package org.apache.lucene.search;

/**
 * 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.
 */

import org.apache.lucene.util.PriorityQueue;
import org.apache.lucene.util.BytesRef;

import java.text.Collator;
import java.util.Locale;

/**
 * Expert: Collects sorted results from Searchable's and collates them.
 * The elements put into this queue must be of type FieldDoc.
 *
 * <p>Created: Feb 11, 2004 2:04:21 PM
 *
 * @since   lucene 1.4
 */
class FieldDocSortedHitQueue extends PriorityQueue<FieldDoc> {

  volatile SortField[] fields = null;

  // used in the case where the fields are sorted by locale
  // based strings
  volatile Collator[] collators = null;


  /**
   * Creates a hit queue sorted by the given list of fields.
   * @param fields Fieldable names, in priority order (highest priority first).
   * @param size  The number of hits to retain.  Must be greater than zero.
   */
  FieldDocSortedHitQueue (int size) {
    initialize (size);
  }


  /**
   * Allows redefinition of sort fields if they are <code>null</code>.
   * This is to handle the case using ParallelMultiSearcher where the
   * original list contains AUTO and we don't know the actual sort
   * type until the values come back.  The fields can only be set once.
   * This method should be synchronized external like all other PQ methods.
   * @param fields
   */
  void setFields (SortField[] fields) {
    this.fields = fields;
    this.collators = hasCollators (fields);
  }


  /** Returns the fields being used to sort. */
  SortField[] getFields() {
    return fields;
  }


  /** Returns an array of collators, possibly <code>null</code>.  The collators
   * correspond to any SortFields which were given a specific locale.
   * @param fields Array of sort fields.
   * @return Array, possibly <code>null</code>.
   */
  private Collator[] hasCollators (final SortField[] fields) {
    if (fields == null) return null;
    Collator[] ret = new Collator[fields.length];
    for (int i=0; i<fields.length; ++i) {
      Locale locale = fields[i].getLocale();
      if (locale != null)
        ret[i] = Collator.getInstance (locale);
    }
    return ret;
  }


  /**
   * Returns whether <code>a</code> is less relevant than <code>b</code>.
   * @param a ScoreDoc
   * @param b ScoreDoc
   * @return <code>true</code> if document <code>a</code> should be sorted after document <code>b</code>.
   */
  @SuppressWarnings("unchecked") @Override
  protected final boolean lessThan(final FieldDoc docA, final FieldDoc docB) {
    final int n = fields.length;
    int c = 0;
    for (int i=0; i<n && c==0; ++i) {
      final int type = fields[i].getType();
      if (type == SortField.STRING) {
        final BytesRef s1 = (BytesRef) docA.fields[i];
        final BytesRef s2 = (BytesRef) docB.fields[i];
        // null values need to be sorted first, because of how FieldCache.getStringIndex()
        // works - in that routine, any documents without a value in the given field are
        // put first.  If both are null, the next SortField is used
        if (s1 == null) {
          c = (s2 == null) ? 0 : -1;
        } else if (s2 == null) {
          c = 1;
        } else if (fields[i].getLocale() == null) {
          c = s1.compareTo(s2);
        } else {
          c = collators[i].compare(s1.utf8ToString(), s2.utf8ToString());
        }
      } else {
        c = docA.fields[i].compareTo(docB.fields[i]);
        if (type == SortField.SCORE) {
          c = -c;
        }
      }
      // reverse sort
      if (fields[i].getReverse()) {
        c = -c;
      }
    }

    // avoid random sort order that could lead to duplicates (bug #31241):
    if (c == 0)
      return docA.doc > docB.doc;

    return c > 0;
  }
}