/*-
 * Copyright (c) 2023 Mateusz Guzik
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

/*
 * This program is intended to be compatible with nproc as found in GNU
 * coreutils.
 *
 * In order to maintain that, do not add any features here if they are not
 * present in said program.  If you are looking for anything more advanced you
 * probably should patch cpuset(1) instead.
 */

#include <sys/param.h>
#include <sys/cpuset.h>

#include <err.h>
#include <errno.h>
#include <getopt.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <sysexits.h>
#include <unistd.h>

#define OPT_ALL		(CHAR_MAX + 1)
#define OPT_IGNORE	(CHAR_MAX + 2)
#define OPT_VERSION	(CHAR_MAX + 3)
#define OPT_HELP	(CHAR_MAX + 4)

static struct option long_opts[] = {
	{ "all", no_argument, NULL, OPT_ALL },
	{ "ignore", required_argument, NULL, OPT_IGNORE },
	{ "version", no_argument, NULL, OPT_VERSION },
	{ "help", no_argument, NULL, OPT_HELP },
	{ NULL, 0, NULL, 0 }
};

static void
help(void)
{
	fprintf(stderr,
    "usage: nproc [--all] [--ignore=count]\n");
	fprintf(stderr,
    "       nproc --help\n");
	fprintf(stderr,
    "       nproc --version\n");
}

static void
usage(void)
{
	help();
	exit(EX_USAGE);
}

/*
 * GNU variant ships with the --version switch.
 *
 * While we don't have anything to put there, print something which is
 * whitespace-compatible with the original. Version number was taken
 * from coreutils this code is in sync with.
 */
static void
version(void)
{
	printf("nproc (neither_GNU nor_coreutils) 8.32\n");
	exit(EXIT_SUCCESS);
}

int
main(int argc, char *argv[])
{
	const char *errstr;
	cpuset_t mask;
	int ch, cpus, ignore;
	bool all_flag;

	ignore = 0;
	all_flag = false;

	while ((ch = getopt_long(argc, argv, "", long_opts, NULL)) != -1) {
		switch (ch) {
		case OPT_ALL:
			all_flag = true;
			break;
		case OPT_IGNORE:
			ignore = strtonum(optarg, 0, INT_MAX, &errstr);
			if (errstr)
				errx(1, "bad ignore count: %s", errstr);
			break;
		case OPT_VERSION:
			version();
			__builtin_unreachable();
		case OPT_HELP:
			help();
			exit(EXIT_SUCCESS);
		default:
			usage();
		}
	}

	argc -= optind;
	argv += optind;

	if (argc != 0)
		usage();

	if (all_flag) {
		cpus = sysconf(_SC_NPROCESSORS_CONF);
		if (cpus == -1)
			err(1, "sysconf");
	} else {
		CPU_ZERO(&mask);
		if (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_TID, -1,
		    sizeof(mask), &mask) != 0)
			err(1, "cpuset_getaffinity");
		cpus = CPU_COUNT(&mask);
	}

	if (ignore >= cpus)
		cpus = 1;
	else
		cpus -= ignore;

	printf("%u\n", cpus);

	exit(EXIT_SUCCESS);
}