/*=============================================================================#
 # Copyright (c) 2007, 2020 Stephan Wahlbrink and others.
 # 
 # This program and the accompanying materials are made available under the
 # terms of the Eclipse Public License 2.0 which is available at
 # https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 # which is available at https://www.apache.org/licenses/LICENSE-2.0.
 # 
 # SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 # 
 # Contributors:
 #     Stephan Wahlbrink <sw@wahlbrink.eu> - initial API and implementation
 #=============================================================================*/

package org.eclipse.statet.ltk.ui.sourceediting;

import java.util.ArrayList;
import java.util.List;

import org.eclipse.jface.text.IRegion;
import org.eclipse.jface.viewers.ISelectionChangedListener;
import org.eclipse.jface.viewers.SelectionChangedEvent;
import org.eclipse.ui.texteditor.IUpdate;

import org.eclipse.statet.jcommons.collections.CopyOnWriteIdentityListSet;


/**
 * History of structure selections.
 * 
 * @see StructureSelectHandler
 */
public class StructureSelectionHistory {
	
	
	private final ISourceEditor sourceEditor;
	
	private final List<IRegion> history;
	
	private final ISelectionChangedListener selectionListener;
	private int selectionChangeListenerCounter;
	
	private final CopyOnWriteIdentityListSet<IUpdate> updateActions= new CopyOnWriteIdentityListSet<>();
	
	
	public StructureSelectionHistory(final ISourceEditor editor) {
		this.sourceEditor= editor;
		this.history= new ArrayList<>();
		this.selectionListener= new ISelectionChangedListener() {
			@Override
			public void selectionChanged(final SelectionChangedEvent event) {
				if (StructureSelectionHistory.this.selectionChangeListenerCounter == 0) {
					flush();
				}
			}
		};
		this.sourceEditor.getViewer().getSelectionProvider().addSelectionChangedListener(this.selectionListener);
	}
	
	
	public void addUpdateListener(final IUpdate action) {
		this.updateActions.add(action);
	}
	
	private final void updateState() {
		for (final IUpdate action : this.updateActions.toList()) {
			action.update();
		}
	}
	
	public boolean isEmpty() {
		return this.history.isEmpty();
	}
	
	public void remember(final IRegion range) {
		this.history.add(range);
		updateState();
	}
	
	public IRegion getLast() {
		if (isEmpty()) {
			return null;
		}
		final IRegion result= this.history.remove(this.history.size() - 1);
		updateState();
		return result;
	}
	
	public void flush() {
		if (this.history.isEmpty()) {
			return;
		}
		this.history.clear();
		updateState();
	}
	
	public void ignoreSelectionChanges() {
		this.selectionChangeListenerCounter++;
	}
	
	public void listenToSelectionChanges() {
		this.selectionChangeListenerCounter--;
	}
	
	public void dispose() {
		this.sourceEditor.getViewer().getSelectionProvider().removeSelectionChangedListener(this.selectionListener);
	}
	
}