gplib/include/gp/function.hpp

#pragma once
#include "gp/exception.hpp"
#include "gp/algorithm/tmp_manip.hpp"
#include "gp/algorithm/move.hpp"

namespace gp{

	template <typename>
	class function;

	template <typename ret, typename ...args>
	class function<ret(args...)>{
		struct virtual_callable
		{
			virtual void inplace_move(char*) = 0;
			virtual virtual_callable* all_copy() = 0;
			virtual void inplace_copy(char*) = 0;
			virtual virtual_callable* all_move() = 0;
			virtual ~virtual_callable() = default;
			virtual ret operator() (args...) = 0;
		};

		template<typename fn>
		class callable final : public virtual_callable{
			typename gp::remove_reference<fn>::type internal_representation;
		public:
			callable(const fn func)
			: internal_representation{gp::move(func)}
			{}

			callable(callable&) = default;
			callable(callable&&) = default;

			virtual ~callable() override = default;

			virtual void inplace_copy(char* ptr) override {
				new(ptr) callable(*this);
			}

			virtual virtual_callable* all_copy() override {
				return new callable(*this);
			}	

			virtual void inplace_move(char* ptr) override {
				new(ptr) callable(gp::move(*this));
			}

			virtual virtual_callable* all_move() override {
				return new callable(gp::move(*this));
			}	

			ret operator() (args... arg_list) override
			{
				return internal_representation(arg_list...);
			}
		};

		// tweak a way to store a size in there for trivial copy
		enum state_t : uint8_t{
			INACTIVE = 0,
			ACTIVE = 1,
			NO_SOO = 0,
			SOO = 2
		};

		state_t state{};
		union{
			virtual_callable* functor = nullptr;
			char inplace[12];
		} self;
		
	public:
		template <typename T>
		function& operator=(T& t) 
		{
			if(state & ACTIVE)
			{
				if(state & SOO)
				{
					((virtual_callable*)self.inplace)->~virtual_callable();
				}
				else
				{
					delete self.functor;
				}
			}
			if(!(t.state & ACTIVE))
			{
				state = INACTIVE;
				return;
			}
			if constexpr (!std::is_same_v<T, function<ret(args...)>>) {
				if constexpr (sizeof(callable<T>) <= sizeof(self))
				{
					new((void*)self.inplace) callable<T>(t);
					state = (state_t)(ACTIVE | SOO);
				}
				else
				{
					self.functor = new callable<T>(t);
					state = (state_t)(ACTIVE | NO_SOO);
				}
			} else {
				if(t.state & SOO)
				{
					auto& ref = t.self.functor;
					ref->inplace_copy((char*)&self);
					state = (state_t)(ACTIVE | SOO);
				}
				else
				{
					self.functor = t.self.functor->all_copy();
					state = (state_t)(ACTIVE | NO_SOO);
				}
			}
		}

		function() 
		{
			state = INACTIVE;
		}

		template<typename T>
		function<>(T& t) 
		{
			if constexpr (!std::is_same_v<T, function<ret(args...)>>) {
				if constexpr (sizeof(callable<T>) <= sizeof(self))
				{
					new((void*)self.inplace) callable<T>(t);
					state = (state_t)(ACTIVE | SOO);
				}
				else
				{
					self.functor = new callable<T>(t);
					state = (state_t)(ACTIVE | NO_SOO);
				}
			} else {
				if(t.state & SOO)
				{
					t.self.functor->inplace_copy(self.inplace);
					state = (state_t)(ACTIVE | SOO);
				}
				else
				{
					self.functor = t.self.functor->all_copy();
					state = (state_t)(ACTIVE | NO_SOO);
				}
			}
		}

		template <typename T>
		function(T&& t) 
		{
			if constexpr (!std::is_same_v<T, function<ret(args...)>>) {
				if constexpr (sizeof(callable<T>) <= sizeof(self))
				{
					new((void*)self.inplace) callable<T>(gp::move(t));
					state = (state_t)(ACTIVE | SOO);
				}
				else
				{
					self.functor = new callable<T>(gp::move(t));
					state = (state_t)(ACTIVE | NO_SOO);
				}
			} else {
				if(t.state & SOO)
				{
					auto& ref = t.self.functor;
					ref->inplace_move((char*)&self);
					state = (state_t)(ACTIVE | SOO);
				}
				else
				{
					self.functor = t.self.functor->all_move();
					state = (state_t)(ACTIVE | NO_SOO);
				}
			}
		}

		ret operator()(args... arg_list) const {
			if constexpr (gp_config::has_exceptions)
			{
				if(!(state & ACTIVE))
				{
					throw bad_functor{};
				}
			}
			if(state & SOO)
			{
				return (*(virtual_callable*)&self)(arg_list...);
			}
			else
			{
				return (*self.functor)(arg_list...);
			}
			
		}

		~function()
		{
			if(state & ACTIVE)
			{
				if(state & SOO)
				{
					((virtual_callable*)&self)->~virtual_callable();
				}
				else
				{
					delete self.functor;
				}
			}
			
		}
	};

}