// Copyright (c) 2000
// Utrecht University (The Netherlands),
// ETH Zurich (Switzerland),
// INRIA Sophia-Antipolis (France),
// Max-Planck-Institute Saarbruecken (Germany),
// and Tel-Aviv University (Israel).  All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL$
// $Id$
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Stefan Schirra
//                 Andreas Fabri
//                 Geert-Jan Giezeman
//                 Michael Seel
//                 Sylvain Pion

#ifndef CGAL_OBJECT_H
#define CGAL_OBJECT_H

#include <CGAL/config.h>
#include <CGAL/assertions.h>

#include <iterator>
#include <typeinfo>

#include <variant>
#include <optional>
#include <boost/any.hpp>
#include <memory>

namespace CGAL {

class Object
{
    std::shared_ptr<boost::any> obj;

    // returns an any pointer from a variant
    struct Any_from_variant {
      template<typename T>
      boost::any* operator()(const T& t) const {
        return new boost::any(t);
      }
    };

    template<class T>
    friend const T* object_cast(const Object * o);

    template<class T>
    friend T object_cast(const Object & o);

  public:

    struct private_tag{};

    Object() : obj() { }

    template <class T>
    Object(T && t, private_tag) : obj(new boost::any(std::forward<T>(t))) { }

    // implicit constructor from optionals containing variants
    template<typename ... T>
    Object(const std::optional< std::variant<T...> >& t)
      : obj( t ? std::visit(Any_from_variant(), *t) : nullptr) { }

    // implicit constructor from  variants
    template<typename ... T>
    Object(const std::variant<T...>& v)
      : obj(std::visit(Any_from_variant(), v)) { }

    template <class T>
    bool assign(T &t) const
    {
      const T* res = boost::any_cast<T>(obj.get());
      if (!res) return false;
      t = *res;
      return true;
    }

    bool
    empty() const
    {
      return !obj;
    }

    // is_empty() is kept for backward compatibility.
    // empty() was introduced for consistency with e.g. std::vector::empty().
    bool
    is_empty() const
    {
        return empty();
    }

    // safe-bool conversion
    explicit operator bool() const {
      return !empty();
    }


    template <class T>
    bool is() const
    {
      return obj && boost::any_cast<T>(obj.get());
    }

    const std::type_info & type() const
    {
      if(obj)
        return obj->type();
      else
        return typeid(void);
    }

#ifndef CGAL_NO_DEPRECATED_CODE
    // The comparisons with nullptr are only there for Nef...
  bool operator==(std::nullptr_t /*CGAL_assertion_code(n)*/) const
  { /*CGAL_assertion(n == 0);*/ return empty(); }
  bool operator!=(std::nullptr_t /*CGAL_assertion_code(n)*/) const
  { /*CGAL_assertion(n == 0);*/ return !empty(); }
#endif // CGAL_NO_DEPRECATED_CODE

};


template <class T>
inline
Object
make_object(T && t)
{
    return Object(std::forward<T>(t), Object::private_tag());
}

template <class T>
inline
bool
assign(T& t, const Object& o)
{
    return o.assign(t);
}


struct Bad_object_cast
  : public std::bad_cast
{
    virtual const char * what() const noexcept
    {
        return "CGAL::bad_object_cast: "
               "failed conversion using CGAL::object_cast";
    }
};


template <class T>
inline
const T * object_cast(const Object * o)
{
  return boost::any_cast<T>((o->obj).get());
}

template <class T>
inline
T object_cast(const Object & o)
{
  const T * result = boost::any_cast<T>((o.obj).get());
  if (!result)
    throw Bad_object_cast();
  return *result;
}

} //namespace CGAL

#endif // CGAL_OBJECT_H