///////////////////////////////////////////////////////////////////////////////

// keeper_matcher.hpp

//

//  Copyright 2007 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)



#ifndef BOOST_XPRESSIVE_DETAIL_CORE_MATCHER_KEEPER_MATCHER_HPP_EAN_10_04_2005

#define BOOST_XPRESSIVE_DETAIL_CORE_MATCHER_KEEPER_MATCHER_HPP_EAN_10_04_2005



// MS compatible compilers support #pragma once

#if defined(_MSC_VER) && (_MSC_VER >= 1020)

# pragma once

#endif



#include <boost/mpl/bool.hpp>

#include <boost/xpressive/detail/detail_fwd.hpp>

#include <boost/xpressive/detail/core/quant_style.hpp>

#include <boost/xpressive/detail/core/state.hpp>



namespace boost { namespace xpressive { namespace detail

{



    ///////////////////////////////////////////////////////////////////////////////

    // keeper_matcher

    //  Xpr can be either a static_xpression, or a shared_matchable

    template<typename Xpr>

    struct keeper_matcher

      : quant_style<quant_variable_width, unknown_width::value, Xpr::pure>

    {

        keeper_matcher(Xpr const &xpr, bool pure = Xpr::pure)

          : xpr_(xpr)

          , pure_(pure)

        {

        }



        template<typename BidiIter, typename Next>

        bool match(match_state<BidiIter> &state, Next const &next) const

        {

            return Xpr::pure || this->pure_

              ? this->match_(state, next, mpl::true_())

              : this->match_(state, next, mpl::false_());

        }



        template<typename BidiIter, typename Next>

        bool match_(match_state<BidiIter> &state, Next const &next, mpl::true_) const

        {

            BidiIter const tmp = state.cur_;



            // matching xpr is guaranteed to not produce side-effects, don't bother saving state

            if(!this->xpr_.match(state))

            {

                return false;

            }

            else if(next.match(state))

            {

                return true;

            }



            state.cur_ = tmp;

            return false;

        }



        template<typename BidiIter, typename Next>

        bool match_(match_state<BidiIter> &state, Next const &next, mpl::false_) const

        {

            BidiIter const tmp = state.cur_;



            // matching xpr could produce side-effects, save state

            memento<BidiIter> mem = save_sub_matches(state);



            if(!this->xpr_.match(state))

            {

                reclaim_sub_matches(mem, state, false);

                return false;

            }

            else if(next.match(state))

            {

                reclaim_sub_matches(mem, state, true);

                return true;

            }



            restore_sub_matches(mem, state);

            state.cur_ = tmp;

            return false;

        }



        Xpr xpr_;

        bool pure_; // false if matching xpr_ could modify the sub-matches

    };



}}}



#endif

