import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;


public interface TimeServer
{
    /**
     * @return current time from specific server.
     */
    public long getCurrentTime ();

    /**
     * @return delay in response from specific server
     */
    public double getDelay ();
}



class LocalTime implements TimeServer
{
    public long getCurrentTime ()
    {
	return System.currentTimeMillis();
    }

    public double getDelay ()
    {
	return 0;
    }
}


class InternetTime implements TimeServer
{
    private double myRoundTripDelay = 0;
    private String myHost;

    public InternetTime (String host)
    {
	myHost = host;
    }

    public long getCurrentTime ()
    {
        try {
            // Send request
            DatagramSocket socket = new DatagramSocket();
            InetAddress address = InetAddress.getByName(myHost);
            byte[] buf = new NtpMessage().toByteArray();
            DatagramPacket packet = new DatagramPacket(buf, buf.length, address, NtpMessage.NTP_PORT);

            // Set the transmit timestamp *just* before sending the packet
            // ToDo: Does this actually improve performance or not?
            NtpMessage.encodeTimestamp(packet.getData(), 40,
                                       (System.currentTimeMillis()/1000.0) 
                                       + NtpMessage.SECONDS_1900_TO_EPOCH);

            socket.send(packet);

            // Get response
            packet = new DatagramPacket(buf, buf.length);
            socket.setSoTimeout(10*1000);
            try {
                socket.receive(packet);
            } catch (InterruptedIOException iie) {
                socket.close();
                return -1;
            }

            // Immediately record the incoming timestamp
            double destinationTimestamp = (System.currentTimeMillis()/1000.0) + 
		                          NtpMessage.SECONDS_1900_TO_EPOCH;

            // Process response
            NtpMessage msg = new NtpMessage(packet.getData());
            socket.close();
 
            myRoundTripDelay = (destinationTimestamp-msg.originateTimestamp) -
                               (msg.receiveTimestamp-msg.transmitTimestamp);
            return (long)((msg.transmitTimestamp - NtpMessage.SECONDS_1900_TO_EPOCH)*1000);
        } catch (IOException ioe) {
            //ioe.printStackTrace();
            return -1;
        }
    }

    public double getDelay ()
    {
	return myRoundTripDelay;
    }
}