content: package org.apache.lucene.analysis.ngram;
  
  /**
   * 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;
  
  import org.apache.lucene.analysis.TokenFilter;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  
  /**
   * Tokenizes the input into n-grams of the given size(s).
   */
  public final class NGramTokenFilter extends TokenFilter {
    public static final int DEFAULT_MIN_NGRAM_SIZE = 1;
    public static final int DEFAULT_MAX_NGRAM_SIZE = 2;
  
    private int minGram, maxGram;
    
    private char[] curTermBuffer;
    private int curTermLength;
    private int curGramSize;
    private int curPos;
    private int tokStart;
    
    private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
    private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
  
    /**
     * Creates NGramTokenFilter with given min and max n-grams.
     * @param input {@link TokenStream} holding the input to be tokenized
     * @param minGram the smallest n-gram to generate
     * @param maxGram the largest n-gram to generate
     */
    public NGramTokenFilter(TokenStream input, int minGram, int maxGram) {
      super(input);
      if (minGram < 1) {
        throw new IllegalArgumentException("minGram must be greater than zero");
      }
      if (minGram > maxGram) {
        throw new IllegalArgumentException("minGram must not be greater than maxGram");
      }
      this.minGram = minGram;
      this.maxGram = maxGram;
    }
  
    /**
     * Creates NGramTokenFilter with default min and max n-grams.
     * @param input {@link TokenStream} holding the input to be tokenized
     */
    public NGramTokenFilter(TokenStream input) {
      this(input, DEFAULT_MIN_NGRAM_SIZE, DEFAULT_MAX_NGRAM_SIZE);
    }
  
    /** Returns the next token in the stream, or null at EOS. */
    @Override
    public final boolean incrementToken() throws IOException {
      while (true) {
        if (curTermBuffer == null) {
          if (!input.incrementToken()) {
            return false;
          } else {
            curTermBuffer = termAtt.buffer().clone();
            curTermLength = termAtt.length();
            curGramSize = minGram;
            curPos = 0;
            tokStart = offsetAtt.startOffset();
          }
        }
        while (curGramSize <= maxGram) {
          while (curPos+curGramSize <= curTermLength) {     // while there is input
            clearAttributes();
            termAtt.copyBuffer(curTermBuffer, curPos, curGramSize);
            offsetAtt.setOffset(tokStart + curPos, tokStart + curPos + curGramSize);
            curPos++;
            return true;
          }
          curGramSize++;                         // increase n-gram size
          curPos = 0;
        }
        curTermBuffer = null;
      }
    }
  
    @Override
    public void reset() throws IOException {
      super.reset();
      curTermBuffer = null;
    }
  }
  