/*******************************************************************************
 * Copyright (c) 2000, 2017 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.team.internal.ui.synchronize;

import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.eclipse.core.resources.IMarker;
import org.eclipse.core.resources.IMarkerDelta;
import org.eclipse.core.resources.IResource;
import org.eclipse.core.resources.IResourceChangeEvent;
import org.eclipse.core.resources.IResourceChangeListener;
import org.eclipse.core.resources.IWorkspaceRoot;
import org.eclipse.core.resources.IWorkspaceRunnable;
import org.eclipse.core.resources.ResourcesPlugin;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.core.runtime.IStatus;
import org.eclipse.jface.util.IPropertyChangeListener;
import org.eclipse.jface.viewers.AbstractTreeViewer;
import org.eclipse.jface.viewers.StructuredViewer;
import org.eclipse.swt.custom.BusyIndicator;
import org.eclipse.swt.widgets.Control;
import org.eclipse.team.core.ITeamStatus;
import org.eclipse.team.core.TeamException;
import org.eclipse.team.core.synchronize.ISyncInfoSetChangeEvent;
import org.eclipse.team.core.synchronize.ISyncInfoSetChangeListener;
import org.eclipse.team.core.synchronize.ISyncInfoTreeChangeEvent;
import org.eclipse.team.core.synchronize.SyncInfoSet;
import org.eclipse.team.internal.core.BackgroundEventHandler;
import org.eclipse.team.internal.ui.Policy;
import org.eclipse.team.internal.ui.TeamUIMessages;
import org.eclipse.team.internal.ui.TeamUIPlugin;
import org.eclipse.team.internal.ui.Utils;
import org.eclipse.team.ui.synchronize.ISynchronizeModelElement;

import com.ibm.icu.text.DateFormat;
import com.ibm.icu.text.SimpleDateFormat;

/**
 * Handler that serializes the updating of a synchronize model provider.
 * All modifications to the synchronize model are performed in this
 * handler's thread.
 */
public class SynchronizeModelUpdateHandler extends BackgroundEventHandler implements IResourceChangeListener, ISyncInfoSetChangeListener {
	private static final IWorkspaceRoot ROOT = ResourcesPlugin.getWorkspace().getRoot();

	// Event that indicates that the markers for a set of elements has changed
	private static final int MARKERS_CHANGED = 1;
	private static final int BUSY_STATE_CHANGED = 2;
	private static final int RESET = 3;
	private static final int SYNC_INFO_SET_CHANGED = 4;

	private AbstractSynchronizeModelProvider provider;

	private Set<ISynchronizeModelElement> pendingLabelUpdates = Collections.synchronizedSet(new HashSet<>());

	// Flag to indicate the need for an early dispath in order to show
	// busy for elements involved in an operation
	private boolean dispatchEarly = false;

	private static final int EARLY_DISPATCH_INCREMENT = 100;

	/**
	 * Custom event for posting marker changes
	 */
	class MarkerChangeEvent extends Event {
		private final ISynchronizeModelElement[] elements;
		public MarkerChangeEvent(ISynchronizeModelElement[] elements) {
			super(MARKERS_CHANGED);
			this.elements = elements;
		}
		public ISynchronizeModelElement[] getElements() {
			return elements;
		}
	}

	/**
	 * Custom event for posting busy state changes
	 */
	class BusyStateChangeEvent extends Event {

		private final ISynchronizeModelElement element;
		private final boolean isBusy;
		public BusyStateChangeEvent(ISynchronizeModelElement element, boolean isBusy) {
			super(BUSY_STATE_CHANGED);
			this.element = element;
			this.isBusy = isBusy;
		}
		public ISynchronizeModelElement getElement() {
			return element;
		}
		public boolean isBusy() {
			return isBusy;
		}
	}

	/**
	 * Custom event for posting sync info set changes
	 */
	class SyncInfoSetChangeEvent extends Event {
		private final ISyncInfoSetChangeEvent event;
		public SyncInfoSetChangeEvent(ISyncInfoSetChangeEvent event) {
			super(SYNC_INFO_SET_CHANGED);
			this.event = event;
		}
		public ISyncInfoSetChangeEvent getEvent() {
			return event;
		}
	}

	private IPropertyChangeListener listener = event -> {
		if (event.getProperty() == ISynchronizeModelElement.BUSY_PROPERTY) {
			Object source = event.getSource();
			if (source instanceof ISynchronizeModelElement)
				updateBusyState((ISynchronizeModelElement)source, ((Boolean)event.getNewValue()).booleanValue());
		}
	};

	private boolean performingBackgroundUpdate;

