text: // sol3
  
  // The MIT License (MIT)
  
  // Copyright (c) 2013-2020 Rapptz, ThePhD and contributors
  
  // Permission is hereby granted, free of charge, to any person obtaining a copy of
  // this software and associated documentation files (the "Software"), to deal in
  // the Software without restriction, including without limitation the rights to
  // use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
  // the Software, and to permit persons to whom the Software is furnished to do so,
  // subject to the following conditions:
  
  // The above copyright notice and this permission notice shall be included in all
  // copies or substantial portions of the Software.
  
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
  // FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
  // COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
  // IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  // CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  
  #ifndef SOL_STACK_CHECK_UNQUALIFIED_HPP
  #define SOL_STACK_CHECK_UNQUALIFIED_HPP
  
  #include <sol/stack_core.hpp>
  #include <sol/usertype_traits.hpp>
  #include <sol/inheritance.hpp>
  #include <memory>
  #include <functional>
  #include <utility>
  #include <cmath>
  #include <optional>
  #if SOL_IS_ON(SOL_STD_VARIANT_I_)
  #include <variant>
  #endif // variant shenanigans
  
  namespace sol { namespace stack {
  	namespace stack_detail {
  		inline bool impl_check_metatable(lua_State* L, int index, const std::string& metakey, bool poptable) {
  			luaL_getmetatable(L, &metakey[0]);
  			const type expectedmetatabletype = static_cast<type>(lua_type(L, -1));
  			if (expectedmetatabletype != type::lua_nil) {
  				if (lua_rawequal(L, -1, index) == 1) {
  					lua_pop(L, 1 + static_cast<int>(poptable));
  					return true;
  				}
  			}
  			lua_pop(L, 1);
  			return false;
  		}
  
  		template <typename T, bool poptable = true>
  		inline bool check_metatable(lua_State* L, int index = -2) {
  			return impl_check_metatable(L, index, usertype_traits<T>::metatable(), poptable);
  		}
  
  		template <type expected, int (*check_func)(lua_State*, int)>
  		struct basic_check {
  			template <typename Handler>
  			static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  				tracking.use(1);
  				bool success = check_func(L, index) == 1;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, expected, type_of(L, index), "");
  				}
  				return success;
  			}
  		};
  	} // namespace stack_detail
  
  	template <typename T, typename>
  	struct unqualified_interop_checker {
  		template <typename Handler>
  		static bool check(lua_State*, int, type, Handler&&, record&) {
  			return false;
  		}
  	};
  
  	template <typename T, typename>
  	struct qualified_interop_checker {
  		template <typename Handler>
  		static bool check(lua_State* L, int index, type index_type, Handler&& handler, record& tracking) {
  			return stack_detail::unqualified_interop_check<T>(L, index, index_type, std::forward<Handler>(handler), tracking);
  		}
  	};
  
  	template <typename T, type expected, typename>
  	struct unqualified_checker {
  		template <typename Handler>
  		static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  			if constexpr (std::is_same_v<T, bool>) {
  				tracking.use(1);
  				bool success = lua_isboolean(L, index) == 1;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, expected, type_of(L, index), "");
  				}
  				return success;
  			}
  			else if constexpr (meta::any_same_v<T, char /* , char8_t*/, char16_t, char32_t>) {
  				return stack::check<std::basic_string<T>>(L, index, std::forward<Handler>(handler), tracking);
  			}
  			else if constexpr (std::is_integral_v<T> || std::is_same_v<T, lua_Integer>) {
  				tracking.use(1);
  #if SOL_LUA_VESION_I_ >= 503
  				// Lua 5.3 and greater checks for numeric precision
  #if SOL_IS_ON(SOL_STRINGS_ARE_NUMBERS_I_)
  				// imprecise, sloppy conversions
  				int isnum = 0;
  				lua_tointegerx(L, index, &isnum);
  				const bool success = isnum != 0;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::number, type_of(L, index), detail::not_a_number_or_number_string_integral);
  				}
  #elif SOL_IS_ON(SOL_NUMBER_PRECISION_CHECKS_I_)
  				// this check is precise, do not convert
  				if (lua_isinteger(L, index) == 1) {
  					return true;
  				}
  				const bool success = false;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::number, type_of(L, index), detail::not_a_number_integral);
  				}
  #else
  				// Numerics are neither safe nor string-convertible
  				type t = type_of(L, index);
  				const bool success = t == type::number;
  #endif
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::number, type_of(L, index), detail::not_a_number);
  				}
  				return success;
  #else
  				// Lua 5.2 and below checks
  #if SOL_IS_OFF(SOL_STRINGS_ARE_NUMBERS_I_)
  				// must pre-check, because it will convert
  				type t = type_of(L, index);
  				if (t != type::number) {
  					// expected type, actual type
  					handler(L, index, type::number, t, detail::not_a_number);
  					return false;
  				}
  #endif // Do not allow strings to be numbers
  
