module ecs.block_allocator;

import ecs.manager;

import std.experimental.allocator;
import std.experimental.allocator.mallocator : AlignedMallocator, Mallocator;

struct BlockAllocator//(uint block_size, uint blocks_in_allocation)
{
    private uint block_size;
    private uint blocks_in_allocation;

    void* next_block = null;

    void* getBlock() nothrow @nogc
    {
        if (next_block is null)
            allocBlock();
        void* ret = next_block;
        next_block = *cast(void**) next_block;
        return ret;
    }

    void freeBlock(void* block) nothrow @nogc
    {
        *cast(void**)block = next_block;
        next_block = block;
    }

    private void allocBlock() nothrow @nogc
    {
        next_block = cast(void*) AlignedMallocator.instance.alignedAllocate(
                block_size * blocks_in_allocation, block_size);
        foreach (i; 0 .. blocks_in_allocation - 1)
        {
            void** pointer = cast(void**)(next_block + i * block_size);
            *pointer = next_block + (i + 1) * block_size;
        }
        void** pointer = cast(void**)(
                next_block + (blocks_in_allocation - 1) * block_size);
        *pointer = null;
    }
}