/*
 * Copyright 2001-2004 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ 

package org.apache.commons.beanutils;

import java.io.Serializable;
import java.util.Comparator;
import org.apache.commons.beanutils.PropertyUtils;
import org.apache.commons.collections.comparators.ComparableComparator;

/**
 * <p>
 * This comparator compares two beans by the specified bean property. 
 * It is also possible to compare beans based on nested, indexed, 
 * combined, mapped bean properties. Please see the {@link PropertyUtilsBean} 
 * documentation for all property name possibilities. 
 *
 * </p><p>
 * <strong>Note:</strong> The BeanComparator passes the values of the specified 
 * bean property to a ComparableComparator, if no comparator is 
 * specified in the constructor. If you are comparing two beans based 
 * on a property that could contain "null" values, a suitable <code>Comparator</code> 
 * or <code>ComparatorChain</code> should be supplied in the constructor. 
 * </p>
 *
 * @author     <a href"mailto:epugh@upstate.com">Eric Pugh</a>
 * @author Tim O'Brien 
 */
public class BeanComparator implements Comparator, Serializable {

    private String property;
    private Comparator comparator;

    /** 
     * <p>Constructs a Bean Comparator without a property set.
     * </p><p>
     * <strong>Note</strong> that this is intended to be used 
     * only in bean-centric environments.
     * </p><p>
     * Until {@link #setProperty} is called with a non-null value.
     * this comparator will compare the Objects only.
     * </p>
     */
    public BeanComparator() {
        this( null );
    }

    /**
     * <p>Constructs a property-based comparator for beans.
     * This compares two beans by the property 
     * specified in the property parameter. This constructor creates 
     * a <code>BeanComparator</code> that uses a <code>ComparableComparator</code>
     * to compare the property values. 
     * </p>
     * 
     * <p>Passing "null" to this constructor will cause the BeanComparator 
     * to compare objects based on natural order, that is 
     * <code>java.lang.Comparable</code>. 
     * </p>
     *
     * @param property String Name of a bean property, which may contain the 
     * name of a simple, nested, indexed, mapped, or combined 
     * property. See {@link PropertyUtilsBean} for property query language syntax. 
     * If the property passed in is null then the actual objects will be compared
     */
    public BeanComparator( String property ) {
        this( property, ComparableComparator.getInstance() );
    }

    /**
     * Constructs a property-based comparator for beans.
     * This constructor creates 
     * a BeanComparator that uses the supplied Comparator to compare 
     * the property values. 
     * 
     * @param property Name of a bean property, can contain the name 
     * of a simple, nested, indexed, mapped, or combined 
     * property. See {@link PropertyUtilsBean} for property query language  
     * syntax. 
     * @param comparator BeanComparator will pass the values of the 
     * specified bean property to this Comparator. 
     * If your bean property is not a comparable or 
     * contains null values, a suitable comparator 
     * may be supplied in this constructor.
     */
    public BeanComparator( String property, Comparator comparator ) {
        setProperty( property );
        this.comparator = comparator;
    }

    /**
     * Sets the method to be called to compare two JavaBeans
     *
     * @param property String method name to call to compare 
     * If the property passed in is null then the actual objects will be compared
     */
    public void setProperty( String property ) {
        this.property = property;
    }


    /**
     * Gets the property attribute of the BeanComparator
     *
     * @return String method name to call to compare. 
     * A null value indicates that the actual objects will be compared
     */
    public String getProperty() {
        return property;
    }


    /**
     * Gets the Comparator being used to compare beans.
     */
    public Comparator getComparator() {
        return comparator;
    }


    /**
     * Compare two JavaBeans by their shared property.
     * If {@link #getProperty} is null then the actual objects will be compared.
     *
     * @param  o1 Object The first bean to get data from to compare against
     * @param  o2 Object The second bean to get data from to compare
     * @return int negative or positive based on order
     */
    public int compare( Object o1, Object o2 ) {
        
        if ( property == null ) {
            // compare the actual objects
            return comparator.compare( o1, o2 );
        }
        
        try {
            Object value1 = PropertyUtils.getProperty( o1, property );
            Object value2 = PropertyUtils.getProperty( o2, property );
            return comparator.compare( value1, value2 );
        }
        catch ( Exception e ) {
            throw new ClassCastException( e.toString() );
        }
    }
    
    /**
     * Two <code>BeanComparator</code>'s are equals if and only if
     * the wrapped comparators and the property names to be compared
     * are equal.
     */
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof BeanComparator)) return false;

        final BeanComparator beanComparator = (BeanComparator) o;

        if (!comparator.equals(beanComparator.comparator)) return false;
        if (property != null)
        {
            if (!property.equals(beanComparator.property)) return false;
        }
        else
        {
            return (beanComparator.property == null);
        }

        return true;
    }

    /**
     * Hashcode compatible with equals.
     */ 
    public int hashCode() {
        int result;
        result = comparator.hashCode();
        return result;
    }
}