//HW2

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>

int main(int argc, char ** argv)
{
  time_t t0, t1;
  clock_t c0, c1;

  t0 = time(NULL);
  c0 = clock();

  int check = 1;
  int ptoc[2];
  int ctop[2];

  pid_t pid;
  if(pipe(ctop) != 0 || pipe(ptoc) != 0){
    printf("Pipe failed");
    exit(-1);
  }

  while(check < argc){

    int a = 0;
    int b = 0;
    
    pid = getpid();
    printf("Parent Process ID: %d\n", pid);

    a = atoi(argv[check++]); 
    b = atoi(argv[check++]);
    int a1 = a;
    int b1 = b;
    int tmp1;

    if(b > a){
      tmp1 = a;
      a = b;
      b = tmp1;
    }

    switch(fork()){
    case -1: printf("ERROR"); break;

    case 0:
      pid = getpid();
      printf("Child Process ID: %d\n", pid);
      int mod = -1; 
      char buff[10]; 

      while(mod != 0 && mod != 1){
	sprintf(buff, "%d, %d", a, b);
	write(ctop[1], &buff, sizeof(buff));

	read(ptoc[0], &mod, sizeof(mod));
	//      printf("The GCD of %d and %d is %d\n",a1, b1, mod);

	printf("%d = %d * %d + %d\n", a, b, (a/b), mod);
	if(b < (a/b)){
	b = (a/b);	
	a = mod;
	}
      }
 
      t1 = time(NULL);
      c1 = clock(); 

      printf("Elapsed time since January 1, 1970:\t%d\n",(long)(t1));
      printf("Elapsed clock time:\t%d\n",(int)(c1));
      close(ctop[1]); 
      exit(0);
      break;
    }

    printf("PARENT PROCESS\n"); 
    setFlag(ctop[0], O_NONBLOCK);
    char buff[10];
    int num;
    int tmp;

    read(ctop[0], &buff, sizeof(buff)); 
    sscanf(buff, "%d, %d", &a, &b); 

    //    num = gcd(&a, &b);
    if(b > a){
      tmp = a;
      a = b;
      b = tmp;
    }
    num = a % b;

    write(ptoc[1], &num, sizeof(num));  // WRONG
    close(ptoc[1]);
  }

  //  t1 = time(NULL); //get time since Jan 1, 1970
  //  c1 = clock(); 

  //  printf("Elapsed time since January 1, 1970:\t%d\n",(long)(t1 - t0));
  //  printf("Elapsed clock time:\t%d\n",(int)(c1 - c0));

  close(ctop[0]);
  return 0;
}

setFlag(int fd, int flags)
{
  int val;

  if ((val = fcntl(fd, F_GETFL, 0)) < 0)
    perror("fcntl F_GETFL error");

  val |= flags;
  if(fcntl(fd, F_SETFL, val) < 0 )
    perror("fcntl F_GETFL error");
}

int gcd(int *a, int *b)
{
  int tmp;
 
  while(((*a) % (*b) != 0) && ((*a) % (*b) != 1))
    {
        if((*b) > (*a)){
	  tmp = (*a);
	  (*a) = (*b);
	  (*b) = tmp;
	}

	(*a) %= (*b);

        if((*b) > (*a)){
	  tmp = (*a);
	  (*a) = (*b);
	  (*b) = tmp;
	}
    }

  if(((*a) % (*b)) == 0)
    return (int)(*b);
  else
    return 1;
}