// Copyright (C) 2017 Michel Morin.
//
// 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)

#ifndef BOOST_ITERATOR_DISTANCE_HPP
#define BOOST_ITERATOR_DISTANCE_HPP

#include <boost/config.hpp>
#include <boost/iterator/iterator_categories.hpp>
#include <boost/iterator/iterator_traits.hpp>

namespace boost {
namespace iterators {

namespace detail {
template <typename SinglePassIterator>
inline BOOST_CXX14_CONSTEXPR typename iterator_difference<SinglePassIterator>::type
distance_impl(
    SinglePassIterator first
    , SinglePassIterator last
    , single_pass_traversal_tag
)
{
    typename iterator_difference<SinglePassIterator>::type n = 0;

    while (first != last)
    {
        ++first;
        ++n;
    }

    return n;
}

template <typename RandomAccessIterator>
inline BOOST_CXX14_CONSTEXPR typename iterator_difference<RandomAccessIterator>::type
distance_impl(
    RandomAccessIterator first
    , RandomAccessIterator last
    , random_access_traversal_tag
)
{
    return last - first;
}
}

namespace distance_adl_barrier {
template <typename SinglePassIterator>
inline BOOST_CXX14_CONSTEXPR typename iterator_difference<SinglePassIterator>::type
distance(SinglePassIterator first, SinglePassIterator last)
{
    return detail::distance_impl(
               first, last, typename iterator_traversal<SinglePassIterator>::type()
           );
}
}

using namespace distance_adl_barrier;

} // namespace iterators

using namespace iterators::distance_adl_barrier;

} // namespace boost

#endif
