lucene/test-framework/src/java/org/apache/lucene/analysis/MockTokenFilter.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;

import static org.apache.lucene.util.automaton.Automata.makeEmpty;
import static org.apache.lucene.util.automaton.Automata.makeString;

import java.io.IOException;
import java.util.Arrays;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.util.automaton.CharacterRunAutomaton;
import org.apache.lucene.util.automaton.Operations;

/**
 * A tokenfilter for testing that removes terms accepted by a DFA.
 *
 * <ul>
 *   <li>Union a list of singletons to act like a stopfilter.
 *   <li>Use the complement to act like a keepwordfilter
 *   <li>Use a regex like <code>.{12,}</code> to act like a lengthfilter
 * </ul>
 */
public final class MockTokenFilter extends TokenFilter {
  /** Empty set of stopwords */
  public static final CharacterRunAutomaton EMPTY_STOPSET = new CharacterRunAutomaton(makeEmpty());

  /** Set of common english stopwords */
  public static final CharacterRunAutomaton ENGLISH_STOPSET =
      new CharacterRunAutomaton(
          Operations.union(
              Arrays.asList(
                  makeString("a"),
                  makeString("an"),
                  makeString("and"),
                  makeString("are"),
                  makeString("as"),
                  makeString("at"),
                  makeString("be"),
                  makeString("but"),
                  makeString("by"),
                  makeString("for"),
                  makeString("if"),
                  makeString("in"),
                  makeString("into"),
                  makeString("is"),
                  makeString("it"),
                  makeString("no"),
                  makeString("not"),
                  makeString("of"),
                  makeString("on"),
                  makeString("or"),
                  makeString("such"),
                  makeString("that"),
                  makeString("the"),
                  makeString("their"),
                  makeString("then"),
                  makeString("there"),
                  makeString("these"),
                  makeString("they"),
                  makeString("this"),
                  makeString("to"),
                  makeString("was"),
                  makeString("will"),
                  makeString("with"))));

  private final CharacterRunAutomaton filter;

  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final PositionIncrementAttribute posIncrAtt =
      addAttribute(PositionIncrementAttribute.class);
  private int skippedPositions;

  /**
   * Create a new MockTokenFilter.
   *
   * @param input TokenStream to filter
   * @param filter DFA representing the terms that should be removed.
   */
  public MockTokenFilter(TokenStream input, CharacterRunAutomaton filter) {
    super(input);
    this.filter = filter;
  }

  @Override
  public boolean incrementToken() throws IOException {
    // TODO: fix me when posInc=false, to work like FilteringTokenFilter in that case and not return
    // initial token with posInc=0 ever

    // return the first non-stop word found
    skippedPositions = 0;
    while (input.incrementToken()) {
      if (!filter.run(termAtt.buffer(), 0, termAtt.length())) {
        posIncrAtt.setPositionIncrement(posIncrAtt.getPositionIncrement() + skippedPositions);
        return true;
      }
      skippedPositions += posIncrAtt.getPositionIncrement();
    }
    // reached EOS -- return false
    return false;
  }

  @Override
  public void end() throws IOException {
    super.end();
    posIncrAtt.setPositionIncrement(posIncrAtt.getPositionIncrement() + skippedPositions);
  }

  @Override
  public void reset() throws IOException {
    super.reset();
    skippedPositions = 0;
  }
}