private class WindowSystemMonitor implements PropertyChangeListener, ComponentListener {

        private Set openedSoFar = null;

        private TopComponent shouldBeShown;

        /**
         * Must be called before adding this listener to environment if in hope that
         * it will provide (initial) open/close events.
         */
        private void enableOpenCloseEvents() {
            List list = Arrays.asList(SuggestionsScanner.openedTopComponents());
            openedSoFar = new HashSet(list);
            shouldBeShown = null;
        }

        /** Reacts to changes */
        public void propertyChange(PropertyChangeEvent ev) {
            String prop = ev.getPropertyName();
            if (prop.equals(TopComponent.Registry.PROP_OPENED)) {

                if (allOpenedClientsCount > 0) {
                    // determine what components have been closed, window system does not
                    // provide any other listener to do it in more smart way

                    List list = Arrays.asList(SuggestionsScanner.openedTopComponents());
                    Set actual = new HashSet(list);

                    if (openedSoFar != null) {
                        Iterator it = openedSoFar.iterator();
                        while(it.hasNext()) {
                            TopComponent tc = (TopComponent) it.next();
                            if (actual.contains(tc) ) continue;
                            handleTopComponentClosed(tc);
                        }

                        Iterator ita = actual.iterator();
                        while(ita.hasNext()) {
                            TopComponent tc = (TopComponent) ita.next();
                            if (openedSoFar.contains(tc)) continue;
                            assert shouldBeShown == null : "Multiple opened TCs in burst without showing them one-by-one is not handled"; // NOI18N
                            // defer actual action to componentShown, We need to assure opened TC is
                            // selected one. At this moment previous one is still selected.
                            shouldBeShown = tc;
                        }
                    }

                    openedSoFar = actual;
                } else {
                    componentsChanged();
                    openedSoFar = null;
                }
            }
        }

        public void componentShown(ComponentEvent e) {
            if (shouldBeShown != null) {
                handleTopComponentOpened(shouldBeShown);
                shouldBeShown = null;
            }
        }

        public void componentHidden(ComponentEvent e) {
            //XXX it does not support both "current file" and "all opened" clients at same time
            if (allOpenedClientsCount == 0) {
                componentsChanged();
            }
        }

        public void componentResized(ComponentEvent e) {
            // Don't care
        }

        public void componentMoved(ComponentEvent e) {
            // Don't care
        }

    }