/* See LICENSE file for copyright and license details. */
#include <libsimple-arg.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

NUSAGE(2, "number ...");


#if defined(__GNUC__)
__attribute__((__pure__))
#endif
static int
check_luhn(const char *s)
{
	unsigned sum = 0;

	switch (strlen(s) & 1U) {
		for (;;) {
		case 0:
			if ('0' <= *s && *s <= '4')
				sum += 2U * (unsigned)(*s - '0');
			else if ('5' <= *s && *s <= '9')
				sum += 2U * (unsigned)(*s - '0') - 9U;
			else if (*s)
				return 0;
			else
				break;
			s++;

			/* fall through */

		case 1:
			if ('0' <= *s && *s <= '9')
				sum += (unsigned)(*s - '0');
			else if (*s)
				return 0;
			else
				break;
			s++;

			sum %= 10U;
		}
	}

	return (sum % 10U) == 0U;
}


int
main(int argc, char *argv[])
{
	int use_colour;
	int ret = 0;
	int r, ok;

	ARGBEGIN {
	default:
		usage();
	} ARGEND;

	if (!argc)
		usage();

	use_colour = isatty(STDOUT_FILENO);

	for (; *argv; argv++) {
		ok = check_luhn(*argv);
		ret |= !ok;
		r = printf("%s%s %s%s\n", use_colour ? ok ? "\033[1;32m" : "\033[1;31m" : "",
		           *argv, ok ? "is OK" : "is invalid", use_colour ? "\033[m" : "");
		if (r < 0) {
			fprintf(stderr, "%s: printf: %s\n", argv0, strerror(errno));
			exit(2);
		}
	}

	if (fflush(stdout) || fclose(stdout)) {
		fprintf(stderr, "%s: printf: %s\n", argv0, strerror(errno));
		exit(2);
	}

	return ret;
}