/*
* 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.
*/
package org.apache.lucene.analysis.reverse;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import java.io.IOException;
/**
* Reverse token string, for example "country" => "yrtnuoc".
* <p>
* If <code>marker</code> is supplied, then tokens will be also prepended by
* that character. For example, with a marker of \u0001, "country" =>
* "\u0001yrtnuoc". This is useful when implementing efficient leading
* wildcards search.
*/
public final class ReverseStringFilter extends TokenFilter {
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final char marker;
private static final char NOMARKER = '\uFFFF';
/**
* Example marker character: U+0001 (START OF HEADING)
*/
public static final char START_OF_HEADING_MARKER = '\u0001';
/**
* Example marker character: U+001F (INFORMATION SEPARATOR ONE)
*/
public static final char INFORMATION_SEPARATOR_MARKER = '\u001F';
/**
* Example marker character: U+EC00 (PRIVATE USE AREA: EC00)
*/
public static final char PUA_EC00_MARKER = '\uEC00';
/**
* Example marker character: U+200F (RIGHT-TO-LEFT MARK)
*/
public static final char RTL_DIRECTION_MARKER = '\u200F';
/**
* Create a new ReverseStringFilter that reverses all tokens in the
* supplied {@link TokenStream}.
* <p>
* The reversed tokens will not be marked.
* </p>
*
* @param in {@link TokenStream} to filter
*/
public ReverseStringFilter(TokenStream in) {
this(in, NOMARKER);
}
/**
* Create a new ReverseStringFilter that reverses and marks all tokens in the
* supplied {@link TokenStream}.
* <p>
* The reversed tokens will be prepended (marked) by the <code>marker</code>
* character.
* </p>
*
* @param in {@link TokenStream} to filter
* @param marker A character used to mark reversed tokens
*/
public ReverseStringFilter(TokenStream in, char marker) {
super(in);
this.marker = marker;
}
@Override
public boolean incrementToken() throws IOException {
if (input.incrementToken()) {
int len = termAtt.length();
if (marker != NOMARKER) {
len++;
termAtt.resizeBuffer(len);
termAtt.buffer()[len - 1] = marker;
}
reverse( termAtt.buffer(), 0, len );
termAtt.setLength(len);
return true;
} else {
return false;
}
}
/**
* Reverses the given input string
*
* @param input the string to reverse
* @return the given input string in reversed order
*/
public static String reverse(final String input ){
final char[] charInput = input.toCharArray();
reverse( charInput, 0, charInput.length );
return new String( charInput );
}
/**
* Reverses the given input buffer in-place
* @param buffer the input char array to reverse
*/
public static void reverse(final char[] buffer) {
reverse(buffer, 0, buffer.length);
}
/**
* Partially reverses the given input buffer in-place from offset 0
* up to the given length.
* @param buffer the input char array to reverse
* @param len the length in the buffer up to where the
* buffer should be reversed
*/
public static void reverse(final char[] buffer, final int len) {
reverse( buffer, 0, len );
}
/**
* Partially reverses the given input buffer in-place from the given offset
* up to the given length.
* @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;
}
}
}