/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Middleware LLC.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 *
 */
package org.hibernate.transform;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.hibernate.internal.CoreMessageLogger;

import org.jboss.logging.Logger;

Distinctions the result tuples in the final result based on the defined
equality of the tuples.
 Since this transformer is stateless, all instances would be considered equal. So for optimization purposes we limit it to a single, singleton instance. 
Author:
Steve Ebersole/**
 * Distinctions the result tuples in the final result based on the defined
 * equality of the tuples.
 * <p/>
 * Since this transformer is stateless, all instances would be considered equal.
 * So for optimization purposes we limit it to a single, singleton {@link #INSTANCE instance}.
 *
 * @author Steve Ebersole
 */
public class DistinctResultTransformer extends BasicTransformerAdapter {

	public static final DistinctResultTransformer INSTANCE = new DistinctResultTransformer();

    private static final CoreMessageLogger LOG = Logger.getMessageLogger(CoreMessageLogger.class,
                                                                       DistinctResultTransformer.class.getName());

	
Helper class to handle distincting
/**
	 * Helper class to handle distincting
	 */
	private static final class Identity {
		final Object entity;

		private Identity(Object entity) {
			this.entity = entity;
		}

		
{@inheritDoc}
/**
		 * {@inheritDoc}
		 */
		@Override
        public boolean equals(Object other) {
			return Identity.class.isInstance( other )
					&& this.entity == ( ( Identity ) other ).entity;
		}

		
{@inheritDoc}
/**
		 * {@inheritDoc}
		 */
		@Override
        public int hashCode() {
			return System.identityHashCode( entity );
		}
	}

	
Disallow instantiation of DistinctResultTransformer.
/**
	 * Disallow instantiation of DistinctResultTransformer.
	 */
	private DistinctResultTransformer() {
	}

	
Uniquely distinct each tuple row here.
/**
	 * Uniquely distinct each tuple row here.
	 */
	@Override
    public List transformList(List list) {
		List result = new ArrayList( list.size() );
		Set distinct = new HashSet();
		for ( int i = 0; i < list.size(); i++ ) {
			Object entity = list.get( i );
			if ( distinct.add( new Identity( entity ) ) ) {
				result.add( entity );
			}
		}
		LOG.debugf( "Transformed: %s rows to: %s distinct results", list.size(), result.size() );
		return result;
	}

	
Serialization hook for ensuring singleton uniqueing.
Returns:
The singleton instance : INSTANCE/**
	 * Serialization hook for ensuring singleton uniqueing.
	 *
	 * @return The singleton instance : {@link #INSTANCE}
	 */
	private Object readResolve() {
		return INSTANCE;
	}
}