expander-revealer.hpp

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/*
  EXPANDER-REVEALER.hpp  -  functor components for standard UI element actions

  Copyright (C)         Lumiera.org
    2018,               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 STAGE_MODEL_EXPANDER_REVEALER_H
#define STAGE_MODEL_EXPANDER_REVEALER_H


#include "lib/error.hpp"

#include <functional>
#include <utility>


namespace stage {
namespace model {

  using std::move;
  
  
  class Expander
    {
    public:
      using ProbeFun = std::function<bool(void)>;
      using ChangeFun = std::function<void(bool)>;
      
    private:
      ProbeFun probeState_;
      ChangeFun changeState_;
      
    public:
      Expander() { }
      Expander(ProbeFun detectCurrExpansionState, ChangeFun expand_collapse)
        : probeState_{move (detectCurrExpansionState)}
        , changeState_{move (expand_collapse)}
        {
          ENSURE (canExpand());
        }
      
      bool
      canExpand()  const
        {
          return bool{probeState_}
             and bool{changeState_};
        }
      
      explicit
      operator bool()  const
        {
          REQUIRE (canExpand());
          return probeState_();
        }
      
      bool
      operator() (bool shallExpand)
        {
          REQUIRE (canExpand());
          bool currState = probeState_();
          if (currState != shallExpand)
            changeState_(shallExpand);
          return currState;
        }
      
      /* === alternate "expressive" API === */
      bool
      expand (bool yes =true)
        {
          return this->operator() (yes);
        }
      
      bool
      collapse()
        {
          return expand (false);
        }
      
      bool
      isExpanded()  const
        {
          return bool{*this};
        }
    };
  
  
  
  class Revealer
    {
    public:
      using RevealeItFun = std::function<void()>;
      
    private:
      RevealeItFun revealIt_;
      
    public:
      Revealer() { }
      Revealer(RevealeItFun how_to_uncover_the_element)
        : revealIt_{move (how_to_uncover_the_element)}
        {
          ENSURE (canReveal());
        }
      
      bool
      canReveal()  const
        {
          return bool{revealIt_};
        }
      
      void
      operator()()
        {
          REQUIRE (canReveal());
          revealIt_();
        }
    };
  
  
  
}} // namespace stage::model
#endif /*STAGE_MODEL_EXPANDER_REVEALER_H*/