#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>
#include <limits.h>
#include <errno.h>

int open_file(const char *path) {
	int fd = open(path, O_RDONLY);
	if (fd < 0) {
		fprintf(stderr, "ps: %s: %s\n", path, strerror(errno));
		return -1;
	}

	return fd;
}

int pscan(const char *pid) {
	char path[PATH_MAX + 1];
	char cmdline[PATH_MAX + 1];

	/* Arguments */
	snprintf(path, sizeof(path), "/proc/%s/cmdline", pid);
	int fd = open_file(path);
	if (fd == -1)
		return 1;

	read(fd, cmdline, sizeof(cmdline));
	close(fd);

	printf("%5s  %5s\n", pid, cmdline);
	return 0;
}

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

	int opt;
	while ((opt = getopt(argc, argv, "o:")) != -1) {
		switch (opt) {
			case 'o':
				break;

			default:
				printf("ps [o] [PID]\n\t-o Options (nice, tty, cmd, pid, nice)\n");
				return 0;
		}
	}

	DIR *dp = opendir("/proc");
	if (dp == NULL) {
		fprintf(stderr, "ps: /proc: %s\n", strerror(errno));
		return 1;
	}

	printf("PID    CMD\n");

	int ret = 0;
	struct dirent *ep;
	while ((ep = readdir(dp)) != NULL)
		if (atoi(ep->d_name))
			if (pscan(ep->d_name))
				ret = 1;

	closedir(dp);
	return ret;
}