package org.apache.lucene.analysis.icu;

/**
 * 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.
 */

import org.apache.lucene.analysis.TokenStream;

import com.ibm.icu.text.Normalizer2;

/**
 * A TokenFilter that applies search term folding to Unicode text,
 * applying foldings from UTR#30 Character Foldings.
 * <p>
 * This filter applies the following foldings from the report to unicode text:
 * <ul>
 * <li>Accent removal
 * <li>Case folding
 * <li>Canonical duplicates folding
 * <li>Dashes folding
 * <li>Diacritic removal (including stroke, hook, descender)
 * <li>Greek letterforms folding
 * <li>Han Radical folding
 * <li>Hebrew Alternates folding
 * <li>Jamo folding
 * <li>Letterforms folding
 * <li>Math symbol folding
 * <li>Multigraph Expansions: All
 * <li>Native digit folding
 * <li>No-break folding
 * <li>Overline folding
 * <li>Positional forms folding
 * <li>Small forms folding
 * <li>Space folding
 * <li>Spacing Accents folding
 * <li>Subscript folding
 * <li>Superscript folding
 * <li>Suzhou Numeral folding
 * <li>Symbol folding
 * <li>Underline folding
 * <li>Vertical forms folding
 * <li>Width folding
 * </ul>
 * <p>
 * Additionally, Default Ignorables are removed, and text is normalized to NFKC.
 * All foldings, case folding, and normalization mappings are applied recursively
 * to ensure a fully folded and normalized result.
 * </p>
 */
public final class ICUFoldingFilter extends ICUNormalizer2Filter {
  private static final Normalizer2 normalizer =  Normalizer2.getInstance(
      ICUFoldingFilter.class.getResourceAsStream("utr30.nrm"), 
      "utr30", Normalizer2.Mode.COMPOSE);
  
  /**
   * Create a new ICUFoldingFilter on the specified input
   */
  public ICUFoldingFilter(TokenStream input) {
    super(input, normalizer);
  }
}