  #if SOL_IS_ON(SOL_NUMBER_PRECISION_CHECKS_I_)
  				int isnum = 0;
  				const lua_Number v = lua_tonumberx(L, index, &isnum);
  				const bool success = isnum != 0 && static_cast<lua_Number>(llround(v)) == v;
  #else
  				const bool success = true;
  #endif // Safe numerics and number precision checking
  				if (!success) {
  					// Use defines to provide a better error message!
  #if SOL_IS_ON(SOL_STRINGS_ARE_NUMBERS_I_)
  					handler(L, index, type::number, type_of(L, index), detail::not_a_number_or_number_string);
  #elif SOL_IS_ON(SOL_NUMBER_PRECISION_CHECKS_I_)
  					handler(L, index, type::number, t, detail::not_a_number_or_number_string);
  #else
  					handler(L, index, type::number, t, detail::not_a_number);
  #endif
  				}
  				return success;
  #endif
  			}
  			else if constexpr (std::is_floating_point_v<T> || std::is_same_v<T, lua_Number>) {
  				tracking.use(1);
  #if SOL_IS_ON(SOL_STRINGS_ARE_NUMBERS_I_)
  				bool success = lua_isnumber(L, index) == 1;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::number, type_of(L, index), detail::not_a_number_or_number_string);
  				}
  				return success;
  #else
  				type t = type_of(L, index);
  				bool success = t == type::number;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::number, t, detail::not_a_number);
  				}
  				return success;
  #endif // Strings are Numbers
  			}
  			else if constexpr (meta::any_same_v<T, type, this_state, this_main_state, this_environment, variadic_args>) {
  				(void)L;
  				(void)index;
  				(void)handler;
  				tracking.use(0);
  				return true;
  			}
  			else if constexpr (is_unique_usertype_v<T>) {
  				using proper_T = typename unique_usertype_traits<T>::type;
  				const type indextype = type_of(L, index);
  				tracking.use(1);
  				if (indextype != type::userdata) {
  					handler(L, index, type::userdata, indextype, "value is not a userdata");
  					return false;
  				}
  				if (lua_getmetatable(L, index) == 0) {
  					return true;
  				}
  				int metatableindex = lua_gettop(L);
  				if (stack_detail::check_metatable<detail::unique_usertype<proper_T>>(L, metatableindex)) {
  					void* memory = lua_touserdata(L, index);
  					memory = detail::align_usertype_unique_destructor(memory);
  					detail::unique_destructor& pdx = *static_cast<detail::unique_destructor*>(memory);
  					bool success = &detail::usertype_unique_alloc_destroy<proper_T, T> == pdx;
  					if (!success) {
  						memory = detail::align_usertype_unique_tag<true>(memory);
  #if 0
  						// New version
  #else
  						const char*& name_tag = *static_cast<const char**>(memory);
  						success = usertype_traits<T>::qualified_name() == name_tag;
  #endif
  						if (!success) {
  							handler(L, index, type::userdata, indextype, "value is a userdata but is not the correct unique usertype");
  						}
  					}
  					return success;
  				}
  				lua_pop(L, 1);
  				handler(L, index, type::userdata, indextype, "unrecognized userdata (not pushed by sol?)");
  				return false;
  			}
  			else if constexpr (meta::any_same_v<T, lua_nil_t, std::nullopt_t, nullopt_t>) {
  				bool success = lua_isnil(L, index);
  				if (success) {
  					tracking.use(1);
  					return success;
  				}
  				tracking.use(0);
  				success = lua_isnone(L, index);
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, expected, type_of(L, index), "");
  				}
  				return success;
  			}
  			else if constexpr (std::is_same_v<T, env_key_t>) {
  				tracking.use(1);
  				type t = type_of(L, index);
  				if (t == type::table || t == type::none || t == type::lua_nil || t == type::userdata) {
  					return true;
  				}
  				handler(L, index, type::table, t, "value cannot not have a valid environment");
  				return true;
  			}
  			else if constexpr (std::is_same_v<T, detail::non_lua_nil_t>) {
