package org.apache.lucene.analysis.th;

/**
 * Copyright 2006 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.
 */

import java.io.IOException;
import java.io.Reader;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.core.LowerCaseFilter;
import org.apache.lucene.analysis.core.StopAnalyzer;
import org.apache.lucene.analysis.core.StopFilter;
import org.apache.lucene.analysis.standard.StandardFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.analysis.util.CharArraySet;
import org.apache.lucene.analysis.util.StopwordAnalyzerBase;
import org.apache.lucene.util.Version;

/**
 * {@link Analyzer} for Thai language. It uses {@link java.text.BreakIterator} to break words.
 * <p>
 * <a name="version"/>
 * <p>You must specify the required {@link Version}
 * compatibility when creating ThaiAnalyzer:
 * <ul>
 *   <li> As of 3.6, a set of Thai stopwords is used by default
 * </ul>
 */
public final class ThaiAnalyzer extends StopwordAnalyzerBase {
  
  /** File containing default Thai stopwords. */
  public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";
  /**
   * The comment character in the stopwords file.  
   * All lines prefixed with this will be ignored.
   */
  private static final String STOPWORDS_COMMENT = "#";
  
  /**
   * Returns an unmodifiable instance of the default stop words set.
   * @return default stop words set.
   */
  public static CharArraySet 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 CharArraySet DEFAULT_STOP_SET;

    static {
      try {
        DEFAULT_STOP_SET = loadStopwordSet(false, ThaiAnalyzer.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.
   * 
   * @param matchVersion lucene compatibility version
   */
  public ThaiAnalyzer(Version matchVersion) {
    this(matchVersion, matchVersion.onOrAfter(Version.LUCENE_36) ? DefaultSetHolder.DEFAULT_STOP_SET : StopAnalyzer.ENGLISH_STOP_WORDS_SET);
  }
  
  /**
   * Builds an analyzer with the given stop words.
   * 
   * @param matchVersion lucene compatibility version
   * @param stopwords a stopword set
   */
  public ThaiAnalyzer(Version matchVersion, CharArraySet stopwords) {
    super(matchVersion, stopwords);
  }

  /**
   * 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 StandardFilter}, {@link LowerCaseFilter}, {@link ThaiWordFilter}, and
   *         {@link StopFilter}
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName,
      Reader reader) {
    if (matchVersion.onOrAfter(Version.LUCENE_48)) {
      final Tokenizer source = new ThaiTokenizer(reader);
      TokenStream result = new LowerCaseFilter(matchVersion, source);
      result = new StopFilter(matchVersion, result, stopwords);
      return new TokenStreamComponents(source, result);
    } else {
      final Tokenizer source = new StandardTokenizer(matchVersion, reader);
      TokenStream result = new StandardFilter(matchVersion, source);
      if (matchVersion.onOrAfter(Version.LUCENE_31))
        result = new LowerCaseFilter(matchVersion, result);
      result = new ThaiWordFilter(matchVersion, result);
      return new TokenStreamComponents(source, new StopFilter(matchVersion,
        result, stopwords));
    }
  }
}
