/* Copyright 2002 - 2016, The libsigc++ Development Team
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, see <https://www.gnu.org/licenses/>.
 */
#ifndef SIGC_VISIT_EACH_HPP
#define SIGC_VISIT_EACH_HPP

#include <sigc++/type_traits.h>
#include <type_traits>
#include <utility> // std::forward
#include <functional>

namespace sigc
{

struct trackable;

#ifndef DOXYGEN_SHOULD_SKIP_THIS
namespace internal
{

template<typename Base, typename Derived>
constexpr bool is_base_of_or_same_v =
  std::is_base_of<std::decay_t<Base>, std::decay_t<Derived>>::value ||
  std::is_same<std::decay_t<Base>, std::decay_t<Derived>>::value;

/// Helper struct for visit_each_trackable().
template<typename T_action>
struct limit_trackable_target
{
  template<typename T_type>
  void operator()(T_type&& type) const
  {
    // Only call action_() if T_Type derives from trackable.
    if constexpr (is_base_of_or_same_v<sigc::trackable, T_type>)
    {
      std::invoke(action_, type);
    }
    else
    {
      // Prevent 'unreferenced formal parameter' warning from MSVC by 'using' type
      static_cast<void>(type);
    }
  }

  explicit limit_trackable_target(const T_action& action) : action_(action) {}

  limit_trackable_target(const limit_trackable_target& src) = delete;
  limit_trackable_target& operator=(const limit_trackable_target& src) = delete;
  limit_trackable_target(limit_trackable_target&& src) = delete;
  limit_trackable_target& operator=(limit_trackable_target&& src) = delete;

  T_action action_;
};

} /* namespace internal */
#endif // DOXYGEN_SHOULD_SKIP_THIS

// struct visitor was introduced as a result of https://bugzilla.gnome.org/show_bug.cgi?id=724496
// The advantage of using specializations of a template struct instead of overloads of
// a template function is described by Herb Sutter in http://www.gotw.ca/publications/mill17.htm
// In libsigc++ the main reason for using this technique is that we can avoid using ADL
// (argument-dependent lookup), and therefore there is no risk that a visit_each() overload
// in e.g. Boost is selected by mistake.

/** sigc::visitor<T_functor>::do_visit_each() performs a functor on each of the targets of a
 * functor.
 * All unknown types just call @a action on them.
 * Add specializations that specialize the @a T_functor argument for your own
 * functor types, so that subobjects get visited. This is needed to enable
 * auto-disconnection support for your functor types.
 *
 * @par Example:
 *   @code
 *   namespace some_ns
 *   {
 *     struct some_functor
 *     {
 *       void operator()() {}
 *       some_possibly_sigc_trackable_derived_type some_data_member;
 *       some_other_functor_type some_other_functor;
 *     };
 *   }
 *
 *   namespace sigc
 *   {
 *     template <>
 *     struct visitor<some_ns::some_functor>
 *     {
 *       template <typename T_action>
 *       static void do_visit_each(const T_action& action,
 *                                 const some_ns::some_functor& target)
 *       {
 *         sigc::visit_each(action, target.some_data_member);
 *         sigc::visit_each(action, target.some_other_functor);
 *       }
 *     };
 *   }
 *   @endcode
 *
 * @ingroup sigcfunctors
 */
template<typename T_functor>
struct visitor
{
  template<typename T_action>
  static void do_visit_each(const T_action& action, const T_functor& functor)
  {
    action(functor);
  }
};

/** This function performs a functor on each of the targets of a functor.
 *
 * @ingroup sigcfunctors
 */
template<typename T_action, typename T_functor>
void
visit_each(const T_action& action, const T_functor& functor)
{
  sigc::visitor<T_functor>::do_visit_each(action, functor);
}

/** This function performs a functor on each of the targets
 * of a functor limited to a restricted type.
 *
 * It is currently used only to call slot_do_bind and slot_do_unbind
 * only on trackable-derived arguments of the functors, like a compile-time version of
 *   if(dynamic_cast<trackable*)(&arg) { slot_do_unbind(arg); }
 * This also depends on do_visit_each() method overloads for
 * limit_trackable_target<slot_do_bind/slot_do_unbind> parameters
 * in the visitor<slot> template specialization.
 * TODO: Remove the need for slot_do_bind/slot_do_unbind, limit_trackable_target,
 * and visit_each_trackable() by just using a constexpr_if
 * (previously known as static_if) if that ends up in C++17.
 *
 * @ingroup sigcfunctors
 */
template<typename T_action, typename T_functor>
void
visit_each_trackable(const T_action& action, const T_functor& functor)
{
  internal::limit_trackable_target<T_action> limited_action(action);

  sigc::visit_each(limited_action, functor);
}

} /* namespace sigc */
#endif