  				return !stack::unqualified_check<lua_nil_t>(L, index, std::forward<Handler>(handler), tracking);
  			}
  			else if constexpr (meta::is_specialization_of_v<T, basic_lua_table>) {
  				tracking.use(1);
  				type t = type_of(L, index);
  				if (t != type::table) {
  					handler(L, index, type::table, t, "value is not a table");
  					return false;
  				}
  				return true;
  			}
  			else if constexpr (meta::is_specialization_of_v<T, basic_bytecode>) {
  				tracking.use(1);
  				type t = type_of(L, index);
  				if (t != type::function) {
  					handler(L, index, type::function, t, "value is not a function that can be dumped");
  					return false;
  				}
  				return true;
  			}
  			else if constexpr (meta::is_specialization_of_v<T, basic_environment>) {
  				tracking.use(1);
  				if (lua_getmetatable(L, index) == 0) {
  					return true;
  				}
  				type t = type_of(L, -1);
  				if (t == type::table || t == type::none || t == type::lua_nil) {
  					lua_pop(L, 1);
  					return true;
  				}
  				if (t != type::userdata) {
  					lua_pop(L, 1);
  					handler(L, index, type::table, t, "value does not have a valid metatable");
  					return false;
  				}
  				return true;
  			}
  			else if constexpr (std::is_same_v<T, metatable_key_t>) {
  				tracking.use(1);
  				if (lua_getmetatable(L, index) == 0) {
  					return true;
  				}
  				type t = type_of(L, -1);
  				if (t == type::table || t == type::none || t == type::lua_nil) {
  					lua_pop(L, 1);
  					return true;
  				}
  				if (t != type::userdata) {
  					lua_pop(L, 1);
  					handler(L, index, expected, t, "value does not have a valid metatable");
  					return false;
  				}
  				return true;
  			}
  			else if constexpr (std::is_same_v<T, luaL_Stream*> || std::is_same_v<T, luaL_Stream>) {
  				if (lua_getmetatable(L, index) == 0) {
  					type t = type_of(L, index);
  					handler(L, index, expected, t, "value is not a valid luaL_Stream (has no metatable/is not a valid value)");
  					return false;
  				}
  				luaL_getmetatable(L, LUA_FILEHANDLE);
  				if (type_of(L, index) != type::table) {
  					type t = type_of(L, index);
  					lua_pop(L, 1);
  					handler(L,
  						index,
  						expected,
  						t,
  						"value is not a valid luaL_Stream (there is no metatable for luaL_Stream -- did you forget to "
  						"my_lua_state.open_libraries(sol::lib::state) or equivalent?)");
  					return false;
  				}
  				int is_stream_table = lua_compare(L, -1, -2, LUA_OPEQ);
  				lua_pop(L, 2);
  				if (is_stream_table == 0) {
  					type t = type_of(L, index);
  					handler(L, index, expected, t, "value is not a valid luaL_Stream (incorrect metatable)");
  					return false;
  				}
  				return true;
  			}
  			else if constexpr (meta::is_optional_v<T>) {
  				using ValueType = typename T::value_type;
  				(void)handler;
  				type t = type_of(L, index);
  				if (t == type::none) {
  					tracking.use(0);
  					return true;
  				}
  				if (t == type::lua_nil) {
  					tracking.use(1);
  					return true;
  				}
  				return stack::unqualified_check<ValueType>(L, index, no_panic, tracking);
  			}
  #if SOL_IS_ON(SOL_GET_FUNCTION_POINTER_UNSAFE_I_)
  			else if constexpr (std::is_function_v<T> || (std::is_pointer_v<T> && std::is_function_v<std::remove_pointer_t<T>>)) {
  				return stack_detail::check_function_pointer<std::remove_pointer_t<T>>(L, index, std::forward<Handler>(handler), tracking);
  			}
  #endif
  			else if constexpr (expected == type::userdata) {
  				if constexpr (meta::any_same_v<T, userdata_value> || meta::is_specialization_of_v<T, basic_userdata>) {
  					tracking.use(1);
  					type t = type_of(L, index);
  					bool success = t == type::userdata;
  					if (!success) {
  						// expected type, actual type
