/*!
 * \file    utl/utility/invoke.h
 * \brief   invoke() and invoke traits implementation
 */
#ifndef __utl_utility_invoke_h__
#define __utl_utility_invoke_h__

#include <utl/core/impl.h>
#include <utl/meta/meta.h>

#include <type_traits>
#include <functional>
#include <utility>

//! \defgroup utility Utility

/*!
 * \ingroup utility
 * \defgroup util_invoke Invoke
 */
//! @{
namespace utl {

#if !defined __cpp_lib_is_invocable
   namespace detail {

      template <class T>
      struct is_ref_wrapper : meta::false_ {};
      template <class U>
      struct is_ref_wrapper<std::reference_wrapper<U>> : meta::true_ {};

      // 1
      template <class T, class Type, class T1, class... Args,
         meta::enable_if_t<
            std::is_member_function_pointer<std::decay_t<Type T::*>>::value &&
            std::is_base_of<T, std::decay_t<T1>>::value,
            int> =0
      >
      decltype(auto) invoke_impl_(Type T::* f, T1&& t1, Args&&... args) {
         return (std::forward<T1>(t1).*f)(std::forward<Args>(args)...);
      }

      // 2
      template <class T, class Type, class T1, class... Args,
         meta::enable_if_t<
            std::is_member_function_pointer<std::decay_t<Type T::*>>::value &&
            is_ref_wrapper<std::decay_t<T1>>::value,
            int> =0
      >
      decltype(auto) invoke_impl_(Type T::* f, T1&& t1, Args&&... args) {
         return (t1.get().*f)(std::forward<Args>(args)...);
      }

      // 3
      template <class T, class Type, class T1, class... Args,
         meta::enable_if_t<
            std::is_member_function_pointer<std::decay_t<Type T::*>>::value &&
            !std::is_base_of<T, std::decay_t<T1>>::value &&
            !is_ref_wrapper<std::decay_t<T1>>::value,
            int> =0
      >
      decltype(auto) invoke_impl_(Type T::* f, T1&& t1, Args&&... args) {
         return ((*std::forward<T1>(t1)).*f)(std::forward<Args>(args)...);
      }

      // 4
      template <class T, class Type, class T1, class... Args,
         meta::enable_if_t<
            std::is_member_object_pointer<std::decay_t<Type T::*>>::value &&
            std::is_base_of<T, std::decay_t<T1>>::value,
            int> =0
      >
      decltype(auto) invoke_impl_(Type T::* f, T1&& t1, Args&&... args) {
         return std::forward<T1>(t1).*f;
      }

      // 5
      template <class T, class Type, class T1, class... Args,
         meta::enable_if_t<
            std::is_member_object_pointer<std::decay_t<Type T::*>>::value &&
            is_ref_wrapper<std::decay_t<T1>>::value,
            int> =0
      >
      decltype(auto) invoke_impl_(Type T::* f, T1&& t1, Args&&... args) {
         return t1.get().*f;
      }

      // 6
      template <class T, class Type, class T1, class... Args,
         meta::enable_if_t<
            std::is_member_object_pointer<std::decay_t<Type T::*>>::value &&
            !std::is_base_of<T, std::decay_t<T1>>::value &&
            !is_ref_wrapper<std::decay_t<T1>>::value,
            int> =0
      >
      decltype(auto) invoke_impl_(Type T::* f, T1&& t1, Args&&... args) {
         return (*std::forward<T1>(t1)).*f;
      }

      template <class F, class... Args>
      decltype(auto) invoke_impl_(F&& f, Args&&... args) {
         return std::forward<F>(f)(std::forward<Args>(args)...);
      }

   } // namespace detail

   //! Invoke the Callable object \c fn with the parameters args.
   //! As by INVOKE(std::forward<F>(f), std::forward<Args>(args)...).
   //!
   //! \note
   //! This implementation fills the lack of an invoke() utility for builds
   //! pre-c++17.
   //!
   //! \param fn     Callable object to be invoked
   //! \param args   Arguments to pass to \c fn
   //! \return       The return of the Callable underling functionality
   //!
   template<typename Callable, typename... Args>
   inline decltype(auto) invoke(Callable&& fn, Args&&... args) {
      return detail::invoke_impl_(
         std::forward<Callable>(fn), std::forward<Args>(args)...
      );
   }

   //!
   //! \brief
   //!   Determines whether \c F can be invoked with the arguments \c Args....
   //!
   //! Formally, determines whether invoke(declval<Fn>(), declval<ArgTypes>()...)
   //! is well formed when treated as an unevaluated operand,
   //! where invoke is \c Callable.
   //!
   //! \note
   //! This implementation fills the lack of an invoke() utility for builds
   //! pre-c++17.
   //!
   //! \tparam F     The candidate type to check if its invocable
   //! \tparam Args  The arguments for the call
   //! \return    If \c F is invocable
   //!   \arg  true  Is invocable
   //!   \arg  false Is not invocable
   template <typename F, typename... Args>
   struct is_invocable :
      std::is_constructible<
         std::function<void(Args ...)>,
         std::reference_wrapper<typename std::remove_reference<F>::type>
      > { };

   //! \brief
   //!   Determines whether \c F can be invoked with the arguments \c Args...
   //!   to yield a result that is convertible to \c R.
   //!
   //! Formally, determines whether invoke(declval<Fn>(), declval<ArgTypes>()...)
   //! is well formed when treated as an unevaluated operand, where invoke is \c Callable.
   //!
   //! \tparam R     The return type of invocable functionality
   //! \tparam F     The candidate type to check if its invocable
   //! \tparam Args  The arguments to pass to \c F
   //! \return    If \c F is invocable
   //!   \arg  true  Is invocable
   //!   \arg  false Is not invocable
   template <typename R, typename F, typename... Args>
   struct is_invocable_r :
      std::is_constructible<
         std::function<R(Args ...)>,
         std::reference_wrapper<typename std::remove_reference<F>::type>
      > { };

   /*!
    * invoke_result (SFINAE friendly)
    */
   //! @{
   namespace detail {
      template<typename Callable, typename... Args>
      struct try_invoke {
         using type =  decltype (
            detail::invoke_impl_(std::declval<Callable&&>(), std::declval<Args&&>()...)
         );
      };

      template<bool B, typename Callable, typename... Args>
      struct invoke_result_ {
         using type = meta::nil_;
      };

      template <typename Callable, typename... Args>
      struct invoke_result_ <true, Callable, Args...> {
         using type = meta::invoke_t<
            meta::quote<try_invoke>, Callable, Args...
         >;
      };
   }
   //! trait that deduces the return type of an INVOKE expression at compile time.
   //!
   //! \tparam Callable The candidate type to check if its invocable
   //! \tparam Args     The arguments to pass to \c F
   //!
   //! \b member \n
   //! \::type    The return type of the \c Callable type if invoked with the arguments Args....
   template <typename Callable, typename... Args>
   using invoke_result = detail::invoke_result_<
      is_invocable<Callable, Args...>::value,
      Callable,
      Args...
   >;

   //! trait that deduces the return type of an INVOKE expression at compile time.
   //!
   //! \tparam Callable The candidate type to check if its invocable
   //! \tparam Args     The arguments to pass to \c F
   //!
   //! \return    The type of the \c Callable type if invoked with the arguments Args....
   template<typename Callable, typename... Args>
   using invoke_result_t = meta::eval <
      invoke_result<Callable, Args...>
   >;
   //! @}

#else

#endif
}

//! @}


#endif /* __utl_utility_invoke_h__ */