TopDocsCollector.cs

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/* 
 * 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.
 */

using System;
using Lucene.Net.Util;

namespace Lucene.Net.Search
{
    public abstract class TopDocsCollector<T> : Collector where T : ScoreDoc
    {
        
        // This is used in case topDocs() is called with illegal parameters, or there
        // simply aren't (enough) results.
        protected internal static readonly TopDocs EMPTY_TOPDOCS = new TopDocs(0, new ScoreDoc[0], System.Single.NaN);
        
        protected internal PriorityQueue<T> pq;
        
        protected internal int internalTotalHits;
        
        protected internal TopDocsCollector(PriorityQueue<T> pq)
        {
            this.pq = pq;
        }
        
        protected internal virtual void  PopulateResults(ScoreDoc[] results, int howMany)
        {
            for (int i = howMany - 1; i >= 0; i--)
            {
                results[i] = pq.Pop();
            }
        }

        public /*protected internal*/ virtual TopDocs NewTopDocs(ScoreDoc[] results, int start)
        {
            return results == null?EMPTY_TOPDOCS:new TopDocs(internalTotalHits, results);
        }

        public virtual int TotalHits
        {
            get { return internalTotalHits; }
        }

        public TopDocs TopDocs()
        {
            // In case pq was populated with sentinel values, there might be less
            // results than pq.size(). Therefore return all results until either
            // pq.size() or totalHits.
            return TopDocs(0, internalTotalHits < pq.Size()?internalTotalHits:pq.Size());
        }
        
        public TopDocs TopDocs(int start)
        {
            // In case pq was populated with sentinel values, there might be less
            // results than pq.size(). Therefore return all results until either
            // pq.size() or totalHits.
            return TopDocs(start, internalTotalHits < pq.Size()?internalTotalHits:pq.Size());
        }
        
        public TopDocs TopDocs(int start, int howMany)
        {
            
            // In case pq was populated with sentinel values, there might be less
            // results than pq.size(). Therefore return all results until either
            // pq.size() or totalHits.
            int size = internalTotalHits < pq.Size()?internalTotalHits:pq.Size();
            
            // Don't bother to throw an exception, just return an empty TopDocs in case
            // the parameters are invalid or out of range.
            if (start < 0 || start >= size || howMany <= 0)
            {
                return NewTopDocs(null, start);
            }
            
            // We know that start < pqsize, so just fix howMany. 
            howMany = System.Math.Min(size - start, howMany);
            ScoreDoc[] results = new ScoreDoc[howMany];
            
            // pq's pop() returns the 'least' element in the queue, therefore need
            // to discard the first ones, until we reach the requested range.
            // Note that this loop will usually not be executed, since the common usage
            // should be that the caller asks for the last howMany results. However it's
            // needed here for completeness.
            for (int i = pq.Size() - start - howMany; i > 0; i--)
            {
                pq.Pop();
            }
            
            // Get the requested results from pq.
            PopulateResults(results, howMany);
            
            return NewTopDocs(results, start);
        }
    }
}