/*=============================================================================
    Copyright (c) 2001-2011 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(BOOST_FUSION_AT_KEY_20060304_1755)
#define BOOST_FUSION_AT_KEY_20060304_1755

#include <boost/fusion/support/config.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/fusion/sequence/intrinsic_fwd.hpp>
#include <boost/fusion/sequence/intrinsic/has_key.hpp>
#include <boost/fusion/algorithm/query/find.hpp>
#include <boost/fusion/iterator/deref_data.hpp>
#include <boost/fusion/support/tag_of.hpp>
#include <boost/fusion/support/category_of.hpp>
#include <boost/fusion/support/detail/access.hpp>
#include <boost/mpl/empty_base.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/or.hpp>

namespace boost {
namespace fusion {
// Special tags:
struct sequence_facade_tag;
struct boost_array_tag; // boost::array tag
struct mpl_sequence_tag; // mpl sequence tag
struct std_pair_tag; // std::pair tag

namespace extension {
template <typename Tag>
struct at_key_impl
{
    template <typename Seq, typename Key>
    struct apply
    {
        typedef typename
        result_of::deref_data<
        typename result_of::find<Seq, Key>::type
        >::type
        type;

        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
        static type
        call(Seq& seq)
        {
            return fusion::deref_data(fusion::find<Key>(seq));
        }
    };
};

template <>
struct at_key_impl<sequence_facade_tag>
{
    template <typename Sequence, typename Key>
    struct apply : Sequence::template at_key_impl<Sequence, Key> {};
};

template <>
struct at_key_impl<boost_array_tag>;

template <>
struct at_key_impl<mpl_sequence_tag>;

template <>
struct at_key_impl<std_pair_tag>;
}

namespace detail {
template <typename Sequence, typename Key, typename Tag>
struct at_key_impl
    : mpl::if_<
      mpl::or_<
      typename extension::has_key_impl<Tag>::template apply<Sequence, Key>
, traits::is_unbounded<Sequence>
>
, typename extension::at_key_impl<Tag>::template apply<Sequence, Key>
, mpl::empty_base
>::type
{};
}

namespace result_of {
template <typename Sequence, typename Key>
struct at_key
    : detail::at_key_impl<Sequence, Key, typename detail::tag_of<Sequence>::type>
{};
}

template <typename Key, typename Sequence>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline typename
lazy_disable_if<
is_const<Sequence>
, result_of::at_key<Sequence, Key>
>::type
at_key(Sequence& seq)
{
    return result_of::at_key<Sequence, Key>::call(seq);
}

template <typename Key, typename Sequence>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline typename result_of::at_key<Sequence const, Key>::type
at_key(Sequence const& seq)
{
    return result_of::at_key<Sequence const, Key>::call(seq);
}
}
}

#endif
