package datalinklayer;

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

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

	public void run() {
		if (isSender)
			senderLoop();
		else
			receiverLoop();
	}
	
	/**
	 * The sender loop
	 */
	public void senderLoop() {
		long startTime = System.currentTimeMillis();
		Frame pkg = null;
		
		// CHANGED: Prepare a second frame
		Frame pkg2 = null;
		
		// Start with the first frame
		pkg = produceNextFrameForSending();
		linkToPhysical(pkg);
		startTimer();

		// Loop until you have nothing left to say
		while (msgToSend.length()>1) {
			
			// Sleep a little
			try {Thread.sleep(Simulation.protocolDelay);} catch (InterruptedException e) {}
			
			// Check whether a frame has arrived
			Frame receivedFrame = physicalToLink();
			if (receivedFrame!=null) {
				if (Simulation.SHOWINTERNALS) System.out.println(this.name + " received a message with ID=" + receivedFrame.seqNr  + ", ACK=" + receivedFrame.ackBit + " and data=\"" + receivedFrame.data + "\" from its physical layer ");
				// If we get an acknowledgement we can continue
				if (receivedFrame.ackBit && (receivedFrame.seqNr==currentSeqNr)) {
					currentSeqNr++;
					pkg = produceNextFrameForSending();
					linkToPhysical(pkg);
					
					// CHANGED: Send the second package
					currentSeqNr++;
					pkg2 = produceNextFrameForSending();
					linkToPhysical(pkg2);
					
					// Old
					startTimer();
				}
			}	
			// Check whether the timer went off and retransmit
			if (timerExpired()) {
				if (Simulation.SHOWINTERNALS) System.out.println(this.name  + " timed out waiting for ACK of package " + currentSeqNr);
				linkToPhysical(pkg);
				
				// CHANGED: To avoid a nullpointerexception at the beginning
				if (pkg2 != null) 
				linkToPhysical(pkg2);
				
				// OLD
				startTimer();
			}
		} // loop ends when the whole message has been transmitted
		if (Simulation.SHOWINTERNALS) System.out.println("Finished transmission after " + (System.currentTimeMillis()-startTime) + " milliseconds.");
	}
	
	/**
	 * The receiver loop
	 */
	public void receiverLoop() {
		Frame pkg = null;
		
		// Loop forever
		while (true) {
			
			// Sleep a little
			try {Thread.sleep(Simulation.protocolDelay);} catch (InterruptedException e) {}
			
			// Check for new packages
			Frame receivedFrame = physicalToLink();
			
			// If we get the message we expect and it is not garbled, we send back an acknowledgement
			if (receivedFrame!=null && receivedFrame.seqNr<=currentSeqNr) {
				if (Simulation.SHOWINTERNALS) System.out.println(this.name + " received a message with ID=" + receivedFrame.seqNr  + ", ACK=" + receivedFrame.ackBit + " and data=\"" + receivedFrame.data + "\" from its physical layer ");
				boolean calculatedParity = receivedFrame.calculateParity();
				if (calculatedParity == receivedFrame.parityBit) {
					pkg = new Frame(receivedFrame.seqNr,null,true);
					linkToPhysical(pkg);
					if (receivedFrame.seqNr==currentSeqNr) {
						currentSeqNr++;
						msgReceived = msgReceived + receivedFrame.data;
						if (Simulation.SHOWMESSAGE) System.out.println(" String transmitted so far: " + msgReceived);
					}
				}
				// Else the message was garbled, so we forget about it (doing nothing but waiting for retransmission)
				else
					if (Simulation.SHOWINTERNALS) System.out.println(this.name  + ": Parity of message " + receivedFrame.seqNr + " does not match");

			}
		} 
	}


	// Prepares the next frame that can be sent
	private Frame produceNextFrameForSending() {
		Frame msg = new Frame(currentSeqNr,msgToSend.substring(0, Simulation.packageSize), false);
		msgToSend = msgToSend.substring(Simulation.packageSize,msgToSend.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 (or lose it with some probability)
	private void linkToPhysical(Frame f) {
			if (Math.random()>Simulation.lossProbability) p.queueOut.add(f);
			if (Simulation.SHOWINTERNALS) System.out.println(name + " handed a message with ID=" + f.seqNr  + ", ACK=" + f.ackBit + " and data=\"" + f.data + "\" 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;
	}
					
}