gplib/include/gp/function.hpp

#pragma once

#include "gp/exception.hpp"
#include "gp/algorithm/modifiers.hpp"
#include "gp/algorithm/move.hpp"
#include "gp/algorithm/tmp_manip.hpp"
#include "gp/allocator/allocator.hpp"
#include "gp/optional.hpp"

namespace gp{

	namespace details {
		template<typename pred, typename returner>
		auto ensure(pred a, returner b) {
			gp_config::assertion(a(), "could not ensure predicate");
			return b();
		}
	}

	template <typename fn>
	class function;

	template <typename ret, typename ...args>
	class function<ret(args...)>{
		using fn_ptr = char*;

		using invoke_fn_t = ret (*)(fn_ptr, args&&...);
		using condestruct_fn_t = void (*) (fn_ptr, fn_ptr);

		gp::optional<gp::reference_wrapper<allocator>> alloc;
		invoke_fn_t invokator;
		condestruct_fn_t condestructor;
		fn_ptr data_ptr;
		size_t data_size;


		template<typename func>
		static ret invoke(func* fn, args&&... fw_args) {
			return (*fn)(gp::forward<args>(fw_args)...);
		}

		template<typename func>
		static void condestruct(func* dest, func* src) {
			if(dest != nullptr) {
				new (dest) func(*src);
			} else {
				src->~func();
			}
		}

		static void nop_condestruct(char*, char*) {
			return;
		}

	public:
		function(allocator& alloc_v)
		: alloc(alloc_v)
		, invokator(nullptr)
		, condestructor(nullptr)
		, data_ptr(nullptr)
		, data_size(0)
		{}

		template<typename func>
		function(func f, allocator& alloc_v)
		: alloc(alloc_v)
		, invokator(reinterpret_cast<invoke_fn_t>(invoke<func>))
		, condestructor(reinterpret_cast<condestruct_fn_t>(condestruct<func>))
		, data_ptr(
			sizeof(func) <= sizeof(data_ptr) 
			? nullptr
			: details::ensure(
				[&](){return alloc.has_value();}, 
				[&](){return (char*)(alloc.value().get().allocate(sizeof(func)));}
			)
		)
		, data_size(
			sizeof(func)
		)
		{
			gp_config::assertion(data_size <= sizeof(func) || !(alloc.has_value() && data_ptr == nullptr), "allocator failed in function");
			this->condestructor(data_size <= sizeof(data_ptr) ? (char*)&data_ptr : data_ptr, reinterpret_cast<char*>(&f));
		}

		template<typename func>
		function(func f, nullopt_t alloc_v)
		: alloc(alloc_v)
		, invokator(reinterpret_cast<invoke_fn_t>(invoke<func>))
		, condestructor(reinterpret_cast<condestruct_fn_t>(condestruct<func>))
		, data_ptr()
		, data_size(
			details::ensure(
				[&](){return sizeof(func) <= sizeof(data_ptr);}, 
				[&](){return sizeof(func);}
			)
		)
		{
			this->condestructor((char*)&data_ptr, reinterpret_cast<char*>(&f));
		}

		function(function const& rhs)
		: alloc(rhs.alloc)
		, invokator(rhs.invokator)
		, condestructor(rhs.condestructor)
		, data_ptr(
			rhs.data_size <= sizeof(data_ptr) 
			? 0 
			: details::ensure(
				[&](){return alloc.has_value();}, 
				[&](){return (char*)(alloc.value().get().allocate(rhs.data_size));}
			)
		)
		, data_size(rhs.data_size)
		{
			gp_config::assertion(data_size <= sizeof(data_ptr) || !(alloc.has_value() && data_ptr == nullptr), "allocator failed in function");
			if(
				data_size != 0
				and rhs.data_size != 0
			) this->condestructor(
				data_size <= sizeof(data_ptr) ? (char*)&data_ptr : data_ptr, 
				data_size <= sizeof(data_ptr) ? (char*)&(rhs.data_ptr) : rhs.data_ptr
			);
		}

		function(function&& rhs)
		: alloc(rhs.alloc)
		, invokator(rhs.invokator)
		, condestructor(rhs.condestructor)
		, data_ptr(rhs.data_size <= sizeof(data_ptr) ? nullptr : rhs.data_ptr)
		, data_size(rhs.data_size)
		{
			if(data_size != 0 && data_size <= sizeof(data_ptr)) {
				condestructor((char*)&data_ptr, (char*)&rhs.data_ptr);
				condestructor(nullptr, (char*)&rhs.data_ptr);
			}
			rhs.data_ptr = nullptr;
			rhs.data_size = 0;
		}

		~function(){
			if(data_size <= 0) {
				return;
			}
			if(data_ptr != nullptr && alloc.has_value()) {
				condestructor(nullptr, data_ptr);
				alloc.value().get().deallocate(data_ptr);
				data_ptr = nullptr;
			}
			if(data_size < sizeof(data_ptr))
			{
				condestructor(nullptr, (char*)&data_ptr);
			}
		}

		function& operator=(function&& rhs) {
			gp::swap(alloc, rhs.alloc);
			gp::swap(invokator, rhs.invokator);
			gp::swap(condestructor, rhs.condestructor);
			gp::swap(data_ptr,rhs.data_ptr);
			gp::swap(data_size,rhs.data_size);
			return *this;
		}

		function& operator=(function& rhs) {
			alloc = rhs.alloc;
			invokator = rhs.invokator;
			condestructor = rhs.condestructor;

			/* Cleanup */

			if(data_size > sizeof(data_ptr)) {
				condestructor(nullptr, data_ptr);
				alloc.value().get().deallocate(data_ptr);
			} else if(data_size) {
				condestructor(nullptr, (char*)&data_ptr);
			}

			/* Reallocation */
			
			data_size = rhs.data_size;
			data_ptr = data_size <= sizeof(data_ptr) 
				? 0 
				: details::ensure(
					[&](){return alloc.has_value();}, 
					[&](){return (char*)(alloc.value().get().allocate(rhs.data_size));}
				);
			
			gp_config::assertion(!(alloc.has_value() && data_size > 8 && data_ptr != nullptr), "allocator failed in function");

			if(
				data_size > 0
			) this->condestructor(
				data_size <= sizeof(data_ptr) ? (char*)&data_ptr : data_ptr, 
				data_size <= sizeof(data_ptr) ? (char*)&rhs.data_ptr : rhs.data_ptr
			);
			return *this;
		}

		ret operator()(args&&... argv) {
			return invokator(data_size <= sizeof(data_ptr) ? (fn_ptr)&data_ptr : data_ptr, gp::forward<args>(argv)...);
		}

		bool ready() {
			return invokator != nullptr;
		}
	};

	/*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[16];
		} 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;
				}
			}
			
		}
	};*/

}