/* See LICENSE file for copyright and license details. */
#include "common.h"


static char *reservoir;
static size_t reservoir_off;
static size_t reservoir_size;
static int random_fd;
static const char *random_fname;


void
init_random(int fd, const char *fname, off_t blksize)
{
	struct stat st;

	if (blksize <= 0) {
		blksize = (off_t)64 << 20;
	} else if (blksize > (off_t)1 << 30) {
		weprintf("limiting block size to 1G");
		blksize = 1;
		blksize <<= 30;
	}

	random_fname = fname;
	random_fd = fd;

	reservoir_size = (size_t)blksize;
	reservoir = emalloc(reservoir_size);

	errno = 0;
	if (isatty(random_fd) || errno == EBADF) {
	use_builtin_generator:
		random_fd = -1;
		libsimple_srand();
	} else if (fstat(random_fd, &st)) {
		if (errno == EBADF)
			goto use_builtin_generator;
		eprintf("fstat %s:", random_fname);
	} else if (S_ISFIFO(st.st_mode) || S_ISCHR(st.st_mode) || S_ISSOCK(st.st_mode)) {
		eprintf("%s is of a unsupported inode type (must be TTY, character device, FIFO, or socket)", fname);
	}
}


void
destroy_random(void)
{
	free(reservoir);
}


size_t
max_blksize(void)
{
	return reservoir_size;
}


const char *
get_random(size_t needed)
{
	size_t off;
	ssize_t r;

	if (reservoir_size - reservoir_off >= needed)
		return &reservoir[reservoir_off];

	if (random_fd < 0) {
		libsimple_random_bytes(&libsimple_random_bits, NULL, reservoir, reservoir_off);
		reservoir_off = 0;
		return reservoir;
	}

	for (off = 0; off < reservoir_off;) {
		r = read(random_fd, &reservoir[off], reservoir_off - off);
		if (r <= 0) {
			if (!r)
				eprintf("random source depleted");
			if (errno == EINTR)
				continue;
			eprintf("read %s:", random_fname);
		}
		off += (size_t)r;
	}

	reservoir_off = 0;
	return reservoir;
}


void
used_random(ssize_t amount)
{
	reservoir_off += (size_t)amount;
}