PhraseScorer.cs :  » Search-Engines » dotLucene » Lucene » Net » Search » C# / CSharp Open Source

/*
 * Copyright 2004 The Apache Software Foundation
 * 
 * Licensed 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.Index;

namespace Lucene.Net.Search{
  
  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;
    
    
    internal PhraseScorer(Weight weight, TermPositions[] tps, int[] positions, Similarity similarity, byte[] norms) : base(similarity)
    {
      this.norms = norms;
      this.weight = weight;
      this.value_Renamed = weight.GetValue();
      
      // convert tps to a list
      for (int i = 0; i < tps.Length; i++)
      {
        PhrasePositions pp = new PhrasePositions(tps[i], positions[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
    }
    
    public override int Doc()
    {
      return first.doc;
    }
    
    public override bool Next()
    {
      if (firstTime)
      {
        Init();
        firstTime = false;
      }
      else if (more)
      {
        more = last.Next(); // trigger further scanning
      }
      return DoNext();
    }
    
    // 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 = GetSimilarity().Tf(freq) * value_Renamed; // raw score
      return raw * Similarity.DecodeNorm(norms[first.doc]); // normalize
    }
    
    public override bool SkipTo(int target)
    {
      for (PhrasePositions pp = first; more && pp != null; pp = pp.next)
      {
        more = pp.SkipTo(target);
      }
      if (more)
        Sort(); // re-sort
      return DoNext();
    }
    
    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.Put(pp);
      PqToList();
    }
    
    protected internal void  PqToList()
    {
      last = first = null;
      while (pq.Top() != null)
      {
        PhrasePositions pp = (PhrasePositions) 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 Explanation Explain(int doc)
    {
      Explanation tfExplanation = new Explanation();
      
      while (Next() && Doc() < doc)
      {
      }
      
      float phraseFreq = (Doc() == doc)?freq:0.0f;
      tfExplanation.SetValue(GetSimilarity().Tf(phraseFreq));
      tfExplanation.SetDescription("tf(phraseFreq=" + phraseFreq + ")");
      
      return tfExplanation;
    }
    
    public override System.String ToString()
    {
      return "scorer(" + weight + ")";
    }
  }
}