	/*
	 * Map used to keep track of additions so they can be added in batch at the end of the update
	 */
	private Map<ISynchronizeModelElement, Set<ISynchronizeModelElement>> additionsMap;

	/**
	 * Create the marker update handler.
	 */
	public SynchronizeModelUpdateHandler(AbstractSynchronizeModelProvider provider) {
		super(TeamUIMessages.SynchronizeModelProvider_0, TeamUIMessages.SynchronizeModelUpdateHandler_0); //
		this.provider = provider;
		ResourcesPlugin.getWorkspace().addResourceChangeListener(this);
		provider.getSyncInfoSet().addSyncSetChangedListener(this);
	}

	/**
	 * Return the marker types that are of interest to this handler.
	 * @return the marker types that are of interest to this handler
	 */
	protected String[] getMarkerTypes() {
		return new String[] {IMarker.PROBLEM};
	}

	/**
	 * Return the <code>AbstractTreeViewer</code> associated with this
	 * provider or <code>null</code> if the viewer is not of the proper type.
	 * @return the structured viewer that is displaying the model managed by this provider
	 */
	public StructuredViewer getViewer() {
		return provider.getViewer();
	}

	@Override
	public void resourceChanged(final IResourceChangeEvent event) {
			String[] markerTypes = getMarkerTypes();
			Set<IResource> handledResources = new HashSet<>();
			Set<ISynchronizeModelElement> changes = new HashSet<>();

			// Accumulate all distinct resources that have had problem marker
			// changes
			for (int idx = 0; idx < markerTypes.length; idx++) {
				IMarkerDelta[] markerDeltas = event.findMarkerDeltas(markerTypes[idx], true);
					for (int i = 0; i < markerDeltas.length; i++) {
						IMarkerDelta delta = markerDeltas[i];
						IResource resource = delta.getResource();
						if (!handledResources.contains(resource)) {
							handledResources.add(resource);
							ISynchronizeModelElement[] elements = provider.getClosestExistingParents(delta.getResource());
							if(elements != null && elements.length > 0) {
								for (int j = 0; j < elements.length; j++) {
									ISynchronizeModelElement element = elements[j];
									changes.add(element);
								}
							}
						}
					}
				}

			if (!changes.isEmpty()) {
				updateMarkersFor(changes.toArray(new ISynchronizeModelElement[changes.size()]));
		}
	}

	private void updateMarkersFor(ISynchronizeModelElement[] elements) {
		queueEvent(new MarkerChangeEvent(elements), false /* not on front of queue */);
	}

	protected void updateBusyState(ISynchronizeModelElement element, boolean isBusy) {
		queueEvent(new BusyStateChangeEvent(element, isBusy), false /* not on front of queue */);
	}

	@Override
	protected void processEvent(Event event, IProgressMonitor monitor) throws CoreException {
		switch (event.getType()) {
		case BackgroundEventHandler.RUNNABLE_EVENT :
			executeRunnable(event, monitor);
			break;
		case MARKERS_CHANGED:
			// Changes contains all elements that need their labels updated
			long start = System.currentTimeMillis();
			ISynchronizeModelElement[] elements = getChangedElements(event);
			for (int i = 0; i < elements.length; i++) {
				ISynchronizeModelElement element = elements[i];
				propagateProblemMarkers(element);
				updateParentLabels(element);
			}
			if (Policy.DEBUG_SYNC_MODELS) {
				long time = System.currentTimeMillis() - start;
				DateFormat TIME_FORMAT = new SimpleDateFormat("m:ss.SSS"); //$NON-NLS-1$
				String took = TIME_FORMAT.format(new Date(time));
				System.out.println(took + " for " + elements.length + " files"); //$NON-NLS-1$//$NON-NLS-2$
			}
			break;
		case BUSY_STATE_CHANGED:
			BusyStateChangeEvent e = (BusyStateChangeEvent)event;
			queueForLabelUpdate(e.getElement());
			if (e.isBusy()) {
				// indicate that we want an early dispatch to show busy elements
				dispatchEarly = true;
			}
			break;
		case RESET:
			// Perform the reset immediately
			pendingLabelUpdates.clear();
			provider.reset();
			break;
		case SYNC_INFO_SET_CHANGED:
			// Handle the sync change immediately
			handleChanges(((SyncInfoSetChangeEvent)event).getEvent(), monitor);
		default:
			break;
		}
	}

	private ISynchronizeModelElement[] getChangedElements(Event event) {
		if (event.getType() == MARKERS_CHANGED) {
			return ((MarkerChangeEvent)event).getElements();
		}
		return new ISynchronizeModelElement[0];
	}

