#include <assert.h>
#include "ucore/spool.h"
#include "ucore/utils.h"
#include <string.h>

void uc_pool_init(UCPool *pool, void *buffer, size_t buffer_size, size_t block_size, size_t align)
{
    assert(align > 0);
    assert((align & (align - 1)) == 0); // power of 2


    // enforce minimum for storing free list pointers

    if (align < _Alignof(unsigned char *)) {
        align = _Alignof(unsigned char *);
    }

    if (block_size < sizeof(unsigned char *)) {
        block_size = sizeof(unsigned char *);
    }
    // ensure initial alignment
    size_t stride = UC_ALIGN(block_size, align);

    // align first usable block
    uintptr_t start_addr = (uintptr_t)buffer;
    uintptr_t first_addr = UC_ALIGN(start_addr, align);
    size_t padding = first_addr - start_addr;

    if (padding + stride > buffer_size) {
        pool->capacity = 0;
        pool->free_list = NULL;
    } else {
        size_t usable = buffer_size - padding;
        pool->capacity = usable / stride;

        // build intrusive free list
        unsigned char *p = (unsigned char *)first_addr;
        for (size_t i = 0; i < pool->capacity - 1; ++i) {
            *(unsigned char **)p = p + stride;
            p += stride;
        }
        *(unsigned char **)p = NULL; // last element
        pool->free_list = (unsigned char *)first_addr;
    }

    pool->block_size = stride;
    pool->align      = align;
    pool->start      = (unsigned char *)buffer;
    pool->end        = (unsigned char *)buffer + buffer_size;
}


void *uc_pool_alloc(UCPool *pool)
{
    if (!pool->free_list) {
        return NULL;
    }
    unsigned char *block = pool->free_list;
    pool->free_list = *(unsigned char **)block;

#ifdef DEBUG
    memset(block, 0xCB, pool->block_size);
#endif
    return block;
}
#include <stdio.h>

void uc_pool_free(UCPool *pool, void *p)
{
    if (p == NULL) {
        return;
    }
#ifdef DEBUG
    assert((unsigned char *)p >= pool->start && (unsigned char*)p < pool->end);
    assert(((uintptr_t)p - (uintptr_t)pool->start) % pool->block_size == 0);

    // double-free detection
    for (unsigned char *f = pool->free_list; f; f = *(unsigned char**)f) {
        if (f == p) {
            assert(0 && "Double free detected in pool!");
            return;
        }
    }

    memset(p, 0xDD, pool->block_size);
#endif
     // When not in use, store pointer to next free element inline in the block
    *(unsigned char **)p = pool->free_list;
    pool->free_list = p;
}


void uc_pool_reset(UCPool *pool)
{
   if (pool->capacity == 0)
        return;

    uintptr_t start_addr = (uintptr_t)pool->start;
    uintptr_t first_addr = UC_ALIGN(start_addr, pool->align);

    unsigned char *p = (unsigned char *)first_addr;
    // build intrusive free list
    for (size_t i = 0; i < pool->capacity - 1; ++i) {
        *(unsigned char **)p = p + pool->block_size;
        p += pool->block_size;
    }

    *(unsigned char **)p = NULL;  // last element

    pool->free_list = (unsigned char *)first_addr;
}