PhraseScorer.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 TermPositions = Lucene.Net.Index.TermPositions;

namespace Lucene.Net.Search
{
    
    /// <summary>Expert: Scoring functionality for phrase queries.
    /// <br/>A document is considered matching if it contains the phrase-query terms  
    /// at "valid" positons. What "valid positions" are
    /// depends on the type of the phrase query: for an exact phrase query terms are required 
    /// to appear in adjacent locations, while for a sloppy phrase query some distance between 
    /// the terms is allowed. The abstract method <see cref="PhraseFreq()" /> of extending classes
    /// is invoked for each document containing all the phrase query terms, in order to 
    /// compute the frequency of the phrase query in that document. A non zero frequency
    /// means a match. 
    /// </summary>
    abstract class PhraseScorer:Scorer
    {
        private Weight weight;
        protected internal byte[] norms;
        protected internal float value_Renamed;
        
        private bool firstTime = true;
        private bool more = true;
        protected internal PhraseQueue pq;
        protected internal PhrasePositions first, last;
        
        private float freq; //prhase frequency in current doc as computed by phraseFreq().
        
        internal PhraseScorer(Weight weight, TermPositions[] tps, int[] offsets, Similarity similarity, byte[] norms):base(similarity)
        {
            this.norms = norms;
            this.weight = weight;
            this.value_Renamed = weight.Value;
            
            // convert tps to a list of phrase positions.
            // note: phrase-position differs from term-position in that its position
            // reflects the phrase offset: pp.pos = tp.pos - offset.
            // this allows to easily identify a matching (exact) phrase 
            // when all PhrasePositions have exactly the same position.
            for (int i = 0; i < tps.Length; i++)
            {
                PhrasePositions pp = new PhrasePositions(tps[i], offsets[i]);
                if (last != null)
                {
                    // add next to end of list
                    last.next = pp;
                }
                else
                {
                    first = pp;
                }
                last = pp;
            }
            
            pq = new PhraseQueue(tps.Length); // construct empty pq
            first.doc = - 1;
        }
        
        public override int DocID()
        {
            return first.doc;
        }
        
        public override int NextDoc()
        {
            if (firstTime)
            {
                Init();
                firstTime = false;
            }
            else if (more)
            {
                more = last.Next(); // trigger further scanning
            }
            if (!DoNext())
            {
                first.doc = NO_MORE_DOCS;
            }
            return first.doc;
        }
        
        // next without initial increment
        private bool DoNext()
        {
            while (more)
            {
                while (more && first.doc < last.doc)
                {
                    // find doc w/ all the terms
                    more = first.SkipTo(last.doc); // skip first upto last
                    FirstToLast(); // and move it to the end
                }
                
                if (more)
                {
                    // found a doc with all of the terms
                    freq = PhraseFreq(); // check for phrase
                    if (freq == 0.0f)
                    // no match
                        more = last.Next();
                    // trigger further scanning
                    else
                        return true; // found a match
                }
            }
            return false; // no more matches
        }
        
        public override float Score()
        {
            //System.out.println("scoring " + first.doc);
            float raw = Similarity.Tf(freq) * value_Renamed; // raw score
            return norms == null?raw:raw * Similarity.DecodeNorm(norms[first.doc]); // normalize
        }
        
        public override int Advance(int target)
        {
            firstTime = false;
            for (PhrasePositions pp = first; more && pp != null; pp = pp.next)
            {
                more = pp.SkipTo(target);
            }
            if (more)
            {
                Sort(); // re-sort
            }
            if (!DoNext())
            {
                first.doc = NO_MORE_DOCS;
            }
            return first.doc;
        }

        /// <summary>
        /// Phrase frequency in current doc as computed by PhraseFreq()
        /// </summary>
        /// <returns></returns>
        public float CurrentFreq()
        {
            return freq;
        }

        /// <summary> For a document containing all the phrase query terms, compute the
        /// frequency of the phrase in that document. 
        /// A non zero frequency means a match.
        /// <br/>Note, that containing all phrase terms does not guarantee a match - they have to be found in matching locations.  
        /// </summary>
        /// <returns> frequency of the phrase in current doc, 0 if not found. 
        /// </returns>
        protected internal abstract float PhraseFreq();
        
        private void  Init()
        {
            for (PhrasePositions pp = first; more && pp != null; pp = pp.next)
            {
                more = pp.Next();
            }
            if (more)
            {
                Sort();
            }
        }
        
        private void  Sort()
        {
            pq.Clear();
            for (PhrasePositions pp = first; pp != null; pp = pp.next)
            {
                pq.Add(pp);
            }
            PqToList();
        }
        
        protected internal void  PqToList()
        {
            last = first = null;
            while (pq.Top() != null)
            {
                PhrasePositions pp = pq.Pop();
                if (last != null)
                {
                    // add next to end of list
                    last.next = pp;
                }
                else
                    first = pp;
                last = pp;
                pp.next = null;
            }
        }
        
        protected internal void  FirstToLast()
        {
            last.next = first; // move first to end of list
            last = first;
            first = first.next;
            last.next = null;
        }
        
        public override System.String ToString()
        {
            return "scorer(" + weight + ")";
        }
    }
}