gplib/include/gp/allocator/arena.hpp

#pragma once
#include "gp_config.hpp"
#include "gp/buffer.hpp"
#include <type_traits>
#include <gp/algorithm/tmp_manip.hpp>

namespace gp {
	template<typename page_allocator = int, size_t align = 1>
	class arena {
		page_allocator allocator;
		gp::buffer<char> data;
		size_t last;
		size_t count;
	public: 
		arena()
		: last(0)
		, count(0)
		, data(gp::buffer<char>(nullptr,nullptr))
		{}

		arena(size_t sz)
		: last(0)
		, count(0)
		, data(nullptr,nullptr)
		{
			if constexpr (gp::has_allocator_interface<page_allocator>::value)
			{
				if(sz!=0)
				{
					auto v=allocator.allocate(sz);
					if(v!=nullptr)
					{
						data=gp::buffer<char>(reinterpret_cast<char*>(v),reinterpret_cast<char*>(v)+sz);
					}
				}
			}
		}

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

		void* allocate(size_t sz)
		{
			[[maybe_unused]]
			size_t mod = 0;

			if constexpr (align != 1)
			{
				mod = align - ((intptr_t)data.begin())%align;
			}

			auto ret=data.begin()+last+mod;
			if(data.contains(ret))
			{
				count++;
				last+=sz+mod;
				return &*(ret);
			}
			else
			{
				return nullptr;
			}
		}

		constexpr bool try_reallocate(void*, size_t) {
			return false;
		}

		bool deallocate(void* ptr)
		{
			if(data.contains((char*)ptr))
			{
				count--;
				if(count==0)
				{
					for(auto& i : data)
					{
						i=0;
					}
					last=0;
				}
				return true;
			}
			return false;
		}

		~arena()
		{
			if constexpr(gp::has_allocator_interface<page_allocator>::value)
			{
				allocator.deallocate(&data[0]);
			}
		}
	};
}