  						handler(L, index, type::userdata, t, "");
  					}
  					return success;
  				}
  				else if constexpr (meta::is_specialization_of_v<T, user>) {
  					unqualified_checker<lightuserdata_value, type::userdata> c;
  					(void)c;
  					return c.check(L, index, std::forward<Handler>(handler), tracking);
  				}
  				else {
  					if constexpr (std::is_pointer_v<T>) {
  						return check_usertype<T>(L, index, std::forward<Handler>(handler), tracking);
  					}
  					else if constexpr (meta::is_specialization_of_v<T, std::reference_wrapper>) {
  						using T_internal = typename T::type;
  						return stack::check<T_internal>(L, index, std::forward<Handler>(handler), tracking);
  					}
  					else {
  						return check_usertype<T>(L, index, std::forward<Handler>(handler), tracking);
  					}
  				}
  			}
  			else if constexpr (expected == type::poly) {
  				tracking.use(1);
  				bool success = is_lua_reference_v<T> || !lua_isnone(L, index);
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::poly, type_of(L, index), "");
  				}
  				return success;
  			}
  			else if constexpr (expected == type::lightuserdata) {
  				tracking.use(1);
  				type t = type_of(L, index);
  				bool success = t == type::userdata || t == type::lightuserdata;
  				if (!success) {
  					// expected type, actual type
  					handler(L, index, type::lightuserdata, t, "");
  				}
  				return success;
  			}
  			else if constexpr (expected == type::function) {
  				if constexpr (meta::any_same_v<T, lua_CFunction, std::remove_pointer_t<lua_CFunction>, c_closure>) {
  					tracking.use(1);
  					bool success = lua_iscfunction(L, index) == 1;
  					if (!success) {
  						// expected type, actual type
  						handler(L, index, expected, type_of(L, index), "");
  					}
  					return success;
  				}
  				else {
  					tracking.use(1);
  					type t = type_of(L, index);
  					if (t == type::lua_nil || t == type::none || t == type::function) {
  						// allow for lua_nil to be returned
  						return true;
  					}
  					if (t != type::userdata && t != type::table) {
  						handler(L, index, type::function, t, "must be a function or table or a userdata");
  						return false;
  					}
  					// Do advanced check for call-style userdata?
  					static const auto& callkey = to_string(meta_function::call);
  					if (lua_getmetatable(L, index) == 0) {
  						// No metatable, no __call key possible
  						handler(L, index, type::function, t, "value is not a function and does not have overriden metatable");
  						return false;
  					}
  					if (lua_isnoneornil(L, -1)) {
  						lua_pop(L, 1);
  						handler(L, index, type::function, t, "value is not a function and does not have valid metatable");
  						return false;
  					}
  					lua_getfield(L, -1, &callkey[0]);
  					if (lua_isnoneornil(L, -1)) {
  						lua_pop(L, 2);
  						handler(L, index, type::function, t, "value's metatable does not have __call overridden in metatable, cannot call this type");
  						return false;
  					}
  					// has call, is definitely a function
  					lua_pop(L, 2);
  					return true;
  				}
  			}
  			else if constexpr (expected == type::table) {
  				tracking.use(1);
  				type t = type_of(L, index);
  				if (t == type::table) {
  					return true;
  				}
  				if (t != type::userdata) {
  					handler(L, index, type::table, t, "value is not a table or a userdata that can behave like one");
  					return false;
  				}
  				return true;
  			}
  			else {
  				tracking.use(1);
  				const type indextype = type_of(L, index);
  				bool success = expected == indextype;
  				if (!success) {
  					// expected type, actual type, message
  					handler(L, index, expected, indextype, "");
  				}
  				return success;
  			}
  		}
  	};
  
