.hasNext(); ) {
		SelectionKey sk = (SelectionKey) i.next();
		i.remove();

		if (sk.isAcceptable()) {
		    ServerSocketChannel nextReady = (ServerSocketChannel) sk.channel();

		    SocketChannel ch;
		    try {
			ch = nextReady.accept();
		    }
		    catch (IOException e) {
			System.err.println("could not accept client: " + e);
			continue;
		    }

		    try {
			ch.configureBlocking(false);
		    }
		    catch (IOException io) {
			System.err.println("could not set socket as non-blocking: " + io);
			try { ch.close(); } catch (IOException e) {}
			continue;
		    }

		    Socket s = ch.socket();

		    System.out.println("registering client socket for listening");

		    try {
			acceptKey = ch.register(selector, SelectionKey.OP_READ);
		    }
		    catch (ClosedChannelException e) {
			System.err.println("could not register socket for reading: " + e);
			continue;
		    }

		    continue;
		}

		if (sk.isReadable()) {
		    SocketChannel nextReady = (SocketChannel) sk.channel();
		    Socket s = nextReady.socket();

		    System.out.println("disconnecting client socket");

		    try {
			nextReady.close(); // calls sk.cancel(), de-registers key
		    }
		    catch (IOException e) {
			System.err.println("failure closing socket: " + e);
		    }

		    continue;
		}

		System.err.println("select LOOP");
	    }

	}

    }
}