package org.apache.lucene.analysis;

/**
 * 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 java.io.IOException;

/** Transforms the token stream as per the Porter stemming algorithm.
    Note: the input to the stemming filter must already be in lower case,
    so you will need to use LowerCaseFilter or LowerCaseTokenizer farther
    down the Tokenizer chain in order for this to work properly!
    <P>
    To use this filter with other analyzers, you'll want to write an
    Analyzer class that sets up the TokenStream chain as you want it.
    To use this with LowerCaseTokenizer, for example, you'd write an
    analyzer like this:
    <P>
    <PRE>
    class MyAnalyzer extends Analyzer {
      public final TokenStream tokenStream(String fieldName, Reader reader) {
        return new PorterStemFilter(new LowerCaseTokenizer(reader));
      }
    }
    </PRE>
*/
public final class PorterStemFilter extends TokenFilter {
  private PorterStemmer stemmer;

  public PorterStemFilter(TokenStream in) {
    super(in);
    stemmer = new PorterStemmer();
  }

  /** Returns the next input Token, after being stemmed */
  public final Token next() throws IOException {
    Token token = input.next();
    if (token == null)
      return null;
    else {
      String s = stemmer.stem(token.termText);
      if (s != token.termText) // Yes, I mean object reference comparison here
  	    token.termText = s;
      return token;
    }
  }
}