/**
 * This class models a client using UDP to communite with the server.
 * 
 * @author tyrant
 * @version 1.0.0
 */

import java.net.*;

public class DatagramClient {

	/* datagram socket to communicate with the server. */
	private DatagramSocket clientSocket;
	
	/* the time out for the datagram socket*/
	private static final int TIME_OUT = 5;

	/**
	 * constructor to create the socket and set the time out.
	 * @throws SocketException
	 */
	public DatagramClient() throws SocketException {

		clientSocket = new DatagramSocket();
		clientSocket.setSoTimeout(TIME_OUT);
	}

	/**
	 * method to exchange one byte with the server for 1000 times.
	 * @throws Exception
	 */
	public void run() throws Exception {
		
		long totalTime = 0;
		long startTime = 0;
		long endTime = 0;
		int counterOfPacket = 1;
		int numberOfLost = 0;
		int numberOfDuplicate = 0;
		boolean reSend = true;

		/* byte arrays to store one byte to receive and to send. */
		byte[] sendByte = new byte[1];
		byte[] receiveByte = new byte[1];
		
		sendByte[0] = 'a';

		/* get the ip of local host.*/
		InetAddress host = InetAddress.getLocalHost();

		// get the start time before the while circle.
		startTime = System.currentTimeMillis();

		while (counterOfPacket <= 1000) {

			/*
			 * resend the byte when it is not sent or received correctly.
			 */
			while (reSend) {

				reSend = false;

				// send the packet.
				DatagramPacket sendPacket = new DatagramPacket(sendByte,
						sendByte.length, host, 6000);
				clientSocket.send(sendPacket);

				// recieve the packet.
				try {
					DatagramPacket receivePacket = new DatagramPacket(
							receiveByte, receiveByte.length);
					clientSocket.receive(receivePacket);
				} catch (SocketTimeoutException stoe) {
					++numberOfLost;
					reSend = true;
				}
			}

			/*
			 * check if the byte received is expected.
			 */
			if (sendByte[0] == receiveByte[0]) {
				
				++counterOfPacket;
				sendByte[0]++;
				reSend = true;
			}
			
			/*
			 * if the byte is not the one expected, receive or resend it.
			 */ 
			else {
				++numberOfDuplicate;
				reSend = false;
				try {
					DatagramPacket receivePacket = new DatagramPacket(
							receiveByte, receiveByte.length);
					clientSocket.receive(receivePacket);
				} catch (SocketTimeoutException stoe) {
					++numberOfLost;
					reSend = true;
				}
			}
		}
		
		// get the end time after the while circle.
		endTime = System.currentTimeMillis();

		totalTime = endTime - startTime;

		System.out.println("Total time: " + totalTime + "ms");
		System.out.println("RTT: " + totalTime / 1000.0 + "ms");
		System.out.println("Number of lost: " + numberOfLost);
		System.out.println("Number of duplicate: " + numberOfLost);

		clientSocket.close();
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) throws Exception {

		DatagramClient client = new DatagramClient();
		client.run();
	}
}