/*=============================================================================

    Copyright (c) 2001-2006 Joel de Guzman

    Copyright (c) 2006 Dan Marsden



    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)

==============================================================================*/

#if !defined(FUSION_DISTANCE_IMPL_20060124_2033)

#define FUSION_DISTANCE_IMPL_20060124_2033



#include <boost/mpl/eval_if.hpp>

#include <boost/mpl/placeholders.hpp>

#include <boost/mpl/assert.hpp>

#include <boost/fusion/iterator/distance.hpp>

#include <boost/fusion/support/category_of.hpp>

#include <boost/fusion/algorithm/query/find_if.hpp>

#include <boost/fusion/sequence/intrinsic/end.hpp>

#include <boost/fusion/sequence/intrinsic/value_at.hpp>

#include <boost/type_traits/is_same.hpp>



namespace boost { namespace fusion {



    struct zip_view_iterator_tag;



    struct random_access_iterator_tag;



    namespace detail

    {

        template<typename FoundIt, typename SearchIt>

        struct best_distance

        {

            typedef typename result_of::find_if<

                typename SearchIt::iterators, is_same<traits::category_of<mpl::_>, random_access_iterator_tag> > finder;



            BOOST_MPL_ASSERT_NOT((is_same<typename finder::type, result_of::end<typename SearchIt::iterators> >));



            typedef typename result_of::distance<FoundIt, typename finder::type>::type type;

        };



        template<typename It1, typename It2>

        struct default_distance

            : result_of::distance<

            typename result_of::value_at_c<typename It1::iterators, 0>::type,

            typename result_of::value_at_c<typename It2::iterators, 0>::type>

        {};



        template<typename It1, typename It2>

        struct zip_view_iterator_distance

        {

            typedef typename result_of::find_if<

                typename It1::iterators, is_same<traits::category_of<mpl::_>, random_access_iterator_tag> > finder;

                

            typedef typename mpl::eval_if<

                is_same<typename finder::type, typename result_of::end<typename It1::iterators>::type>,

                detail::default_distance<It1, It2> ,

                detail::best_distance<typename finder::type, It2> >::type type;               

        };

    }



    namespace extension

    {

        template<typename Tag>

        struct distance_impl;



        template<>

        struct distance_impl<zip_view_iterator_tag>

        {

            template<typename It1, typename It2>

            struct apply

                : detail::zip_view_iterator_distance<It1, It2>::type

            {

                static typename detail::zip_view_iterator_distance<It1, It2>::type

                call(It1 const& it1, It2 const& it2)

                {

                    return typename detail::zip_view_iterator_distance<It1, It2>::type();

                }                

            };

        };

    }

}}



#endif

