// Copyright (c) 2014
// INRIA Saclay-Ile de France (France)
//
// This file is part of CGAL (www.cgal.org)
//
// $URL$
// $Id$
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Marc Glisse

#ifndef CGAL_TRANSFORMING_ITERATOR_H
#define CGAL_TRANSFORMING_ITERATOR_H
#include <boost/iterator/iterator_adaptor.hpp>
#include <boost/utility/result_of.hpp>
#include <boost/type_traits/is_empty.hpp>
#include <boost/type_traits/is_reference.hpp>
#include <boost/type_traits/is_integral.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/or.hpp>
#include <CGAL/Default.h>
#include <utility>

// Inspired by the boost version, but more compact and
// without any iterator_category games.

namespace CGAL {
namespace internal {

// non-empty case
template<class T,bool=boost::is_empty<T>::value> struct Functor_as_base {
	Functor_as_base(){}
	Functor_as_base(T const& t):f(t){}
	//template<class T2> Functor_as_base(Functor_as_base<T2> const&g):f(g.functor()){}
	T const& functor()const{return f;}
	T &      functor()     {return f;}
	private:
		T f;
};

// empty case
template<class T> struct Functor_as_base<T,true> : public T {
	Functor_as_base(){}
	Functor_as_base(T const& t):T(t){}
	//template<class T2> Functor_as_base(Functor_as_base<T2> const&g):T(g.functor()){}
	T const& functor()const{return *this;}
	T &      functor()     {return *this;}
};

template <typename Derived, typename F, typename Iter, typename Ref, typename Val>
class transforming_iterator_helper
{
	typedef std::iterator_traits<Iter> Iter_traits;
	typedef typename Iter_traits::reference Iter_ref;
	typedef typename Default::Get<Ref,
		decltype(std::declval<F>()(std::declval<Iter_ref>()))
			>::type reference_;

	typedef typename Default::Get<Val,typename boost::remove_cv<typename boost::remove_reference<reference_>::type>::type>::type value_type;

	// Crappy heuristic. If we have *it that returns a Weighted_point and F that returns a reference to the Point contained in the Weighted_point it takes as argument, we do NOT want the transformed iterator to return a reference to the temporary *it. On the other hand, if *it returns an int n, and F returns a reference to array[n] it is not so good to lose the reference. This probably should be done elsewhere and should at least be made optional...
	typedef typename boost::mpl::if_<
	  boost::mpl::or_<boost::is_reference<Iter_ref>,
			  boost::is_integral<Iter_ref> >,
	  reference_, value_type>::type reference;

	public:
	typedef boost::iterator_adaptor<
		Derived,
		Iter,
		value_type,
		typename Iter_traits::iterator_category,
		reference
			> type;
};
}

template <typename F, typename Iter, typename Ref=Default, typename Val=Default>
class transforming_iterator
: public internal::transforming_iterator_helper<transforming_iterator<F,Iter,Ref,Val>,F,Iter,Ref,Val>::type,
private internal::Functor_as_base<F>
{
	friend class boost::iterator_core_access;
	typedef typename internal::transforming_iterator_helper<transforming_iterator,F,Iter,Ref,Val>::type Base;
	typedef internal::Functor_as_base<F> Functor_base;
	typename Base::reference dereference()const{
		return functor()(*this->base_reference());
	}
	public:
	using Functor_base::functor;
	transforming_iterator(){}
	explicit transforming_iterator(Iter i,F const& f=F())
		:Base(i),Functor_base(f){}
	template<class F2,class I2,class R2,class V2>
	transforming_iterator(
		transforming_iterator<F2,I2,R2,V2> const&i,
		typename boost::enable_if_convertible<I2, Iter>::type* = 0,
		typename boost::enable_if_convertible<F2, F>::type* = 0)
		: Base(i.base()),Functor_base(i.functor()) {}

};

template <typename F, typename Iter> inline
transforming_iterator<F,Iter> make_transforming_iterator(Iter i, F const&f=F()) {
	return transforming_iterator<F,Iter>(i,f);
}

}

#endif // CGAL_TRANSFORMING_ITERATOR_H
