content: /**
   * 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.function;
  
  import org.apache.lucene.index.IndexReader;
  import org.apache.solr.search.function.DocValues;
  import org.apache.solr.search.function.ValueSource;
  import org.apache.lucene.search.FieldCache;
  
  import java.io.IOException;
  import java.util.Map;
  
  /**
   * Obtains the ordinal of the field value from the default Lucene {@link org.apache.lucene.search.FieldCache} using getStringIndex()
   * and reverses the order.
   * <br>
   * The native lucene index order is used to assign an ordinal value for each field value.
   * <br>Field values (terms) are lexicographically ordered by unicode value, and numbered starting at 1.
   * <br>
   * Example of reverse ordinal (rord):<br>
   *  If there were only three field values: "apple","banana","pear"
   * <br>then rord("apple")=3, rord("banana")=2, ord("pear")=1
   * <p>
   *  WARNING: ord() depends on the position in an index and can thus change when other documents are inserted or deleted,
   *  or if a MultiSearcher is used.
   * <br>
   *  WARNING: as of Solr 1.4, ord() and rord() can cause excess memory use since they must use a FieldCache entry
   * at the top level reader, while sorting and function queries now use entries at the segment level.  Hence sorting
   * or using a different function query, in addition to ord()/rord() will double memory use.
   * 
   * @version $Id: ReverseOrdFieldSource.java 1065312 2011-01-30 16:08:25Z rmuir $
   */
  
  public class ReverseOrdFieldSource extends ValueSource {
    public String field;
  
    public ReverseOrdFieldSource(String field) {
      this.field = field;
    }
  
    @Override
    public String description() {
      return "rord("+field+')';
    }
  
    @Override
    public DocValues getValues(Map context, IndexReader reader) throws IOException {
      final FieldCache.StringIndex sindex = FieldCache.DEFAULT.getStringIndex(reader, field);
  
      final int arr[] = sindex.order;
      final int end = sindex.lookup.length;
  
      return new DocValues() {
        @Override
        public float floatVal(int doc) {
          return (float)(end - arr[doc]);
        }
  
        @Override
        public int intVal(int doc) {
          return (end - arr[doc]);
        }
  
        @Override
        public long longVal(int doc) {
          return (long)(end - arr[doc]);
        }
  
        @Override
        public double doubleVal(int doc) {
          return (double)(end - arr[doc]);
        }
  
        @Override
        public String strVal(int doc) {
          // the string value of the ordinal, not the string itself
          return Integer.toString((end - arr[doc]));
        }
  
        @Override
        public String toString(int doc) {
          return description() + '=' + strVal(doc);
        }
      };
    }
  
    @Override
    public boolean equals(Object o) {
      if (o.getClass() !=  ReverseOrdFieldSource.class) return false;
      ReverseOrdFieldSource other = (ReverseOrdFieldSource)o;
      return this.field.equals(other.field);
    }
  
    private static final int hcode = ReverseOrdFieldSource.class.hashCode();
    @Override
    public int hashCode() {
      return hcode + field.hashCode();
    };
  
  }
  