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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.search.uhighlight;
import java.text.BreakIterator;
import java.text.CharacterIterator;
import java.util.Locale;
/**
* A custom break iterator that is used to find break-delimited passages bounded by
* a provided maximum length in the {@link UnifiedHighlighter} context.
* This class uses a {@link BreakIterator} to find the last break after the provided offset
* that would create a passage smaller than maxLen.
* If the {@link BreakIterator} cannot find a passage smaller than the maximum length,
* a secondary break iterator is used to re-split the passage at the first boundary after
* maximum length.
*
* This is useful to split passages created by {@link BreakIterator}s like `sentence` that
* can create big outliers on semi-structured text.
*
*
* WARNING: This break iterator is designed to work with the {@link UnifiedHighlighter}.
*
* TODO: We should be able to create passages incrementally, starting from the offset of the first match and expanding or not
* depending on the offsets of subsequent matches. This is currently impossible because {@link FieldHighlighter} uses
* only the first matching offset to derive the start and end of each passage.
**/
public class BoundedBreakIteratorScanner extends BreakIterator {
private final BreakIterator mainBreak;
private final BreakIterator innerBreak;
private final int maxLen;
private int lastPrecedingOffset = -1;
private int windowStart = -1;
private int windowEnd = -1;
private int innerStart = -1;
private int innerEnd = 0;
private BoundedBreakIteratorScanner(BreakIterator mainBreak,
BreakIterator innerBreak,
int maxLen) {
this.mainBreak = mainBreak;
this.innerBreak = innerBreak;
this.maxLen = maxLen;
}
@Override
public CharacterIterator getText() {
return mainBreak.getText();
}
@Override
public void setText(CharacterIterator newText) {
reset();
mainBreak.setText(newText);
innerBreak.setText(newText);
}
@Override
public void setText(String newText) {
reset();
mainBreak.setText(newText);
innerBreak.setText(newText);
}
private void reset() {
lastPrecedingOffset = -1;
windowStart = -1;
windowEnd = -1;
innerStart = -1;
innerEnd = 0;
}
/**
* Must be called with increasing offset. See {@link FieldHighlighter} for usage.
*/
@Override
public int preceding(int offset) {
if (offset < lastPrecedingOffset) {
throw new IllegalArgumentException("offset < lastPrecedingOffset: " +
"usage doesn't look like UnifiedHighlighter");
}
if (offset > windowStart && offset < windowEnd) {
innerStart = innerEnd;
innerEnd = windowEnd;
} else {
windowStart = innerStart = mainBreak.preceding(offset);
windowEnd = innerEnd = mainBreak.following(offset - 1);
// expand to next break until we reach maxLen
while (innerEnd - innerStart < maxLen) {
int newEnd = mainBreak.following(innerEnd);
if (newEnd == DONE || (newEnd - innerStart) > maxLen) {
break;
}
windowEnd = innerEnd = newEnd;
}
}
if (innerEnd - innerStart > maxLen) {
// the current split is too big,
// so starting from the current term we try to find boundaries on the left first
if (offset - maxLen > innerStart) {
innerStart = Math.max(innerStart,
innerBreak.preceding(offset - maxLen));
}
// and then we try to expand the passage to the right with the remaining size
int remaining = Math.max(0, maxLen - (offset - innerStart));
if (offset + remaining < windowEnd) {
innerEnd = Math.min(windowEnd,
innerBreak.following(offset + remaining));
}
}
lastPrecedingOffset = offset - 1;
return innerStart;
}
/**
* Can be invoked only after a call to preceding(offset+1).
* See {@link FieldHighlighter} for usage.
*/
@Override
public int following(int offset) {
if (offset != lastPrecedingOffset || innerEnd == -1) {
throw new IllegalArgumentException("offset != lastPrecedingOffset: " +
"usage doesn't look like UnifiedHighlighter");
}
return innerEnd;
}
/**
* Returns a {@link BreakIterator#getSentenceInstance(Locale)} bounded to maxLen.
* Secondary boundaries are found using a {@link BreakIterator#getWordInstance(Locale)}.
*/
public static BreakIterator getSentence(Locale locale, int maxLen) {
final BreakIterator sBreak = BreakIterator.getSentenceInstance(locale);
final BreakIterator wBreak = BreakIterator.getWordInstance(locale);
return new BoundedBreakIteratorScanner(sBreak, wBreak, maxLen);
}
@Override
public int current() {
// Returns the last offset of the current split
return this.innerEnd;
}
@Override
public int first() {
throw new IllegalStateException("first() should not be called in this context");
}
@Override
public int next() {
throw new IllegalStateException("next() should not be called in this context");
}
@Override
public int last() {
throw new IllegalStateException("last() should not be called in this context");
}
@Override
public int next(int n) {
throw new IllegalStateException("next(n) should not be called in this context");
}
@Override
public int previous() {
throw new IllegalStateException("previous() should not be called in this context");
}
}