/******************************************************************************
 *  Compilation:  javac MM1Queue.java
 *  Execution:    java MM1Queue lambda mu
 *  Dependencies: Queue.java Histogram.java
 *
 *  Simulate an M/M/1 queue where arrivals and departures are Poisson
 *  processes with arrival rate lambda and service rate mu.
 *
 *  % java MM1Queue .20 .33
 *
 *  % java MM1Queue .20 .25
 *
 *  % java MM1Queue .20 .21
 *
 *
 *  Remarks
 *  -------
 *   - We assume the interrarrival and service times are independent.
 *
 *
 ******************************************************************************/

public class MM1Queue {

    public static void main(String[] args) {
        double lambda = Double.parseDouble(args[0]);  // arrival rate
        double mu     = Double.parseDouble(args[1]);  // service rate

        Queue<Double> q = new Queue<Double>();            // arrival times of customers
        double nextArrival   = StdRandom.exp(lambda);     // time of next arrival
        double nextDeparture = Double.POSITIVE_INFINITY;  // time of next departure

        // histogram object
        Histogram hist = new Histogram(60);

        // simulate an M/M/1 queue
        while (true) {

            // it's an arrival
            if (nextArrival <= nextDeparture) {
                if (q.isEmpty()) nextDeparture = nextArrival + StdRandom.exp(mu);
                q.enqueue(nextArrival);
                nextArrival += StdRandom.exp(lambda);
            }

            // it's a departure
            else {
                double wait = nextDeparture - q.dequeue();
                StdOut.printf("Wait = %6.2f, queue size = %d\n", wait, q.size());
                hist.addDataPoint(Math.min(60,  (int) (Math.round(wait))));
                hist.draw();
                if (q.isEmpty()) nextDeparture = Double.POSITIVE_INFINITY;
                else             nextDeparture += StdRandom.exp(mu);

            }
        }

    }

}