#include "allocator.h"

#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

size_t align(size_t size, size_t al)
{
    size_t padding = size % al;
    if (padding)
        padding = al - padding;
    size_t res;
    if (__builtin_uaddl_overflow(size, padding, &res))
        return 0;
    return res;
}

struct blk_allocator *blka_new(void)
{
    struct blk_allocator *new = malloc(sizeof(struct blk_allocator));
    new->meta = NULL;
    return new;
}

struct blk_meta *blka_alloc(struct blk_allocator *blka, size_t size)
{
    long page_size = sysconf(_SC_PAGESIZE);
    size_t aligned_size = align(size + sizeof(struct blk_meta), page_size);
    struct blk_meta *meta = mmap(NULL, aligned_size, PROT_READ | PROT_WRITE,
                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    if (meta == MAP_FAILED)
        return NULL;
    meta->size = aligned_size - sizeof(struct blk_meta);
    meta->next = blka->meta;
    blka->meta = meta;
    return meta;
}

void blka_free(struct blk_meta *blk)
{
    munmap(blk, blk->size + sizeof(struct blk_meta));
}

void blka_pop(struct blk_allocator *blka)
{
    if (blka->meta == NULL)
        return;

    struct blk_meta *meta = blka->meta;
    blka->meta = blka->meta->next;
    blka_free(meta);
}

void blka_delete(struct blk_allocator *blka)
{
    while (blka->meta)
    {
        blka_pop(blka);
    }
    free(blka);
}