lucene/analysis/morfologik/src/java/org/apache/lucene/analysis/uk/UkrainianMorfologikAnalyzer.java

/*
 * 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.uk;

import java.io.IOException;
import java.io.Reader;
import java.nio.charset.StandardCharsets;
import morfologik.stemming.Dictionary;
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.charfilter.MappingCharFilter;
import org.apache.lucene.analysis.charfilter.NormalizeCharMap;
import org.apache.lucene.analysis.miscellaneous.SetKeywordMarkerFilter;
import org.apache.lucene.analysis.morfologik.MorfologikFilter;
import org.apache.lucene.analysis.standard.StandardTokenizer;
import org.apache.lucene.util.IOUtils;

/**
 * A dictionary-based {@link Analyzer} for Ukrainian.
 *
 * @since 6.2.0
 */
public final class UkrainianMorfologikAnalyzer extends StopwordAnalyzerBase {
  private final CharArraySet stemExclusionSet;

  /** File containing default Ukrainian stopwords. */
  public static final String DEFAULT_STOPWORD_FILE = "stopwords.txt";

  /**
   * 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 =
            WordlistLoader.getSnowballWordSet(
                IOUtils.getDecodingReader(
                    UkrainianMorfologikAnalyzer.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: {@link #DEFAULT_STOPWORD_FILE}. */
  public UkrainianMorfologikAnalyzer() {
    this(DefaultSetHolder.DEFAULT_STOP_SET);
  }

  /**
   * Builds an analyzer with the given stop words.
   *
   * @param stopwords a stopword set
   */
  public UkrainianMorfologikAnalyzer(CharArraySet stopwords) {
    this(stopwords, CharArraySet.EMPTY_SET);
  }

  /**
   * Builds an analyzer with the given stop words. If a non-empty stem exclusion set is provided
   * this analyzer will add a {@link SetKeywordMarkerFilter} before stemming.
   *
   * @param stopwords a stopword set
   * @param stemExclusionSet a set of terms not to be stemmed
   */
  public UkrainianMorfologikAnalyzer(CharArraySet stopwords, CharArraySet stemExclusionSet) {
    super(stopwords);
    this.stemExclusionSet = CharArraySet.unmodifiableSet(CharArraySet.copy(stemExclusionSet));
  }

  @Override
  protected Reader initReader(String fieldName, Reader reader) {
    NormalizeCharMap.Builder builder = new NormalizeCharMap.Builder();
    // different apostrophes
    builder.add("\u2019", "'");
    builder.add("\u2018", "'");
    builder.add("\u02BC", "'");
    builder.add("`", "'");
    builder.add("´", "'");
    // ignored characters
    builder.add("\u0301", "");
    builder.add("\u00AD", "");
    builder.add("ґ", "г");
    builder.add("Ґ", "Г");

    NormalizeCharMap normMap = builder.build();
    reader = new MappingCharFilter(normMap, reader);
    return reader;
  }

  /**
   * Creates a {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents} which tokenizes all
   * the text in the provided {@link Reader}.
   *
   * @return A {@link org.apache.lucene.analysis.Analyzer.TokenStreamComponents} built from an
   *     {@link StandardTokenizer} filtered with {@link LowerCaseFilter}, {@link StopFilter} ,
   *     {@link SetKeywordMarkerFilter} if a stem exclusion set is provided and {@link
   *     MorfologikFilter} on the Ukrainian dictionary.
   */
  @Override
  protected TokenStreamComponents createComponents(String fieldName) {
    Tokenizer source = new StandardTokenizer();
    TokenStream result = new LowerCaseFilter(source);
    result = new StopFilter(result, stopwords);

    if (stemExclusionSet.isEmpty() == false) {
      result = new SetKeywordMarkerFilter(result, stemExclusionSet);
    }

    result = new MorfologikFilter(result, getDictionary());
    return new TokenStreamComponents(source, result);
  }

  private static Dictionary getDictionary() {
    try {
      return Dictionary.read(
          UkrainianMorfologikAnalyzer.class
              .getClassLoader()
              .getResource("ua/net/nlp/ukrainian.dict"));
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }
}