/*=============================================================================
    Copyright (c) 2011 Eric Niebler

    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_SEGMENTED_FOLD_UNTIL_HPP_INCLUDED)
#define BOOST_FUSION_SEGMENTED_FOLD_UNTIL_HPP_INCLUDED

#include <boost/mpl/bool.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/utility/result_of.hpp>
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/remove_reference.hpp>

#include <boost/fusion/support/void.hpp>
#include <boost/fusion/container/list/cons.hpp>
#include <boost/fusion/container/generation/make_cons.hpp>
#include <boost/fusion/view/iterator_range.hpp>
#include <boost/fusion/sequence/intrinsic/begin.hpp>
#include <boost/fusion/sequence/intrinsic/empty.hpp>
#include <boost/fusion/sequence/intrinsic/end.hpp>
#include <boost/fusion/iterator/value_of.hpp>
#include <boost/fusion/iterator/equal_to.hpp>
#include <boost/fusion/iterator/next.hpp>
#include <boost/fusion/support/is_segmented.hpp>
#include <boost/fusion/sequence/intrinsic/segments.hpp>

// fun(rng, state, context)
//  rng: a non-segmented range
//  state: the state of the fold so far
//  context: the path to the current range
//
// returns: (state', fcontinue)

namespace boost { namespace fusion
{
    template<typename Context>
    struct segmented_iterator;

    namespace result_of
    {
        template<typename Cur, typename Context>
        struct make_segmented_iterator
        {
            typedef
                iterator_range<
                    Cur,
                    typename result_of::end<
                        typename remove_reference<
                            typename add_const<
                                typename result_of::deref<
                                    typename Context::car_type::begin_type
                                >::type
                            >::type
                        >::type
                    >::type
                >
            range_type;

            typedef
                segmented_iterator<cons<range_type, Context> >
            type;
        };
    }

    template<typename Cur, typename Context>
    typename result_of::make_segmented_iterator<Cur, Context>::type
    make_segmented_iterator(Cur const& cur, Context const& context)
    {
        typedef result_of::make_segmented_iterator<Cur, Context> impl_type;
        typedef typename impl_type::type type;
        typedef typename impl_type::range_type range_type;
        return type(fusion::make_cons(range_type(cur, fusion::end(*context.car.first)), context));
    }

    typedef mpl::true_  continue_;
    typedef mpl::false_ break_;

    template<typename Value, typename Continue>
    struct result
    {
        typedef Value value_type;
        typedef Continue continue_type;

        result(Value const& val)
          : value(val)
        {}

        value_type value;
    };

    template<typename Continue>
    struct result<void, Continue>
    {
        typedef void_ value_type;
        typedef Continue continue_type;

        result(void_ const&)
        {}

        value_type value;
    };

    template<typename Value>
    result<Value, continue_> make_result_continue(Value const& val)
    {
        return result<Value, continue_>(val);
    }

    template<typename Value>
    result<Value, break_> make_result_break(Value const& val)
    {
        return result<Value, break_>(val);
    }

    namespace detail
    {
        template<
            typename Begin,
            typename End,
            typename State,
            typename Context,
            typename Fun,
            bool IsEmpty = result_of::empty<
                typename result_of::value_of<Begin>::type
            >::type::value>
        struct segmented_fold_until_iterate_skip_empty;

        template<
            typename Begin,
            typename End,
            typename State,
            typename Context,
            typename Fun,
            bool IsDone = result_of::equal_to<Begin, End>::type::value>
        struct segmented_fold_until_iterate;

        template<
            typename Range,
            typename State,
            typename Context,
            typename Fun,
            bool IsSegmented = traits::is_segmented<Range>::type::value>
        struct segmented_fold_until_impl;

        template<typename Segments, typename State, typename Context, typename Fun>
        struct segmented_fold_until_on_segments;

        //auto push_context(cur, end, context)
        //{
        //  return push_back(context, segment_sequence(iterator_range(cur, end)));
        //}

        template<typename Cur, typename End, typename Context>
        struct push_context
        {
            typedef iterator_range<Cur, End>    range_type;
            typedef cons<range_type, Context>   type;

            static type call(Cur const& cur, End const& end, Context const& context)
            {
                return fusion::make_cons(range_type(cur, end), context);
            }
        };

        //auto make_segmented_iterator(cur, end, context)
        //{
        //  return segmented_iterator(push_context(cur, end, context));
        //}
        //
        //auto segmented_fold_until_impl(rng, state, context, fun)
        //{
        //  if (is_segmented(rng))
        //  {
        //    segmented_fold_until_on_segments(segments(rng), state, context, fun);
        //  }
        //  else
        //  {
        //    return fun(rng, state, context);
        //  }
        //}

        template<
            typename Range,
            typename State,
            typename Context,
            typename Fun,
            bool IsSegmented>
        struct segmented_fold_until_impl
        {
            typedef
                segmented_fold_until_on_segments<
                    typename remove_reference<
                        typename add_const<
                            typename result_of::segments<Range>::type
                        >::type
                    >::type,
                    State,
                    Context,
                    Fun
                >
            impl;

            typedef typename impl::type type;

            static type call(Range& rng, State const& state, Context const& context, Fun const& fun)
            {
                return impl::call(fusion::segments(rng), state, context, fun);
            }
        };

        template<
            typename Range,
            typename State,
            typename Context,
            typename Fun>
        struct segmented_fold_until_impl<Range, State, Context, Fun, false>
        {
            typedef
                typename boost::result_of<Fun(
                    Range&,
                    typename add_reference<typename add_const<typename State::value_type>::type>::type,
                    Context const&
                )>::type
            type;
            
            static type call(Range& rng, State const& state, Context const& context, Fun const& fun)
            {
                return fun(rng, state.value, context);
            }
        };

