//  Boost next_prior.hpp header file  ---------------------------------------//

//  (C) Copyright Dave Abrahams and Daniel Walker 1999-2003.

//  Copyright (c) Andrey Semashev 2017

//

//  Distributed under the Boost Software License, Version 1.0.

//  (See accompanying file LICENSE_1_0.txt or copy at

//  http://www.boost.org/LICENSE_1_0.txt)

//  See http://www.boost.org/libs/utility for documentation.

//  Revision History

//  13 Dec 2003  Added next(x, n) and prior(x, n) (Daniel Walker)

#ifndef BOOST_NEXT_PRIOR_HPP_INCLUDED

#define BOOST_NEXT_PRIOR_HPP_INCLUDED

#include <iterator>

#include <boost/config.hpp>

#include <boost/core/enable_if.hpp>

#include <boost/type_traits/has_plus.hpp>

#include <boost/type_traits/has_plus_assign.hpp>

#include <boost/type_traits/has_minus.hpp>

#include <boost/type_traits/has_minus_assign.hpp>

#include <boost/iterator/advance.hpp>

#include <boost/iterator/reverse_iterator.hpp>

namespace boost {

//  Helper functions for classes like bidirectional iterators not supporting

//  operator+ and operator-

//

//  Usage:

//    const std::list<T>::iterator p = get_some_iterator();

//    const std::list<T>::iterator prev = boost::prior(p);

//    const std::list<T>::iterator next = boost::next(prev, 2);

//  Contributed by Dave Abrahams

namespace next_prior_detail {

// The trait attempts to detect if the T type is an iterator. Class-type iterators are assumed

// to have the nested type iterator_category. Strictly speaking, this is not required to be the

// case (e.g. a user can specialize iterator_traits for T without defining T::iterator_category).

// Still, this is a good heuristic in practice, and we can't do anything better anyway.

// Since C++17 we can test for iterator_traits<T>::iterator_category presence instead as it is

// required to be only present for iterators.

template< typename T, typename Void = void >

struct is_iterator_class

{

    static BOOST_CONSTEXPR_OR_CONST bool value = false;

};

template< typename T >

struct is_iterator_class<

    T,

    typename enable_if_has_type<

#if !defined(BOOST_NO_CXX17_ITERATOR_TRAITS)

        typename std::iterator_traits< T >::iterator_category

#else

        typename T::iterator_category

#endif

    >::type

>

{

    static BOOST_CONSTEXPR_OR_CONST bool value = true;

};

template< typename T >

struct is_iterator :

    public is_iterator_class< T >

{

};

template< typename T >

struct is_iterator< T* >

{

    static BOOST_CONSTEXPR_OR_CONST bool value = true;

};

template< typename T, typename Distance, bool HasPlus = has_plus< T, Distance >::value >

struct next_plus_impl;

template< typename T, typename Distance >

struct next_plus_impl< T, Distance, true >

{

    static T call(T x, Distance n)

    {

        return x + n;

    }

};

template< typename T, typename Distance, bool HasPlusAssign = has_plus_assign< T, Distance >::value >

struct next_plus_assign_impl :

    public next_plus_impl< T, Distance >

{

};

template< typename T, typename Distance >

struct next_plus_assign_impl< T, Distance, true >

{

    static T call(T x, Distance n)

    {

        x += n;

        return x;

    }

};

template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value >

struct next_advance_impl :

    public next_plus_assign_impl< T, Distance >

{

};

template< typename T, typename Distance >

struct next_advance_impl< T, Distance, true >

{

    static T call(T x, Distance n)

    {

        boost::iterators::advance(x, n);

        return x;

    }

};

template< typename T, typename Distance, bool HasMinus = has_minus< T, Distance >::value >

struct prior_minus_impl;

template< typename T, typename Distance >

struct prior_minus_impl< T, Distance, true >

{

    static T call(T x, Distance n)

    {

        return x - n;

    }

};

template< typename T, typename Distance, bool HasMinusAssign = has_minus_assign< T, Distance >::value >

struct prior_minus_assign_impl :

    public prior_minus_impl< T, Distance >

{

};

template< typename T, typename Distance >

struct prior_minus_assign_impl< T, Distance, true >

{

    static T call(T x, Distance n)

    {

        x -= n;

        return x;

    }

};

template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value >

struct prior_advance_impl :

    public prior_minus_assign_impl< T, Distance >

{

};

template< typename T, typename Distance >

struct prior_advance_impl< T, Distance, true >

{

    static T call(T x, Distance n)

    {

        // Avoid negating n to sidestep possible integer overflow

        boost::iterators::reverse_iterator< T > rx(x);

        boost::iterators::advance(rx, n);

        return rx.base();

    }

};

} // namespace next_prior_detail

template <class T>

inline T next(T x) { return ++x; }

template <class T, class Distance>

inline T next(T x, Distance n)

{

    return next_prior_detail::next_advance_impl< T, Distance >::call(x, n);

}

template <class T>

inline T prior(T x) { return --x; }

template <class T, class Distance>

inline T prior(T x, Distance n)

{

    return next_prior_detail::prior_advance_impl< T, Distance >::call(x, n);

}

} // namespace boost

#endif  // BOOST_NEXT_PRIOR_HPP_INCLUDED