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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2012, Red Hat Inc. 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 Inc.
 *
 * 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.loader.entity;

import java.io.Serializable;

import org.hibernate.HibernateException;
import org.hibernate.LockMode;
import org.hibernate.LockOptions;
import org.hibernate.engine.spi.LoadQueryInfluencers;
import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.internal.util.collections.ArrayHelper;
import org.hibernate.loader.Loader;
import org.hibernate.persister.entity.OuterJoinLoadable;

/**
* @author Steve Ebersole
*/
class PaddedBatchingEntityLoaderBuilder extends BatchingEntityLoaderBuilder {
	public static final PaddedBatchingEntityLoaderBuilder INSTANCE = new PaddedBatchingEntityLoaderBuilder();

	@Override
	protected UniqueEntityLoader buildBatchingLoader(
			OuterJoinLoadable persister,
			int batchSize,
			LockMode lockMode,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers) {
		return new PaddedBatchingEntityLoader( persister, batchSize, lockMode, factory, influencers );
	}

	@Override
	protected UniqueEntityLoader buildBatchingLoader(
			OuterJoinLoadable persister,
			int batchSize,
			LockOptions lockOptions,
			SessionFactoryImplementor factory,
			LoadQueryInfluencers influencers) {
		return new PaddedBatchingEntityLoader( persister, batchSize, lockOptions, factory, influencers );
	}

	public static class PaddedBatchingEntityLoader extends BatchingEntityLoader {
		private final int[] batchSizes;
		private final Loader[] loaders;

		public PaddedBatchingEntityLoader(
				OuterJoinLoadable persister,
				int maxBatchSize,
				LockMode lockMode,
				SessionFactoryImplementor factory,
				LoadQueryInfluencers loadQueryInfluencers) {
			super( persister );
			this.batchSizes = ArrayHelper.getBatchSizes( maxBatchSize );
			this.loaders = new Loader[ batchSizes.length ];
			for ( int i = 0; i < batchSizes.length; i++ ) {
				this.loaders[i] = new EntityLoader( persister, batchSizes[i], lockMode, factory, loadQueryInfluencers);
			}
			validate( maxBatchSize );
		}

		private void validate(int max) {
			// these are more indicative of internal problems then user error...
			if ( batchSizes[0] != max ) {
				throw new HibernateException( "Unexpected batch size spread" );
			}
			if ( batchSizes[batchSizes.length-1] != 1 ) {
				throw new HibernateException( "Unexpected batch size spread" );
			}
		}

		public PaddedBatchingEntityLoader(
				OuterJoinLoadable persister,
				int maxBatchSize,
				LockOptions lockOptions,
				SessionFactoryImplementor factory,
				LoadQueryInfluencers loadQueryInfluencers) {
			super( persister );
			this.batchSizes = ArrayHelper.getBatchSizes( maxBatchSize );
			this.loaders = new Loader[ batchSizes.length ];
			for ( int i = 0; i < batchSizes.length; i++ ) {
				this.loaders[i] = new EntityLoader( persister, batchSizes[i], lockOptions, factory, loadQueryInfluencers);
			}
			validate( maxBatchSize );
		}

		@Override
		public Object load(Serializable id, Object optionalObject, SessionImplementor session, LockOptions lockOptions) {
			final Serializable[] batch = session.getPersistenceContext()
					.getBatchFetchQueue()
					.getEntityBatch( persister(), id, batchSizes[0], persister().getEntityMode() );

			final int numberOfIds = ArrayHelper.countNonNull( batch );
			if ( numberOfIds <= 1 ) {
				return ( (UniqueEntityLoader) loaders[batchSizes.length-1] ).load( id, optionalObject, session );
			}

			// Uses the first batch-size bigger than the number of actual ids in the batch
			int indexToUse = batchSizes.length-1;
			for ( int i = 0; i < batchSizes.length-1; i++ ) {
				if ( batchSizes[i] >= numberOfIds ) {
					indexToUse = i;
				}
				else {
					break;
				}
			}

			final Serializable[] idsToLoad = new Serializable[ batchSizes[indexToUse] ];
			System.arraycopy( batch, 0, idsToLoad, 0, numberOfIds );
			for ( int i = numberOfIds; i < batchSizes[indexToUse]; i++ ) {
				idsToLoad[i] = id;
			}

			return doBatchLoad( id, loaders[indexToUse], session, idsToLoad, optionalObject, lockOptions );
		}
	}

}