query-resolver.hpp

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/*
  QUERY-RESOLVER.hpp  -  framework for resolving generic queries

  Copyright (C)         Lumiera.org
    2009,               Hermann Vosseler <Ichthyostega@web.de>

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of
  the License, or (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/


#ifndef LUMIERA_QUERY_RESOLVER_H
#define LUMIERA_QUERY_RESOLVER_H

#include "lib/iter-adapter.hpp"
#include "common/query.hpp"
#include "lib/nocopy.hpp"

#include <functional>
#include <memory>
#include <string>

using std::function;

namespace lumiera {
  
  using std::unique_ptr;
  using std::string;
  
  
  class Resolution;
  class QueryResolver;
  class QueryDispatcher;
  
  typedef std::shared_ptr<Resolution> PReso;
  
  
  class Resolution
    : util::NonCopyable
    {
    public:
      typedef Goal::Result Result;
      
      virtual ~Resolution();
      
      friend bool
      checkPoint (PReso const&, Result const& pos)
        {
          return bool(pos);
        }
      
      friend void
      iterNext (PReso& resultSet, Result& pos)
        {
          resultSet->nextResult(pos);
        }
      
      
      virtual Result prepareResolution()    =0;
      
    protected:
      
      virtual void nextResult(Result& pos)  =0;
    };


  class QueryResolver
    : util::NonCopyable
    {
      unique_ptr<QueryDispatcher> dispatcher_;
      
      
    public:
      virtual ~QueryResolver() ;
      
      virtual operator string ()  const    =0; 
      
      
      PReso issue (Goal const& query)  const;
      
      bool canHandle (Goal const&) const;
      
      
      
    protected:  /* ===== API for concrete query resolvers ===== */
      
      virtual bool canHandleQuery (Goal::QueryID const&)  const =0;
      
      using ResolutionMechanism = function<Resolution*(Goal const&)>;
      
      void installResolutionCase (Goal::QueryID const&,
                                  ResolutionMechanism);
      
      QueryResolver();
    };
  
  
  
  
  template<typename RES>
  inline typename Query<RES>::iterator
  Query<RES>::resolveBy (QueryResolver const& resolver)  const
  {
    PReso resultSet = resolver.issue (*this);
    Result first = resultSet->prepareResolution();
    Cursor& start = static_cast<Cursor&> (first);   // note: type RES must be compatible!
    return iterator (resultSet, start);
  }
  
  
  template<typename RES>
  inline typename Query<RES>::iterator
  Query<RES>::operator() (QueryResolver const& resolver)  const
  {
    return resolveBy (resolver);
  }
  
  
  inline bool
  QueryResolver::canHandle(Goal const& query)  const
  {
    return canHandleQuery (query.getQID());
  }
  
  
} // namespace lumiera
#endif