notifier.hpp

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//=============================================================================
//  MuseScore
//  Music Composition & Notation
//
//  Copyright (C) 2018 Werner Schweer
//
//  This program is free software; you can redistribute it and/or modify
//  it under the terms of the GNU General Public License version 2
//  as published by the Free Software Foundation and appearing in
//  the file LICENCE.GPL
//=============================================================================

#ifndef __NOTIFIER_H__
#define __NOTIFIER_H__

namespace Ms {

template<typename Data> class Notifier;

//---------------------------------------------------------
//   Listener
//---------------------------------------------------------

template<typename Data>
class Listener {
      Notifier<Data>* _notifier = nullptr;

   public:
      Listener() = default;
      Listener(Notifier<Data>* n) : _notifier(n) {}
      // do not copy notifier attachment
      Listener(const Listener<Data>&) {}
      Listener(Listener<Data>&&);
      Listener& operator=(const Listener<Data>&) { return *this; }
      Listener& operator=(Listener&&);
      ~Listener();

      void setNotifier(Notifier<Data>* n);

      void detachNotifier(Notifier<Data>* n) { if (_notifier == n) setNotifier(nullptr); }

      Notifier<Data>* notifier() { return _notifier; }
      const Notifier<Data>* notifier() const { return _notifier; }

      virtual void receive(Data d) = 0;

      template<typename T>
      friend void swap(Listener<T>& l1, Listener<T>& l2);
      };

//---------------------------------------------------------
//   Notifier
//---------------------------------------------------------

template<typename Data>
class Notifier {
      std::vector<Listener<Data>*> _listeners;
      bool _atChange = false;

   public:
      Notifier() = default;
      // do not copy listeners list
      Notifier(const Notifier<Data>&) {}
      Notifier& operator=(const Notifier<Data>&) { return *this; }
      ~Notifier()
            {
            _atChange = true; // we don't need to update listeners list anymore
            for (Listener<Data>* l : _listeners)
                  l->detachNotifier(this);
            }

      void addListener(Listener<Data>* l)
            {
            if (_atChange || !l)
                  return;
            _atChange = true;
            _listeners.push_back(l);
            l->setNotifier(this);
            _atChange = false;
            }

      void removeListener(Listener<Data>* l)
            {
            if (_atChange || !l)
                  return;
            _atChange = true;
            _listeners.erase(std::remove(_listeners.begin(), _listeners.end(), l), _listeners.end());
            l->detachNotifier(this);
            _atChange = false;
            }

      void notify(Data d) const
            {
            for (Listener<Data>* l : _listeners)
                  l->receive(d);
            }
      };

template<typename Data>
Listener<Data>::Listener(Listener<Data>&& other)
      {
      if (Notifier<Data>* n = other.notifier()) {
            n->removeListener(other);
            setNotifier(n);
            }
      }

template<typename Data>
Listener<Data>& Listener<Data>::operator=(Listener<Data>&& other)
      {
      if (Notifier<Data>* n = other.notifier()) {
            n->removeListener(other);
            setNotifier(n);
            }
      else
            setNotifier(nullptr);
      }

template<typename Data>
Listener<Data>::~Listener()
      {
      if (_notifier)
            _notifier->removeListener(this);
      }

template<typename Data>
void Listener<Data>::setNotifier(Notifier<Data>* n)
      {
      if (n == _notifier)
            return;
      Notifier<Data>* oldNotifier = _notifier;
      _notifier = n;
      if (oldNotifier)
            oldNotifier->removeListener(this);
      if (_notifier)
            _notifier->addListener(this);
      }

template<typename Data>
void swap(Listener<Data>& l1, Listener<Data>& l2)
      {
      Notifier<Data>* n1 = l1.notifier();
      Notifier<Data>* n2 = l2.notifier();
      l1.setNotifier(n2);
      l2.setNotifier(n1);
      }

}     // namespace Ms
#endif