  	template <typename T>
  	struct unqualified_checker<non_null<T>, type::userdata> : unqualified_checker<T, lua_type_of_v<T>> { };
  
  	template <typename T>
  	struct unqualified_checker<detail::as_value_tag<T>, type::userdata> {
  		template <typename Handler>
  		static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  			const type indextype = type_of(L, index);
  			return check(types<T>(), L, index, indextype, std::forward<Handler>(handler), tracking);
  		}
  
  		template <typename U, typename Handler>
  		static bool check(types<U>, lua_State* L, int index, type indextype, Handler&& handler, record& tracking) {
  			if constexpr (
  				std::is_same_v<T,
  				     lightuserdata_value> || std::is_same_v<T, userdata_value> || std::is_same_v<T, userdata> || std::is_same_v<T, lightuserdata>) {
  				tracking.use(1);
  				if (indextype != type::userdata) {
  					handler(L, index, type::userdata, indextype, "value is not a valid userdata");
  					return false;
  				}
  				return true;
  			}
  			else {
  #if SOL_IS_ON(SOL_USE_INTEROP_I_)
  				if (stack_detail::interop_check<U>(L, index, indextype, handler, tracking)) {
  					return true;
  				}
  #endif // interop extensibility
  				tracking.use(1);
  				if (indextype != type::userdata) {
  					handler(L, index, type::userdata, indextype, "value is not a valid userdata");
  					return false;
  				}
  				if (lua_getmetatable(L, index) == 0) {
  					return true;
  				}
  				int metatableindex = lua_gettop(L);
  				if (stack_detail::check_metatable<U>(L, metatableindex))
  					return true;
  				if (stack_detail::check_metatable<U*>(L, metatableindex))
  					return true;
  				if (stack_detail::check_metatable<detail::unique_usertype<U>>(L, metatableindex))
  					return true;
  				if (stack_detail::check_metatable<as_container_t<U>>(L, metatableindex))
  					return true;
  				bool success = false;
  				bool has_derived = derive<T>::value || weak_derive<T>::value;
  				if (has_derived) {
  #if SOL_IS_ON(SOL_SAFE_STACK_CHECK_I_)
  					luaL_checkstack(L, 1, detail::not_enough_stack_space_string);
  #endif // make sure stack doesn't overflow
  					auto pn = stack::pop_n(L, 1);
  					lua_pushstring(L, &detail::base_class_check_key()[0]);
  					lua_rawget(L, metatableindex);
  					if (type_of(L, -1) != type::lua_nil) {
  						void* basecastdata = lua_touserdata(L, -1);
  						detail::inheritance_check_function ic = reinterpret_cast<detail::inheritance_check_function>(basecastdata);
  						success = ic(usertype_traits<T>::qualified_name());
  					}
  				}
  				lua_pop(L, 1);
  				if (!success) {
  					handler(L, index, type::userdata, indextype, "value at this index does not properly reflect the desired type");
  					return false;
  				}
  				return true;
  			}
  		}
  	};
  
  	template <typename T>
  	struct unqualified_checker<detail::as_pointer_tag<T>, type::userdata> {
  		template <typename Handler>
  		static bool check(lua_State* L, int index, type indextype, Handler&& handler, record& tracking) {
  			if (indextype == type::lua_nil) {
  				tracking.use(1);
  				return true;
  			}
  			return check_usertype<std::remove_pointer_t<T>>(L, index, std::forward<Handler>(handler), tracking);
  		}
  
  		template <typename Handler>
  		static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  			const type indextype = type_of(L, index);
  			return check(L, index, indextype, std::forward<Handler>(handler), tracking);
  		}
  	};
  
  	template <typename... Args>
  	struct unqualified_checker<std::tuple<Args...>, type::poly> {
  		template <typename Handler>
  		static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  			return stack::multi_check<Args...>(L, index, std::forward<Handler>(handler), tracking);
  		}
  	};
  
  	template <typename A, typename B>
  	struct unqualified_checker<std::pair<A, B>, type::poly> {
  		template <typename Handler>
  		static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  			return stack::multi_check<A, B>(L, index, std::forward<Handler>(handler), tracking);
  		}
  	};
  
  #if SOL_IS_ON(SOL_STD_VARIANT_I_)
  
  	template <typename... Tn>
  	struct unqualified_checker<std::variant<Tn...>, type::poly> {
  		typedef std::variant<Tn...> V;
  		typedef std::variant_size<V> V_size;
  		typedef std::integral_constant<bool, V_size::value == 0> V_is_empty;
  
  		template <typename Handler>
  		static bool is_one(std::integral_constant<std::size_t, 0>, lua_State* L, int index, Handler&& handler, record& tracking) {
  			if constexpr (V_is_empty::value) {
  				if (lua_isnone(L, index)) {
  					return true;
  				}
  			}
  			tracking.use(1);
  			handler(L, index, type::poly, type_of(L, index), "value does not fit any type present in the variant");
  			return false;
  		}
  
  		template <std::size_t I, typename Handler>
  		static bool is_one(std::integral_constant<std::size_t, I>, lua_State* L, int index, Handler&& handler, record& tracking) {
  			typedef std::variant_alternative_t<I - 1, V> T;
  			record temp_tracking = tracking;
  			if (stack::check<T>(L, index, no_panic, temp_tracking)) {
  				tracking = temp_tracking;
  				return true;
  			}
  			return is_one(std::integral_constant<std::size_t, I - 1>(), L, index, std::forward<Handler>(handler), tracking);
  		}
  
  		template <typename Handler>
  		static bool check(lua_State* L, int index, Handler&& handler, record& tracking) {
  			return is_one(std::integral_constant<std::size_t, V_size::value>(), L, index, std::forward<Handler>(handler), tracking);
  		}
  	};
  
  #endif // variant shenanigans
  
  }} // namespace sol::stack
  
  #endif // SOL_STACK_CHECK_UNQUALIFIED_HPP
  