/*
* 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.miscellaneous;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.util.StemmerUtil;
import java.io.IOException;
/**
* This filter folds Scandinavian characters åÅäæÄÆ->a and öÖøØ->o.
* It also discriminate against use of double vowels aa, ae, ao, oe and oo, leaving just the first one.
* <p>
* It's a semantically more destructive solution than {@link ScandinavianNormalizationFilter} but
* can in addition help with matching raksmorgas as räksmörgås.
* <p>
* blåbærsyltetøj == blåbärsyltetöj == blaabaarsyltetoej == blabarsyltetoj
* räksmörgås == ræksmørgås == ræksmörgaos == raeksmoergaas == raksmorgas
* <p>
* Background:
* Swedish åäö are in fact the same letters as Norwegian and Danish åæø and thus interchangeable
* when used between these languages. They are however folded differently when people type
* them on a keyboard lacking these characters.
* <p>
* In that situation almost all Swedish people use a, a, o instead of å, ä, ö.
* <p>
* Norwegians and Danes on the other hand usually type aa, ae and oe instead of å, æ and ø.
* Some do however use a, a, o, oo, ao and sometimes permutations of everything above.
* <p>
* This filter solves that mismatch problem, but might also cause new.
* @see ScandinavianNormalizationFilter
*/
public final class ScandinavianFoldingFilter extends TokenFilter {
public ScandinavianFoldingFilter(TokenStream input) {
super(input);
}
private final CharTermAttribute charTermAttribute = addAttribute(CharTermAttribute.class);
private static final char AA = '\u00C5'; // Å
private static final char aa = '\u00E5'; // å
private static final char AE = '\u00C6'; // Æ
private static final char ae = '\u00E6'; // æ
private static final char AE_se = '\u00C4'; // Ä
private static final char ae_se = '\u00E4'; // ä
private static final char OE = '\u00D8'; // Ø
private static final char oe = '\u00F8'; // ø
private static final char OE_se = '\u00D6'; // Ö
private static final char oe_se = '\u00F6'; //ö
@Override
public boolean incrementToken() throws IOException {
if (!input.incrementToken()) {
return false;
}
char[] buffer = charTermAttribute.buffer();
int length = charTermAttribute.length();
int i;
for (i = 0; i < length; i++) {
if (buffer[i] == aa
|| buffer[i] == ae_se
|| buffer[i] == ae) {
buffer[i] = 'a';
} else if (buffer[i] == AA
|| buffer[i] == AE_se
|| buffer[i] == AE) {
buffer[i] = 'A';
} else if (buffer[i] == oe
|| buffer[i] == oe_se) {
buffer[i] = 'o';
} else if (buffer[i] == OE
|| buffer[i] == OE_se) {
buffer[i] = 'O';
} else if (length - 1 > i) {
if ((buffer[i] == 'a' || buffer[i] == 'A')
&& (buffer[i + 1] == 'a'
|| buffer[i + 1] == 'A'
|| buffer[i + 1] == 'e'
|| buffer[i + 1] == 'E'
|| buffer[i + 1] == 'o'
|| buffer[i + 1] == 'O')
) {
length = StemmerUtil.delete(buffer, i + 1, length);
} else if ((buffer[i] == 'o' || buffer[i] == 'O')
&& (buffer[i + 1] == 'e'
|| buffer[i + 1] == 'E'
|| buffer[i + 1] == 'o'
|| buffer[i + 1] == 'O')
) {
length = StemmerUtil.delete(buffer, i + 1, length);
}
}
}
charTermAttribute.setLength(length);
return true;
}
}