/* circQ.c
 * Circular queue of characters
 * Neal Nelson 2010.02.08
 *
 *   Take the command line argument and put it in the circular
 *   queue and take it out. 
 *
 *   Then put it in and take it out 5 times to test the wrap-around.
 *   The string is truncated by the size of the circular buffer.
 */

#include <stdio.h>

#define MAX_BUF 10

static char qbuf[MAX_BUF];
static int rp, wp;

int main(int argc, char **argv)
{ char mybuf[MAX_BUF+1];
  int i,n;

  if (argc != 2)
  {  printf("Usage: cirQ string\n");
     return -1;
  }
  /* Print the arc and argv[1] string */
  printf("argc: %d\nargc[0]: %s\nargv[1]: %s\n", argc, argv[0], argv[1]);

  /* Now print the argv[1] string char by char */
  for (i = 0; argv[1][i] != 0; i++)
  { putchar( argv[1][i] );
  }
  printf("\n");


  /* initialize read and write buffer pointers */
  rp = 0; wp = 0;


  /* Enqueue the argument string into the circular buffer */

  printf("Before enQ: rp: %d, wp: %d\n",rp,wp);
  n = enQ(argv[1]);
  printf("After enQ: rp: %d, wp: %d\n",rp,wp);


  /* Dequeue the circular buffer */

  n = deQ(&mybuf);
  printf("After deQ: rp: %d, wp: %d\n",rp,wp);
  printf("mybuf: %s\n", mybuf);


  printf("Done part 1.\n\n");


/* Now enQ and deQ the argument string 5 times
 * to test the wrap-around
 */

  for (i = 0; i < 5; i++)
  {
    printf("Before enQ: rp: %d, wp: %d\n",rp,wp);
    n = enQ(argv[1]);

    printf("After enQ: rp: %d, wp: %d\n",rp,wp);

    n = deQ(&mybuf);

    printf("After deQ: rp: %d, wp: %d\n",rp,wp);
    printf("mybuf: %s\n", mybuf);
  }

  printf("Done part 2.\n");

  
}


int enQ(char *s)
{ int i;

  /* Return number of characters put in queue.
   * Return 0 if queue full
   */
  printf("rp: %d, wp: %d\n",rp,wp);

  /* put the argument string into the buffer, no 0 EOS */
  for (i = 0; s[i] != 0 && ((wp+1) % MAX_BUF != rp); i++)
  { qbuf[wp] = s[i];
    wp = (wp + 1) % MAX_BUF;
    printf("rp: %d, wp: %d\n",rp,wp);
  }
  return i;
}

int deQ(char *buf)
{ int i;

  /* Fill in the caller's buffer the characters taken from queue.
   * Return 0 if empty.
   */

  for (i = 0; rp != wp; i++)
  { buf[i] = qbuf[rp];
    rp = (rp + 1) % MAX_BUF;
  }
  buf[i] = 0;                /* Jam 0 EOS */

  return i;
}