query-focus-stack.hpp

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/*
  QUERY-FOCUS-STACK.hpp  -  management of current scope within the Session

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

  **Lumiera** 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. See the file COPYING for further details.

*/


#ifndef MOBJECT_SESSION_QUERY_FOCUS_STACK_H
#define MOBJECT_SESSION_QUERY_FOCUS_STACK_H

#include "steam/mobject/session/scope-path.hpp"
#include "lib/nocopy.hpp"

#include <list>

using std::list;


namespace steam {
namespace mobject {
namespace session {
  
  
  
  class QueryFocusStack
    : util::NonCopyable
    {
      
      std::list<ScopePath> paths_;
      
    public:
      QueryFocusStack ()
        : paths_()
        {
          openDefaultFrame();
        }
      
      
      bool empty ()  const;
      size_t size () const;
      
      ScopePath& push (Scope const&);
      ScopePath& top  ();
      void pop_unused ();
      void clear ();
      
      
    private:
      void openDefaultFrame ();
    };
  
  
  
  
  
  
  
  /* __implementation__ */ 
  
  bool
  QueryFocusStack::empty ()  const
  {
    return paths_.empty();
  }
  
  
  size_t
  QueryFocusStack::size ()  const
  {
    return paths_.size();
  }
  
  
  void
  QueryFocusStack::clear ()
  {
    paths_.clear();
    openDefaultFrame();
  }
  
  
  ScopePath&
  QueryFocusStack::push (Scope const& newStartPoint)
  {
    ScopePath newPathFrame (newStartPoint); // may throw
    ENSURE (newPathFrame.isValid() || newStartPoint.isRoot());
    
    paths_.push_back (newPathFrame);
    ENSURE (0 < size());
    return paths_.back();
  }
  
  
  ScopePath&
  QueryFocusStack::top ()
  {
    if ( 0 == size()
      || 0 == paths_.back().ref_count()
       )
      pop_unused();
    
    ENSURE (!empty());
    return paths_.back();
  }
  
  
  void
  QueryFocusStack::pop_unused ()
  {
    if (1 == size() && !paths_.front().isValid())
      return; // unnecessary to evict a base frame repeatedly
    
    while (size() && (0 == paths_.back().ref_count()))
      paths_.pop_back();
    
    if (0 == size())
      openDefaultFrame();
    ENSURE (!empty());
  }
  
  
  void
  QueryFocusStack::openDefaultFrame ()
  {
    REQUIRE (0 == size());
    
    paths_.resize(1);
    
    ENSURE (!paths_.front().empty());
    ENSURE (!paths_.front().isValid()); // i.e. just root scope
  }
  
  
  
  
}}} // namespace mobject::session
#endif /*MOBJECT_SESSION_QUERY_FOCUS_STACK_H*/