	@Override
	protected boolean doDispatchEvents(IProgressMonitor monitor) throws TeamException {
		// Fire label changed
		dispatchEarly = false;
		if (pendingLabelUpdates.isEmpty()) {
			return false;
		} else {
			Utils.asyncExec((Runnable) () -> firePendingLabelUpdates(), getViewer());
			return true;
		}
	}

	/**
	 * Forces the viewer to update the labels for queued elemens
	 * whose label has changed during this round of changes. This method
	 * should only be invoked in the UI thread.
	 */
	protected void firePendingLabelUpdates() {
		if (!Utils.canUpdateViewer(getViewer())) return;
		try {
			Object[] updates = pendingLabelUpdates.toArray(new Object[pendingLabelUpdates.size()]);
			updateLabels(updates);
		} finally {
			pendingLabelUpdates.clear();
		}
	}

	/*
	 * Forces the viewer to update the labels for the given elements
	 */
	private void updateLabels(Object[] elements) {
		StructuredViewer tree = getViewer();
		if (Utils.canUpdateViewer(tree)) {
			tree.update(elements, null);
		}
	}

	/**
	 * Queue all the parent elements for a label update.
	 * @param element the element whose label and parent labels need to be updated
	 */
	public void updateParentLabels(ISynchronizeModelElement element) {
		queueForLabelUpdate(element);
		while (element.getParent() != null) {
			element = (ISynchronizeModelElement)element.getParent();
			queueForLabelUpdate(element);
		}
	}

	/**
	 * Update the label of the given diff node. Diff nodes
	 * are accumulated and updated in a single call.
	 * @param diffNode the diff node to be updated
	 */
	protected void queueForLabelUpdate(ISynchronizeModelElement diffNode) {
		pendingLabelUpdates.add(diffNode);
	}

	/**
	 * Calculate and propagate problem markers in the element model
	 * @param element the ssynchronize element
	 */
	private void propagateProblemMarkers(ISynchronizeModelElement element) {
		IResource resource = element.getResource();
		if (resource != null) {
			String property = provider.calculateProblemMarker(element);
			// If it doesn't have a direct change, a parent might
			boolean recalculateParentDecorations = hadProblemProperty(element, property);
			if (recalculateParentDecorations) {
				ISynchronizeModelElement parent = (ISynchronizeModelElement) element.getParent();
				if (parent != null) {
					propagateProblemMarkers(parent);
				}
			}
		}
	}

	// none -> error
	// error -> none
	// none -> warning
	// warning -> none
	// warning -> error
	// error -> warning
	private boolean hadProblemProperty(ISynchronizeModelElement element, String property) {
		boolean hadError = element.getProperty(ISynchronizeModelElement.PROPAGATED_ERROR_MARKER_PROPERTY);
		boolean hadWarning = element.getProperty(ISynchronizeModelElement.PROPAGATED_WARNING_MARKER_PROPERTY);

		// Force recalculation of parents of phantom resources
		IResource resource = element.getResource();
		if(resource != null && resource.isPhantom()) {
			return true;
		}

