memento-tie.hpp

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/*
  MEMENTO-TIE.hpp  -  capturing and providing state for undoing commands
 
   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 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/item-wrapper.hpp"
#include "lib/format-obj.hpp"
#include "lib/util.hpp"
 
#include <functional>
#include <string>
 
 
namespace steam {
namespace control {
  namespace err = lumiera::error;
  
  using lib::meta::func::bindLast;
  using lib::meta::func::chained;
  using lib::meta::equals_safeInvoke;
  using lib::wrapper::ItemWrapper;
  
  
  template<typename SIG, typename MEM>
  class MementoTie
    {
      using SIG_cap = CommandSignature<SIG,MEM>::CaptureSig;
      using SIG_undo = CommandSignature<SIG,MEM>::UndoOp_Sig;
      
      ItemWrapper<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_.reset();
        }
      
      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 (not 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_ and capture_ and isCaptured_;
        }
      
      operator std::string()  const;
      
    };
  
  
  template<typename SIG, typename MEM>
  MementoTie<SIG,MEM>::operator std::string()  const
  {
    if (not undo_ or not capture_)
      return "·noUNDO·";
    
    if (not isCaptured_)
      return "<mem:missing>";
    
    return "<mem: "
         + util::toString (*memento_)
         + ">";
  }
  
  
  
}} // namespace steam::control
#endif