#include <stdio.h>	/* standard C i/o facilities */
#include <unistd.h>	/* need for call to pipe() */

/* Netprog 99 project 1 test support code 
   DLH 1/11/1999
   Layer 0 expects the cid to reference a pair of pipes descriptors,
   there is a global array of these maintained by the
   function create_communication_id
*/
#define MAXCIDS 10

int pipes[MAXCIDS*2];	/* the array of file (pipe) descriptors */
int cids[MAXCIDS];	/* keeps track of used cids */

int initflag=0;
/* a cid references two file descriptors (pipes):
   pipes[cid*2] is the reading end
   pipes[cid*2+1] is the writing end.
*/

/* This reserves slots in the pipes array (if there is room left) and
   establishes the pipes[cid*2] as the reading end and pipes[cid*2+1] as
   the writing end. Layer 0 uses this information. 
*/

int create_communication_id( read_pipeid, write_pipeid) {
  int i;
  if (! initflag) {
    /* first time called - initialize everything */

    for (i=0;i<MAXCIDS;i++) {
      cids[i]=-1;
      pipes[2*i]=-1;
      pipes[2*i+1]=-1;
    }
    initflag=1;
  }

  /* find an available cid */

  for (i=0;i<MAXCIDS;i++)
    if (cids[i]==-1) {
      cids[i]=1;
      /* found one - now record the pipe descriptors */
      pipes[2*i]=read_pipeid;
      pipes[2*i+1]=write_pipeid;
      printf("CID %d is for pipes %d and %d\n",i,pipes[2*i],pipes[2*i+1]);
      return(i);
    }
  return(-1);	/* no cids left! */
}


/* l0 sends/receives a single bit */

int l0_read( int cid, char *bit) {
  char c;
  int errcode;

  errcode = read(pipes[cid*2],&c,1);
  if (errcode!=1) return(errcode);
  if ((c==0)||(c==1)) {
    *bit=c;
    //    printf("RECEIVED a %d\n",c);
    return(1);
  } 
  return(-1);
}

int l0_write(int cid, char bit) {

  //  printf("SENDING a %c\n",(bit==0)?'0':'1');

  if ((bit==0)||(bit==1)) {
    return(write(pipes[cid*2+1],&bit,1));	
  } else {
    return(-1);		/* invalid value specified */
  }
}