#include <ctype.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define min(x, y) ((x < y) ? (x) : (y))

static int parse_size(size_t *size, const char *s)
{
	char *end;

	if (!size || !s)
		return -1;

	*size = strtoul(s, &end, 10);

	switch (toupper(*end)) {
	case 'G': *size *= 1024;
	case 'M': *size *= 1024;
	case 'K': *size *= 1024;
	case 'B': ++end; break;
	case '\0': return 0;
	default: return -1;
	}

	if (*end)
		return -1;

	return 0;
}

int main(int argc, char *argv[])
{
	uint8_t buf[4096];
	FILE *fp;
	size_t count, size;
	int ret = 0;

	if (argc < 3) {
		fprintf(stderr, "usage: %s <size> <output>\n", argv[0]);
		return -1;
	}

	if (parse_size(&size, argv[1]) != 0) {
		fprintf(stderr, "error: size must be an integer with an optional K, M "
			"or G suffix.\n");
		return -1;
	}

	memset(buf, 0xFF, sizeof buf);

	if (!(fp = fopen(argv[2], "wb"))) {
		fprintf(stderr, "error: unable to open '%s' for writing.\n", argv[2]);
		return -1;
	}

	for (; size; size -= count) {
		count = min(sizeof buf, size);

		if (fwrite(buf, sizeof *buf, count, fp) < count) {
			fprintf(stderr, "error: unable to write to file.\n");
			ret = -1;
		}
	}

	fclose(fp);
	return ret;
}