/*
 * 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 org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.Sort;
import org.apache.lucene.search.TopFieldCollector;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

/**
 * Wraps a lucene query result and adds a close method that allows to release
 * resources after a query has been executed and the results have been read
 * completely.
 */
public final class SortedLuceneQueryHits extends AbstractQueryHits
{

   /**
    * The Logger instance for this class.
    */
   private static final Logger log = LoggerFactory.getLogger("exo.jcr.component.core.SortedLuceneQueryHits");

   /**
    * The upper limit for the initial fetch size.
    */
   private static final int MAX_FETCH_SIZE = 32 * 1024;

   /**
    * The lower limit for the initial fetch size.
    */
   private static final int MIN_FETCH_SIZE = 32;

   /**
    * The IndexReader in use by the lucene hits.
    */
   private final IndexReader reader;

   /**
    * The index searcher.
    */
   private final JcrIndexSearcher searcher;

   /**
    * The query to execute.
    */
   private final Query query;

   /**
    * The sort criteria.
    */
   private final Sort sort;

   /**
    * The index of the current hit. Initially invalid.
    */
   private int hitIndex = -1;

   /**
    * The score docs.
    */
   private final List<ScoreDoc> scoreDocs = new ArrayList<ScoreDoc>();

   /**
    * The total number of hits.
    */
   private int size;

   /**
    * Number of hits to retrieve.
    */
   private int numHits;

   /**
    * Creates a new <code>QueryHits</code> instance wrapping <code>hits</code>.
    *
    * @param reader          the IndexReader in use.
    * @param searcher        the index searcher.
    * @param query           the query to execute.
    * @param sort            the sort criteria.
    * @param resultFetchHint a hint on how many results should be fetched.
    * @throws IOException if an error occurs while reading from the index.
    */
   public SortedLuceneQueryHits(IndexReader reader, JcrIndexSearcher searcher, Query query, Sort sort,
      long resultFetchHint) throws IOException
   {
      this.reader = reader;
      this.searcher = searcher;
      this.query = query;
      this.sort = sort;
      this.numHits = (int)Math.min(Math.max(resultFetchHint, MIN_FETCH_SIZE), MAX_FETCH_SIZE);
      getHits();
   }

   /**
    * {@inheritDoc}
    */
   public int getSize()
   {
      return size;
   }

   /**
    * {@inheritDoc}
    */
   public ScoreNode nextScoreNode() throws IOException
   {
      if (++hitIndex >= size)
      {
         // no more score nodes
         return null;
      }
      else if (hitIndex >= scoreDocs.size())
      {
         // refill at least numHits or twice hitIndex
         this.numHits = Math.max(this.numHits, hitIndex * 2);
         getHits();
      }
      ScoreDoc doc = scoreDocs.get(hitIndex);
      String uuid = reader.document(doc.doc, FieldSelectors.UUID).get(FieldNames.UUID);
      return new ScoreNode(uuid, doc.score, doc.doc);
   }

   /**
    * Skips <code>n</code> hits.
    *
    * @param n the number of hits to skip.
    * @throws IOException if an error occurs while skipping.
    */
   public void skip(int n) throws IOException
   {
      hitIndex += n;
   }

   //-------------------------------< internal >-------------------------------

   private void getHits() throws IOException
   {
      TopFieldCollector collector = TopFieldCollector.create(sort, numHits, false, true, false, false);
      searcher.search(query, collector);

      this.size = collector.getTotalHits();
      ScoreDoc[] docs = collector.topDocs().scoreDocs;
      for (int i = scoreDocs.size(); i < docs.length; i++)
      {
         scoreDocs.add(docs[i]);
      }
      log.debug("getHits() {}/{}", scoreDocs.size(), numHits);
      // double hits for next round
      numHits *= 2;
   }
}