#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <err.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/wait.h>

char *const run_path[] = { "./run", NULL };

void
start_proc()
{
	pid_t p = fork();
	if (p == 0) {
		execv(run_path[0], run_path);
	} else if (p > 0) {
		waitpid(p, NULL, 0);
	} else {
		err(1, "fork()");
	}
}

int
acquire_lock()
{
	int lock_fd;

	if ((lock_fd = open("supervise/lock", O_CREAT | O_TRUNC | O_RDONLY, 0600)) == -1)
		err(1, "open()");

	if (flock(lock_fd, LOCK_EX | LOCK_NB) == -1) {
		if (errno == EWOULDBLOCK) {
			fprintf(stderr, "Could not acquire lock\n");
			exit(1);
		} else {
			err(1, "flock()");
		}
	}

	return lock_fd;
}

void
update_status()
{
	int fd, r;
	unsigned char status[18];

	if ((fd = open("supervise/status.new", O_CREAT | O_TRUNC | O_WRONLY | 0644)) == -1) {
		perror("open()");
		return;
	}

	if ((r = write(fd, status, sizeof(status))) == -1)
		perror("write()");

	if (close(fd) == -1)
		perror("close()");

	if (r < sizeof(status)) {
		fprintf(stderr, "Failed to fully write status.new\n");

		if (unlink("supervise/status.new") == -1)
			perror("unlink()");

		return;
	}

	if (rename("supervise/status.new", "supervise/status") == -1)
		perror("rename()");
}

int
main(int argc, char **argv)
{
	int lock_fd;

	if (argc != 2)
		errx(1, "Usage: %s <dir>\n", argv[0]);

	if (chdir(argv[1]) == -1)
		err(1, "chdir()");

	if (mkdir("supervise", 0700) == -1 && errno != EEXIST)
		err(1, "mkdir()");

	lock_fd = acquire_lock();

	if (mkfifo("supervise/control", 0600) == -1 && errno != EEXIST)
		err(1, "mkfifo()");

	if (mkfifo("supervise/ok", 0600) == -1 && errno != EEXIST)
		err(1, "mkfifo()");

	start_proc(); /* XXX: Main loop goes here */

	if (close(lock_fd) == -1)
		perror("close()");

	return 0;
}