/*
 * 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.exoplatform.services.jcr.impl.core.query.lucene;

import org.apache.lucene.index.IndexReader;

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

/**
 * Abstract base class for <code>FieldComparator</code>s which keep their values
 * (<code>Comparable</code>s) in an array.
 */
public abstract class AbstractFieldComparator extends FieldComparatorBase
{

   /**
    * The values for comparing.
    */
   private final Comparable<?>[] values;

   /**
    * The index readers.
    */

   protected final List<IndexReader> readers = new ArrayList<IndexReader>();

   /**
    * The document number starts for the {@link #readers}.
    */
   protected int[] starts;

   /**
    * Create a new instance with the given number of values.
    *
    * @param numHits  the number of values
    */
   protected AbstractFieldComparator(int numHits)
   {
      values = new Comparable[numHits];
   }

   /**
    * Returns the reader index for document <code>n</code>.
    *
    * @param n document number.
    * @return the reader index.
    */
   protected final int readerIndex(int n)
   {
      int lo = 0;
      int hi = readers.size() - 1;

      while (hi >= lo)
      {
         int mid = (lo + hi) >> 1;
         int midValue = starts[mid];
         if (n < midValue)
         {
            hi = mid - 1;
         }
         else if (n > midValue)
         {
            lo = mid + 1;
         }
         else
         {
            while (mid + 1 < readers.size() && starts[mid + 1] == midValue)
            {
               mid++;
            }
            return mid;
         }
      }
      return hi;
   }

   /**
    * Add the given value to the values array
    *
    * @param slot   index into values
    * @param value  value for adding
    */
   @Override
   public void setValue(int slot, Comparable<?> value)
   {
      values[slot] = value;
   }

   /**
    * Return a value from the values array
    *
    * @param slot  index to retrieve
    * @return  the retrieved value
    */
   @Override
   public Comparable<?> getValue(int slot)
   {
      return values[slot];
   }

   @Override
   public void setNextReader(IndexReader reader, int docBase) throws IOException
   {
      getIndexReaders(readers, reader);

      int maxDoc = 0;
      starts = new int[readers.size() + 1];

      for (int i = 0; i < readers.size(); i++)
      {
         IndexReader r = readers.get(i);
         starts[i] = maxDoc;
         maxDoc += r.maxDoc();
      }
      starts[readers.size()] = maxDoc;
   }

   /**
    * Checks if <code>reader</code> is of type {@link MultiIndexReader} and if
    * so calls itself recursively for each reader within the
    * <code>MultiIndexReader</code> or otherwise adds the reader to the list.
    *
    * @param readers  list of index readers.
    * @param reader   reader to decompose
    */
   private static void getIndexReaders(List<IndexReader> readers, IndexReader reader)
   {
      if (reader instanceof MultiIndexReader)
      {
         for (IndexReader r : ((MultiIndexReader)reader).getIndexReaders())
         {
            getIndexReaders(readers, r);
         }
      }
      else
      {
         readers.add(reader);
      }
   }
}