#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#include <errno.h>
#include <err.h>
#include <dirent.h>
#include <string.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <signal.h>

#define DEFAULT_QUEUE_DIR "."
#define MAX_JOBS 1

int cur_jobs = 0;

void
run_job(char *queuedir, int fd)
{
	char *run;
	switch(fork()) {
	case -1:
		return;
	case 0:
		asprintf(&run, "%s/run", queuedir);
		dup2(fd, STDIN_FILENO);
		close(fd);
		execl(run, "run", (char*)NULL);
		perror("execle()");
		_exit(1);
		break;
	}
}

void
process_queue(char *queuedir, int dfd)
{
	int fd;
	DIR *dir;
	struct dirent *de;
	char *name;

	dir = fdopendir(dfd);
	while ((de = readdir(dir))) {
		if (cur_jobs >= MAX_JOBS)
			break;

		if (strcmp(de->d_name, ".") == 0  || strcmp(de->d_name, "..") == 0)
			continue;

		asprintf(&name, "new/%s", de->d_name);

		fd = open(name, O_RDONLY);
		if (fd == -1) {
			free(name);
			continue;
		}
		unlink(name);
		run_job(queuedir, fd);
		close(fd);
		free(name);
		cur_jobs++;
	}
	
	rewinddir(dir);
	fdclosedir(dir);
}

void
wait_all()
{
	for (;;) {
		int r = waitpid(-1, NULL, WNOHANG);
		if (r == -1) {
			if (errno == ECHILD)
				break;
			else if (errno == EWOULDBLOCK)
				break;
			else
				err(1, "waitpid()");
		}
		cur_jobs--;
	}
}

int
main(int argc, char **argv)
{
	int kq, dfd, ret;
	struct kevent kv[2];
	char *queuedir = NULL, *newdir = NULL;

	if (argc > 1) {
		queuedir = strdup(argv[1]);
	} else {
		queuedir = strdup(DEFAULT_QUEUE_DIR);
	}

	asprintf(&newdir, "%s/new", queuedir);

	dfd = open(newdir, O_RDONLY | O_DIRECTORY);
	if (dfd == -1)
		err(1, "open()");

	kq = kqueue();
	if (kq == -1)
		err(1, "kqueue()");

	EV_SET(&kv[0], dfd, EVFILT_VNODE, EV_ADD | EV_CLEAR, NOTE_WRITE, 0, NULL);
	EV_SET(&kv[1], SIGCHLD, EVFILT_SIGNAL, EV_ADD | EV_CLEAR, 0, 0, NULL);

	if (kevent(kq, kv, 2, NULL, 0, NULL) == -1)
		err(1, "kevent()");

	process_queue(queuedir, dfd);

	for (;;) {
		ret = kevent(kq, NULL, 0, kv, 2, NULL);
		if (ret == 0)
			continue;
		else if (ret == -1) {
			if (errno  == EINTR)
				continue;
			else
				break;
		}

		int i;
		for (i = 0; i < ret; i++) {
			if (kv[i].filter == EVFILT_SIGNAL) {
				if (kv[i].ident == SIGCHLD) {
					wait_all();
					process_queue(queuedir, dfd);
				}
			} else if (kv[i].filter == EVFILT_VNODE) {
				process_queue(queuedir, dfd);
			}
		}
	}

	return 0;
}