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

/* Copyright (C) 2020 Gediminas Jakutis */

#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"

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");

	/* yeah... */
	in->cache = cache;
	in->cache_a = cache;
	in->cache_l = cache;
err:
	return ret;
}

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

	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_next_element_direct(in);
			if (tmp) { /* non-cache reads CAN fail */
				put(in, tmp);
			} else {
				ret = errno;
				break;
			}
		}
	} else if (in->type == stream_in) {
		try_s((ret == stream_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_l = NULL;
	in->cache_a = NULL;
	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;
	dest->cache_a = (struct entry *) src->cache;
	dest->cache_l = (struct entry_l *) src->cache;
	src->cache = NULL;
	src->cache_a = NULL;
	src->cache_l = NULL;
err:
	return ret;
}

int cache_block_copy(struct stream const * const src, struct stream * const 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;
}

int cache_list_copy(struct stream * const src, struct stream * const dest)
{
	int ret = 0;
	struct entry_l *tmp;

	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");

	while ((tmp = get(src))) {
		put(dest, tmp);
	}

	cache_rewind(src);

err:
	return ret;
}

int cache_block_split(struct stream * const src, struct stream * const A, struct stream * const B)
{
	int ret = 0;
	struct settings tmp_settings;

	try(src->n < 2, err, EINVAL, "cannot split single element stream.");

	/* setting up minimal stream basics */
	A->n = src->n / 2;
	B->n = src->n / 2 + (src->n & 1ul);
	A->index = B->index = 0;
	A->type = B->type = stream_cache; /* disallow any stream operations other than split/merge on children */
	A->fd = B->fd = -1; /* if we're splitting, these are for holding cache only */
	/* we only care about these three functions for these temporary streams */
	A->get_next_element_cache = B->get_next_element_cache = src->get_next_element_cache;
	A->place_next_element_cache = B->place_next_element_cache = src->place_next_element_cache;
	A->split = B->split = src->split;
	A->rewind = B->rewind = src->rewind;

	tmp_settings = *src->settings;
	A->settings = B->settings = &tmp_settings;

	/* setting up A */
	tmp_settings.ss = 0;
	tmp_settings.to = A->n;
	try_s((ret = cache_create(A)), err);
	try_s((ret = cache_block_copy(src, A)), err);

	/* setting up B */
	tmp_settings.ss = A->n;
	tmp_settings.to = src->n;
	try_s((ret = cache_create(B)), err);
	try_s((ret = cache_block_copy(src, B)), err);

	A->settings = B->settings = src->settings;

err:
	return ret;
}

int cache_list_split(struct stream * const src, struct stream * const A, struct stream * const B)
{
	int ret = ENOSYS;

	(void) src;
	(void) A;
	(void) B;

	rin_warn("stub!");

	return ret;
}

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

	if (in->index < in->n) {
		ret = (struct entry_l *)(in->cache_a + in->index);
		++in->index;
	}

	return ret;
}

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

	if (in->index < in->n) {
		ret = in->cnode;
		in->cnode = ret->next;
		++in->index;
	}

	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;

	if (!in->cnode) { /* if this is the very first one */
		in->pnode = NULL;
		in->cnode = in->cache_l;
		in->cnode->val = node->val;
		in->cnode->next = NULL;
		in->index = 0;
	} else {
		in->pnode = in->cnode;
		in->cnode = in->cnode + 1; /* lol says librin, lmao */
		in->pnode->next = in->cnode;
		in->cnode->val = node->val;
		in->cnode->next = NULL;
		++in->index;
	}

	return ret;
}

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

	in->pnode = NULL;
	in->cnode = in->cnode ? in->cache_l : NULL;
	in->index = 0;

	return ret;
}