/*
 * Copyright (c) 2002-2006 JGoodies Karsten Lentzsch. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 *  o Redistributions of source code must retain the above copyright notice, 
 *    this list of conditions and the following disclaimer. 
 *     
 *  o Redistributions in binary form must reproduce the above copyright notice, 
 *    this list of conditions and the following disclaimer in the documentation 
 *    and/or other materials provided with the distribution. 
 *     
 *  o Neither the name of JGoodies Karsten Lentzsch nor the names of 
 *    its contributors may be used to endorse or promote products derived 
 *    from this software without specific prior written permission. 
 *     
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

package com.jgoodies.binding.extras;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import com.jgoodies.binding.value.AbstractValueModel;
import com.jgoodies.binding.value.ValueModel;



/**
 * A {@link ValueModel} implementation that avoids <code>null</code> values.
 * It wraps another ValueModel and returns a (non-null) default value
 * if the wrapped ValueModel returns null.<p>
 * 
 * Note that value change events fired by this model may use null
 * as old and/or new value. This is because PropertyChangeEvents use null 
 * to indicate that the old and/or new value is not provided by the event.<p>
 * 
 * <strong>Note:</strong> This class is not yet part of the binary Binding 
 * library; it comes with the Binding distributions as an extra. 
 * <strong>The API is work in progress and may change without notice; 
 * this class may even be completely removed from future distributions.</strong> 
 * If you want to use this class, you may consider copying it into 
 * your codebase.
 * 
 * @author Karsten Lentzsch
 * @version $Revision: 1.3 $
 * 
 * @since 1.1
 */
public final class NonNullValueModel extends AbstractValueModel {
    
    /**
     * Holds the wrapped subject ValueModel.
     */
    private final ValueModel subject;
    
    /**
     * The value returned by this model whenever the
     * underlying (wrapped) ValueModel returns <code>null</code>.
     */
    private final Object defaultValue;
    
    
    // Instance Creation ******************************************************
    
    /**
     * Constructs an NonNullValueModel for the given ValueModel.
     * 
     * @param subject   the underlying (or wrapped) ValueModel 
     * @param defaultValue   the value used whenever the wrapped model
     *     returns <code>null</code>
     *     
     * @throws NullPointerException if the subject or defaultValue is <code>null</code>
     */
    public NonNullValueModel(ValueModel subject, Object defaultValue) {
        this.subject = subject;
        this.defaultValue = defaultValue;
        if (defaultValue == null) 
            throw new NullPointerException("The default value must not be null.");
        
        subject.addValueChangeListener(new SubjectValueChangeHandler());
    }
    
    
    // ValueModel Implementation **********************************************
    
    /**
     * Returns this model's current subject value.
     * 
     * @return this model's current subject value.
     */
    public Object getValue() {
        Object subjectValue = subject.getValue();
        return subjectValue != null
            ? subjectValue
            : defaultValue;
    }
    
    
    /**
     * Sets the given value to the wrapped ValueModel.
     * The value set can be <code>null</code>.
     * 
     * @param newValue   the value to set
     */
    public void setValue(Object newValue) {
        subject.setValue(newValue);
    }
    
    
    // Event Handling *********************************************************
    
    /** 
     * Forwards value changes in the subject to listeners of this model.
     * We don't use the default value if the old and/or new value is null.
     * This is because null has a different meaning in PropertyChangeEvents:
     * it indicates that the value is not available.  
     */
    private final class SubjectValueChangeHandler implements PropertyChangeListener {
        
        public void propertyChange(PropertyChangeEvent evt) {
            fireValueChange(evt.getOldValue(), evt.getNewValue(), true);
        }
    }
    
}
