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Lucene Join Module
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.lucene.search.join;

import java.io.IOException;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.KnnCollector;
import org.apache.lucene.search.knn.KnnCollectorManager;
import org.apache.lucene.search.knn.MultiLeafKnnCollector;
import org.apache.lucene.util.BitSet;
import org.apache.lucene.util.hnsw.BlockingFloatHeap;

/**
 * DiversifyingNearestChildrenKnnCollectorManager responsible for creating {@link
 * DiversifyingNearestChildrenKnnCollector} instances.
 */
public class DiversifyingNearestChildrenKnnCollectorManager implements KnnCollectorManager {

  // the number of docs to collect
  private final int k;
  // filter identifying the parent documents.
  private final BitSetProducer parentsFilter;
  private final BlockingFloatHeap globalScoreQueue;

  /**
   * Constructor
   *
   * @param k - the number of top k vectors to collect
   * @param parentsFilter Filter identifying the parent documents.
   */
  public DiversifyingNearestChildrenKnnCollectorManager(
      int k, BitSetProducer parentsFilter, IndexSearcher indexSearcher) {
    this.k = k;
    this.parentsFilter = parentsFilter;
    this.globalScoreQueue =
        indexSearcher.getIndexReader().leaves().size() > 1 ? new BlockingFloatHeap(k) : null;
  }

  /**
   * Return a new {@link DiversifyingNearestChildrenKnnCollector} instance.
   *
   * @param visitedLimit the maximum number of nodes that the search is allowed to visit
   * @param context the leaf reader context
   */
  @Override
  public KnnCollector newCollector(int visitedLimit, LeafReaderContext context) throws IOException {
    BitSet parentBitSet = parentsFilter.getBitSet(context);
    if (parentBitSet == null) {
      return null;
    }
    if (globalScoreQueue == null) {
      return new DiversifyingNearestChildrenKnnCollector(k, visitedLimit, parentBitSet);
    } else {
      return new MultiLeafKnnCollector(
          k,
          globalScoreQueue,
          new DiversifyingNearestChildrenKnnCollector(k, visitedLimit, parentBitSet));
    }
  }
}