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

void setNonBlocking(int);
void clearbuf(char *);
void parent_handler();
int numToSpawn;
int child2par[100][2];
int par2child[100][2];

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, k;
	
	numToSpawn = (argc - 1) / 2;
printf("num to spawn=%d\n", numToSpawn);
	int parent_pid = getpid();
	signal(SIGUSR1, parent_handler);
	
	int length;
	char buf[1024];
	char buf2[1024];
	int position = 1;
	int pid;
	int m, n, mm, nn;
	
	for(i = 0; i < numToSpawn; i++)
	{
		// open one pipe to read from child
       		if (pipe(child2par[i]) == -1)
			perror("open pipe");
		//open second pipe to write to child
		if (pipe(par2child[i]) == -1)
		   	perror("open pipe");
		
		setNonBlocking(child2par[i][0]);

		sscanf(argv[2*i + 1], "%d", &m);
		sscanf(argv[2*i + 2], "%d", &n);
printf("m=%d, n=%d\n", m, n);
		
		pid = fork();
		switch(pid){
		  case -1:
			perror("fork");
			break;
		  case 0:  	//child
		  	sleep(1);
printf("entered child\n");
			close(child2par[i][0]);
			close(par2child[i][1]);	
			mm=m; nn=n;
			while(nn>0){
			   clearbuf(buf);
			   sprintf(buf, "%d %d", mm, nn);
// printf("buf=%s\n",buf);
			   length = strlen(buf);
			   if (write(child2par[i][1], buf, length) != length)
	   			perror("write to pipe");
			   kill(parent_pid,SIGUSR1);
			   clearbuf(buf2);
			   read(par2child[i][0], buf2, 1024);
// printf("buf2=%s\n",buf2);
			   mm=nn;
			   sscanf(buf2, "%d", &nn);
			}
			printf("GCD(%d, %d)= %d\n", m, n, mm);
			fflush(stdout);
			exit(i);
			break;
		   default:	//parent
// printf("entered parent\n");
		  	//sleep(1);
			close(child2par[i][1]);
			close(par2child[i][0]);
		}//switch
	}//for
	for (i=0; i< numToSpawn; i++)
	{
		k= wait(&j);
printf("waiting i=%d, child pid=%d, j=%d\n",i,k,j);

	}
	printf("Parent dies\n");
}

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;
	
	int work=1;
     while (work ==1) {
        work=0;
	for (i = 0; i < numToSpawn; i++)
	{
		n = read(child2par[i][0], outbuf, 1024);
		if (n != 0) {
			work=1;
			sscanf(outbuf, "%d %d", &a, &b);
			c = a - b;
			while (c >= b)
				c = c - b;
			clearbuf(outbuf);
			sprintf(outbuf, "%d", c);
			length = strlen(outbuf);
			if (write(par2child[i][1], outbuf, length) != length)
	   			perror("write to pipe");
		}
	}
     }
}

void clearbuf(char * b){
	int i;
	for (i=0; i<1024; i++)
		b[i] = '\0';
}