/* Simulation of the COVID Barber Shop for CPSC 641      */
/*                                                       */
/* Written by Carey Williamson, University of Calgary    */
/*                                                       */
/* Usage: cc -o barber barber.c -lm                      */
/*        ./barber                                       */

#include <stdio.h>
#include <stdlib.h>
#include <math.h> /* use man 3 log for the math functions */

#define HAIRCUTS 1000000   /* Number of haircuts to simulate */
#define LAMBDA 6.0      /* Arrival rate of new customers */
#define FARUZ_RATE 5.0   /* Service rate of Faruz */
#define GEMAL_RATE 3.0 /* Service rate of Gemal */
#define END_OF_TIME 999999.9 /* Time far in the future */
#define IDLE 0
#define FARUZ 1
#define GEMAL 2
#define BOTH 3
#define MAX_QUEUE 3      /* Number of chairs in waiting room */

/* Debugging output */
/* #define DEBUG 1 */

/***********************************************************************/
/*                 RANDOM NUMBER GENERATION STUFF                      */
/***********************************************************************/

/* Parameters for random number generation. */
#define MAX_INT 2147483647       /* Maximum positive integer 2^31 - 1 */

/* Generate a random floating point value uniformly distributed in [0,1] */
float Uniform01()
  {
    float randnum;

    /* get a random positive integer from random() */
    randnum = (float) 1.0 * random();

    /* divide by max int to get something in 0..1  */
    randnum = (float) randnum / (1.0 * MAX_INT); 

    return( randnum );
  }

/* Generate a random floating point number from an exponential    */
/* distribution with mean mu.                                     */

float Exponential(mu)
    float mu;
  {
    float randnum, ans;

    randnum = Uniform01();
    ans = -(mu) * log(randnum);

    return( ans );
  }

/***********************************************************************/
/*                 MAIN PROGRAM                                        */
/***********************************************************************/

int main()
  {
    int arrivals, departures, active, qsize, state, who, lost;
    float now, nextarrival, nextdeparture, fdone, gdone, rand;
    int fcuts, gcuts;

    /* Initialization */
    state = IDLE;
    qsize = 0;
    active = 0;
    arrivals = 0;
    departures = 0;
    lost = 0;
    fcuts = 0;
    gcuts = 0;
    now = 0.0;
    fdone = END_OF_TIME;
    gdone = END_OF_TIME;
    nextdeparture = END_OF_TIME;
    nextarrival = now + Exponential(1.0 / LAMBDA);

