/*
 * 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.similarities;

import org.apache.lucene.index.FieldInvertState;
import org.apache.lucene.search.CollectionStatistics;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.TermStatistics;

Simple similarity that gives terms a score that is equal to their query boost. This similarity is typically used with disabled norms since neither document statistics nor index statistics are used for scoring. That said, if norms are enabled, they will be computed the same way as SimilarityBase and BM25Similarity with discounted overlaps so that the Similarity can be changed after the index has been created. /**
 * Simple similarity that gives terms a score that is equal to their query
 * boost. This similarity is typically used with disabled norms since neither
 * document statistics nor index statistics are used for scoring. That said,
 * if norms are enabled, they will be computed the same way as
 * {@link SimilarityBase} and {@link BM25Similarity} with
 * {@link SimilarityBase#setDiscountOverlaps(boolean) discounted overlaps}
 * so that the {@link Similarity} can be changed after the index has been
 * created.
 */
public class BooleanSimilarity extends Similarity {

  private static final Similarity BM25_SIM = new BM25Similarity();

  
Sole constructor /** Sole constructor */
  public BooleanSimilarity() {}

  @Override
  public long computeNorm(FieldInvertState state) {
    return BM25_SIM.computeNorm(state);
  }

  @Override
  public SimScorer scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats) {
    return new BooleanWeight(boost);
  }

  private static class BooleanWeight extends SimScorer {
    final float boost;

    BooleanWeight(float boost) {
      this.boost = boost;
    }

    @Override
    public float score(float freq, long norm) {
      return boost;
    }

    @Override
    public Explanation explain(Explanation freq, long norm) {
      Explanation queryBoostExpl = Explanation.match(boost, "boost, query boost");
      return Explanation.match(
          queryBoostExpl.getValue(),
          "score(" + getClass().getSimpleName() + "), computed from:",
          queryBoostExpl);
    }
  }

}