		if(hadError) {
			if(! (property == ISynchronizeModelElement.PROPAGATED_ERROR_MARKER_PROPERTY)) {
				element.setPropertyToRoot(ISynchronizeModelElement.PROPAGATED_ERROR_MARKER_PROPERTY, false);
				if(property != null) {
					// error -> warning
					element.setPropertyToRoot(property, true);
				}
				// error -> none
				// recalculate parents
				return true;
			}
			return false;
		} else if(hadWarning) {
			if(! (property == ISynchronizeModelElement.PROPAGATED_WARNING_MARKER_PROPERTY)) {
				element.setPropertyToRoot(ISynchronizeModelElement.PROPAGATED_WARNING_MARKER_PROPERTY, false);
				if(property != null) {
					// warning -> error
					element.setPropertyToRoot(property, true);
					return false;
				}
				// warning ->  none
				return true;
			}
			return false;
		} else {
			if(property == ISynchronizeModelElement.PROPAGATED_ERROR_MARKER_PROPERTY) {
				// none -> error
				element.setPropertyToRoot(property, true);
				return false;
			} else if(property == ISynchronizeModelElement.PROPAGATED_WARNING_MARKER_PROPERTY) {
				// none -> warning
				element.setPropertyToRoot(property, true);
				return true;
			}
			return false;
		}
	}

	/*
	 * Queue an event that will reset the provider
	 */
	private void reset() {
		queueEvent(new ResourceEvent(ROOT, RESET, IResource.DEPTH_INFINITE), false);
	}

	public void dispose() {
		shutdown();
		ResourcesPlugin.getWorkspace().removeResourceChangeListener(this);
		provider.getSyncInfoSet().removeSyncSetChangedListener(this);
	}

	@Override
	protected long getShortDispatchDelay() {
		if (dispatchEarly) {
			dispatchEarly = false;
			return EARLY_DISPATCH_INCREMENT;
		}
		return super.getShortDispatchDelay();
	}

	/**
	 * This method is invoked whenever a node is added to the viewer
	 * by the provider or a sub-provider. The handler adds an update
	 * listener to the node and notifies the root provider that
	 * a node was added.
	 * @param element the added element
	 * @param provider the provider that added the element
	 */
	public void nodeAdded(ISynchronizeModelElement element, AbstractSynchronizeModelProvider provider) {
		element.addPropertyChangeListener(listener);
		this.provider.nodeAdded(element, provider);
		if (Policy.DEBUG_SYNC_MODELS) {
			System.out.println("Node added: " + getDebugDisplayLabel(element) + " -> " + getDebugDisplayLabel((ISynchronizeModelElement)element.getParent()) + " : " + getDebugDisplayLabel(provider)); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
		}
	}

	/**
	 * This method is invoked whenever a node is removed the viewer
	 * by the provider or a sub-provider. The handler removes any
	 * listener and notifies the root provider that
	 * a node was removed. The node removed may have children for which
	 * a nodeRemoved callback was not invoked (see modelObjectCleared).
	 * @param element the removed element
	 * @param provider the provider that added the element
	 */
	public void nodeRemoved(ISynchronizeModelElement element, AbstractSynchronizeModelProvider provider) {
		element.removePropertyChangeListener(listener);
		this.provider.nodeRemoved(element, provider);
		if (Policy.DEBUG_SYNC_MODELS) {
			System.out.println("Node removed: " + getDebugDisplayLabel(element) + " -> " + getDebugDisplayLabel((ISynchronizeModelElement)element.getParent()) + " : " + getDebugDisplayLabel(provider)); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
		}
	}

	/**
	 * This method is invoked whenever a model object (i.e. node)
	 * is cleared from the model. This is similar to node removal but
	 * is deep.
	 * @param node the node that was cleared
	 */
	public void modelObjectCleared(ISynchronizeModelElement node) {
		node.removePropertyChangeListener(listener);
		this.provider.modelObjectCleared(node);
		if (Policy.DEBUG_SYNC_MODELS) {
			System.out.println("Node cleared: " + getDebugDisplayLabel(node)); //$NON-NLS-1$
		}
	}

	private String getDebugDisplayLabel(ISynchronizeModelElement node) {
		if (node == null) {
			return "ROOT"; //$NON-NLS-1$
		}
		if (node.getResource() != null) {
			return node.getResource().getFullPath().toString();
		}
		return node.getName();
	}

	private String getDebugDisplayLabel(AbstractSynchronizeModelProvider provider2) {
		return provider2.toString();
	}

	@Override
	public void syncInfoSetReset(SyncInfoSet set, IProgressMonitor monitor) {
		if(provider.isDisposed()) {
			set.removeSyncSetChangedListener(this);
		} else {
			reset();
		}
	}

	@Override
	public void syncInfoChanged(final ISyncInfoSetChangeEvent event, IProgressMonitor monitor) {
		if (! (event instanceof ISyncInfoTreeChangeEvent)) {
			reset();
		} else {
			queueEvent(new SyncInfoSetChangeEvent(event), false);
		}
	}

