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.TokenFilter;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  
  import java.io.IOException;
  
  /**
   * Tokenizes the given token into n-grams of given size(s).
   * <p>
   * This {@link TokenFilter} create n-grams from the beginning edge or ending edge of a input token.
   * </p>
   */
  public final class EdgeNGramTokenFilter extends TokenFilter {
    public static final Side DEFAULT_SIDE = Side.FRONT;
    public static final int DEFAULT_MAX_GRAM_SIZE = 1;
    public static final int DEFAULT_MIN_GRAM_SIZE = 1;
  
    /** Specifies which side of the input the n-gram should be generated from */
    public static enum Side {
  
      /** Get the n-gram from the front of the input */
      FRONT {
        @Override
        public String getLabel() { return "front"; }
      },
  
      /** Get the n-gram from the end of the input */
      BACK  {
        @Override
        public String getLabel() { return "back"; }
      };
  
      public abstract String getLabel();
  
      // Get the appropriate Side from a string
      public static Side getSide(String sideName) {
        if (FRONT.getLabel().equals(sideName)) {
          return FRONT;
        }
        if (BACK.getLabel().equals(sideName)) {
          return BACK;
        }
        return null;
      }
    }
  
    private final int minGram;
    private final int maxGram;
    private Side side;
    private char[] curTermBuffer;
    private int curTermLength;
    private int curGramSize;
    private int tokStart;
    
    private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
    private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
  
    /**
     * Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range
     *
     * @param input {@link TokenStream} holding the input to be tokenized
     * @param side the {@link Side} from which to chop off an n-gram
     * @param minGram the smallest n-gram to generate
     * @param maxGram the largest n-gram to generate
     */
    public EdgeNGramTokenFilter(TokenStream input, Side side, int minGram, int maxGram) {
      super(input);
  
      if (side == null) {
        throw new IllegalArgumentException("sideLabel must be either front or back");
      }
  
      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;
      this.side = side;
    }
  
    /**
     * Creates EdgeNGramTokenFilter that can generate n-grams in the sizes of the given range
     *
     * @param input {@link TokenStream} holding the input to be tokenized
     * @param sideLabel the name of the {@link Side} from which to chop off an n-gram
     * @param minGram the smallest n-gram to generate
     * @param maxGram the largest n-gram to generate
     */
    public EdgeNGramTokenFilter(TokenStream input, String sideLabel, int minGram, int maxGram) {
      this(input, Side.getSide(sideLabel), minGram, maxGram);
    }
  
    @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;
            tokStart = offsetAtt.startOffset();
          }
        }
        if (curGramSize <= maxGram) {
          if (! (curGramSize > curTermLength         // if the remaining input is too short, we can't generate any n-grams
              || curGramSize > maxGram)) {       // if we have hit the end of our n-gram size range, quit
            // grab gramSize chars from front or back
            int start = side == Side.FRONT ? 0 : curTermLength - curGramSize;
            int end = start + curGramSize;
            clearAttributes();
            offsetAtt.setOffset(tokStart + start, tokStart + end);
            termAtt.copyBuffer(curTermBuffer, start, curGramSize);
            curGramSize++;
            return true;
          }
        }
        curTermBuffer = null;
      }
    }
  
    @Override
    public void reset() throws IOException {
      super.reset();
      curTermBuffer = null;
    }
  }
  