content: package org.apache.lucene.analysis.fa;
  
  /**
   * 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.File;
  import java.io.IOException;
  import java.io.Reader;
  import java.util.Hashtable;
  import java.util.Set;
  
  import org.apache.lucene.analysis.Analyzer;
  import org.apache.lucene.analysis.LowerCaseFilter;
  import org.apache.lucene.analysis.StopFilter;
  import org.apache.lucene.analysis.StopwordAnalyzerBase;
  import org.apache.lucene.analysis.CharReader;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.Tokenizer;
  import org.apache.lucene.analysis.WordlistLoader;
  import org.apache.lucene.analysis.ar.ArabicLetterTokenizer;
  import org.apache.lucene.analysis.ar.ArabicNormalizationFilter;
  import org.apache.lucene.analysis.standard.StandardTokenizer;
  
  import org.apache.lucene.util.IOUtils;
  import org.apache.lucene.util.Version;
  
  /**
   * {@link Analyzer} for Persian.
   * <p>
   * This Analyzer uses {@link ArabicLetterTokenizer} which implies tokenizing around
   * zero-width non-joiner in addition to whitespace. Some persian-specific variant forms (such as farsi
   * yeh and keheh) are standardized. "Stemming" is accomplished via stopwords.
   * </p>
   */
  public final class PersianAnalyzer extends StopwordAnalyzerBase {
  
    /**
     * File containing default Persian stopwords.
     * 
     * Default stopword list is from
     * http://members.unine.ch/jacques.savoy/clef/index.html The stopword list is
     * BSD-Licensed.
     * 
     */
    public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
  
    /**
     * The comment character in the stopwords file. All lines prefixed with this
     * will be ignored
     */
    public static final String STOPWORDS_COMMENT = "#";
    
    /**
     * Returns an unmodifiable instance of the default stop-words set.
     * @return an unmodifiable instance of the default stop-words set.
     */
    public static Set<?> getDefaultStopSet(){
      return DefaultSetHolder.DEFAULT_STOP_SET;
    }
    
    /**
     * Atomically loads the DEFAULT_STOP_SET in a lazy fashion once the outer class 
     * accesses the static final set the first time.;
     */
    private static class DefaultSetHolder {
      static final Set<?> DEFAULT_STOP_SET;
  
      static {
        try {
          DEFAULT_STOP_SET = loadStopwordSet(false, PersianAnalyzer.class, DEFAULT_STOPWORD_FILE, STOPWORDS_COMMENT);
        } catch (IOException ex) {
          // default set should always be present as it is part of the
          // distribution (JAR)
          throw new RuntimeException("Unable to load default stopword set");
        }
      }
    }
  
    /**
     * Builds an analyzer with the default stop words:
     * {@link #DEFAULT_STOPWORD_FILE}.
     */
    public PersianAnalyzer(Version matchVersion) {
      this(matchVersion, DefaultSetHolder.DEFAULT_STOP_SET);
    }
    
    /**
     * Builds an analyzer with the given stop words 
     * 
     * @param matchVersion
     *          lucene compatibility version
     * @param stopwords
     *          a stopword set
     */
    public PersianAnalyzer(Version matchVersion, Set<?> stopwords){
      super(matchVersion, stopwords);
    }
  
    /**
     * Builds an analyzer with the given stop words.
     * @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
     */
    @Deprecated
    public PersianAnalyzer(Version matchVersion, String... stopwords) {
      this(matchVersion, StopFilter.makeStopSet(matchVersion, stopwords));
    }
  
    /**
     * Builds an analyzer with the given stop words.
     * @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
     */
    @Deprecated
    public PersianAnalyzer(Version matchVersion, Hashtable<?, ?> stopwords) {
      this(matchVersion, stopwords.keySet());
    }
  
    /**
     * Builds an analyzer with the given stop words. Lines can be commented out
     * using {@link #STOPWORDS_COMMENT}
     * @deprecated use {@link #PersianAnalyzer(Version, Set)} instead
     */
    @Deprecated
    public PersianAnalyzer(Version matchVersion, File stopwords) throws IOException {
      this(matchVersion, WordlistLoader.getWordSet(
          IOUtils.getDecodingReader(stopwords, IOUtils.CHARSET_UTF_8),
          STOPWORDS_COMMENT, matchVersion));
    }
  
    /**
     * Creates
     * {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
     * used to tokenize all the text in the provided {@link Reader}.
     * 
     * @return {@link org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents}
     *         built from a {@link StandardTokenizer} filtered with
     *         {@link LowerCaseFilter}, {@link ArabicNormalizationFilter},
     *         {@link PersianNormalizationFilter} and Persian Stop words
     */
    @Override
    protected TokenStreamComponents createComponents(String fieldName,
        Reader reader) {
      final Tokenizer source;
      if (matchVersion.onOrAfter(Version.LUCENE_31)) {
        source = new StandardTokenizer(matchVersion, reader);
      } else {
        source = new ArabicLetterTokenizer(matchVersion, reader);
      }
      TokenStream result = new LowerCaseFilter(matchVersion, source);
      result = new ArabicNormalizationFilter(result);
      /* additional persian-specific normalization */
      result = new PersianNormalizationFilter(result);
      /*
       * the order here is important: the stopword list is normalized with the
       * above!
       */
      return new TokenStreamComponents(source, new StopFilter(matchVersion, result, stopwords));
    }
    
    /** 
     * Wraps the Reader with {@link PersianCharFilter}
     */
    @Override
    protected Reader initReader(Reader reader) {
      return matchVersion.onOrAfter(Version.LUCENE_31) ? 
         new PersianCharFilter(CharReader.get(reader)) :
         reader;
    }
  }
  