	/*
	 * Handle the sync info set change event in the UI thread.
	 */
	private void handleChanges(final ISyncInfoSetChangeEvent event, final IProgressMonitor monitor) {
		runViewUpdate(() -> {
			provider.handleChanges((ISyncInfoTreeChangeEvent)event, monitor);
			firePendingLabelUpdates();
		}, true /* preserve expansion */);
	}

	@Override
	public void syncInfoSetErrors(SyncInfoSet set, ITeamStatus[] errors, IProgressMonitor monitor) {
		// When errors occur we currently don't process them. It may be possible to decorate
		// elements in the model with errors, but currently we prefer to let ignore and except
		// another listener to display them.
	}

	public ISynchronizeModelProvider getProvider() {
		return provider;
	}

	public void connect(IProgressMonitor monitor) {
		getProvider().getSyncInfoSet().connect(this, monitor);
	}

	public void runViewUpdate(final Runnable runnable, final boolean preserveExpansion) {
		if (Utils.canUpdateViewer(getViewer()) || isPerformingBackgroundUpdate()) {
			internalRunViewUpdate(runnable, preserveExpansion);
		} else {
			if (Thread.currentThread() != getEventHandlerJob().getThread()) {
				// Run view update should only be called from the UI thread or
				// the update handler thread.
				// We will log the problem for now and make it an assert later
				TeamUIPlugin.log(IStatus.WARNING, "View update invoked from invalid thread", new TeamException("View update invoked from invalid thread")); //$NON-NLS-1$ //$NON-NLS-2$
			}
			final Control ctrl = getViewer().getControl();
			if (ctrl != null && !ctrl.isDisposed()) {
				ctrl.getDisplay().syncExec(() -> {
					if (!ctrl.isDisposed()) {
						BusyIndicator.showWhile(ctrl.getDisplay(), () -> internalRunViewUpdate(runnable, preserveExpansion));
					}
				});
			}
		}
	}

	/*
	 * Return whether the event handler is performing a background view update.
	 * In other words, a client has invoked <code>performUpdate</code>.
	 */
	public boolean isPerformingBackgroundUpdate() {
		return Thread.currentThread() == getEventHandlerJob().getThread() && performingBackgroundUpdate;
	}

	/*
	 * Method that can be called from the UI thread to update the view model.
	 */
	private void internalRunViewUpdate(final Runnable runnable, boolean preserveExpansion) {
		StructuredViewer viewer = getViewer();
		IResource[] expanded = null;
		IResource[] selected = null;
		try {
			if (Utils.canUpdateViewer(viewer)) {
				viewer.getControl().setRedraw(false);
				if (preserveExpansion) {
					expanded = provider.getExpandedResources();
					selected = provider.getSelectedResources();
				}
				if (viewer instanceof AbstractTreeViewer && additionsMap == null)
					additionsMap = new HashMap<>();
			}
			runnable.run();
		} finally {
			if (Utils.canUpdateViewer(viewer)) {
				try {
					if (additionsMap != null && !additionsMap.isEmpty() && Utils.canUpdateViewer(viewer)) {
						for (Iterator iter = additionsMap.keySet().iterator(); iter.hasNext();) {
							ISynchronizeModelElement parent = (ISynchronizeModelElement) iter.next();
							if (Policy.DEBUG_SYNC_MODELS) {
								System.out.println("Adding child view items of " + parent.getName()); //$NON-NLS-1$
							}
							Set<ISynchronizeModelElement> toAdd = additionsMap.get(parent);
							((AbstractTreeViewer)viewer).add(parent, toAdd.toArray(new Object[toAdd.size()]));
						}
						additionsMap = null;
					}
					if (expanded != null) {
						provider.expandResources(expanded);
					}
					if (selected != null) {
						provider.selectResources(selected);
					}
				} finally {
					viewer.getControl().setRedraw(true);
				}
			}
		}

		ISynchronizeModelElement root = provider.getModelRoot();
		if(root instanceof SynchronizeModelElement)
			((SynchronizeModelElement)root).fireChanges();
	}

