public class SlidingWindowReceiverTest {
    /* Create a 5-slot receiving window.
     * Assume that each packet contains a four bit field for its
     * sequence number. Therefore the usable range of sequence numbers
     * is 0 <= seqNr < 2^4 = 16. */
    private static SlidingWindowReceiver swr = 
        new SlidingWindowReceiver(5, 16);

    /* Visualization functions. */
    private static void showGetNextPacket(String retval) {
        System.out.print ("\t\t\t   " + 
                          (retval != null? retval : "<null>" ));
        System.out.println ("    \t\t" + swr.show());
    }

    private static void showHandlePacket(int ack, int s, String data) {
        System.out.print("--- [" + s + ": " + data + "] -->");
        System.out.println("\t\t\t\t" + swr.show());
        if (ack >= 0) {
            System.out.println("<-- [ACK "+ ack + "] ---");
        }
    }

    public static void main(String[] args) throws Exception {
        String[] data = {"And ", "then ", "the ", "quick ", "brown ", "fox ", 
                         "jumped ", "over ", "the ", "lazy ", "dog."};
        /* Testing sequence: positive values indicate that the
         * corresponding data element (see above) is delivered,
         * negative values indicate that the upper layer requests a
         * packet. */
        int[] trace = {1, 2, 3, -1, -1, 4, 5, 6, -1, 0, -1, -1, 7, 8, 9, -1,
                       -1, 6, 7, 8, -1, -1, 5, 9, -1, 10, -1, -1, 9, 8, -1, 
                       -1, -1};
        // Commence testing sequence.
         StringBuffer message = new StringBuffer();
 
        System.out.println("     handlePacket\tgetNextPacket\t\t\tReceiver Window");
        String u = "----------------";
        System.out.println(u+u+u+u+u);
        for (int i = 0; i < trace.length; i++) {
            if (trace[i] < 0) {
                /* Upper layer requests next packet. */
                String next = (String)swr.getNextPacket();
                if (next != null) {
                    message = message.append(next);
                }
                /* Visualize on screen. */
                showGetNextPacket(next);
            } else {
                /* Lower layer delivers next packet. */
                int ack = swr.handlePacket(trace[i], data[trace[i]]);
                /* visualize on screen */
                showHandlePacket(ack, trace[i], data[trace[i]]);
            }
        }
        System.out.println(message.toString());
    }
}