/*
 * 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.facet.taxonomy;

import java.io.IOException;
import java.util.List;

import org.apache.lucene.facet.FacetsCollector;
import org.apache.lucene.facet.FacetsCollector.MatchingDocs;
import org.apache.lucene.facet.FacetsConfig;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.DoubleValues;
import org.apache.lucene.search.DoubleValuesSource;
import org.apache.lucene.util.IntsRef;

/** Aggregates sum of values from {@link
 *  FunctionValues#doubleVal}, for each facet label.
 *
 *  @lucene.experimental */
public class TaxonomyFacetSumValueSource extends FloatTaxonomyFacets {
  private final OrdinalsReader ordinalsReader;

  /**
   * Aggreggates double facet values from the provided
   * {@link DoubleValuesSource}, pulling ordinals using {@link
   * DocValuesOrdinalsReader} against the default indexed
   * facet field {@link FacetsConfig#DEFAULT_INDEX_FIELD_NAME}.
   */
   public TaxonomyFacetSumValueSource(TaxonomyReader taxoReader, FacetsConfig config,
                                     FacetsCollector fc, DoubleValuesSource valueSource) throws IOException {
    this(new DocValuesOrdinalsReader(FacetsConfig.DEFAULT_INDEX_FIELD_NAME), taxoReader, config, fc, valueSource);
   }

  /**
   * Aggreggates float facet values from the provided
   *  {@link DoubleValuesSource}, and pulls ordinals from the
   *  provided {@link OrdinalsReader}.
   */
  public TaxonomyFacetSumValueSource(OrdinalsReader ordinalsReader, TaxonomyReader taxoReader,
                                     FacetsConfig config, FacetsCollector fc, DoubleValuesSource vs) throws IOException {
    super(ordinalsReader.getIndexFieldName(), taxoReader, config);
    this.ordinalsReader = ordinalsReader;
    sumValues(fc.getMatchingDocs(), fc.getKeepScores(), vs);
  }

  private static DoubleValues scores(MatchingDocs hits) {
    return new DoubleValues() {

      int index = -1;

      @Override
      public double doubleValue() throws IOException {
        return hits.scores[index];
      }

      @Override
      public boolean advanceExact(int doc) throws IOException {
        index++;
        return true;
      }
    };
  }

  private void sumValues(List<MatchingDocs> matchingDocs, boolean keepScores, DoubleValuesSource valueSource) throws IOException {

    IntsRef scratch = new IntsRef();
    for(MatchingDocs hits : matchingDocs) {
      OrdinalsReader.OrdinalsSegmentReader ords = ordinalsReader.getReader(hits.context);
      DoubleValues scores = keepScores ? scores(hits) : null;
      DoubleValues functionValues = valueSource.getValues(hits.context, scores);
      DocIdSetIterator docs = hits.bits.iterator();
      
      int doc;
      while ((doc = docs.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
        ords.get(doc, scratch);
        if (functionValues.advanceExact(doc)) {
          float value = (float) functionValues.doubleValue();
          for (int i = 0; i < scratch.length; i++) {
            values[scratch.ints[i]] += value;
          }
        }
      }
    }

    rollup();
  }
  
}