/*
 * Author: Wenbing Zhao
 * Last Modified: 9/18/2006
 * For EEC484/584 Project 1
 */

import java.util.*;

public abstract class DataLinkLayer {
    public static final int MAX_SEQ = 1;
    public static final int EVENT_FRAME_ARRIVAL = 0;
    public static final int EVENT_TIMEOUT = 1;
    public static final int EVENT_PACKET_TOSEND = 2;
    public static final long TIMEOUT = 1000; // in millisecond

    java.util.Timer m_timer;
    SendTimerTask m_timerTask = new SendTimerTask();

    // state variable to indicate if we should process an event
    boolean m_wakeup = false;

    // state variable to indicate the type of event that occurred
    int m_event = -1;

    PhysicalLayer m_physicalLayer = null;

    public DataLinkLayer(PhysicalLayer pl) {
	m_physicalLayer = pl;
    }

    // to be implemented by sub-classes for actual sending side
    // and receiving side protocol
    public abstract void run();

    int increment(int seq) {
	int newseq;
	if(seq < MAX_SEQ)
	    newseq = seq + 1;
	else
	    newseq = 0;
	return newseq; 
    }

    void sendFrameToPhysicalLayer(Frame frame) {
	m_physicalLayer.send(frame.toBytes());
    }

    Frame receiveFrameFromPhysicalLayer() {
	byte[] receivedData = m_physicalLayer.receive();
	Frame frame = new Frame(receivedData);
	return frame;
    }

    void startTimer() {
	try {
	    m_timer = new java.util.Timer();
	    m_timer.schedule(new SendTimerTask(), TIMEOUT);
	} catch(Exception e) {}
    }

    void stopTimer() {
	try {
	    m_timer.cancel();
	} catch(Exception e) {}
    }

    public synchronized int waitForEvent() {
	while(!m_wakeup) {
	    try {
		wait();
	    } catch (InterruptedException e) {}
	}
	m_wakeup = false;
	return m_event;
    }

    public synchronized void onFrameArrival() {
	m_wakeup = true;
	m_event = EVENT_FRAME_ARRIVAL;
	notifyAll();
    }

    public synchronized void onTimeout() {
	m_wakeup = true;
	m_event = EVENT_TIMEOUT;
	notifyAll();
    }

    public class SendTimerTask extends TimerTask {
	public void run() {
	    onTimeout();
	}
    }
}