/*
 * 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.
 */
package org.apache.lucene.analysis.fr;


import java.io.IOException;
import java.io.Reader;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.CharArraySet;
import org.apache.lucene.analysis.LowerCaseFilter;
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.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.snowball.SnowballFilter;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.analysis.util.ElisionFilter;
import org.apache.lucene.util.IOUtils;

Analyzer for French language. 

Supports an external list of stopwords (words that
will not be indexed at all) and an external list of exclusions (word that will
not be stemmed, but indexed).
A default set of stopwords is used unless an alternative list is specified, but the
exclusion list is empty by default.

NOTE: This class uses the same Version dependent settings as StandardAnalyzer.
Since:
3.1/**
 * {@link Analyzer} for French language. 
 * <p>
 * Supports an external list of stopwords (words that
 * will not be indexed at all) and an external list of exclusions (word that will
 * not be stemmed, but indexed).
 * A default set of stopwords is used unless an alternative list is specified, but the
 * exclusion list is empty by default.
 * </p>
 *
 * <p><b>NOTE</b>: This class uses the same {@link org.apache.lucene.util.Version}
 * dependent settings as {@link StandardAnalyzer}.</p>
 *
 * @since 3.1
 */
public final class FrenchAnalyzer extends StopwordAnalyzerBase {

  
File containing default French stopwords. /** File containing default French stopwords. */
  public final static String DEFAULT_STOPWORD_FILE = "french_stop.txt";
  
  
Default set of articles for ElisionFilter /** Default set of articles for ElisionFilter */
  public static final CharArraySet DEFAULT_ARTICLES = CharArraySet.unmodifiableSet(
      new CharArraySet(Arrays.asList(
          "l", "m", "t", "qu", "n", "s", "j", "d", "c", "jusqu", "quoiqu", "lorsqu", "puisqu"), true));

  
Contains words that should be indexed but not stemmed.
/**
   * Contains words that should be indexed but not stemmed.
   */
  private final CharArraySet excltable;

  
Returns an unmodifiable instance of the default stop-words set.
Returns:
an unmodifiable instance of the default stop-words set./**
   * Returns an unmodifiable instance of the default stop-words set.
   * @return an unmodifiable instance of the default stop-words set.
   */
  public static CharArraySet getDefaultStopSet(){
    return DefaultSetHolder.DEFAULT_STOP_SET;
  }
  
  private static class DefaultSetHolder {
    static final CharArraySet DEFAULT_STOP_SET;
    static {
      try {
        DEFAULT_STOP_SET = WordlistLoader.getSnowballWordSet(IOUtils.getDecodingReader(SnowballFilter.class, 
                DEFAULT_STOPWORD_FILE, StandardCharsets.UTF_8));
      } 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 (getDefaultStopSet). /**
   * Builds an analyzer with the default stop words ({@link #getDefaultStopSet}).
   */
  public FrenchAnalyzer() {
    this(DefaultSetHolder.DEFAULT_STOP_SET);
  }
  
  
Builds an analyzer with the given stop words
Params:
stopwords – 
         a stopword set/**
   * Builds an analyzer with the given stop words
   * 
   * @param stopwords
   *          a stopword set
   */
  public FrenchAnalyzer(CharArraySet stopwords){
    this(stopwords, CharArraySet.EMPTY_SET);
  }
  
  
Builds an analyzer with the given stop words
Params:
stopwords – 
         a stopword set
stemExclutionSet – 
         a stemming exclusion set/**
   * Builds an analyzer with the given stop words
   * 
   * @param stopwords
   *          a stopword set
   * @param stemExclutionSet
   *          a stemming exclusion set
   */
  public FrenchAnalyzer(CharArraySet stopwords,
      CharArraySet stemExclutionSet) {
    super(stopwords);
    this.excltable = CharArraySet.unmodifiableSet(CharArraySet
        .copy(stemExclutionSet));
  }

  
Creates TokenStreamComponents used to tokenize all the text in the provided Reader. 
Returns:
TokenStreamComponents built from a StandardTokenizer filtered with ElisionFilter, LowerCaseFilter, StopFilter, SetKeywordMarkerFilter if a stem exclusion set is provided, and FrenchLightStemFilter/**
   * Creates
   * {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
   * used to tokenize all the text in the provided {@link Reader}.
   * 
   * @return {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents}
   *         built from a {@link StandardTokenizer} filtered with
   *         {@link ElisionFilter},
   *         {@link LowerCaseFilter}, {@link StopFilter},
   *         {@link SetKeywordMarkerFilter} if a stem exclusion set is
   *         provided, and {@link FrenchLightStemFilter}
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName) {
    final Tokenizer source = new StandardTokenizer();
    TokenStream result = new ElisionFilter(source, DEFAULT_ARTICLES);
    result = new LowerCaseFilter(result);
    result = new StopFilter(result, stopwords);
    if(!excltable.isEmpty())
      result = new SetKeywordMarkerFilter(result, excltable);
    result = new FrenchLightStemFilter(result);
    return new TokenStreamComponents(source, result);
  }

  @Override
  protected TokenStream normalize(String fieldName, TokenStream in) {
    TokenStream result = new ElisionFilter(in, DEFAULT_ARTICLES);
    result = new LowerCaseFilter(result);
    return result;
  }
}