/*=============================================================================
    Copyright (c) 2001-2011 Joel de Guzman

    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_AT_05042005_0722)
#define FUSION_AT_05042005_0722

#include <boost/fusion/support/config.hpp>
#include <boost/mpl/int.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/or.hpp>
#include <boost/mpl/less.hpp>
#include <boost/mpl/empty_base.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/fusion/sequence/intrinsic_fwd.hpp>
#include <boost/fusion/support/tag_of.hpp>
#include <boost/fusion/support/category_of.hpp>

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

namespace extension {
template <typename Tag>
struct at_impl
{
    template <typename Sequence, typename N>
    struct apply;
};

template <>
struct at_impl<sequence_facade_tag>
{
    template <typename Sequence, typename N>
    struct apply : Sequence::template at<Sequence, N> {};
};

template <>
struct at_impl<boost_tuple_tag>;

template <>
struct at_impl<boost_array_tag>;

template <>
struct at_impl<mpl_sequence_tag>;

template <>
struct at_impl<std_pair_tag>;

template <>
struct at_impl<std_tuple_tag>;
}

namespace detail {
template <typename Sequence, typename N, typename Tag>
struct at_impl
    : mpl::if_<
      mpl::or_<
      mpl::less<N, typename extension::size_impl<Tag>::template apply<Sequence>::type>
, traits::is_unbounded<Sequence>
>
, typename extension::at_impl<Tag>::template apply<Sequence, N>
, mpl::empty_base
>::type
{};
}

namespace result_of {
template <typename Sequence, typename N>
struct at
    : detail::at_impl<Sequence, N, typename detail::tag_of<Sequence>::type>
{};

template <typename Sequence, int N>
struct at_c
    : at<Sequence, mpl::int_<N> >
{};
}

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

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

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

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

#endif
