gplib/include/gp/optional.hpp

#pragma once
#include <type_traits>
#include "gp_config.hpp"
#include "gp/exception.hpp"
#include "gp/algorithm/move.hpp"

namespace gp{
	struct nullopt_t{};

	constexpr nullopt_t nullopt;

	// TODO: Add allocators to the template
	template<typename T, bool B = std::is_final<T>::value || std::is_fundamental<T>::value>
	class optional;

	template<typename T>
	class optional<T,true>{
		bool ready = false;
		char buffer[sizeof(T)];
	public:
		constexpr optional()
		: ready{false}
		{}

		constexpr optional(nullopt_t)
		: ready{false}
		{}

		constexpr optional(T& value)
		: ready{true}
		{
			new(buffer) T(value);
		}

		constexpr optional(T&& value)
		: ready{true}
		{
			new(buffer) T(gp::move(value));
		}

		optional& operator=(nullopt_t) {
			if(ready) {
				((T*)buffer)->~T();
				ready = false;
			}
			return *this;
		}

		optional& operator=(T& value) {
			if(ready) {
				*(T*)buffer = value;
			} else {
				ready = true;
				new(buffer) T(value);
			}
			return *this;
		}

		optional& operator=(T&& value) {
			if(ready) {
				*(T*)buffer = gp::move(value);
			} else {
				ready = true;
				new(buffer) T(gp::move(value));
			}
			return *this;
		}


		constexpr bool has_value()
		{
			return ready;
		}

		constexpr T& value()
		{
			if constexpr (gp_config::has_exceptions)
			{
				if(!ready)
				{
					throw bad_optional{};
				}
			} else {
				gp_config::assertion(ready, "bad optional access");
			}
			return *reinterpret_cast<T*>(buffer);
		}
	};

	// TODO: Add allocators to the template
	template<typename T>
	class optional<T,false>{
		bool ready = false;
		T* ptr;
	public:
		constexpr optional()
		: ready{false}
		{}

		constexpr optional(nullopt_t)
		: ready{false}
		{}

		template<typename U>
		constexpr optional(U& value)
		: ready{true}
		{
			ptr = new U(value); // TODO: Use allocators
		}

		template<typename U>
		constexpr optional(U&& value)
		: ready{true}
		{
			ptr = new U(gp::move(value)); // TODO: Use allocators
		}

		optional& operator=(nullopt_t) {
			if(ready) {
				delete ptr;
				ready = false;
			}
			return *this;
		}

		template<typename U>
		optional& operator=(U& value) {
			if(ready) {
				if constexpr (std::is_same_v<T, U>) {
					*ptr = value;
				} else {
					delete ptr; // TODO: Use allocators
					ptr = new U(value); // TODO: Use allocators
				}
			} else {
				ready = true;
				ptr = new U(value); // TODO: Use allocators
			}
			return *this;
		}

		template<typename U>
		optional& operator=(U&& value) {
			if(ready) {
				if constexpr (std::is_same_v<T, U>) {
					*ptr = gp::move(value);
				} else {
					delete ptr; // TODO: Use allocators
					ptr = new U(gp::move(value)); // TODO: Use allocators
				}
			} else {
				ready = true;
				ptr = new U(gp::move(value)); // TODO: Use allocators
			}
			return *this;
		}

		template<>
		optional& operator=<optional>(optional& value) {
			if(ready) {
					*ptr = value;
			} else {
				ready = true;
				ptr = new optional(value.value()); // TODO: Use allocators
			}
			return *this;
		}

		template<>
		optional& operator=<optional>(optional&& value){
			if(ready) {
					delete ptr; // TODO: Use allocators
			}
			if(value.ready) {
				ptr = value.ptr;
				value.ready = false;
				ready = true;
				return *this;
			} else {
				ready = false;
				return *this;
			}
		}

		operator T&() {
			gp_config::assertion(ready, "bad optional access");
			return *ptr;
		}

		constexpr bool has_value()
		{
			return ready;
		}

		constexpr T& value()
		{
			if constexpr (gp_config::has_exceptions)
			{
				if(!ready)
				{
					throw bad_optional{};
				}
			} else {
				gp_config::assertion(ready, "bad optional access");
			}
			return *ptr;
		}

		~optional() {
			if(ready) {
				delete ptr; // TODO: Use allocators
			}
		}
	};
}