lucene/analysis/common/src/java/org/apache/lucene/analysis/core/DecimalDigitFilter.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.core;

import java.io.IOException;
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;

/**
 * Folds all Unicode digits in {@code [:General_Category=Decimal_Number:]} to Basic Latin digits
 * ({@code 0-9}).
 */
public final class DecimalDigitFilter extends TokenFilter {
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);

  /** Creates a new DecimalDigitFilter over {@code input} */
  public DecimalDigitFilter(TokenStream input) {
    super(input);
  }

  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      char buffer[] = termAtt.buffer();
      int length = termAtt.length();

      for (int i = 0; i < length; i++) {
        int ch = Character.codePointAt(buffer, i, length);
        // look for digits outside of basic latin
        if (ch > 0x7F && Character.isDigit(ch)) {
          // replace with equivalent basic latin digit
          buffer[i] = (char) ('0' + Character.getNumericValue(ch));
          // if the original was supplementary, shrink the string
          if (ch > 0xFFFF) {
            length = StemmerUtil.delete(buffer, i + 1, length);
            termAtt.setLength(length);
          }
        }
      }

      return true;
    } else {
      return false;
    }
  }
}