gplib/include/gp/allocator/arena.hpp

#pragma once

#include "gp_config.hpp"

#include "gp/algorithm/min_max.hpp"
#include "gp/algorithm/tmp_manip.hpp"
#include "gp/buffer.hpp"
#include "gp/math/integer_math.hpp"
#include "gp/allocator/allocator.hpp"

#include <type_traits>

namespace gp {
	class arena : public allocator {
		gp::optional<gp::reference_wrapper<allocator>> allocator_v;
		size_t next;
		size_t count;
		gp::buffer<char> data;
	public: 
		arena()
		: next(0)
		, count(0)
		, data(gp::buffer<char>(nullptr,nullptr))
		{}

		arena(allocator& allocator_p, size_t sz)
		: allocator_v(allocator_p)
		, next(0)
		, count(0)
		, data(nullptr,nullptr)
		{
			if(sz != 0)
			{
				auto v = allocator_v.value().get().allocate(sz);
				if(v != nullptr)
				{
					data=gp::buffer<char>(reinterpret_cast<char*>(v),reinterpret_cast<char*>(v)+sz);
				}
			}
		}

		arena(char* pos, size_t sz)
		: next(0)
		, count(0)
		, data(pos,pos+sz)
		{}

		void reset() {
			next = count = 0;
		}

		virtual void* allocate(size_t sz)
		{
			size_t align = gp::min((1 << gp::math::log2(sz)), 16);
			size_t padding = align - (reinterpret_cast<uintptr_t>(data.begin().data + next)) % align;

			auto ret=data.begin()+padding+next;
			if(data.contains(ret))
			{
				count++;
				next+=padding+sz;
				return ret.data;
			}
			else
			{
				return nullptr;
			}
		}

		/**
		 * @return false whatever happens
		 */
		virtual bool try_reallocate(void*, size_t) {
			return false;
		}

		/**
		 * @brief Deallocates the memory if every deallocated block as been deallocated, else marks one deallocation
		 * 
		 * @param ptr the memory to deallocate
		 * @return true if either a deallocation or block release happened
		 * @return false if the pointer was not within the managed area
		 */
		virtual bool deallocate(void* ptr)
		{
			if(data.contains((char*)ptr))
			{
				count--;
				if(count==0)
				{
					for(auto& i : data)
					{
						i=0;
					}
					next=0;
				}
				return true;
			}
			return false;
		}

		virtual ~arena()
		{
			if(allocator_v.has_value())
			{
				allocator_v.value().get().deallocate(&data[0]);
			}
		}
	};
}