lucene/analysis/common/src/java/org/apache/lucene/analysis/ga/IrishLowerCaseFilter.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.ga;


import java.io.IOException;

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;

/**
 * Normalises token text to lower case, handling t-prothesis
 * and n-eclipsis (i.e., that 'nAthair' should become 'n-athair')
 */
public final class IrishLowerCaseFilter extends TokenFilter {
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);

  /**
   * Create an IrishLowerCaseFilter that normalises Irish token text.
   */
  public IrishLowerCaseFilter(TokenStream in) {
    super(in);
  }
  
  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      char[] chArray = termAtt.buffer();
      int chLen = termAtt.length();
      int idx = 0;

      if (chLen > 1 && (chArray[0] == 'n' || chArray[0] == 't') && isUpperVowel(chArray[1])) {
        chArray = termAtt.resizeBuffer(chLen + 1);
        for (int i = chLen; i > 1; i--) {
          chArray[i] = chArray[i - 1];
        }
        chArray[1] = '-';
        termAtt.setLength(chLen + 1);
        idx = 2;
        chLen = chLen + 1;
      }

      for (int i = idx; i < chLen;) {
        i += Character.toChars(Character.toLowerCase(chArray[i]), chArray, i);
       }
      return true;
    } else {
      return false;
    }
  }
  
  private boolean isUpperVowel (int v) {
    switch (v) {
      case 'A':
      case 'E':
      case 'I':
      case 'O':
      case 'U':
      // vowels with acute accent (fada)
      case '\u00c1':
      case '\u00c9':
      case '\u00cd':
      case '\u00d3':
      case '\u00da':
        return true;
      default:
        return false;
    }
  }
}