content: package org.apache.solr.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;
  
  import org.apache.lucene.analysis.TokenFilter;
  import org.apache.lucene.analysis.TokenStream;
  import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
  import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
  
  /**
   * This class produces a special form of reversed tokens, suitable for
   * better handling of leading wildcards. Tokens from the input TokenStream
   * are reversed and prepended with a special "reversed" marker character.
   * If <code>withOriginal<code> argument is <code>true</code> then first the
   * original token is returned, and then the reversed token (with
   * <code>positionIncrement == 0</code>) is returned. Otherwise only reversed
   * tokens are returned.
   * <p>Note: this filter doubles the number of tokens in the input stream when
   * <code>withOriginal == true</code>, which proportionally increases the size
   * of postings and term dictionary in the index.
   */
  public final class ReversedWildcardFilter extends TokenFilter {
    
    private boolean withOriginal;
    private char markerChar;
    private State save;
    private CharTermAttribute termAtt;
    private PositionIncrementAttribute posAtt;
  
    protected ReversedWildcardFilter(TokenStream input, boolean withOriginal, char markerChar) {
      super(input);
      this.termAtt = addAttribute(CharTermAttribute.class);
      this.posAtt = addAttribute(PositionIncrementAttribute.class);
      this.withOriginal = withOriginal;
      this.markerChar = markerChar;
    }
  
    @Override
    public boolean incrementToken() throws IOException {
      if( save != null ) {
        // clearAttributes();  // not currently necessary
        restoreState(save);
        save = null;
        return true;
      }
  
      if (!input.incrementToken()) return false;
  
      // pass through zero-length terms
      int oldLen = termAtt.length();
      if (oldLen ==0) return true;
      int origOffset = posAtt.getPositionIncrement();
      if (withOriginal == true){
        posAtt.setPositionIncrement(0);
        save = captureState();
      }
      char [] buffer = termAtt.resizeBuffer(oldLen + 1);
      buffer[oldLen] = markerChar;
      reverse(buffer, 0, oldLen + 1);
  
      posAtt.setPositionIncrement(origOffset);
      termAtt.copyBuffer(buffer, 0, oldLen +1);
      return true;
    }
    
  
    /**
     * Partially reverses the given input buffer in-place from the given offset
     * up to the given length, keeping surrogate pairs in the correct (non-reversed) order.
     * @param buffer the input char array to reverse
     * @param start the offset from where to reverse the buffer
     * @param len the length in the buffer up to where the
     *        buffer should be reversed
     */
    public static void reverse(final char[] buffer, final int start, final int len) {
      /* modified version of Apache Harmony AbstractStringBuilder reverse0() */
      if (len < 2)
        return;
      int end = (start + len) - 1;
      char frontHigh = buffer[start];
      char endLow = buffer[end];
      boolean allowFrontSur = true, allowEndSur = true;
      final int mid = start + (len >> 1);
      for (int i = start; i < mid; ++i, --end) {
        final char frontLow = buffer[i + 1];
        final char endHigh = buffer[end - 1];
        final boolean surAtFront = allowFrontSur
            && Character.isSurrogatePair(frontHigh, frontLow);
        if (surAtFront && (len < 3)) {
          // nothing to do since surAtFront is allowed and 1 char left
          return;
        }
        final boolean surAtEnd = allowEndSur
            && Character.isSurrogatePair(endHigh, endLow);
        allowFrontSur = allowEndSur = true;
        if (surAtFront == surAtEnd) {
          if (surAtFront) {
            // both surrogates
            buffer[end] = frontLow;
            buffer[--end] = frontHigh;
            buffer[i] = endHigh;
            buffer[++i] = endLow;
            frontHigh = buffer[i + 1];
            endLow = buffer[end - 1];
          } else {
            // neither surrogates
            buffer[end] = frontHigh;
            buffer[i] = endLow;
            frontHigh = frontLow;
            endLow = endHigh;
          }
        } else {
          if (surAtFront) {
            // surrogate only at the front
            buffer[end] = frontLow;
            buffer[i] = endLow;
            endLow = endHigh;
            allowFrontSur = false;
          } else {
            // surrogate only at the end
            buffer[end] = frontHigh;
            buffer[i] = endHigh;
            frontHigh = frontLow;
            allowEndSur = false;
          }
        }
      }
      if ((len & 0x01) == 1 && !(allowFrontSur && allowEndSur)) {
        // only if odd length
        buffer[end] = allowFrontSur ? endLow : frontHigh;
      }
    }
  
  }
  