gplib/include/gp/utils/pointers.hpp

#pragma once

#include "gp/functional/bind_front.hpp"
#include "gp/algorithms/move.hpp"
#include "gp/containers/buffer.hpp"
#include "gp/functional/function.hpp"

#include <atomic>
#include <concepts>

namespace gp {

	template<typename T>
	class unique_ptr {
		T* data;
		gp::allocator& owner;

		void dirty_clear() {
			if(data) {
				data->~T();
				owner.deallocate(data);
			}
		}
	public:
		unique_ptr(T* _data, gp::allocator& _owner)
		: data(_data)
		, owner(_owner)
		{}

		template<typename ...U>
		static unique_ptr make(gp::allocator& owner, U&&... args) {
			auto ptr = owner.allocate(sizeof(T));
			return unique_ptr(new(ptr) T(gp::forward<U>(args)...), owner);
		}

		template<typename U>
		unique_ptr<U> cast() {
			auto save = data;
			data = nullptr; 
			return unique_ptr<U>(save, owner);
		}

		T* operator->() {
			return data;
		}

		T& operator*() {
			return *data;
		}

		operator bool() {
			return data != nullptr;
		}

		unique_ptr(unique_ptr&) = delete;

		unique_ptr(unique_ptr&& oth)
		: data(oth.data)
		, owner(oth.owner)
		{
			oth.data = nullptr;
		}

		unique_ptr& operator=(unique_ptr&) = delete;

		unique_ptr& operator=(unique_ptr&& oth) {
			dirty_clear();
			data = oth.data;
			owner = oth.owner;
		}

		~unique_ptr() {
			dirty_clear();
		}
	};

	template<typename T>
	class shared_ptr {
		T* data;
		std::atomic_int* refcounter;
		gp::allocator& owner;

		shared_ptr(T* _data, gp::allocator& _owner)
		: data(_data)
		, refcounter((std::atomic_int*)owner.allocate(sizeof(std::atomic_int)))
		, owner(_owner)
		{
			refcounter->store(1);
		}

		shared_ptr(T* _data, std::atomic_int* refctr, gp::allocator& _owner)
		: data(_data)
		, refcounter(refctr)
		, owner(_owner)
		{
			refcounter->store(1);
		}

		void dirty_clear() {
			if(!refcounter) return;
			if(refcounter->fetch_sub(1, std::memory_order::acq_rel) == 0) {
				if(data) {
					data->~T();
					owner.deallocate(refcounter);
					owner.deallocate(data);
				}
			}
		}
	public:
		template<typename ...U>
		static shared_ptr make(gp::allocator& owner, U&&... args) {
			auto ptr = owner.allocate(sizeof(T));
			return shared_ptr(new(ptr) T(gp::forward<U>(args)...), owner);
		}

		template<typename U>
		shared_ptr<U> cast() {
			return shared_ptr<U>(data, refcounter, owner);
		}

		T* operator->() {
			return data;
		}

		T& operator*() {
			return *data;
		}

		operator bool() {
			return data != nullptr;
		}

		shared_ptr(shared_ptr& oth) {
			oth.refcounter->fetch_add(1, std::memory_order::acquire);
			
			data = oth.data;
			refcounter = oth.refcounter;
			owner = oth.owner;		
		}

		shared_ptr(shared_ptr&& oth)
		: data(oth.data)
		, owner(oth.owner)
		{
			oth.data = nullptr;
			oth.refcounter = nullptr;
		}

		shared_ptr& operator=(shared_ptr& oth) {
			dirty_clear();
			(*oth.refcounter)++;
			
			data = oth.data;
			refcounter = oth.refcounter;
			owner = oth.owner;	
		}

		shared_ptr& operator=(shared_ptr&& oth) {
			dirty_clear();
			data = oth.data;
			owner = oth.owner;
		}

		~shared_ptr() {
			dirty_clear();
		}
	};

	template<std::copyable T>
	struct resource_traits {
		using identifier = uint64_t;
		static constexpr bool create_if_not_exist = false;

		static T* create(const identifier&, gp::allocator&);

		static T* retrieve(const identifier&, gp::allocator&);

		static bool imprint(const identifier&, const T& value);

		static bool annihilate(const identifier&);
	};

	template<std::copyable T>
	requires std::copyable<typename resource_traits<T>::identifier>
	class resource_ptr 
	{
		typename resource_traits<T>::identifier _identifier;
		gp::allocator& _alloc;
		T* value = nullptr;

		operator T&() {
			if(!value) {
				value = resource_traits<T>::retrieve(_identifier, _alloc);
			}
			if(value) return *value;
			else if constexpr (resource_traits<T>::create_if_not_exist) {
				value = resource_traits<T>::create(_identifier, _alloc);
				if(value) return *value;
			}
			gp_config::assertion(false, "unavailable resource lead to crash");
		}

		gp::optional<T&> read() {
			if(!value) {
				value = resource_traits<T>::retrieve(_identifier, _alloc);
			}
			if(value) return *value;
			else if constexpr (resource_traits<T>::create_if_not_exist) {
				value = resource_traits<T>::create(_identifier, _alloc);
				if(value) return *value;
			}
			return gp::nullopt;
		}

		gp::optional<T&> force_read() {
			value = resource_traits<T>::retrieve(_identifier, _alloc);
			if(value) return *value;
			return gp::nullopt;
		}

		template<typename U>
		requires std::is_base_of_v<T, U>
		gp::optional<T&> operator=(U& new_value) {
			if(resource_traits<T>::imprint(_identifier, new_value)) {
				if(value) {
					value->~T();
					gp_config::assertion(_alloc.deallocate((void*)value), "deallocation failure during exchange");
				}
				value = _alloc.allocate(sizeof(U));
				gp_config::assertion(value != nullptr, "could not allocate during resource transcription");
				new(value) U(new_value);
				return *value;
			}
			return gp::nullopt;
		}

		template<typename U>
		requires std::is_base_of_v<T, U>
		gp::optional<T&> operator=(const U& new_value) {
			if(resource_traits<T>::imprint(_identifier, new_value)) {
				if(value) {
					value->~T();
					gp_config::assertion(_alloc.deallocate((void*)value), "deallocation failure during exchange");
				}
				value = _alloc.allocate(sizeof(U));
				gp_config::assertion(value != nullptr, "could not allocate during resource transcription");
				new(value) U(new_value);
				return *value;
			}
			return gp::nullopt;
		}


		template<>
		gp::optional<T&> operator=<gp::nullopt_t>(const gp::nullopt_t) {
			if(resource_traits<T>::annihilate(_identifier)) {
				if(value) {
					value->~T();
					gp_config::assertion(_alloc.deallocate((void*)value), "deallocation failure during exchange");
				}
				value = nullptr;
			}
			return gp::nullopt;
		}
	};
}