/*******************************************************************************
 * Copyright (c) 2006, 2015 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Stefan Xenos <sxenos@gmail.com> - Bug 335792
 ******************************************************************************/

package org.eclipse.core.databinding.observable.value;

import org.eclipse.core.databinding.observable.IObservablesListener;
import org.eclipse.core.databinding.observable.ObservableEvent;

/**
 * Value changing event describing a pending change of an
 * {@link IObservableValue} object's current value. Listeners can veto the
 * pending change by setting {@link #veto} to <code>true</code>.
 *
 * @param <T>
 *            the type of value being observed
 *
 * @since 1.0
 *
 */
public class ValueChangingEvent<T> extends ObservableEvent {

	/**
	 *
	 */
	private static final long serialVersionUID = 2305345286999701156L;

	static final Object TYPE = new Object();

	/**
	 * Description of the change to the source observable value. Listeners must
	 * not change this field.
	 */
	public ValueDiff<T> diff;

	/**
	 * Flag for vetoing this change. Default value is <code>false</code>, can be
	 * set to <code>true</code> by listeners to veto this change.
	 */
	public boolean veto = false;

	/**
	 * Creates a new value changing event.
	 *
	 * @param source
	 *            the source observable value
	 * @param diff
	 *            the value change
	 */
	public ValueChangingEvent(IObservableValue<T> source, ValueDiff<T> diff) {
		super(source);
		this.diff = diff;
	}

	/**
	 * @return the observable value from which this event originated
	 */
	@SuppressWarnings("unchecked")
	public IObservableValue<T> getObservableValue() {
		return (IObservableValue<T>) source;
	}

	@SuppressWarnings("unchecked")
	@Override
	protected void dispatch(IObservablesListener listener) {
		((IValueChangingListener<T>) listener).handleValueChanging(this);
	}

	@Override
	protected Object getListenerType() {
		return TYPE;
	}

}