#include <stdio.h>
#include <signal.h>
#include <fcntl.h>

void setNonBlocking(int);
void parent_handler();
int count = 0;
int pipesin[1];
int pipesout[1];

main(int argc, char **argv)
{
	// check the command line input to make sure it's pairs of numbers
	if (argc % 2 == 0 || argc == 1)
	{
		printf("input must be a set of pairs of numbers");
	        exit(0);
	}
	int i = 1;
	int j;
	
	int parent_pid = getpid();
	signal(SIGUSR1, parent_handler);
	
	int pipev[2];
	int pipev2[2];
	int length;
	char buf[1024];
	char buf2[1024];
	int position = 1;
	int pid;
	int m, n, next, last;
	
	// open one pipe to read from child
       	if (pipe(pipev) == -1)
		perror("open pipe");
	//open second pipe to write to child
	if (pipe(pipev2) == -1)
		perror("open pipe");
		
	//pipesin[count] = pipev[0];
	//pipesout[count] = pipev2[1];
	//setNonBlocking(pipesin[count]);
	count++;
        //close(pipev[1]);
	//close(pipev2[0]);

	sscanf(argv[position], "%d", &m);
	sscanf(argv[position + 1], "%d", &n);
	
	pid = fork();
	/* error */
	if (pid < 0)
		perror("fork");
	/* child */
	else if (pid == 0)
	{
		sprintf(buf, "%s %s", m, n);
		length = strlen(buf);
		if (write(pipev[1], buf, length) != length)
			perror("write to pipe");
		next = m;
		last = n;
		while(1)
		{
			next = last;
			read(pipev2[0], buf2, 1024);
			sscanf(buf2, "%d", &last);
			if (last == 0) 
			{
				printf("GCD(%d, %d) = %d ", m, n, next);
				exit(0);
			}
			sprintf(buf, "%d %d", next, last);
	       		if (write(pipev[1], buf, length) != length)
	   			perror("write to pipe");
			kill(parent_pid, SIGUSR1);
		}
	}
	else
	{
		wait(pid);
		exit(0);
	}
}

void setNonBlocking(int fd)
{
	int val;
	if ((val = fcntl(fd, F_GETFL, 0)) < 0)
		perror("fcntl F_GETFL error");
	val |= O_NONBLOCK;	// turn on flags
	if (fcntl(fd, F_SETFL, val)<0)
		perror("fcntl F_SETFL error");
}

void parent_handler()
{
	signal(SIGUSR1, parent_handler);
	char outbuf[1024];
	int a, b, c, i, n, length;
	
	for (i = 0; i < count; i++)
	{
		n = read(pipesin[i], outbuf, 1024);
		if (n != 0)
			break;
	}
	sscanf(outbuf, "%d %d", &a, &b);
	c = a - b;
	while (c >= b)
		c = c - b;
	sprintf(outbuf, "%d", c);
	length = strlen(outbuf);
	if (write(pipesout[count], outbuf, length) != length)
	   	perror("write to pipe");
}