package primer5;

import java.net.*;
import java.io.*;
import java.util.*;

public class TimeClient {

	public final static int DEFAULT_PORT = 37;
	public final static String DEFAULT_HOST = "time.nist.gov";

	public static void main(String[] args) {

		String hostname = DEFAULT_HOST;
		int port = DEFAULT_PORT;

		if (args.length > 0)
			hostname = args[0];

		if (args.length > 1)
			try {
				port = Integer.parseInt(args[1]);
			} catch (NumberFormatException ex) {

			}

		// 1900 <-> 1970

		TimeZone gmt = TimeZone.getTimeZone("GMT");
		Calendar epoch1900 = Calendar.getInstance(gmt);
		epoch1900.set(1900, 00, 01, 00, 00, 00);
		long epoch1900ms = epoch1900.getTime().getTime();
		Calendar epoch1970 = Calendar.getInstance(gmt);
		epoch1970.set(1970, 00, 01, 00, 00, 00);
		long epoch1970ms = epoch1970.getTime().getTime();
		long differenceInMS = epoch1970ms - epoch1900ms;
		long differenceBetweenEpochs = differenceInMS / 1000;

		try (Socket theSocket = new Socket(hostname, port)) {
			InputStream raw = theSocket.getInputStream();
			long secondsSince1900 = 0;
			for (int i = 0; i < 4; i++)
				secondsSince1900 = (secondsSince1900 << 8) | raw.read();

			long secondsSince1970 = secondsSince1900 - differenceBetweenEpochs;
			long msSince1970 = secondsSince1970 * 1000;
			Date time = new Date(msSince1970);

			System.out.println("It is " + time + " at " + hostname);
		} catch (IOException ex) {
			System.err.println(ex);
		}
	}

}