w-link.hpp

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/*
  W-LINK.hpp  -  smart-link to GTK widget

   Copyright (C)
     2018,            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 STAGE_MODEL_W_LINK_H
#define STAGE_MODEL_W_LINK_H


#include "lib/error.hpp"
#include "lib/format-string.hpp"

#include <type_traits>
#include <sigc++/trackable.h>


namespace stage {
namespace model {
  
  namespace error = lumiera::error;
  using error::LUMIERA_ERROR_BOTTOM_VALUE;
  
  using util::_Fmt;
  
  
  template<class TAR>
  class WLink
    {
      
      TAR* widget_;
      
      
    public:
     ~WLink()
        {
          try {
            this->clear();
          }
          ERROR_LOG_AND_IGNORE (stage, "Detaching managed WLink from Widget")
        }
      WLink()  noexcept
        : widget_{nullptr}
        { }
      
      explicit
      WLink (TAR& targetWidget)
        : widget_{attachTo (targetWidget)}
        { }
      
      WLink (WLink const& r)
        : widget_{r.widget_? attachTo(*r.widget_) : nullptr}
        { }
      
      WLink (WLink && rr)
        : widget_{rr.widget_? attachTo(*rr.widget_) : nullptr}
        {
          rr.clear();
        }
      
      WLink&
      operator= (WLink other)  
        {
          swap (*this, other);
          return *this;
        }
      
      friend void
      swap (WLink& l, WLink& r)
        {
          TAR* tl = l.widget_;
          TAR* tr = r.widget_;
          if (tl == tr) return;
          r.clear();
          l.clear();
          if (tr) l.widget_ = l.attachTo (*tr);
          if (tl) r.widget_ = r.attachTo (*tl);
        }
      
      
      explicit
      operator bool()  const
        {
          return bool{widget_};
        }
      
      TAR&
      operator* ()  const
        {
          __ensureAlive();
          return *widget_;
        }
      
      TAR*
      operator-> ()  const
        {
          __ensureAlive();
          return widget_;
        }
      
      
      bool isValid()  const { return bool{*this}; }
      bool isActive() const { return bool{*this}; }
      
      
      void
      clear()
        {
          if (widget_)
            widget_->remove_destroy_notify_callback (&widget_);
          widget_ = nullptr;
        }
      
      void
      connect (TAR& otherTarget)
        {
          if (widget_ == &otherTarget) return;
          clear();
          widget_ = attachTo (otherTarget);
        }
      
    private:
      void
      __ensureAlive()  const
        {
          if (not widget_)
            throw error::State ("zombie widget encountered"
                               , LERR_(BOTTOM_VALUE));
        }
      
      TAR*
      attachTo (TAR& target)
        {
          static_assert (std::is_base_of<sigc::trackable, TAR>()
                        ,"target type required to be sigc::trackable");
          
          try {
              target.add_destroy_notify_callback (&widget_
                                                 ,[](void* p)
                                                    {
                                                      TAR* & widgetPtr = *static_cast<TAR**>(p);
                                                      ASSERT (widgetPtr);
                                                      widgetPtr = nullptr;
                                                      return p;
                                                    });
              return &target;
            }
          catch (std::exception& problem)
            {
              throw error::External (problem, _Fmt{"WLink could not attach to %s. Problem is %s"} % target % problem);
            }
          catch (...)
            {
              ERROR (stage, "Unknown exception while attaching WLink");
              throw error::External (_Fmt{"WLink could not attach to %s due to unidentified Problems"} % target);
            }
        }
    };
  
  
}} // namespace stage::model
#endif /*STAGE_MODEL_W_LINK_H*/