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

static void readcfg(const char *cfg, char *buf, size_t len) {
	FILE *fp = fopen(cfg, "r");
	if (fp == NULL) {
		fprintf(stderr, "hostname: %s\n", strerror(errno));
		exit(1);
	}

	if (fgets(buf, len, fp) == NULL) {
		fprintf(stderr, "hostname: fgets returned NULL: %s\n", strerror(errno));

		fclose(fp);
		exit(1);
	}

	/* Remove \n from string */
	*(strrchr(buf, '\n')) = '\0';

	fclose(fp);
}

int main(int argc, char **argv) {
	char hostname[HOST_NAME_MAX + 1];
	char *newhost = NULL;
	int config = 0;

	int opt;
	while ((opt = getopt(argc, argv, "c:F:")) != -1) {
		switch (opt) {
			case 'F':
			case 'c':
				readcfg(optarg, hostname, sizeof(hostname));

				config = 1;
				newhost = hostname;
				break;

			default:
				printf("hostname [cF] [hostname]\n\t-c/-F PATH Use config file\n");
				return 0;
		}
	}

	argc -= optind;
	argv += optind;

	if (newhost == NULL)
		newhost = argv[0];

	/* Set hostname */
	if (argc == 1 || config) {
		if (sethostname(newhost, strlen(newhost)) < 0) {
			fprintf(stderr, "hostname: %s\n", strerror(errno));
			return 1;
		}

		return 0;
	}

	/* Get hostname */
	if (gethostname(hostname, sizeof(hostname)) < 0) {
		fprintf(stderr, "hostname: %s\n", strerror(errno));
		return 1;
	}

	puts(hostname);
	return 0;
}