org.apache.lucene.search.suggest.fst.WFSTCompletionLookup Maven / Gradle / Ivy
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/*
* 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.search.suggest.fst;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Set;
import org.apache.lucene.search.suggest.InputIterator;
import org.apache.lucene.search.suggest.Lookup;
import org.apache.lucene.search.suggest.SortedInputIterator;
import org.apache.lucene.store.ByteArrayDataInput;
import org.apache.lucene.store.ByteArrayDataOutput;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.Directory;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.Accountables;
import org.apache.lucene.util.ArrayUtil;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.CharsRefBuilder;
import org.apache.lucene.util.IntsRefBuilder;
import org.apache.lucene.util.OfflineSorter.ByteSequencesWriter;
import org.apache.lucene.util.fst.Builder;
import org.apache.lucene.util.fst.FST;
import org.apache.lucene.util.fst.FST.Arc;
import org.apache.lucene.util.fst.FST.BytesReader;
import org.apache.lucene.util.fst.PositiveIntOutputs;
import org.apache.lucene.util.fst.Util;
import org.apache.lucene.util.fst.Util.Result;
import org.apache.lucene.util.fst.Util.TopResults;
/**
* Suggester based on a weighted FST: it first traverses the prefix,
* then walks the n shortest paths to retrieve top-ranked
* suggestions.
*
* NOTE:
* Input weights must be between 0 and {@link Integer#MAX_VALUE}, any
* other values will be rejected.
*
* @lucene.experimental
*/
// redundant 'implements Accountable' to workaround javadocs bugs
public class WFSTCompletionLookup extends Lookup implements Accountable {
/**
* FST, weights are encoded as costs: (Integer.MAX_VALUE-weight)
*/
// NOTE: like FSTSuggester, this is really a WFSA, if you want to
// customize the code to add some output you should use PairOutputs.
private FST fst = null;
/**
* True if exact match suggestions should always be returned first.
*/
private final boolean exactFirst;
/** Number of entries the lookup was built with */
private long count = 0;
private final Directory tempDir;
private final String tempFileNamePrefix;
/**
* Calls {@link #WFSTCompletionLookup(Directory,String,boolean) WFSTCompletionLookup(null,null,true)}
*/
public WFSTCompletionLookup(Directory tempDir, String tempFileNamePrefix) {
this(tempDir, tempFileNamePrefix, true);
}
/**
* Creates a new suggester.
*
* @param exactFirst true if suggestions that match the
* prefix exactly should always be returned first, regardless
* of score. This has no performance impact, but could result
* in low-quality suggestions.
*/
public WFSTCompletionLookup(Directory tempDir, String tempFileNamePrefix, boolean exactFirst) {
this.exactFirst = exactFirst;
this.tempDir = tempDir;
this.tempFileNamePrefix = tempFileNamePrefix;
}
@Override
public void build(InputIterator iterator) throws IOException {
if (iterator.hasPayloads()) {
throw new IllegalArgumentException("this suggester doesn't support payloads");
}
if (iterator.hasContexts()) {
throw new IllegalArgumentException("this suggester doesn't support contexts");
}
count = 0;
BytesRef scratch = new BytesRef();
InputIterator iter = new WFSTInputIterator(tempDir, tempFileNamePrefix, iterator);
IntsRefBuilder scratchInts = new IntsRefBuilder();
BytesRefBuilder previous = null;
PositiveIntOutputs outputs = PositiveIntOutputs.getSingleton();
Builder builder = new Builder<>(FST.INPUT_TYPE.BYTE1, outputs);
while ((scratch = iter.next()) != null) {
long cost = iter.weight();
if (previous == null) {
previous = new BytesRefBuilder();
} else if (scratch.equals(previous.get())) {
continue; // for duplicate suggestions, the best weight is actually
// added
}
Util.toIntsRef(scratch, scratchInts);
builder.add(scratchInts.get(), cost);
previous.copyBytes(scratch);
count++;
}
fst = builder.finish();
}
@Override
public boolean store(DataOutput output) throws IOException {
output.writeVLong(count);
if (fst == null) {
return false;
}
fst.save(output, output);
return true;
}
@Override
public boolean load(DataInput input) throws IOException {
count = input.readVLong();
