lucene/analysis/phonetic/src/java/org/apache/lucene/analysis/phonetic/DoubleMetaphoneFilter.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.phonetic;

import java.io.IOException;
import java.util.LinkedList;

import org.apache.commons.codec.language.DoubleMetaphone;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;

/**
 * Filter for DoubleMetaphone (supporting secondary codes)
 */
public final class DoubleMetaphoneFilter extends TokenFilter {

  private static final String TOKEN_TYPE = "DoubleMetaphone";
  
  private final LinkedList<State> remainingTokens = new LinkedList<>();
  private final DoubleMetaphone encoder = new DoubleMetaphone();
  private final boolean inject;
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
  private final PositionIncrementAttribute posAtt = addAttribute(PositionIncrementAttribute.class);

  /** Creates a DoubleMetaphoneFilter with the specified maximum code length, 
   *  and either adding encoded forms as synonyms (<code>inject=true</code>) or
   *  replacing them.
   */
  public DoubleMetaphoneFilter(TokenStream input, int maxCodeLength, boolean inject) {
    super(input);
    this.encoder.setMaxCodeLen(maxCodeLength);
    this.inject = inject;
  }

  @Override
  public boolean incrementToken() throws IOException {
    for(;;) {

      if (!remainingTokens.isEmpty()) {
        // clearAttributes();  // not currently necessary
        restoreState(remainingTokens.removeFirst());
        return true;
      }

      if (!input.incrementToken()) return false;

      int len = termAtt.length();
      if (len==0) return true; // pass through zero length terms
      
      int firstAlternativeIncrement = inject ? 0 : posAtt.getPositionIncrement();

      String v = termAtt.toString();
      String primaryPhoneticValue = encoder.doubleMetaphone(v);
      String alternatePhoneticValue = encoder.doubleMetaphone(v, true);

      // a flag to lazily save state if needed... this avoids a save/restore when only
      // one token will be generated.
      boolean saveState=inject;

      if (primaryPhoneticValue!=null && primaryPhoneticValue.length() > 0 && !primaryPhoneticValue.equals(v)) {
        if (saveState) {
          remainingTokens.addLast(captureState());
        }
        posAtt.setPositionIncrement( firstAlternativeIncrement );
        firstAlternativeIncrement = 0;
        termAtt.setEmpty().append(primaryPhoneticValue);
        saveState = true;
      }

      if (alternatePhoneticValue!=null && alternatePhoneticValue.length() > 0
              && !alternatePhoneticValue.equals(primaryPhoneticValue)
              && !primaryPhoneticValue.equals(v)) {
        if (saveState) {
          remainingTokens.addLast(captureState());
          saveState = false;
        }
        posAtt.setPositionIncrement( firstAlternativeIncrement );
        termAtt.setEmpty().append(alternatePhoneticValue);
        saveState = true;
      }

      // Just one token to return, so no need to capture/restore
      // any state, simply return it.
      if (remainingTokens.isEmpty()) {
        return true;
      }

      if (saveState) {
        remainingTokens.addLast(captureState());
      }
    }
  }

  @Override
  public void reset() throws IOException {
    input.reset();
    remainingTokens.clear();
  }
}