module ecs.entity_allocator;

import ecs.manager;

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

struct EntityAllocator
{
    void* next_block;

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

    private void allocBlock()
    {
        next_block = cast(void*) AlignedMallocator.instance.alignedAllocate(
                EntityManager.page_size * EntityManager.pages_in_block, EntityManager.page_size);
        foreach (i; 0 .. EntityManager.pages_in_block - 1)
        {
            void** pointer = cast(void**)(next_block + i * EntityManager.page_size);
            *pointer = next_block + (i + 1) * EntityManager.page_size;
        }
        void** pointer = cast(void**)(
                next_block + (EntityManager.pages_in_block - 1) * EntityManager.page_size);
        *pointer = null;
    }
}