content: package org.apache.lucene.analysis.ar;
  
  /**
   * 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.CharArraySet;
  import org.apache.lucene.analysis.KeywordMarkerFilter;
  import org.apache.lucene.analysis.StopFilter;
  import org.apache.lucene.analysis.StopwordAnalyzerBase;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.Tokenizer;
  import org.apache.lucene.analysis.WordlistLoader;
  import org.apache.lucene.analysis.standard.StandardTokenizer;
  import org.apache.lucene.util.IOUtils;
  import org.apache.lucene.util.Version;
  
  /**
   * {@link Analyzer} for Arabic. 
   * <p>
   * This analyzer implements light-stemming as specified by:
   * <i>
   * Light Stemming for Arabic Information Retrieval
   * </i>    
   * http://www.mtholyoke.edu/~lballest/Pubs/arab_stem05.pdf
   * <p>
   * The analysis package contains three primary components:
   * <ul>
   *  <li>{@link ArabicNormalizationFilter}: Arabic orthographic normalization.
   *  <li>{@link ArabicStemFilter}: Arabic light stemming
   *  <li>Arabic stop words file: a set of default Arabic stop words.
   * </ul>
   * 
   */
  public final class ArabicAnalyzer extends StopwordAnalyzerBase {
  
    /**
     * File containing default Arabic 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
     * @deprecated use {@link WordlistLoader#getWordSet(Reader, String, Version)} directly  
     */
    // TODO make this private 
    @Deprecated
    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, ArabicAnalyzer.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");
        }
      }
    }
    
    private final Set<?> stemExclusionSet;
  
    /**
     * Builds an analyzer with the default stop words: {@link #DEFAULT_STOPWORD_FILE}.
     */
    public ArabicAnalyzer(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 ArabicAnalyzer(Version matchVersion, Set<?> stopwords){
      this(matchVersion, stopwords, CharArraySet.EMPTY_SET);
    }
  
    /**
     * Builds an analyzer with the given stop word. If a none-empty stem exclusion set is
     * provided this analyzer will add a {@link KeywordMarkerFilter} before
     * {@link ArabicStemFilter}.
     * 
     * @param matchVersion
     *          lucene compatibility version
     * @param stopwords
     *          a stopword set
     * @param stemExclusionSet
     *          a set of terms not to be stemmed
     */
    public ArabicAnalyzer(Version matchVersion, Set<?> stopwords, Set<?> stemExclusionSet){
      super(matchVersion, stopwords);
      this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(
          matchVersion, stemExclusionSet));
    }
  
    /**
     * Builds an analyzer with the given stop words.
     * @deprecated use {@link #ArabicAnalyzer(Version, Set)} instead
     */
    @Deprecated
    public ArabicAnalyzer( Version matchVersion, String... stopwords ) {
      this(matchVersion, StopFilter.makeStopSet(matchVersion, stopwords ));
    }
  
    /**
     * Builds an analyzer with the given stop words.
     * @deprecated use {@link #ArabicAnalyzer(Version, Set)} instead
     */
    @Deprecated
    public ArabicAnalyzer( 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 #ArabicAnalyzer(Version, Set)} instead
     */
    @Deprecated
    public ArabicAnalyzer( 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 an {@link StandardTokenizer} filtered with
     *         {@link LowerCaseFilter}, {@link StopFilter},
     *         {@link ArabicNormalizationFilter}, {@link KeywordMarkerFilter}
     *         if a stem exclusion set is provided and {@link ArabicStemFilter}.
     */
    @Override
    protected TokenStreamComponents createComponents(String fieldName,
        Reader reader) {
      final Tokenizer source = matchVersion.onOrAfter(Version.LUCENE_31) ? 
          new StandardTokenizer(matchVersion, reader) : new ArabicLetterTokenizer(matchVersion, reader);
      TokenStream result = new LowerCaseFilter(matchVersion, source);
      // the order here is important: the stopword list is not normalized!
      result = new StopFilter( matchVersion, result, stopwords);
      // TODO maybe we should make ArabicNormalization filter also KeywordAttribute aware?!
      result = new ArabicNormalizationFilter(result);
      if(!stemExclusionSet.isEmpty()) {
        result = new KeywordMarkerFilter(result, stemExclusionSet);
      }
      return new TokenStreamComponents(source, new ArabicStemFilter(result));
    }
  }
  
  