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ModeShape implementation of the JCR API
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/*
 * ModeShape (http://www.modeshape.org)
 *
 * 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.modeshape.jcr.query.engine.process;

import org.mapdb.Serializer;
import org.modeshape.common.logging.Logger;
import org.modeshape.jcr.query.BufferManager;
import org.modeshape.jcr.query.BufferManager.DistinctBuffer;
import org.modeshape.jcr.query.NodeSequence;
import org.modeshape.jcr.query.RowExtractors;
import org.modeshape.jcr.query.RowExtractors.ExtractFromRow;
import org.modeshape.jcr.query.Tuples;
import org.modeshape.jcr.query.model.TypeSystem;
import org.modeshape.jcr.query.model.TypeSystem.TypeFactory;

/**
 * A {@link NodeSequence} that wraps another {@link NodeSequence} and returns only those rows that are seen for the first time.
 * 
 * @author Randall Hauch ([email protected])
 */
public class DistinctSequence extends DelegatingSequence {

    protected static final Logger LOGGER = Logger.getLogger(DistinctSequence.class);

    protected final ExtractFromRow keyExtractor;
    private final RowFilter filter;
    protected final boolean trace = LOGGER.isTraceEnabled();

    /**
     * Create a new distinct sequence given the type system and buffer manager.
     * 
     * @param delegate the node sequence that is to be wrapped; may not be null
     * @param types the system of type factories; may not be null
     * @param bufferMgr the buffer manager that should be used to create a temporary buffer into which records of the rows can be
     *        kept; may not be null
     * @param useHeap true if the temporary buffer should use the heap, or false if it should store data off-heap
     */
    @SuppressWarnings( "unchecked" )
    public DistinctSequence( NodeSequence delegate,
                             TypeSystem types,
                             BufferManager bufferMgr,
                             boolean useHeap ) {
        super(delegate);
        this.keyExtractor = RowExtractors.extractUniqueKey(delegate.width(), types);
        TypeFactory keyType = types.getNodeKeyFactory();
        Serializer keySerializer = bufferMgr.serializerFor(keyType);
        Serializer serializer = Tuples.serializer(keySerializer, delegate.width());
        final DistinctBuffer