/**
 * Sliding window
 */
public class ReliableSender extends SenderProtocol {

    private Channel channel;

    private Timer timer;

    private Packet[] window;

    private int windowSize;

    private int base;

    private double timeoutValue;

    private int nextSeqNum;

    ReliableSender(Channel aChannel, int aWindowSize, double aTimeout) {
        channel      = aChannel;
        timer        = new Timer(this);
        windowSize   = aWindowSize;
        timeoutValue = aTimeout;
        nextSeqNum   = 1;
        window       = new Packet[windowSize];
        base         = nextSeqNum;
    }

    void send(Data aDataChunk) {
        Packet sentPacket = new Packet(nextSeqNum, aDataChunk);
        channel.send(sentPacket);
        window[nextSeqNum % windowSize] = sentPacket;

        boolean windowEmpty = nextSeqNum == base;
        if(windowEmpty)
            timer.start(timeoutValue);

        nextSeqNum++;

        boolean windowFull = nextSeqNum % windowSize == base % windowSize;
        if(windowFull)
            blockData();

        Simulator.getInstance().log("reliable sender sent " + sentPacket);
    }

    public void receive(Packet aPacket) {
       Simulator.getInstance().log("reliable sender receives " + aPacket);
       base = aPacket.getSeqNum() + 1;
       acceptData();
       boolean windowEmpty = base == nextSeqNum;
       if(windowEmpty)
           timer.stop();
       else
           timer.start(timeoutValue);
    }

    public void timeout(Timer aTimer) {
        Packet sentPacket;
        Simulator.getInstance().log("*** reliable sender timeouts ***");
        timer.start(timeoutValue);
        for(int i = base; i < nextSeqNum; i++) {
            sentPacket = window[i % windowSize];
            Simulator.getInstance().log("reliable sender resends " + sentPacket);
            channel.send(sentPacket);
        }
    }
}