	/**
	 * Execute a runnable which performs an update of the model being displayed
	 * by the handler's provider. The runnable should be executed in a thread-safe manner
	 * which esults in the view being updated.
	 * @param runnable the runnable which updates the model.
	 * @param preserveExpansion whether the expansion of the view should be preserver
	 * @param updateInUIThread if <code>true</code>, the model will be updated in the
	 * UI thread. Otherwise, the model will be updated in the handler thread and the view
	 * updated in the UI thread at the end.
	 */
	public void performUpdate(final IWorkspaceRunnable runnable, boolean preserveExpansion, boolean updateInUIThread) {
		if (updateInUIThread) {
			queueEvent(new BackgroundEventHandler.RunnableEvent(getUIUpdateRunnable(runnable, preserveExpansion), true), true);
		} else {
			queueEvent(new BackgroundEventHandler.RunnableEvent(getBackgroundUpdateRunnable(runnable, preserveExpansion), true), true);
		}
	}

	/**
	 * Wrap the runnable in an outer runnable that preserves expansion.
	 */
	private IWorkspaceRunnable getUIUpdateRunnable(final IWorkspaceRunnable runnable, final boolean preserveExpansion) {
		return monitor -> {
			final CoreException[] exception = new CoreException[] { null };
			runViewUpdate(() -> {
				try {
					runnable.run(monitor);
				} catch (CoreException e) {
					exception[0] = e;
				}
			}, true /* preserve expansion */);
			if (exception[0] != null)
				throw exception[0];
		};
	}

	/*
	 * Wrap the runnable in an outer runnable that preserves expansion if requested
	 * and refreshes the view when the update is completed.
	 */
	private IWorkspaceRunnable getBackgroundUpdateRunnable(final IWorkspaceRunnable runnable, final boolean preserveExpansion) {
		return new IWorkspaceRunnable() {
			IResource[] expanded;
			IResource[] selected;
			@Override
			public void run(IProgressMonitor monitor) throws CoreException {
				if (preserveExpansion)
					recordExpandedResources();
				try {
					performingBackgroundUpdate = true;
					runnable.run(monitor);
				} finally {
					performingBackgroundUpdate = false;
				}
				updateView();

			}
			private void recordExpandedResources() {
				final StructuredViewer viewer = getViewer();
				if (viewer != null && !viewer.getControl().isDisposed() && viewer instanceof AbstractTreeViewer) {
					viewer.getControl().getDisplay().syncExec(() -> {
						if (viewer != null && !viewer.getControl().isDisposed()) {
							expanded = provider.getExpandedResources();
							selected = provider.getSelectedResources();
						}
					});
				}
			}
			private void updateView() {
				// Refresh the view and then set the expansion
				runViewUpdate(() -> {
					provider.getViewer().refresh();
					if (expanded != null)
						provider.expandResources(expanded);
					if (selected != null)
						provider.selectResources(selected);
				}, false /* do not preserve expansion (since it is done above) */);
			}
		};
	}

	/*
	 * Execute the RunnableEvent
	 */
	private void executeRunnable(Event event, IProgressMonitor monitor) {
		try {
			// Dispatch any queued results to clear pending output events
			dispatchEvents(Policy.subMonitorFor(monitor, 1));
		} catch (TeamException e) {
			handleException(e);
		}
		try {
			((RunnableEvent)event).run(Policy.subMonitorFor(monitor, 1));
		} catch (CoreException e) {
			handleException(e);
		}
	}

	/**
	 * Add the element to the viewer.
	 * @param parent the parent of the element which is already added to the viewer
	 * @param element the element to be added to the viewer
	 */
	protected void doAdd(ISynchronizeModelElement parent, ISynchronizeModelElement element) {
		if (additionsMap == null) {
			if (Policy.DEBUG_SYNC_MODELS) {
				System.out.println("Added view item " + element.getName()); //$NON-NLS-1$
			}
			AbstractTreeViewer viewer = (AbstractTreeViewer)getViewer();
			viewer.add(parent, element);
		} else {
			// Accumulate the additions
			if (Policy.DEBUG_SYNC_MODELS) {
				System.out.println("Queueing view item for addition " + element.getName()); //$NON-NLS-1$
			}
			Set<ISynchronizeModelElement> toAdd = additionsMap.get(parent);
			if (toAdd == null) {
				toAdd = new HashSet<>();
				additionsMap.put(parent, toAdd);
			}
			toAdd.add(element);
		}
	}
}