package arq;



import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import comm.MyBuffer;
import comm.MyFile;
import comm.MyFrame;
import comm.TxRx;

public class sender {

	MyFile file;;
	int maxSeq; //seq goes from 0 to maxSeq
	int windowSize; //max. number of data packets not acknowledged
	int localPort; //the local port used to tx and rx packets
	int destPort; //the port at the other point
	MyBuffer buffer;
	List<Integer> framesWaitingACK; //a list of tx. sequence numbers waiting for ACK

	/**
	 *
	 * @param x
	 * @param y
	 * @return the modular when the first value is negative
	 */
	private Integer mod(int x, int y)
	{
	    Integer result = x % y;
	    if (result < 0)
	    {
	        result += y;
	    }
	    return result;
	}

	/**
	 * Remove all frames from framesWaitingACK with a seq number before the seqReceived
	 * Remember how Go-Back-N works!!!
	 * @param seqReceived is the seq received
	 */
	private void removePreviousFramesBuffer(int seqReceived) {
		Integer rmSeq = mod(seqReceived-1,this.maxSeq+1);

		while (this.framesWaitingACK.contains(rmSeq)) {
			this.framesWaitingACK.remove(rmSeq);
			this.buffer.ack(rmSeq);
			rmSeq = mod(rmSeq-1,this.maxSeq+1);
		}
	}

	//constructor
	public sender(int windowSize, int maxSeq, int localPort, int destPort, String fileName) {
		this.file = new MyFile(fileName);
		this.maxSeq = maxSeq;
		this.windowSize = windowSize;
		this.localPort = localPort;
		this.destPort = destPort;
		buffer = new MyBuffer(windowSize);
		System.out.println("Buffer with "+windowSize+" positions");
		framesWaitingACK = new ArrayList<Integer>();
	}

	public static void main(String[] args) {
		int seq=0;

		if (args.length != 6) {
			System.out.println("Usage: sender windowSize maxSeq localPort destPort fileName debug");
			System.exit(-1);
		}
		sender s = new sender(Integer.parseInt(args[0]), Integer.parseInt(args[1]), Integer.parseInt(args[2]),
				Integer.parseInt(args[3]), args[4].toString()); //sender object
		MyFrame rxFrame; //used to receive the control frame from the receiver
		boolean debug;
		Random rnd = new Random();
		rnd.setSeed(47);
		int readBytes;
		TxRx txrx = new TxRx(s.localPort);
		boolean ack = false;

		//this is used for debugging
		if (Integer.parseInt(args[5]) == 0) //output information
			debug = false;
		else
			debug = true;


		MyFrame[] framesSended = new MyFrame[s.windowSize];	//we need to build the first frame before the while loop
		for(int i = 0; i<s.windowSize; i++) {
		readBytes = rnd.nextInt(1000)+100; //random number of bytes to be read
		//read the first readBytes from the file
		String readString = s.file.nextBytes(readBytes);
		MyFrame frame = new MyFrame(0,i,readString);
		framesSended[i] = frame;
		}
		//the funny part starts here
		do { //frame is null 9when all content from the file was sent
			for(int i = 0; i<s.windowSize; i++) {
				s.buffer.addFrame(framesSended[i]);
				s.framesWaitingACK.add(new Integer(seq));
			}
			//frame about to be tx. added to the buffer
			// It is **key** to understand how buffer works!!!
			//seq number waiting for ACK... add it to the framesWaitingACK list
			//not strictly necessary in stop&wait
			ack = false;
			//this is Stop&Wait, so we have to wait for the ACK of the ongoing frame
			//before next frame can be processed
			int numberAck =0;
			while(numberAck!=s.windowSize) {

				if (debug)
					System.out.println("Transmitting frame: " + seq);

				txrx.send(s.buffer.getFrame(seq), s.destPort); //transmitting the frame!!!
				rxFrame = TxRx.getPacketFrame(txrx.receive()); //waiting till a control frame is received
				//control frame received
				if (rxFrame.CRCOK()) {
					//frame received and correct... what code does it have?
					if (rxFrame.getCode() == 1){ //ACK (RR)
						if (debug)
							System.out.println("ACK received with seq: " + rxFrame.getSeq());
						s.removePreviousFramesBuffer(rxFrame.getSeq());
						ack = true;
						numberAck++;//we can leave this while and build the next frame
					}
					else if (rxFrame.getCode() == 2) { //REJ received. Frame in buffer will be retransmitted
						if (debug)
							System.out.println("REJ received with seq: " + rxFrame.getSeq());
					}
					else
						System.out.println("Duplex is not implemented");
				}
				else
					System.out.println("The CRC is wrong!!!"); //Data frame will be transmitted again
			seq++;
			}
			for(int i = 0; i<s.windowSize; i++) {
				//OK, the next data frame can be generated
				readBytes = rnd.nextInt(1000)+100; //random for educational purposes only!
				String readString;
				readString = s.file.nextBytes(readBytes);
				MyFrame frame;
				if (readString != null) {
					seq = (seq+1)%(s.maxSeq+1); //new seq number

					frame = new MyFrame(0,seq,readString);
					framesSended[i] = frame;
				}
				else
					frame = null;



			}

		}while(true);
	}

}