memento-tie.hpp

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/*
  MEMENTO-TIE.hpp  -  capturing and providing state for undoing commands

  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 CONTROL_MEMENTO_TIE_H
#define CONTROL_MEMENTO_TIE_H

#include "lib/meta/maybe-compare.hpp"
#include "lib/meta/function-closure.hpp"
#include "steam/control/command-signature.hpp"
#include "lib/replaceable-item.hpp"
#include "lib/format-obj.hpp"
#include "lib/util.hpp"

#include <boost/operators.hpp>
#include <functional>
#include <string>


namespace steam {
namespace control {
  namespace err = lumiera::error;
  
  using boost::equality_comparable;
  using lib::meta::func::bindLast;
  using lib::meta::func::chained;
  using lib::meta::equals_safeInvoke;
  using lib::wrapper::ReplaceableItem;
  
  
  template<typename SIG, typename MEM>
  class MementoTie
    : public equality_comparable<MementoTie<SIG,MEM>>
    {
      typedef typename CommandSignature<SIG,MEM>::CaptureSig SIG_cap;
      typedef typename CommandSignature<SIG,MEM>::UndoOp_Sig SIG_undo;
      
      ReplaceableItem<MEM> memento_; 
      
      bool isCaptured_;
      
      function<SIG_undo> undo_;
      function<SIG_cap> capture_;
      
      
      void capture (MEM const& mementoVal)
        {
          memento_ = mementoVal;
          isCaptured_ = true;
        }
      
      
    public:
      MementoTie()
        : MementoTie (function<SIG_undo>(), function<SIG_cap>())
        { }
      
      MementoTie (function<SIG_undo> const& undoFunc,
                  function<SIG_cap> const& captureFunc)
        : memento_()
        , isCaptured_(false)
        , undo_(undoFunc)
        , capture_(captureFunc)
        { }
      
      
      void
      clear()
        {
          isCaptured_ = false;
          memento_.clear();
        }
      
      function<SIG>
      tieUndoFunc()
        {
          using std::bind;
          
          return bindLast( undo_           // getState() bound to last argument of undo(...)
                         , bind (&MementoTie::getState, this)
                         );
        }
      
      function<SIG>
      tieCaptureFunc()
        {
          return chained(capture_
                        ,[this](MEM const& mementoVal){ capture (mementoVal); }
                        );
        }
      
      
      MEM&
      getState ()
        {
          if (!isCaptured_)
            throw err::State{"need to invoke memento state capturing beforehand"
                            , LERR_(MISSING_MEMENTO)};
          return memento_;
        }
      
      
      explicit
      operator bool()  const
        {
          return isValid();
        }
      
      bool
      isValid ()  const
        {
          return undo_ && capture_ && isCaptured_;
        }
      
      operator std::string()  const;
      
    };
  
  
  template<typename SIG, typename MEM>
  MementoTie<SIG,MEM>::operator std::string()  const
  {
    if (!undo_ || !capture_)
      return "·noUNDO·";
    
    if (!isCaptured_)
      return "<mem:missing>";
    
    return "<mem: "
         + util::toString (memento_.get())
         + ">";
  }
  
  
  
}} // namespace steam::control
#endif