/*
 * 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.cn.smart;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.Set;

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.TokenStream;
import org.apache.lucene.analysis.Tokenizer;
import org.apache.lucene.analysis.WordlistLoader;
import org.apache.lucene.analysis.en.PorterStemFilter;
import org.apache.lucene.util.IOUtils;


SmartChineseAnalyzer is an analyzer for Chinese or mixed Chinese-English text.
The analyzer uses probabilistic knowledge to find the optimal word segmentation for Simplified Chinese text.
The text is first broken into sentences, then each sentence is segmented into words.


Segmentation is based upon the Hidden Markov Model. 
A large training corpus was used to calculate Chinese word frequency probability.


This analyzer requires a dictionary to provide statistical data. 
SmartChineseAnalyzer has an included dictionary out-of-box.


The included dictionary data is from ICTCLAS1.0.
Thanks to ICTCLAS for their hard work, and for contributing the data under the Apache 2 License!

@lucene.experimental
Since:
3.1/**
 * <p>
 * SmartChineseAnalyzer is an analyzer for Chinese or mixed Chinese-English text.
 * The analyzer uses probabilistic knowledge to find the optimal word segmentation for Simplified Chinese text.
 * The text is first broken into sentences, then each sentence is segmented into words.
 * </p>
 * <p>
 * Segmentation is based upon the <a href="http://en.wikipedia.org/wiki/Hidden_Markov_Model">Hidden Markov Model</a>. 
 * A large training corpus was used to calculate Chinese word frequency probability.
 * </p>
 * <p>
 * This analyzer requires a dictionary to provide statistical data. 
 * SmartChineseAnalyzer has an included dictionary out-of-box.
 * </p>
 * <p>
 * The included dictionary data is from <a href="http://www.ictclas.org">ICTCLAS1.0</a>.
 * Thanks to ICTCLAS for their hard work, and for contributing the data under the Apache 2 License!
 * </p>
 * @lucene.experimental
 *
 * @since 3.1
 */
public final class SmartChineseAnalyzer extends Analyzer {

  private final CharArraySet stopWords;
  
  private static final String DEFAULT_STOPWORD_FILE = "stopwords.txt";
  
  private static final String STOPWORD_FILE_COMMENT = "//";
  
  
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;
  }
  
  
Atomically loads the DEFAULT_STOP_SET in a lazy fashion once the outer class 
accesses the static final set the first time.;
/**
   * 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 = loadDefaultStopWordSet();
      } 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");
      }
    }

    static CharArraySet loadDefaultStopWordSet() throws IOException {
      // make sure it is unmodifiable as we expose it in the outer class
      return CharArraySet.unmodifiableSet(WordlistLoader.getWordSet(IOUtils
          .getDecodingReader(SmartChineseAnalyzer.class, DEFAULT_STOPWORD_FILE,
              StandardCharsets.UTF_8), STOPWORD_FILE_COMMENT));
    }
  }

  
Create a new SmartChineseAnalyzer, using the default stopword list.
/**
   * Create a new SmartChineseAnalyzer, using the default stopword list.
   */
  public SmartChineseAnalyzer() {
    this(true);
  }

  

Create a new SmartChineseAnalyzer, optionally using the default stopword list.


The included default stopword list is simply a list of punctuation.
If you do not use this list, punctuation will not be removed from the text!

Params:
useDefaultStopWords – true to use the default stopword list./**
   * <p>
   * Create a new SmartChineseAnalyzer, optionally using the default stopword list.
   * </p>
   * <p>
   * The included default stopword list is simply a list of punctuation.
   * If you do not use this list, punctuation will not be removed from the text!
   * </p>
   * 
   * @param useDefaultStopWords true to use the default stopword list.
   */
  public SmartChineseAnalyzer(boolean useDefaultStopWords) {
    stopWords = useDefaultStopWords ? DefaultSetHolder.DEFAULT_STOP_SET
      : CharArraySet.EMPTY_SET;
  }

  
 Create a new SmartChineseAnalyzer, using the provided Set of stopwords. 

Note: the set should include punctuation, unless you want to index punctuation!

Params:
stopWords – Set of stopwords to use./**
   * <p>
   * Create a new SmartChineseAnalyzer, using the provided {@link Set} of stopwords.
   * </p>
   * <p>
   * Note: the set should include punctuation, unless you want to index punctuation!
   * </p>
   * @param stopWords {@link Set} of stopwords to use.
   */
  public SmartChineseAnalyzer(CharArraySet stopWords) {
    this.stopWords = stopWords == null ? CharArraySet.EMPTY_SET : stopWords;
  }

  @Override
  public TokenStreamComponents createComponents(String fieldName) {
    final Tokenizer tokenizer = new HMMChineseTokenizer();
    TokenStream result = tokenizer;
    // result = new LowerCaseFilter(result);
    // LowerCaseFilter is not needed, as SegTokenFilter lowercases Basic Latin text.
    // The porter stemming is too strict, this is not a bug, this is a feature:)
    result = new PorterStemFilter(result);
    if (!stopWords.isEmpty()) {
      result = new StopFilter(result, stopWords);
    }
    return new TokenStreamComponents(tokenizer, result);
  }

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