/*
 * 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.solr.search.similarities;

import org.apache.lucene.search.similarities.DFISimilarity;
import org.apache.lucene.search.similarities.Independence;
import org.apache.lucene.search.similarities.IndependenceChiSquared;
import org.apache.lucene.search.similarities.IndependenceSaturated;
import org.apache.lucene.search.similarities.IndependenceStandardized;
import org.apache.lucene.search.similarities.Similarity;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.schema.SimilarityFactory;

/**
 * Factory for {@link DFISimilarity}
 * <p>
 * You must specify the measure of divergence from independence ("independenceMeasure")
 * <ul>
 *   <li>"Standardized": {@link IndependenceStandardized}</li>
 *   <li>"Saturated": {@link IndependenceSaturated}</li>
 *   <li>"ChiSquared": {@link IndependenceChiSquared}</li>
 * </ul>
 * Optional settings:
 * <ul>
 *  <li>discountOverlaps (bool): Sets {@link org.apache.lucene.search.similarities.SimilarityBase#setDiscountOverlaps(boolean)}</li>
 * </ul>
 *
 * @lucene.experimental
 */
public class DFISimilarityFactory extends SimilarityFactory {

  private boolean discountOverlaps;
  private Independence independenceMeasure;

  @Override
  public void init(SolrParams params) {
    super.init(params);
    discountOverlaps = params.getBool(ClassicSimilarityFactory.DISCOUNT_OVERLAPS, true);
    independenceMeasure = parseIndependenceMeasure(params.get("independenceMeasure"));
  }

  @Override
  public Similarity getSimilarity() {
    DFISimilarity sim = new DFISimilarity(independenceMeasure);
    sim.setDiscountOverlaps(discountOverlaps);
    return sim;
  }
  
  private Independence parseIndependenceMeasure(String expr) {
    if ("ChiSquared".equals(expr)) {
      return new IndependenceChiSquared();
    } else if ("Standardized".equals(expr)) {
      return new IndependenceStandardized();
    } else if ("Saturated".equals(expr)) {
      return new IndependenceSaturated();
    } else {
      throw new RuntimeException("Invalid independence measure: " + expr);
    }
  }
}