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 org.apache.lucene.index.IndexReader;
  import org.apache.lucene.index.Term;
  import org.apache.lucene.search.MultiTermQuery.RewriteMethod;
  
  /** @lucene.internal Only public to be accessible by spans package. */
  public abstract class ScoringRewrite<Q extends Query> extends TermCollectingRewrite<Q> {
  
    /** A rewrite method that first translates each term into
     *  {@link BooleanClause.Occur#SHOULD} clause in a
     *  BooleanQuery, and keeps the scores as computed by the
     *  query.  Note that typically such scores are
     *  meaningless to the user, and require non-trivial CPU
     *  to compute, so it's almost always better to use {@link
     *  MultiTermQuery#CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} instead.
     *
     *  <p><b>NOTE</b>: This rewrite method will hit {@link
     *  BooleanQuery.TooManyClauses} if the number of terms
     *  exceeds {@link BooleanQuery#getMaxClauseCount}.
     *
     *  @see #setRewriteMethod */
    public final static ScoringRewrite<BooleanQuery> SCORING_BOOLEAN_QUERY_REWRITE = new ScoringRewrite<BooleanQuery>() {
      @Override
      protected BooleanQuery getTopLevelQuery() {
        return new BooleanQuery(true);
      }
      
      @Override
      protected void addClause(BooleanQuery topLevel, Term term, float boost) {
        final TermQuery tq = new TermQuery(term);
        tq.setBoost(boost);
        topLevel.add(tq, BooleanClause.Occur.SHOULD);
      }
      
      // Make sure we are still a singleton even after deserializing
      protected Object readResolve() {
        return SCORING_BOOLEAN_QUERY_REWRITE;
      }    
    };
    
    /** Like {@link #SCORING_BOOLEAN_QUERY_REWRITE} except
     *  scores are not computed.  Instead, each matching
     *  document receives a constant score equal to the
     *  query's boost.
     * 
     *  <p><b>NOTE</b>: This rewrite method will hit {@link
     *  BooleanQuery.TooManyClauses} if the number of terms
     *  exceeds {@link BooleanQuery#getMaxClauseCount}.
     *
     *  @see #setRewriteMethod */
    public final static RewriteMethod CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE = new RewriteMethod() {
      @Override
      public Query rewrite(IndexReader reader, MultiTermQuery query) throws IOException {
        final BooleanQuery bq = SCORING_BOOLEAN_QUERY_REWRITE.rewrite(reader, query);
        // TODO: if empty boolean query return NullQuery?
        if (bq.clauses().isEmpty())
          return bq;
        // strip the scores off
        final Query result = new ConstantScoreQuery(bq);
        result.setBoost(query.getBoost());
        return result;
      }
  
      // Make sure we are still a singleton even after deserializing
      protected Object readResolve() {
        return CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE;
      }
    };
  
    @Override
    public Q rewrite(final IndexReader reader, final MultiTermQuery query) throws IOException {
      final Q result = getTopLevelQuery();
      final int[] size = new int[1]; // "trick" to be able to make it final
      collectTerms(reader, query, new TermCollector() {
        public boolean collect(Term t, float boost) throws IOException {
          addClause(result, t, query.getBoost() * boost);
          size[0]++;
          return true;
        }
      });
      query.incTotalNumberOfTerms(size[0]);
      return result;
    }
  }
  