package datalinklayer;

public class LinkLayer extends Thread {
	String intendedMessage;
	PhysicalLayer p;
	int currentSeqNr;
	long timerStart;
	boolean isSender;
	String name;
	String receivedSoFar = "";

	public LinkLayer(PhysicalLayer p1, String m1, String nm) {
		name = nm;
		intendedMessage = m1;
		p = p1;
		currentSeqNr = 0;
		if (intendedMessage!=null) isSender = true; else isSender=false;
	}

	// The main action for senders and receivers
	public void run() {
		long startTime = System.currentTimeMillis();
		Frame pkg = null;
		/** Added  **/
		Frame pkg2 = null;
		/** Added: Flag for receiver to see whether 1st package has arrived **/
		boolean ack1 = false;
		
		// If peer hase something to send, start with the first frame
		if (isSender) {
			/** Changed: Now two packages at initialization **/
			pkg = produceNextFrameForSending();
			currentSeqNr++;
			pkg2 = produceNextFrameForSending();
			linkToPhysical(pkg);
			linkToPhysical(pkg2);
			startTimer();
		}
		
		// Loop forever if you are receiver, or loop until you have nothing left to say as sender
		while (!isSender || intendedMessage.length()-1>=Simulation.packageSize) {
			
			// Sleep a little
			try {Thread.sleep(Simulation.protocolDelay);} catch (InterruptedException e) {}
			
			// Check whether a frame has arrived
			Frame received = physicalToLink();
			if (received!=null) {
				// If we are a sender and get an acknowledgement we can continue
				if (isSender && received.ackBit && (received.seqNr==currentSeqNr)) {
					
					/** Changed: Now two packages are produced **/
					currentSeqNr++;
					pkg = produceNextFrameForSending();
					
					currentSeqNr++;
					pkg2 = produceNextFrameForSending();
					linkToPhysical(pkg);
					linkToPhysical(pkg2);
					startTimer();
				}
				// If we are the receiver and get the message we expect (or an older one) we send back an acknowledgement
				if (!isSender && received.seqNr<=currentSeqNr) {
						boolean calculatedParity = received.calculateParity();
						if (calculatedParity == received.parityBit) {
							// Create acknowledgement package (no data)
							// Is it the message we were waiting for?
							
							/** Changed: Check whether it is the first or the second package for our window **/
							if (received.seqNr==currentSeqNr && ack1==false) {
								ack1 = true;
								currentSeqNr++;
								receivedSoFar = receivedSoFar + received.data;
							}
							if (received.seqNr==currentSeqNr && ack1) {
								pkg = new Frame(received.seqNr,null,true);
								linkToPhysical(pkg);
								currentSeqNr++;
								receivedSoFar = receivedSoFar + received.data;
								System.out.println("   " + receivedSoFar);
								ack1 = false;
							}
						}
						// Else the message was garbled, so we forget about it (doing nothing but waiting for retransmission)
						else {
							System.out.println(this.name  + ": Parity of message " + received.seqNr + " does not match");
						}
				}
			}
			
			// If we are sender, we check whether the timer went off and retransmit
			if (isSender && timerExpired()) {
				System.out.println(this.name  + " timed out waiting for ACK of package " + currentSeqNr);
				linkToPhysical(pkg);
				linkToPhysical(pkg2);
				startTimer();
			}
	
		} // end of looping
		System.out.println("Finished transmission after " + (System.currentTimeMillis()-startTime) + " milliseconds.");
	}


	// Prepares the next frame that can be sent
	private Frame produceNextFrameForSending() {
		Frame msg = new Frame(currentSeqNr,intendedMessage.substring(0, Simulation.packageSize), false);
		intendedMessage = intendedMessage.substring(Simulation.packageSize,intendedMessage.length());
		return msg;
	}

	// Starts the retransmission timer
	private void startTimer() {
		timerStart = System.currentTimeMillis();
	}
	
	// Checks if the retransmission timer is expired
	private boolean timerExpired() {
		if (System.currentTimeMillis()-timerStart>Simulation.retransmissionTimeOut) return true;
		else return false;
	}

	// Give a frame to the physical layer
	private void linkToPhysical(Frame f) {
			p.queueOut.add(f);
			System.out.println(name + " just handed a message with ID " + f.seqNr  + " and ACK=" + f.ackBit + " to its physical layer ");
	}
	
	// Get a frame from the physical layer
	public Frame physicalToLink() {
		if (p.queueIn.size()>0)
				return p.queueIn.poll();
		else return null;
	}
					
}