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 org.apache.lucene.analysis.Tokenizer;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
  import org.apache.lucene.util.AttributeSource;
  
  import java.io.IOException;
  import java.io.Reader;
  
  /**
   * Tokenizes the input into n-grams of the given size(s).
   */
  public final class NGramTokenizer extends Tokenizer {
    public static final int DEFAULT_MIN_NGRAM_SIZE = 1;
    public static final int DEFAULT_MAX_NGRAM_SIZE = 2;
  
    private int minGram, maxGram;
    private int gramSize;
    private int pos = 0;
    private int inLen;
    private String inStr;
    private boolean started = false;
    
    private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
    private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
  
    /**
     * Creates NGramTokenizer with given min and max n-grams.
     * @param input {@link Reader} holding the input to be tokenized
     * @param minGram the smallest n-gram to generate
     * @param maxGram the largest n-gram to generate
     */
    public NGramTokenizer(Reader input, int minGram, int maxGram) {
      super(input);
      init(minGram, maxGram);
    }
  
    /**
     * Creates NGramTokenizer with given min and max n-grams.
     * @param source {@link AttributeSource} to use
     * @param input {@link Reader} holding the input to be tokenized
     * @param minGram the smallest n-gram to generate
     * @param maxGram the largest n-gram to generate
     */
    public NGramTokenizer(AttributeSource source, Reader input, int minGram, int maxGram) {
      super(source, input);
      init(minGram, maxGram);
    }
  
    /**
     * Creates NGramTokenizer with given min and max n-grams.
     * @param factory {@link org.apache.lucene.util.AttributeSource.AttributeFactory} to use
     * @param input {@link Reader} holding the input to be tokenized
     * @param minGram the smallest n-gram to generate
     * @param maxGram the largest n-gram to generate
     */
    public NGramTokenizer(AttributeFactory factory, Reader input, int minGram, int maxGram) {
      super(factory, input);
      init(minGram, maxGram);
    }
  
    /**
     * Creates NGramTokenizer with default min and max n-grams.
     * @param input {@link Reader} holding the input to be tokenized
     */
    public NGramTokenizer(Reader input) {
      this(input, DEFAULT_MIN_NGRAM_SIZE, DEFAULT_MAX_NGRAM_SIZE);
    }
    
    private void init(int minGram, int maxGram) {
      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;
    }
  
    /** Returns the next token in the stream, or null at EOS. */
    @Override
    public final boolean incrementToken() throws IOException {
      clearAttributes();
      if (!started) {
        started = true;
        gramSize = minGram;
        char[] chars = new char[1024];
        input.read(chars);
        inStr = new String(chars).trim();  // remove any trailing empty strings 
        inLen = inStr.length();
      }
  
      if (pos+gramSize > inLen) {            // if we hit the end of the string
        pos = 0;                           // reset to beginning of string
        gramSize++;                        // increase n-gram size
        if (gramSize > maxGram)            // we are done
          return false;
        if (pos+gramSize > inLen)
          return false;
      }
  
      int oldPos = pos;
      pos++;
      termAtt.setEmpty().append(inStr, oldPos, oldPos+gramSize);
      offsetAtt.setOffset(correctOffset(oldPos), correctOffset(oldPos+gramSize));
      return true;
    }
    
    @Override
    public final void end() {
      // set final offset
      final int finalOffset = inLen;
      this.offsetAtt.setOffset(finalOffset, finalOffset);
    }    
    
    @Override
    public void reset(Reader input) throws IOException {
      super.reset(input);
      reset();
    }
  
    @Override
    public void reset() throws IOException {
      super.reset();
      started = false;
      pos = 0;
    }
  }
  