content: package org.apache.lucene.search;
  
  /**
   * 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.
   */
  
  import java.io.IOException;
  import java.util.PriorityQueue;
  
  import org.apache.lucene.index.IndexReader;
  import org.apache.lucene.index.Term;
  
  /**
   * Base rewrite method for collecting only the top terms
   * via a priority queue.
   * @lucene.internal Only public to be accessible by spans package.
   */
  public abstract class TopTermsRewrite<Q extends Query> extends TermCollectingRewrite<Q> {
  
    private final int size;
    
    /** 
     * Create a TopTermsBooleanQueryRewrite for 
     * at most <code>size</code> terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size</code>, then it will be used instead. 
     */
    public TopTermsRewrite(int size) {
      this.size = size;
    }
    
    /** return the maximum priority queue size */
    public int getSize() {
      return size;
    }
    
    /** return the maximum size of the priority queue (for boolean rewrites this is BooleanQuery#getMaxClauseCount). */
    protected abstract int getMaxSize();
    
    @Override
    public Q rewrite(final IndexReader reader, final MultiTermQuery query) throws IOException {
      final int maxSize = Math.min(size, getMaxSize());
      final PriorityQueue<ScoreTerm> stQueue = new PriorityQueue<ScoreTerm>();
      collectTerms(reader, query, new TermCollector() {
        public boolean collect(Term t, float boost) {
          // ignore uncompetitive hits
          if (stQueue.size() >= maxSize && boost <= stQueue.peek().boost)
            return true;
          // add new entry in PQ
          st.term = t;
          st.boost = boost;
          stQueue.offer(st);
          // possibly drop entries from queue
          st = (stQueue.size() > maxSize) ? stQueue.poll() : new ScoreTerm();
          return true;
        }
        
        // reusable instance
        private ScoreTerm st = new ScoreTerm();
      });
      
      final Q q = getTopLevelQuery();
      for (final ScoreTerm st : stQueue) {
        addClause(q, st.term, query.getBoost() * st.boost); // add to query
      }
      query.incTotalNumberOfTerms(stQueue.size());
      
      return q;
    }
  
    @Override
    public int hashCode() {
      return 31 * size;
    }
  
    @Override
    public boolean equals(Object obj) {
      if (this == obj) return true;
      if (obj == null) return false;
      if (getClass() != obj.getClass()) return false;
      final TopTermsRewrite other = (TopTermsRewrite) obj;
      if (size != other.size) return false;
      return true;
    }
    
    private static class ScoreTerm implements Comparable<ScoreTerm> {
      public Term term;
      public float boost;
      
      public int compareTo(ScoreTerm other) {
        if (this.boost == other.boost)
          return other.term.compareTo(this.term);
        else
          return Float.compare(this.boost, other.boost);
      }
    }
    
  }
  