jpa/plugins/org.eclipse.jpt.utility/src/org/eclipse/jpt/utility/internal/model/value/TransformationPropertyValueModel.java

/*******************************************************************************
 * Copyright (c) 2007, 2008 Oracle. 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:
 *     Oracle - initial API and implementation
 ******************************************************************************/
package org.eclipse.jpt.utility.internal.model.value;

import org.eclipse.jpt.utility.internal.Transformer;
import org.eclipse.jpt.utility.model.event.PropertyChangeEvent;
import org.eclipse.jpt.utility.model.value.PropertyValueModel;

/**
 * A <code>TransformationPropertyValueModel</code> wraps another
 * <code>PropertyValueModel</code> and uses a <code>Transformer</code>
 * to transform the wrapped value before it is returned by <code>value()</code>.
 * <p>
 * As an alternative to building a <code>Transformer</code>,
 * a subclass of <code>TransformationPropertyValueModel</code> can
 * either override the <code>transform_(Object)</code> method or,
 * if something other than null should be returned when the wrapped value
 * is null, override the <code>transform(Object)</code> method.
 */
public class TransformationPropertyValueModel<T1, T2>
	extends PropertyValueModelWrapper<T1>
	implements PropertyValueModel<T2>
{
	protected final Transformer<T1, T2> transformer;


	// ********** constructors/initialization **********

	/**
	 * Construct a property value model with the specified nested
	 * property value model and the default transformer.
	 * Use this constructor if you want to override the
	 * <code>transform_(Object)</code> or <code>transform(Object)</code>
	 * method instead of building a <code>Transformer</code>.
	 */
	public TransformationPropertyValueModel(PropertyValueModel<? extends T1> valueHolder) {
		super(valueHolder);
		this.transformer = this.buildTransformer();
	}

	/**
	 * Construct an property value model with the specified nested
	 * property value model and transformer.
	 */
	public TransformationPropertyValueModel(PropertyValueModel<? extends T1> valueHolder, Transformer<T1, T2> transformer) {
		super(valueHolder);
		this.transformer = transformer;
	}

	protected Transformer<T1, T2> buildTransformer() {
		return new DefaultTransformer();
	}


	// ********** PropertyValueModel implementation **********

	public T2 getValue() {
		// transform the object returned by the nested value model before returning it
		return this.transform(this.valueHolder.getValue());
	}


	// ********** PropertyValueModelWrapper implementation **********

	@Override
	protected void valueChanged(PropertyChangeEvent event) {
		// transform the values before propagating the change event
	    @SuppressWarnings("unchecked")
		Object oldValue = this.transform((T1) event.getOldValue());
	    @SuppressWarnings("unchecked")
		Object newValue = this.transform((T1) event.getNewValue());
		this.firePropertyChanged(VALUE, oldValue, newValue);
	}


	// ********** behavior **********

	/**
	 * Transform the specified value and return the result.
	 * This is called by #value() and #valueChanged(PropertyChangeEvent).
	 */
	protected T2 transform(T1 value) {
		return this.transformer.transform(value);
	}

	/**
	 * Transform the specified, non-null, value and return the result.
	 */
	protected T2 transform_(T1 value) {
		throw new UnsupportedOperationException();
	}


	// ********** default transformer **********

	/**
	 * The default transformer will return null if the wrapped value is null.
	 * If the wrapped value is not null, it is transformed by a subclass
	 * implementation of #transform_(Object).
	 */
	protected class DefaultTransformer implements Transformer<T1, T2> {
		public T2 transform(T1 value) {
			return (value == null) ? null : TransformationPropertyValueModel.this.transform_(value);
		}
	}

}