package primer56;

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

public class UDPTimeClient {

	public final static int DEFAULT_PORT = 37;
	public final static String DEFAULT_HOST = "time-a.nist.gov";
	
	public static void main(String[] args) {
		
		
		System.getProperties().put("proxySet", "true");
		System.getProperties().put("proxyHost", "proxy.rcub.bg.ac.rs");
		System.getProperties().put("proxyPort", "8080");
		
		
		InetAddress host;
		int port = DEFAULT_PORT;
		
		try{
			if(args.length > 0)
				host = InetAddress.getByName(args[0]);
			else
				host = InetAddress.getByName(DEFAULT_HOST); 
		}catch(Exception ex){
			System.out.println("Usage: java UDPTimeClient host port");
			return;
		}

		if(args.length > 1){
			try{
				port = Integer.parseInt(args[1]);
				if(port <=0 || port > 65535) port = DEFAULT_PORT;
			}catch(Exception ex){}
		}
		
		try{
			UDPPoke poker = new UDPPoke(host, port);
			byte[] response = poker.poke();
			if(response == null){
				System.out.println("No response within alotted time");
				return;
			}else if(response.length!=4){
				System.out.println("Unrecognized response format");
				return;
			}
			
			// The time protocol sets the epoch at 1900,
			// the Java Date class at 1970. This number
			// converts between them
			long differenceBetweenEpochs = 2208988800L;
			
			long secondsSince1900 = 0;
			for(int i=0; i<4; i++){
				secondsSince1900 = 
					(secondsSince1900<<8)| (response[i] & 0x000000FF);
						// "& 0x000000FF" je neophodno!!! jer je response[i] tipa byte,
						// a najuzi tip nad kojim se izvrsavaju bitske (i aritmeticke)
						// operacije je int. Ako bi izostalo "& 0x000000FF", bila bi
						// izvrsena implicitna promocija byte u int, pri cemu se
						// vrsi dopunjavanje sleva bitovima znaka, sto ovde moze biti 1,
						// u kom slucaju se dobija pogresan rezultat
			}
			
			long secondsSince1970 =
				secondsSince1900 - differenceBetweenEpochs;
			long msSince1970 = secondsSince1970 * 1000;
			Date time = new Date(msSince1970);
			
			System.out.println(time);
		}catch(Exception ex){
			System.err.println(ex);
			ex.printStackTrace();
		}
	}

}