text: // Taken from QtCurve (C) Craig Drummond, 2007 - 2010
  
  /*
   * Copyright (C) Pedram Pourang (aka Tsu Jan) 2014-2019 <tsujan2000@gmail.com>
   *
   * Kvantum 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 3 of the License, or
   * (at your option) any later version.
   *
   * Kvantum 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, see <http://www.gnu.org/licenses/>.
   */
  
  #include "shortcuthandler.h"
  
  #include <QEvent>
  #include <QKeyEvent>
  #include <QMenu>
  #include <QMenuBar>
  
  namespace Kvantum {
  ShortcutHandler::ShortcutHandler(QObject *parent) : QObject(parent), itsAltDown_(false)
  {
  }
  
  ShortcutHandler::~ShortcutHandler()
  {
  }
  
  bool ShortcutHandler::hasSeenAlt(const QWidget *widget) const
  {
      if (widget && !widget->isEnabled())
          return false;
  
      if (qobject_cast<const QMenu*>(widget)) {
          return itsOpenMenus_.count() && itsOpenMenus_.last()==widget;
      } else {
          return (itsOpenMenus_.isEmpty() &&
                  itsSeenAlt_.contains(const_cast<QWidget*>(widget->window())));
      }
      return false;
  }
  
  bool ShortcutHandler::showShortcut(const QWidget *widget) const
  {
      return itsAltDown_ && hasSeenAlt(widget);
  }
  
  void ShortcutHandler::widgetDestroyed(QObject *o)
  {
      itsUpdated_.remove(static_cast<QWidget *>(o));
      itsOpenMenus_.removeAll(static_cast<QWidget *>(o));
  }
  
  void ShortcutHandler::updateWidget(QWidget *w)
  {
      if(!itsUpdated_.contains(w))
      {
          itsUpdated_.insert(w);
          w->update();
  #if (QT_VERSION >= QT_VERSION_CHECK(5,0,0))
          connect(w, &QObject::destroyed, this, &ShortcutHandler::widgetDestroyed);
  #else
          connect(w, SIGNAL(destroyed(QObject *)), this, SLOT(widgetDestroyed(QObject *)));
  #endif
      }
  }
  
  bool ShortcutHandler::eventFilter(QObject *o, QEvent *e)
  {
      if (!o->isWidgetType())
          return QObject::eventFilter(o, e);
  
      QWidget *widget = qobject_cast<QWidget*>(o);
      switch (e->type()) {
      case QEvent::KeyPress:
          if (Qt::Key_Alt == static_cast<QKeyEvent*>(e)->key()) {
              itsAltDown_ = true;
              if (qobject_cast<QMenu*>(widget)) {
                  itsSeenAlt_.insert(widget);
                  updateWidget(widget);
                  if (widget->parentWidget() &&
                      widget->parentWidget()->window()) {
                      itsSeenAlt_.insert(widget->parentWidget()->window());
                  }
              } else {
                  widget = widget->window();
                  itsSeenAlt_.insert(widget);
                  QList<QWidget*> l = widget->findChildren<QWidget*>();
                  for (int pos = 0;pos < l.size();++pos) {
                      QWidget *w = l.at(pos);
                      if (!(w->isWindow() || !w->isVisible())) {
                          updateWidget(w);
                      }
                  }
                  QList<QMenuBar*> m = widget->findChildren<QMenuBar*>();
                  for (int i = 0; i < m.size(); ++i)
                      updateWidget(m.at(i));
              }
          }
          break;
      case QEvent::WindowDeactivate:
      case QEvent::KeyRelease:
          if (QEvent::WindowDeactivate == e->type() ||
              Qt::Key_Alt == static_cast<QKeyEvent*>(e)->key()) {
              itsAltDown_ = false;
              QSet<QWidget*>::ConstIterator it(itsUpdated_.constBegin()),
                  end(itsUpdated_.constEnd());
              for (;it != end;++it)
                  (*it)->update();
              if (!itsUpdated_.contains(widget))
                  widget->update();
              itsSeenAlt_.clear();
              itsUpdated_.clear();
          }
          break;
      case QEvent::Show:
          if (qobject_cast<QMenu*>(widget)) {
              QWidget *prev = itsOpenMenus_.count() ? itsOpenMenus_.last() : 0L;
              itsOpenMenus_.append(widget);
              if (itsAltDown_ && prev)
                  prev->update();
  #if (QT_VERSION >= QT_VERSION_CHECK(5,0,0))
              connect(widget, &QObject::destroyed, this, &ShortcutHandler::widgetDestroyed);
  #else
              connect(widget, SIGNAL(destroyed(QObject*)), this, SLOT(widgetDestroyed(QObject*)));
  #endif
          }
          break;
      case QEvent::Hide:
          if (qobject_cast<QMenu*>(widget)) {
              itsSeenAlt_.remove(widget);
              itsUpdated_.remove(widget);
              itsOpenMenus_.removeAll(widget);
              if (itsAltDown_) {
                  if (itsOpenMenus_.count()) {
                      itsOpenMenus_.last()->update();
                  } else if (widget->parentWidget() &&
                             widget->parentWidget()->window())
                      widget->parentWidget()->window()->update();
              }
          }
          break;
      case QEvent::Close:
          // Reset widget when closing
          itsSeenAlt_.remove(widget);
          itsUpdated_.remove(widget);
          itsSeenAlt_.remove(widget->window());
          itsOpenMenus_.removeAll(widget);
          if (itsAltDown_) {
              if (itsOpenMenus_.count()) {
                  itsOpenMenus_.last()->update();
              } else if (widget->parentWidget() &&
                         widget->parentWidget()->window())
                  widget->parentWidget()->window()->update();
          }
          break;
      default:
          break;
      }
      return QObject::eventFilter(o, e);
  }
  }
  