    while( departures < HAIRCUTS )
      {
	/* determine next event */
	if( nextarrival < nextdeparture )
	  {
#ifdef DEBUG
	    printf("Customer arrival at time %8.6f\n", nextarrival);
#endif
	    now = nextarrival;
	    arrivals++;
	    active++;
	    if( state == IDLE )
	      {
		rand = Uniform01();
/* #define MM1K 1 */
#ifdef MM1K
#define FARUZ_RATE 8.0   /* Service rate of Faruz */
#define GEMAL_RATE 0.0   /* Service rate of Gemal */
		if( rand < 1.0 )
#else
		if( rand < 0.5 )
#endif
		  {
		    who = FARUZ;
		    state = FARUZ;
#ifdef DEBUG
		    printf("State is now FARUZ\n");
#endif
		    fdone = now + Exponential(1.0/FARUZ_RATE);
#ifdef DEBUG
		    printf("Faruz cutting hair until %8.6f\n", fdone);
#endif
		    nextdeparture = fdone;
		  }
		else
		  {
		    who = GEMAL;
		    state = GEMAL;
#ifdef DEBUG
		    printf("State is now GEMAL\n");
#endif
		    gdone = now + Exponential(1.0/GEMAL_RATE);
#ifdef DEBUG
		    printf("Gemal cutting hair until %8.6f\n", gdone);
#endif
		    nextdeparture = gdone;
		  }
	      }
	    else if( state == FARUZ )
	      {
		state = BOTH;
		gdone = now + Exponential(1.0/GEMAL_RATE);
#ifdef DEBUG
		printf("State is now BOTH\n");
#endif
#ifdef DEBUG
		printf("Gemal also cutting hair until %8.6f\n", gdone);
#endif
		if( gdone < nextdeparture )
		  {
		    nextdeparture = gdone;
		    who = GEMAL;
		  }
	      }
	    else if( state == GEMAL )
	      {
		state = BOTH;
#ifdef DEBUG
		printf("State is now BOTH\n");
#endif
		fdone = now + Exponential(1.0/FARUZ_RATE);
#ifdef DEBUG
		printf("Faruz also cutting hair until %8.6f\n", fdone);
#endif
		if( fdone < nextdeparture )
		  {
		    nextdeparture = fdone;
		    who = FARUZ;
		  }
	      }
	    else if( state == BOTH )
	      {
		if( qsize < MAX_QUEUE )
		  {
		    qsize++;
#ifdef DEBUG
		    printf("Waiting room now has %d customers!\n", qsize);
#endif
		  }
		else
		  {
#ifdef DEBUG
		    printf("Waiting room overflow! You have lost a customer!!! :-(\n");
#endif
		    lost++;
		    active--;
		  }
	      }
	    nextarrival = now + Exponential(1.0 / LAMBDA);
	  }
	else
	  {
#ifdef DEBUG
	    printf("Next event is departure at time %8.6f\n",
		   nextdeparture);
#endif
	    now = nextdeparture;
	    departures++;
	    active--;
	    if( who == FARUZ )
	      {
		fcuts++;
		if( qsize > 0 )
		  {
		    qsize--;
#ifdef DEBUG
		    printf("Waiting room now has %d customers\n", qsize);
#endif
		    nextdeparture = gdone;
		    who = GEMAL;
		    fdone = now + Exponential(1.0/FARUZ_RATE);
#ifdef DEBUG
		    printf("Faruz resumes cutting hair until %8.6f\n", fdone);
#endif
		    if( fdone < nextdeparture )
		      {
			nextdeparture = fdone;
			who = FARUZ;
		      }
		  }
		else if( state == FARUZ )
		  {
		    state = IDLE;
		    fdone = END_OF_TIME;
		    nextdeparture = END_OF_TIME;
#ifdef DEBUG
		    printf("State is now IDLE\n");
#endif
		  }
		else if( state == BOTH )
		  {
		    state = GEMAL;
		    who = GEMAL;
#ifdef DEBUG
		    printf("State is now GEMAL\n");
#endif
		    nextdeparture = gdone;
		  }
	      }
	    else
	      {
		gcuts++;
		if( qsize > 0 )
		  {
		    qsize--;
#ifdef DEBUG
		    printf("Waiting room now has %d customers\n", qsize);
#endif
		    nextdeparture = fdone;
		    who = FARUZ;
		    gdone = now + Exponential(1.0/GEMAL_RATE);
#ifdef DEBUG
		    printf("Gemal resumes cutting hair until %8.6f\n", gdone);
#endif
		    if( gdone < nextdeparture )
		      {
			nextdeparture = gdone;
			who = GEMAL;
		      }
		  }
		else if( state == GEMAL )
		  {
		    state = IDLE;
		    gdone = END_OF_TIME;
		    nextdeparture = END_OF_TIME;
#ifdef DEBUG
		    printf("State is now IDLE\n");
#endif
		  }
		else if( state == BOTH )
		  {
		    state = FARUZ;
		    who = FARUZ;
		    nextdeparture = fdone;
#ifdef DEBUG
		    printf("State is now FARUZ\n");
#endif
		  }
	      }
	  }
      }

    printf("\n");
    printf("COVID Barber Shop: LAMBDA %3.2f FARUZ %3.2f GEMAL %3.2f MAX_QUEUE %d\n",
	   LAMBDA, FARUZ_RATE, GEMAL_RATE, MAX_QUEUE);
    printf("Target number of haircuts: %d\n", HAIRCUTS);
    printf("Faruz: %d  Gemal: %d\n", fcuts, gcuts);
    printf("Time: %8.6f  Arrivals: %d  Departures: %d  In system: %d\n",
	   now, arrivals, departures, active);
    printf("Lost: %d (%5.2f%%)\n", lost, 100.0*lost/arrivals);
  }