/*
 * Author: Wenbing Zhao
 * Last Modified: 11/10/2006
 * For EEC484/584 Project 2
 */
import java.util.*; // for timers

public class Packet {
    public static final int MAX_PACKET_PAYLOAD = 1024;
    public static final int HEADER_LEN = 12; // size of 3 integers
    // max_packet_size = payload length + header fields
    public static final int MAX_PACKET_SIZE = MAX_PACKET_PAYLOAD + 
	HEADER_LEN;

    public int seq; // sequence number for duplicate detection
    public int ack; // acked sequence number
    public int length; // payload length
    public byte[] payload = new byte[MAX_PACKET_PAYLOAD];

    private java.util.Timer m_timer;
    private SendTimerTask m_timerTask = new SendTimerTask();
    // set right before initial sending to enable timeout callback
    private TransportLayer m_transportLayer = null; 

    // constructor to be used when sending
    public Packet() {
	seq = -1;
	ack = -1;
	length = 0;
    }

    // constructor to be used when receiving
    public Packet(byte[] receivedData) {
	int index = 0;

	// set seq number
	byte[] intArray = {receivedData[index], receivedData[index+1],
			   receivedData[index+2], receivedData[index+3]};
	seq = ByteArrayUtils.readInt(intArray);
	index += 4;

	// set ack sequence number
	intArray[0] = receivedData[index++];
	intArray[1] = receivedData[index++];
	intArray[2] = receivedData[index++];
	intArray[3] = receivedData[index++];
	ack = ByteArrayUtils.readInt(intArray);

	// payload length
	intArray[0] = receivedData[index++];
	intArray[1] = receivedData[index++];
	intArray[2] = receivedData[index++];
	intArray[3] = receivedData[index++];
	length = ByteArrayUtils.readInt(intArray);

	for(int i=0; i<length; i++) {
	    payload[i] = receivedData[index+i];
	}
    }

    public void setTransportLayer(TransportLayer tl) {
	m_transportLayer = tl;
    }

    public byte[] toBytes() {
	// we want to construct a byte array consisting
	// a sequence number, an ack, 
	// a length field (4 bytes), and the payload
	int totalLen = length + HEADER_LEN;
	byte[] data = new byte[totalLen];
	//System.out.println("Send total length: "+totalLen);

	int i = 0;
	byte[] intArray = new byte[4];
	ByteArrayUtils.writeInt(intArray, seq);
	int k = 0;
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];

	ByteArrayUtils.writeInt(intArray, ack);
	k = 0;
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];

	ByteArrayUtils.writeInt(intArray, length);
	k = 0;
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];
	data[i++] = intArray[k++];

	for(int j=0; j<length; j++,i++)
	    data[i] = payload[j];

	return data;
    }

    void startTimer() {
	print("...start timer for packet");
	try {
	    if(m_timer != null)
		m_timer.cancel();
	    m_timer = new java.util.Timer();
	    m_timer.schedule(new SendTimerTask(), TransportLayer.TIMEOUT);
	} catch(Exception e) {}
    }

    void stopTimer() {
	print("...cancel timer for packet");
	try {
	    m_timer.cancel();
	    m_timer = null;
	} catch(Exception e) {}
    }

    public class SendTimerTask extends TimerTask {
	public void run() {
	    print("...timeout for packet");
	    m_transportLayer.onTimeout();
	}
    }

    public void printWithPayload(String comment) {
	System.out.println(comment+": seq="+seq+", ack="+ack+", len="+length+
			   " \""+new String(payload)+"\"");
    }
    public void print(String comment) {
	System.out.println(comment+": seq="+seq+", ack="+ack+", len="+length);
    }
}