/*
 * Copyright (c) 2020 Cisco and/or its affiliates.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * \file pool.c
 * \brief Implementation of fixed-size pool allocator.
 *
 * NOTE:
 *  - Ideally, we should have a single realloc per resize, that would encompass
 *  both the free indices vector and bitmap, by nesting data structures. Because
 *  of the added complexity, and by lack of evidence of the need for this, we
 *  currently rely on a simpler implementation.
 */

#include <assert.h>
#include <stdlib.h> // calloc

#include "common.h"
#include "pool.h"

#include <stdio.h> // XXX

void
_pool_init(void ** pool_ptr, size_t elt_size, size_t init_size, size_t max_size)
{
    assert(pool_ptr);
    assert(elt_size);

    init_size = next_pow2(init_size);

    if (max_size && init_size > max_size)
        goto ERR_MAX_SIZE;

    /* The initial pool size is rounded to the next power of two */
    size_t alloc_size = next_pow2(init_size);

    pool_hdr_t * ph = calloc(POOL_HDRLEN + alloc_size * elt_size, 1);
    if (!ph)
        goto ERR_MALLOC;

    ph->elt_size = elt_size;
    ph->alloc_size = alloc_size;
    ph->max_size = max_size;

    /* Free indices */
    off_t * free_indices;
    vector_init(free_indices, init_size, max_size);
    for(unsigned i = 0; i < init_size; i++)
        free_indices[i] = (init_size - 1) - i;
    vector_len(free_indices) = init_size;
    ph->free_indices = free_indices;

    /* Free bitmap */
    uint_fast32_t * fb = ph->free_bitmap;
    bitmap_init(fb, init_size, max_size);
    bitmap_set_to(fb, init_size);
    ph->free_bitmap = fb;

    *pool_ptr = (uint8_t*)ph + POOL_HDRLEN;

    return;

ERR_MALLOC:
ERR_MAX_SIZE:
    *pool_ptr = NULL;
    return;
}

void
_pool_free(void ** pool_ptr)
{
    pool_hdr_t * ph = pool_hdr(*pool_ptr);
    vector_free(ph->free_indices);
    bitmap_free(ph->free_bitmap);

    free(pool_hdr(*pool_ptr));
    *pool_ptr = NULL;
}

void
_pool_resize(void ** pool_ptr, size_t elt_size)
{
    pool_hdr_t * ph = pool_hdr(*pool_ptr);
    size_t old_size = ph->alloc_size;
    size_t new_size = old_size * 2;

    if (ph->max_size && new_size > ph->max_size)
        goto ERR_MAX_SIZE;

    /* Double pool storage */
    ph = realloc(ph, POOL_HDRLEN + new_size * elt_size);
    if (!ph)
        goto ERR_REALLOC;
    ph->elt_size = elt_size;
    ph->alloc_size = new_size;

    /*
     * After resize, the pool will have new free indices, ranging from
     * old_size to (new_size - 1)
     */
    vector_ensure_pos(ph->free_indices, old_size);
    for (unsigned i = 0; i < old_size; i++)
        ph->free_indices[i] = new_size - 1 - i;
    vector_len(ph->free_indices) = old_size;

    /* We also need to update the bitmap */
    bitmap_ensure_pos(&(ph->free_bitmap), new_size - 1);
    bitmap_set_range(ph->free_bitmap, old_size, new_size - 1);

    /* Reassign pool pointer */
    *pool_ptr = (uint8_t*)ph + POOL_HDRLEN;

    return;

ERR_REALLOC:
ERR_MAX_SIZE:
    *pool_ptr = NULL;
    return;
}

off_t
_pool_get(void ** pool_ptr, void ** elt, size_t elt_size)
{
    pool_hdr_t * ph = pool_hdr(*pool_ptr);
    uint64_t l = vector_len(ph->free_indices);
    if (l == 0) {
        _pool_resize(pool_ptr, elt_size);
        ph = pool_hdr(*pool_ptr);
        l = vector_len(ph->free_indices);
    }
    off_t free_id = ph->free_indices[l - 1];
    vector_len(ph->free_indices)--;
    bitmap_unset(ph->free_bitmap, free_id);
    *elt = *pool_ptr + free_id * elt_size;
    memset(*elt, 0, elt_size);
    return free_id;
}

void
_pool_put(void ** pool_ptr, void ** elt, size_t elt_size)
{
    pool_hdr_t * ph = pool_hdr(*pool_ptr);
    uint64_t l = vector_len(ph->free_indices);
    vector_ensure_pos(ph->free_indices, l);
    off_t freed_id = (*elt - *pool_ptr) / elt_size;
    ph->free_indices[l] = freed_id;
    vector_len(ph->free_indices)++;
    bitmap_set(ph->free_bitmap, freed_id);
}