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;
  
  import org.apache.lucene.search.*;
  
  /**
   * Extra lucene sorting utilities & convenience methods
   *
   * @version $Id: Sorting.java 778893 2009-05-26 21:34:53Z yonik $
   *
   */
  
  public class Sorting {
  
  
    /** Returns a {@link SortField} for a string field.
     *  If nullLast and nullFirst are both false, then default lucene string sorting is used where
     *  null strings sort first in an ascending sort, and last in a descending sort.
     *
     * @param fieldName   the name of the field to sort on
     * @param reverse     true for a reverse (desc) sort
     * @param nullLast    true if null should come last, regardless of sort order
     * @param nullFirst   true if null should come first, regardless of sort order
     * @return SortField
     */
    public static SortField getStringSortField(String fieldName, boolean reverse, boolean nullLast, boolean nullFirst) {
      if (nullLast) {
        if (!reverse) return new SortField(fieldName, nullStringLastComparatorSource);
        else return new SortField(fieldName, SortField.STRING, true);
      } else if (nullFirst) {
        if (reverse) return new SortField(fieldName, nullStringLastComparatorSource, true);
        else return new SortField(fieldName, SortField.STRING, false);
      } else {
        return new SortField(fieldName, SortField.STRING, reverse);
      }
    }
  
  
    static final FieldComparatorSource nullStringLastComparatorSource = new MissingStringLastComparatorSource(null);
  }
  
  