// nice.c, version 1.0.2
// OMKOV coreutils implementation of POSIX nice
// Copyright (C) 2020, Jakob Wakeling
// MIT Licence

#include "util/error.h"
#include "util/optget.h"

#include <unistd.h>

#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>

#define VERSION "1.0.2"

static struct lop lops[] = {
	{ "help",    ARG_NUL, 256 },
	{ "version", ARG_NUL, 257 },
	{ NULL, 0, 0 }
};

static int n = 10;

static void hlp(void);
static void ver(void);

int main(int ac, char *av[]) { A0 = av[0];
	struct opt opt = OPTGET_INIT; opt.str = "n:"; opt.lops = lops;
	for (int o; (o = optget(&opt, av, 0)) != -1;) switch (o) {
	case 'n': {
		register char *s = opt.arg; register int c; bool neg = false;
		if (*s == '+') { ++s; } else if (*s == '-') { ++s; neg = true; }
		for (n = 0; *s >= '0' && *s <= '9'; ++s) { c = *s - '0';
			if (n > (INT_MAX - c) / 10) { break; } n = n * 10 + c;
		}
		
		if (*s) { error(1, "%s: invalid nice value", opt.arg); }
		if (neg) { n = -n; } break;
	}
	case 256: { hlp(); return 0; }
	case 257: { ver(); return 0; }
	default: { return 1; }
	}
	
	if (ac == 1) { printf("%d\n", nice(0)); return 0; }
	else if (opt.ind == ac) { error(1, "missing operand"); }
	
	errno = 0; nice(n); if (errno) { warn("%s", serr()); }
	execvp(av[opt.ind], &av[opt.ind]);
	
	warn("%s: %s", av[opt.ind], serr());
	return errno = ENOENT ? 127 : 126;
}

/* Print help information */
static void hlp(void) {
	puts("nice - invoke with an altered nice value\n");
	puts("usage: nice [-n increment] [command [argument...]]\n");
	puts("options:");
	puts("  -n increment  Nice increment value");
	puts("  --help        Display help information");
	puts("  --version     Display version information");
}

/* Print version information */
static void ver(void) {
	puts("OMKOV coreutils nice, version " VERSION);
	puts("Copyright (C) 2020, Jakob Wakeling");
	puts("MIT Licence (https://opensource.org/licenses/MIT)");
}