/* SPDX-License-Identifier: LGPL-2.1-only */

/* Copyright (C) 2020-2021 Gediminas Jakutis */

#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <rin/definitions.h>
#include <rin/diagnostic.h>
#include "defs.h"
#include "stream.h"
#include "cache.h"

static int cache_readfile(struct stream * const in);

int cache_create(struct stream * const in)
{
	int ret = 0;
	void *cache;

	try(in->settings->access != cached, err, EINVAL, "cannot create cache: stream is uncached");
	try(!(cache = calloc(in->n, in->settings->stride)), err, ENOMEM, "out of memory");

	in->cache = cache;
	in->cnode = NULL;
err:
	return ret;
}

int cache_populate(struct stream * const in)
{
	int ret = 0;
	size_t i;
	struct entry_l *tmp;
	struct entry_l tmp_store;

	try(in->settings->access != cached, err, EINVAL, "cannot populate cache: stream is uncached");
	try(!in->cache, err, EINVAL, "stream has no cache allocated");

	/* if reading a a randstream, fall back to the one-element-at-a-time mode */
	if (in->type == stream_randread) {
		for (i = 0; i < in->n && !ret; ++i) {
			errno = 0;
			tmp = in->get(in, &tmp_store);
			if (tmp) { /* non-cache reads CAN fail */
				in->put(in, tmp);
			} else {
				ret = errno;
				break;
			}
		}
	} else if (in->type == stream_in) {
		try_s((ret == cache_readfile(in)), err);
	} else {
		try(1, err, EINVAL, "cannot populate a non-reading stream cache");
	}

err:
	return ret;
}

int cache_destroy(struct stream * const in)
{
	int ret = 0;

	try(in->settings->access != cached, err, EINVAL, "cannot destroy cache: stream is uncached");
	free(in->cache);
	in->cache = NULL;
err:
	return ret;
}

int cache_transfer(struct stream * const src, struct stream * const dest)
{
	int ret = 0;

	try(src->settings->access != cached || dest->settings->access != cached, err, EINVAL, "cannot transfer caches of uncached streams");
	try(!src->cache, err, EINVAL, "no cache to transfer");
	try(dest->cache, err, EINVAL, "cannot transfer cache: recipient cache already exists");

	dest->cache = src->cache;
	src->cache = NULL;
err:
	return ret;
}

/* Optimized copying routine for cached array streams.
 * The layout let's us basically just use memcpy instead of slow and wasteful
 * get-put loop, all while completely avoiding the inefficient get-loop for seeking.
 */
int cache_block_copy(struct stream * const restrict src, struct stream * const restrict dest)
{
	int ret = 0;

	try(src->settings->access != cached || dest->settings->access != cached, err, EINVAL, "cannot cache-copy between uncached streams");
	try(!src->cache, err, EINVAL, "no cache to transfer");
	try(src->n < dest->settings->to, err, EINVAL, "invalid copy size");
	try(!dest->cache, err, EINVAL, "no cache to transfer to");

	memcpy(dest->cache, src->cache_a + dest->settings->ss, (dest->settings->to - dest->settings->ss) * dest->settings->stride);
	dest->n = dest->settings->to - dest->settings->ss;

err:
	return ret;
}

struct entry_l *cached_get_array(struct stream * const in, struct entry_l * const store)
{
	struct entry_l *ret = NULL;

	if (in->index < in->n) {
		store->val = in->cache_a[in->index].val;
		++in->index;
		ret = store;
	}

	return ret;
}

struct entry_l *cached_get_list(struct stream * const in, struct entry_l * const store)
{
	struct entry_l *ret = NULL;

	if (in->cnode) {
		ret = in->cnode;
		in->cnode = ret->next;
		*store = *ret;
		ret = store;
	}

	return ret;
}

int cached_put_array(struct stream * const in, const struct entry_l * const data)
{
	int ret = 0;

	if (in->index < in->n) {
		in->cache_a[in->index].val = data->val;
		++in->index;
	}

	return ret;
}

/* This is were fun with the fact mergesort is NOT an in-place algorightm begins.
 * Since we only ever need to "put" on a) generating data and b) merging lists,
 * we basically have to generate the list anew each and every time. For generating,
 * it's a no-brainer, but for lists, while reusing existing nodes COULD be done in
 * a chached variant, file variant cannot do this, as cross-file links are not
 * something that could be handled without going into pretty insane (and laughably
 * inefficient) lenghts either way.
 *
 * And thus alas, we have no option but to just make a list anew
 */
int cached_put_list(struct stream * const restrict in, const struct entry_l * const node)
{
	int ret = 0;

	try(in->index >= in->n, err, EINVAL, "can't add element: out of cache bounds");

	if (!in->cnode) { /* if this is the very first one */
		in->cnode = in->cache_l;
	} else {
		in->cnode->next = in->cnode + 1; /* lol says librin, lmao */
		in->cnode = in->cnode->next;
	}

	in->cnode->val = node->val;
	in->cnode->next = NULL;

err:
	return ret;
}

static int cache_readfile(struct stream * const in)
{
	ssize_t ret = 0;
	size_t remaining = in->n * in->settings->stride;
	ssize_t bytesread = 0;
	size_t i;

	try(in->fd < 3, err, EINVAL, "no file open for reading");

	do {
		ret = read(in->fd, in->cache + bytesread, remaining);
		if (ret < 0) {
			try(errno != EAGAIN, err, errno, "Writing to stream failed with %zi", ret);
		} else {
			bytesread += ret;
			remaining -= ret;
		}
	} while (ret);

	/* if this is a list, we need to adjust the link pointers from file offsets
	 * to buffer addresses. 'Cept for the last one, which needs to be NULL.
	 */
	if (in->settings->format == list) {
		for (i = 0; i < (in->n - 1); ++i) {
			in->cache_l[i].nextaddr = in->cache + in->cache_l[i].offset;
		}
		in->cnode = in->cache_l;
	}

err:
	return ret;
}