/*
 * 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;


import java.io.IOException;
import java.util.Objects;

import org.apache.lucene.index.IndexReader;

A Query wrapper that allows to give a boost to the wrapped query. Boost values that are less than one will give less importance to this query compared to other ones while values that are greater than one will give more importance to the scores returned by this query. More complex boosts can be applied by using FunctionScoreQuery in the lucene-queries module /**
 * A {@link Query} wrapper that allows to give a boost to the wrapped query.
 * Boost values that are less than one will give less importance to this
 * query compared to other ones while values that are greater than one will
 * give more importance to the scores returned by this query.
 *
 * More complex boosts can be applied by using FunctionScoreQuery in the
 * lucene-queries module
 */
public final class BoostQuery extends Query {

  private final Query query;
  private final float boost;

  
Sole constructor: wrap query in such a way that the produced scores will be boosted by boost. /** Sole constructor: wrap {@code query} in such a way that the produced
   *  scores will be boosted by {@code boost}. */
  public BoostQuery(Query query, float boost) {
    this.query = Objects.requireNonNull(query);
    if (Float.isFinite(boost) == false || Float.compare(boost, 0f) < 0) {
      throw new IllegalArgumentException("boost must be a positive float, got " + boost);
    }
    this.boost = boost;
  }

  
Return the wrapped Query. /**
   * Return the wrapped {@link Query}.
   */
  public Query getQuery() {
    return query;
  }

  
Return the applied boost.
/**
   * Return the applied boost.
   */
  public float getBoost() {
    return boost;
  }

  @Override
  public boolean equals(Object other) {
    return sameClassAs(other) &&
           equalsTo(getClass().cast(other));
  }
  
  private boolean equalsTo(BoostQuery other) {
    return query.equals(other.query) && 
           Float.floatToIntBits(boost) == Float.floatToIntBits(other.boost);
  }

  @Override
  public int hashCode() {
    int h = classHash();
    h = 31 * h + query.hashCode();
    h = 31 * h + Float.floatToIntBits(boost);
    return h;
  }

  @Override
  public Query rewrite(IndexReader reader) throws IOException {
    final Query rewritten = query.rewrite(reader);

    if (boost == 1f) {
      return rewritten;
    }

    if (rewritten.getClass() == BoostQuery.class) {
      BoostQuery in = (BoostQuery) rewritten;
      return new BoostQuery(in.query, boost * in.boost);
    }

    if (boost == 0f && rewritten.getClass() != ConstantScoreQuery.class) {
      // so that we pass needScores=false
      return new BoostQuery(new ConstantScoreQuery(rewritten), 0f);
    }

    if (query != rewritten) {
      return new BoostQuery(rewritten, boost);
    }

    return super.rewrite(reader);
  }

  @Override
  public void visit(QueryVisitor visitor) {
    query.visit(visitor.getSubVisitor(BooleanClause.Occur.MUST, this));
  }

  @Override
  public String toString(String field) {
    StringBuilder builder = new StringBuilder();
    builder.append("(");
    builder.append(query.toString(field));
    builder.append(")");
    builder.append("^");
    builder.append(boost);
    return builder.toString();
  }

  @Override
  public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException {
    return query.createWeight(searcher, scoreMode, BoostQuery.this.boost * boost);
  }

}