rjp/rjp++/include/dispatch.hpp

/**
	rjp++
	Copyright (C) 2020 rexy712

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef RJP_DISPATCH_HPP
#define RJP_DISPATCH_HPP

#include "rjp_internal.hpp"
#include <type_traits> //is_same, true_type, false_type
#include <utility> //forward
#include <exception>

namespace rjp{

	class missing_dispatch_handler : public std::exception
	{
	public:
		const char* what(void)const noexcept override{
			return "Argument not handled in rjp::dispatch";
		}
	};
	namespace detail{
		template<RJP_data_type T>
		struct to_value_type;

		template<>
		struct to_value_type<rjp_json_object>{
			using type = rjp::object;
		};
		template<>
		struct to_value_type<rjp_json_string>{
			using type = rjp::string_val;
		};
		template<>
		struct to_value_type<rjp_json_integer>{
			using type = rjp::integer;
		};
		template<>
		struct to_value_type<rjp_json_dfloat>{
			using type = rjp::dfloat;
		};
		template<>
		struct to_value_type<rjp_json_boolean>{
			using type = rjp::boolean;
		};
		template<>
		struct to_value_type<rjp_json_array>{
			using type = rjp::array;
		};
		template<>
		struct to_value_type<rjp_json_null>{
			using type = rjp::null;
		};
		template<RJP_data_type T>
		using to_value_type_t = typename to_value_type<T>::type;

		template<RJP_data_type T>
		struct next_data_type;
		template<>
		struct next_data_type<rjp_json_object>{
			static constexpr RJP_data_type value = rjp_json_string;
		};
		template<>
		struct next_data_type<rjp_json_string>{
			static constexpr RJP_data_type value = rjp_json_integer;
		};
		template<>
		struct next_data_type<rjp_json_integer>{
			static constexpr RJP_data_type value = rjp_json_dfloat;
		};
		template<>
		struct next_data_type<rjp_json_dfloat>{
			static constexpr RJP_data_type value = rjp_json_boolean;
		};
		template<>
		struct next_data_type<rjp_json_boolean>{
			static constexpr RJP_data_type value = rjp_json_array;
		};
		template<>
		struct next_data_type<rjp_json_array>{
			static constexpr RJP_data_type value = rjp_json_null;
		};

		template<RJP_data_type T>
		struct has_next_data_type_helper{
			template<class U, bool = (sizeof(U) == sizeof(U))>
			static std::true_type check(U*);
			static std::false_type check(...);

			static constexpr bool value = std::is_same<std::true_type,decltype(check((next_data_type<T>*)0))>::value;
		};
		template<RJP_data_type T>
		struct has_next_data_type{
			static constexpr bool value = has_next_data_type_helper<T>::value;
		};

		template<class T, class Param>
		struct has_operator_for{
			template<class U, class = decltype(std::declval<U>()(std::declval<Param>()))>
			static std::true_type check(U*);
			static std::false_type check(...);

			static constexpr bool value = std::is_same<std::true_type,decltype(check((void*)0))>::value;
		};
		template<class Param, class T, class... Ts>
		struct has_operator_for_any{
			static constexpr bool value = has_operator_for<T, Param>::value || has_operator_for_any<Param,Ts...>::value;
		};
		template<class Param, class T>
		struct has_operator_for_any<Param,T>{
			static constexpr bool value = has_operator_for<T,Param>::value;
		};
		template<class Func, class Val, RJP_data_type T>
		decltype(auto) dispatch_helper(Func&& fun, Val&& v){
			if(v.type() == T){
				return std::forward<Func>(fun)(static_cast<detail::to_value_type_t<T>>(std::forward<Val>(v)));
			}
			if constexpr(detail::has_next_data_type<T>::value){
				return dispatch_helper<Func,Val,detail::next_data_type<T>::value>(std::forward<Func>(fun), std::forward<Val>(v));
			}
			throw missing_dispatch_handler{}; //deals with -Wreturn-type warnings
		}
	}
	template<class Func, class Val>
	decltype(auto) dispatch(Func&& fun, Val&& v){
		return detail::dispatch_helper<Func,Val,rjp_json_object>(std::forward<Func>(fun), std::forward<Val>(v));
	}
	template<class... Ts>
	struct dispatcher : public Ts...
	{
		using Ts::operator()...;

		template<typename std::enable_if<!detail::has_operator_for_any<const value&,Ts...>::value,void>::type* = nullptr>
		decltype(auto) operator()(const value&)const{}
	};

	template<class... Ts>
	dispatcher(Ts&&...) -> dispatcher<Ts...>;
}

#endif