#define _POSIX_C_SOURCE 200809L
#define _XOPEN_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include <errno.h>

/* Public domain by Nathan Wagner */

/* reads a long from a string.  returns -1 if completely
 * read, number of characters read otherwise,
 * or zero if it can't read a string
 * clears errno, which may be reset again by strtol()
 */
static int readint(char *s, long *i) {
	long val;
	char *end;
	errno = 0;
	val = strtol(s, &end, 10);

	/* Check for various possible errors */

	if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
			|| (errno != 0 && val == 0)) {
		perror("strtol");
		return 0;
	}

	if (end == s) {
		fprintf(stderr, "No digits were found\n");
		return 0;
	}

	/* If we got here, strtol() successfully parsed a number */

	*i = val;

	if (*end != '\0') {
	 	/* Not necessarily an error... */
		/* printf("Further characters after number: %s\n", endptr); */
		return end - s;
	}

	return -1;
}

static void usage(void) {
	fprintf(stderr, "usage: nice [-n increment] utility [argument...]\n");
	exit(1);
}

int main(int ac, char *av[]) {
	int arg;
	arg = 1;
	long nval;
	if (arg < ac && !strcmp(av[arg], "-n")) {
		char *s = 0;
		if (av[arg][2]) {
			s = av[arg]+2;
		} else if (++arg < ac) {
			s = av[arg];
		}
		if (s && (readint(s, &nval) == -1)) {
			nice((int)nval);
			arg++;
		} else {
			usage();
		}
	}

	if (arg < ac) {
		execvp(av[arg], &av[arg]);
		switch (errno) {
			case ENOENT:
				fprintf(stderr, "nice: ");
				perror(av[arg]);
			       	return 127;
			default:
				fprintf(stderr, "nice: ");
				perror(av[arg]);
				return 126;
		}
	} else {
		usage();
	}

	return 1;
}