content: package org.apache.lucene.search.highlight;
  /**
   * 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.
   */
  
  import java.io.IOException;
  import java.util.HashSet;
  import java.util.Iterator;
  
  import org.apache.lucene.index.IndexReader;
  import org.apache.lucene.index.Term;
  import org.apache.lucene.search.BooleanClause;
  import org.apache.lucene.search.BooleanQuery;
  import org.apache.lucene.search.FilteredQuery;
  import org.apache.lucene.search.Query;
  import org.apache.lucene.util.StringHelper;
  
  /**
   * Utility class used to extract the terms used in a query, plus any weights.
   * This class will not find terms for MultiTermQuery, TermRangeQuery and PrefixQuery classes
   * so the caller must pass a rewritten query (see Query.rewrite) to obtain a list of 
   * expanded terms. 
   * 
   */
  public final class QueryTermExtractor
  {
  
  	/**
  	 * Extracts all terms texts of a given Query into an array of WeightedTerms
  	 *
  	 * @param query      Query to extract term texts from
  	 * @return an array of the terms used in a query, plus their weights.
  	 */
  	public static final WeightedTerm[] getTerms(Query query) 
  	{
  		return getTerms(query,false);
  	}
  
  	/**
  	 * Extracts all terms texts of a given Query into an array of WeightedTerms
  	 *
  	 * @param query      Query to extract term texts from
  	 * @param reader used to compute IDF which can be used to a) score selected fragments better 
  	 * b) use graded highlights eg changing intensity of font color
  	 * @param fieldName the field on which Inverse Document Frequency (IDF) calculations are based
  	 * @return an array of the terms used in a query, plus their weights.
  	 */
  	public static final WeightedTerm[] getIdfWeightedTerms(Query query, IndexReader reader, String fieldName) 
  	{
  	    WeightedTerm[] terms=getTerms(query,false, fieldName);
  	    int totalNumDocs=reader.numDocs();
  	    for (int i = 0; i < terms.length; i++)
          {
  	        try
              {
                  int docFreq=reader.docFreq(new Term(fieldName,terms[i].term));
                  // docFreq counts deletes
                  if(totalNumDocs < docFreq) {
                    docFreq = totalNumDocs;
                  }
                  //IDF algorithm taken from DefaultSimilarity class
                  float idf=(float)(Math.log((float)totalNumDocs/(double)(docFreq+1)) + 1.0);
                  terms[i].weight*=idf;
              } 
  	        catch (IOException e)
              {
  	            //ignore 
              }
          }
  		return terms;
  	}
  
  	/**
  	 * Extracts all terms texts of a given Query into an array of WeightedTerms
  	 *
  	 * @param query      Query to extract term texts from
  	 * @param prohibited <code>true</code> to extract "prohibited" terms, too
  	 * @param fieldName  The fieldName used to filter query terms
     * @return an array of the terms used in a query, plus their weights.
     */
  	public static final WeightedTerm[] getTerms(Query query, boolean prohibited, String fieldName) 
  	{
  		HashSet<WeightedTerm> terms=new HashSet<WeightedTerm>();
  		if(fieldName!=null)
  		{
  		    fieldName= StringHelper.intern(fieldName);
  		}
  		getTerms(query,terms,prohibited,fieldName);
  		return terms.toArray(new WeightedTerm[0]);
  	}
  	
  	/**
  	 * Extracts all terms texts of a given Query into an array of WeightedTerms
  	 *
  	 * @param query      Query to extract term texts from
  	 * @param prohibited <code>true</code> to extract "prohibited" terms, too
     * @return an array of the terms used in a query, plus their weights.
     */
  	public static final WeightedTerm[] getTerms(Query query, boolean prohibited) 
  	{
  	    return getTerms(query,prohibited,null);
  	}	
  
  	//fieldname MUST be interned prior to this call
  	private static final void getTerms(Query query, HashSet<WeightedTerm> terms,boolean prohibited, String fieldName) 
  	{
         	try
         	{
      		if (query instanceof BooleanQuery)
      			getTermsFromBooleanQuery((BooleanQuery) query, terms, prohibited, fieldName);
      		else
      			if(query instanceof FilteredQuery)
      				getTermsFromFilteredQuery((FilteredQuery)query, terms,prohibited, fieldName);
      			else
      		{
  	       		HashSet<Term> nonWeightedTerms=new HashSet<Term>();
  	       		query.extractTerms(nonWeightedTerms);
  	       		for (Iterator<Term> iter = nonWeightedTerms.iterator(); iter.hasNext();)
  				{
  					Term term = iter.next();
  				    if((fieldName==null)||(term.field()==fieldName))
  					{
  						terms.add(new WeightedTerm(query.getBoost(),term.text()));
  					}
  				}
      		}
  	      }
  	      catch(UnsupportedOperationException ignore)
  	      {
  	    	  //this is non-fatal for our purposes
         	  }		        			        	
  	}
  
  	/**
  	 * extractTerms is currently the only query-independent means of introspecting queries but it only reveals
  	 * a list of terms for that query - not the boosts each individual term in that query may or may not have.
  	 * "Container" queries such as BooleanQuery should be unwrapped to get at the boost info held
  	 * in each child element. 
  	 * Some discussion around this topic here:
  	 * http://www.gossamer-threads.com/lists/lucene/java-dev/34208?search_string=introspection;#34208
  	 * Unfortunately there seemed to be limited interest in requiring all Query objects to implement
  	 * something common which would allow access to child queries so what follows here are query-specific
  	 * implementations for accessing embedded query elements. 
  	 */
  	private static final void getTermsFromBooleanQuery(BooleanQuery query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName)
  	{
  		BooleanClause[] queryClauses = query.getClauses();
  		for (int i = 0; i < queryClauses.length; i++)
  		{
  			if (prohibited || queryClauses[i].getOccur()!=BooleanClause.Occur.MUST_NOT)
  				getTerms(queryClauses[i].getQuery(), terms, prohibited, fieldName);
  		}
  	}	
  	private static void getTermsFromFilteredQuery(FilteredQuery query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName)
  	{
  		getTerms(query.getQuery(),terms,prohibited,fieldName);		
  	}
  	
  }
  