        //auto segmented_fold_until_on_segments(segs, state, context, fun)
        //{
        //  auto cur = begin(segs), end = end(segs);
        //  for (; cur != end; ++cur)
        //  {
        //    if (empty(*cur))
        //      continue;
        //    auto context` = push_context(cur, end, context);
        //    state = segmented_fold_until_impl(*cur, state, context`, fun);
        //    if (!second(state))
        //      return state;
        //  }
        //}

        template<typename Begin,typename End,typename State,typename Context,typename Fun,bool IsEmpty>
        struct segmented_fold_until_iterate_skip_empty
        {
            // begin != end and !empty(*begin)
            typedef
                push_context<Begin, End, Context>
            push_context_impl;

            typedef
                typename push_context_impl::type
            next_context_type;

            typedef
                segmented_fold_until_impl<
                    typename remove_reference<
                        typename add_const<
                            typename result_of::deref<Begin>::type
                        >::type
                    >::type,
                    State,
                    next_context_type,
                    Fun
                >
            fold_recurse_impl;

            typedef
                typename fold_recurse_impl::type
            next_state_type;

            typedef
                segmented_fold_until_iterate<
                    typename result_of::next<Begin>::type,
                    End,
                    next_state_type,
                    Context,
                    Fun
                >
            next_iteration_impl;

            typedef
                typename mpl::eval_if<
                    typename next_state_type::continue_type,
                    next_iteration_impl,
                    mpl::identity<next_state_type>
                >::type
            type;

            static type call(Begin const& beg, End const& end, State const& state,
                             Context const& context, Fun const& fun)
            {
                return call(beg, end, state, context, fun, typename next_state_type::continue_type());
            }

            static type call(Begin const& beg, End const& end, State const& state,
                             Context const& context, Fun const& fun, mpl::true_) // continue
            {
                return next_iteration_impl::call(
                    fusion::next(beg),
                    end,
                    fold_recurse_impl::call(
                        *beg,
                        state,
                        push_context_impl::call(beg, end, context),
                        fun),
                    context,
                    fun);
            }

            static type call(Begin const& beg, End const& end, State const& state,
                             Context const& context, Fun const& fun, mpl::false_) // break
            {
                return fold_recurse_impl::call(
                    *beg,
                    state,
                    push_context_impl::call(beg, end, context),
                    fun);
            }
        };

        template<typename Begin, typename End, typename State, typename Context, typename Fun>
        struct segmented_fold_until_iterate_skip_empty<Begin, End, State, Context, Fun, true>
        {
            typedef
                segmented_fold_until_iterate<
                    typename result_of::next<Begin>::type,
                    End,
                    State,
                    Context,
                    Fun
                >
            impl;
            
            typedef typename impl::type type;

            static type call(Begin const& beg, End const& end, State const& state,
                             Context const& context, Fun const& fun)
            {
                return impl::call(fusion::next(beg), end, state, context, fun);
            }
        };

        template<typename Begin, typename End, typename State, typename Context, typename Fun, bool IsDone>
        struct segmented_fold_until_iterate
        {
            typedef
                segmented_fold_until_iterate_skip_empty<Begin, End, State, Context, Fun>
            impl;
            
            typedef typename impl::type type;

            static type call(Begin const& beg, End const& end, State const& state,
                             Context const& context, Fun const& fun)
            {
                return impl::call(beg, end, state, context, fun);
            }
        };

        template<typename Begin, typename End, typename State, typename Context, typename Fun>
        struct segmented_fold_until_iterate<Begin, End, State, Context, Fun, true>
        {
            typedef State type;

            static type call(Begin const&, End const&, State const& state,
                             Context const&, Fun const&)
            {
                return state;
            }
        };

        template<typename Segments, typename State, typename Context, typename Fun>
        struct segmented_fold_until_on_segments
        {
            typedef
                segmented_fold_until_iterate<
                    typename result_of::begin<Segments>::type,
                    typename result_of::end<Segments>::type,
                    State,
                    Context,
                    Fun
                >
            impl;

            typedef typename impl::type type;

            static type call(Segments& segs, State const& state, Context const& context, Fun const& fun)
            {
                return impl::call(fusion::begin(segs), fusion::end(segs), state, context, fun);
            }
        };

    }

    //auto segmented_fold_until(rng, state, fun)
    //{
    //  return first(segmented_fold_until_impl(rng, state, nil, fun));
    //}

    namespace result_of
    {
        template<typename Range, typename State, typename Fun>
        struct segmented_fold_until
        {
            typedef
                detail::segmented_fold_until_impl<
                    Range,
                    result<State, continue_>,
                    fusion::nil,
                    Fun
                >
            impl;

            typedef
                typename impl::type::value_type
            type;
        };
    }

    template<typename Range, typename State, typename Fun>
    typename result_of::segmented_fold_until<Range, State, Fun>::type
    segmented_fold_until(Range& rng, State const& state, Fun const& fun)
    {
        typedef typename result_of::segmented_fold_until<Range, State, Fun>::impl impl;
        return impl::call(rng, state, fusion::nil(), fun).value;
    }

    template<typename Range, typename State, typename Fun>
    typename result_of::segmented_fold_until<Range const, State, Fun>::type
    segmented_fold_until(Range const& rng, State const& state, Fun const& fun)
    {
        typedef typename result_of::segmented_fold_until<Range const, State, Fun>::impl impl;
        return impl::call(rng, state, fusion::nil(), fun).value;
    }
}}

#endif