#include <stralloc.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <assert.h>

#include "args.h"

int readline (int fd, stralloc * sa)
{
	int ret;
	char c;
	sa->len = 0;
	while (1) {
		ret = read (fd, &c, 1);
		if (ret < 0)
			continue;
		if (ret == 0)
			break;
		if (!stralloc_append (sa, &c))
			return 0;
		if (c == '\n')
			break;
	}
	if (sa->len == 0)
		return 0;
	return 1;
}

void reverse (stralloc * sa)
{
	int p, q;
	char tmp;
	assert (sa->len);
	q = sa->len - 1;
	if (sa->s[q] == '\n')
		q--;
	for (p = 0; p < q; ++p, --q) {
		tmp = sa->s[p];
		sa->s[p] = sa->s[q];
		sa->s[q] = tmp;
	}
}

int main ()
{
	int p1[2];
	int p2[2];
	int pid;
	stralloc sa = {0};

	if (pipe (p1) < 0) {
		perror ("pipe");
		return 1;
	}
	if (pipe (p2) < 0) {
		perror ("pipe");
		return 1;
	}
	pid = fork ();
	if (pid < 0) {
		perror ("fork");
		return 1;
	}
	if (pid == 0) {   /* Child */
		dup2 (p1[0], 0);
		close (p1[0]); close (p1[1]);
		dup2 (p2[1], 1);
		close (p2[0]); close (p2[1]);
		execlp ("tr", "tr", ARG1, ARG2, NULL);
		perror ("execlp");
		return 1;
	}
	/* Parent */
	pid = fork ();
	if (pid < 0) {
		perror ("fork");
		return 1;
	}
	if (pid > 0) {    /* Child */
		close (p1[0]); close (p1[1]);
		close (p2[1]);
		/* Read lines from p2[0], reverse and write to 1 */
		while (readline (p2[0], &sa)) {
			reverse (&sa);
			write (1, sa.s, sa.len);
		}
		return 0;
	}
	/* Parent */
	close (p1[0]); close (p2[0]); close (p2[1]);
	/* Read lines from 0, reverse and write to p1[1] */
	while (readline (0, &sa)) {
		reverse (&sa);
		write (p1[1], sa.s, sa.len);
	}
	return 0;
}