/*******************************************************************************
 * Copyright (c) 2005 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
 *******************************************************************************/
package org.eclipse.jface.databinding.updatables;

import org.eclipse.jface.databinding.ChangeEvent;
import org.eclipse.jface.databinding.IChangeListener;
import org.eclipse.jface.databinding.IUpdatableValue;
import org.eclipse.jface.databinding.UpdatableValue;

/**
 * An abstract class for implementing updatable values of type boolean that
 * track changes of another updatable value.
 * <p>
 * <strong>EXPERIMENTAL</strong>. This class or interface has been added as
 * part of a work in progress. There is no guarantee that this API will remain
 * unchanged during the 3.2 release cycle. Please do not use this API without
 * consulting with the Platform/UI team.
 * </p>
 * 
 * @since 3.2
 * 
 */
public abstract class ConditionalUpdatableValue extends UpdatableValue {

	private final IUpdatableValue[] innerUpdatableValues;

	IChangeListener changeListener = new IChangeListener() {
		public void handleChange(ChangeEvent changeEvent) {
			fireChangeEvent(ChangeEvent.CHANGE, null, null);
		}
	};

	/**
	 * Creates a new instance.
	 * 
	 * @param innerUpdatableValue
	 */
	public ConditionalUpdatableValue(IUpdatableValue innerUpdatableValue) {
		this(new IUpdatableValue[]{innerUpdatableValue});
	}

	/**
	 * Creates a new instance.
	 * 
	 * @param innerUpdatableValues
	 */
	public ConditionalUpdatableValue(IUpdatableValue[] innerUpdatableValues) {
		this.innerUpdatableValues = innerUpdatableValues;
		for (int i = 0; i < innerUpdatableValues.length; i++) {
			innerUpdatableValues[i].addChangeListener(changeListener);
		}
	}
	
	public void setValue(Object value) {
		throw new UnsupportedOperationException();
	}

	public Object getValue() {
		Object[] currentValues = new Object[innerUpdatableValues.length];
		for (int i = 0; i < currentValues.length; i++) {
			currentValues[i] = innerUpdatableValues[i].getValue();
		}		
		return new Boolean(compute(currentValues.length==1?currentValues[0]:currentValues));
	}

	/**
	 * To be implemented by subclasses.
	 * 
	 * @param currentValue
	 *            the current value of the tracked updatable value, or
	 *            the array of the current values of the tracked updatable values.
	 * @return a boolean result
	 */
	abstract protected boolean compute(Object currentValue);

	public Class getValueType() {
		return Boolean.class;
	}

	public void dispose() {
		super.dispose();
		for (int i = 0; i < innerUpdatableValues.length; i++) {
			innerUpdatableValues[i].removeChangeListener(changeListener);
		}		
	}

}