/* See LICENSE file for copyright and license details. */
#ifdef __linux__
#ifndef _DEFAULT_SOURCE
#define _DEFAULT_SOURCE
#endif
#endif
#ifdef _WIN32
#ifndef _CRT_RAND_S
#define _CRT_RAND_S
#endif
#endif

#include <errno.h>
#include <limits.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifndef _WIN32
#include <unistd.h>
#include <sys/random.h>
#endif

#include "arg.h"
#include "config.h"

char *argv0;

static unsigned char rbuf[256];
static size_t rpos = sizeof rbuf;

static void
die(const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vfprintf(stderr, fmt, ap);
	va_end(ap);

	if (fmt[0] && fmt[strlen(fmt)-1] == ':') {
		fputc(' ', stderr);
		perror(NULL);
	} else {
		fputc('\n', stderr);
	}

	exit(1);
}

static void
usage(void)
{
	fprintf(stderr, "usage: %s [-v] [-n n] [-l l]\n", argv0 ? argv0 : "rg");
	exit(1);
}

static int
fillrand(unsigned char *buf, size_t n)
{
#ifdef _WIN32
	size_t i;
	unsigned int r;
	int k;

	for (i = 0; i < n; ) {
		if (rand_s(&r) != 0)
			return -1;
		for (k = 0; k < 4 && i < n; k++)
			buf[i++] = (unsigned char)(r >> (8 * k));
	}
	return 0;
#else
	size_t off;
	ssize_t r;

	off = 0;
	while (off < n) {
		r = getrandom(buf + off, n - off, 0);
		if (r < 0) {
			if (errno == EINTR)
				continue;
			return -1;
		}
		if (r == 0)
			return -1;
		off += (size_t)r;
	}
	return 0;
#endif
}

static unsigned char
randbyte(void)
{
	if (rpos >= sizeof rbuf) {
		if (fillrand(rbuf, sizeof rbuf) < 0)
			die("rg: rng:");
		rpos = 0;
	}
	return rbuf[rpos++];
}

static uint32_t
randu32(void)
{
	return ((uint32_t)randbyte() << 24) |
	    ((uint32_t)randbyte() << 16) |
	    ((uint32_t)randbyte() << 8) |
	    (uint32_t)randbyte();
}

static uint32_t
randbelow(uint32_t n)
{
	uint32_t x, min;

	if (n <= 1)
		return 0;
	/* reject [0, 2^32 % n) so x % n is unbiased */
	min = (uint32_t)(-n) % n;
	do {
		x = randu32();
	} while (x < min);
	return x % n;
}

static int
eint(const char *s)
{
	char *end;
	long v;

	if (s == NULL || s[0] == '\0')
		usage();
	errno = 0;
	v = strtol(s, &end, 10);
	if (errno || end == s || *end != '\0' || v < INT_MIN || v > INT_MAX)
		die("rg: invalid number '%s'", s);
	return (int)v;
}

int
main(int argc, char *argv[])
{
	int i, j, n, l, alen;

	n = defn;
	l = defl;

	ARGBEGIN {
	case 'n':
		n = eint(EARGF(usage()));
		break;
	case 'l':
		l = eint(EARGF(usage()));
		break;
	case 'v':
		puts("rg-" VERSION);
		return 0;
	default:
		usage();
	} ARGEND

	if (argc)
		usage();
	if (n < minn || n > maxn)
		die("rg: n must be %d..%d", minn, maxn);
	if (l < minl || l > maxl)
		die("rg: l must be %d..%d", minl, maxl);

	alen = (int)strlen(alphabet);
	if (alen < 1)
		die("rg: empty alphabet");

	for (i = 0; i < n; i++) {
		for (j = 0; j < l; j++)
			putchar(alphabet[randbelow((uint32_t)alen)]);
		putchar('\n');
	}

	return 0;
}