/*
 * 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.cjk;


import java.io.IOException;

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.standard.StandardTokenizer;

/**
 * An {@link Analyzer} that tokenizes text with {@link StandardTokenizer},
 * normalizes content with {@link CJKWidthFilter}, folds case with
 * {@link LowerCaseFilter}, forms bigrams of CJK with {@link CJKBigramFilter},
 * and filters stopwords with {@link StopFilter}
 */
public final class CJKAnalyzer extends StopwordAnalyzerBase {

  /**
   * File containing default CJK stopwords.
   * <p>
   * Currently it contains some common English words that are not usually
   * useful for searching and some double-byte interpunctions.
   */
  public final static String DEFAULT_STOPWORD_FILE = "stopwords.txt";

  /**
   * 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 = loadStopwordSet(false, CJKAnalyzer.class, DEFAULT_STOPWORD_FILE, "#");
      } 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 which removes words in {@link #getDefaultStopSet()}.
   */
  public CJKAnalyzer() {
    this(DefaultSetHolder.DEFAULT_STOP_SET);
  }
  
  /**
   * Builds an analyzer with the given stop words
   * 
   * @param stopwords
   *          a stopword set
   */
  public CJKAnalyzer(CharArraySet stopwords){
    super(stopwords);
  }

  @Override
  protected TokenStreamComponents createComponents(String fieldName) {
    final Tokenizer source = new StandardTokenizer();
    // run the widthfilter first before bigramming, it sometimes combines characters.
    TokenStream result = new CJKWidthFilter(source);
    result = new LowerCaseFilter(result);
    result = new CJKBigramFilter(result);
    return new TokenStreamComponents(source, new StopFilter(result, stopwords));
  }

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