this.fst = new FST<>(input, input, PositiveIntOutputs.getSingleton());
return true;
}
@Override
public List lookup(CharSequence key, Set contexts, boolean onlyMorePopular, int num) {
if (contexts != null) {
throw new IllegalArgumentException("this suggester doesn't support contexts");
}
assert num > 0;
if (onlyMorePopular) {
throw new IllegalArgumentException("this suggester only works with onlyMorePopular=false");
}
if (fst == null) {
return Collections.emptyList();
}
BytesRefBuilder scratch = new BytesRefBuilder();
scratch.copyChars(key);
int prefixLength = scratch.length();
Arc arc = new Arc<>();
// match the prefix portion exactly
Long prefixOutput = null;
try {
prefixOutput = lookupPrefix(scratch.get(), arc);
} catch (IOException bogus) { throw new RuntimeException(bogus); }
if (prefixOutput == null) {
return Collections.emptyList();
}
List results = new ArrayList<>(num);
CharsRefBuilder spare = new CharsRefBuilder();
if (exactFirst && arc.isFinal()) {
spare.copyUTF8Bytes(scratch.get());
results.add(new LookupResult(spare.toString(), decodeWeight(prefixOutput + arc.nextFinalOutput())));
if (--num == 0) {
return results; // that was quick
}
}
// complete top-N
TopResults completions = null;
try {
completions = Util.shortestPaths(fst, arc, prefixOutput, weightComparator, num, !exactFirst);
assert completions.isComplete;
} catch (IOException bogus) {
throw new RuntimeException(bogus);
}
BytesRefBuilder suffix = new BytesRefBuilder();
for (Result completion : completions) {
scratch.setLength(prefixLength);
// append suffix
Util.toBytesRef(completion.input, suffix);
scratch.append(suffix);
spare.copyUTF8Bytes(scratch.get());
results.add(new LookupResult(spare.toString(), decodeWeight(completion.output)));
}
return results;
}
private Long lookupPrefix(BytesRef scratch, Arc arc) throws /*Bogus*/IOException {
assert 0 == fst.outputs.getNoOutput().longValue();
long output = 0;
BytesReader bytesReader = fst.getBytesReader();
fst.getFirstArc(arc);
byte[] bytes = scratch.bytes;
int pos = scratch.offset;
int end = pos + scratch.length;
while (pos < end) {
if (fst.findTargetArc(bytes[pos++] & 0xff, arc, arc, bytesReader) == null) {
return null;
} else {
output += arc.output().longValue();
}
}
return output;
}
/**
* Returns the weight associated with an input string,
* or null if it does not exist.
*/
public Object get(CharSequence key) {
if (fst == null) {
return null;
}
Arc arc = new Arc<>();
Long result = null;
try {
result = lookupPrefix(new BytesRef(key), arc);
} catch (IOException bogus) { throw new RuntimeException(bogus); }
if (result == null || !arc.isFinal()) {
return null;
} else {
return Integer.valueOf(decodeWeight(result + arc.nextFinalOutput()));
}
}
/** cost -> weight */
private static int decodeWeight(long encoded) {
return (int)(Integer.MAX_VALUE - encoded);
}
/** weight -> cost */
private static int encodeWeight(long value) {
if (value < 0 || value > Integer.MAX_VALUE) {
throw new UnsupportedOperationException("cannot encode value: " + value);
}
return Integer.MAX_VALUE - (int)value;
}
private static final class WFSTInputIterator extends SortedInputIterator {
WFSTInputIterator(Directory tempDir, String tempFileNamePrefix, InputIterator source) throws IOException {
super(tempDir, tempFileNamePrefix, source);
assert source.hasPayloads() == false;
}
@Override
protected void encode(ByteSequencesWriter writer, ByteArrayDataOutput output, byte[] buffer, BytesRef spare, BytesRef payload, Set contexts, long weight) throws IOException {
if (spare.length + 4 >= buffer.length) {
buffer = ArrayUtil.grow(buffer, spare.length + 4);
}
output.reset(buffer);
output.writeBytes(spare.bytes, spare.offset, spare.length);
output.writeInt(encodeWeight(weight));
writer.write(buffer, 0, output.getPosition());
}
@Override
protected long decode(BytesRef scratch, ByteArrayDataInput tmpInput) {
scratch.length -= 4; // int
// skip suggestion:
tmpInput.reset(scratch.bytes, scratch.offset+scratch.length, 4);
return tmpInput.readInt();
}
}
static final Comparator weightComparator = new Comparator () {
@Override
public int compare(Long left, Long right) {
return left.compareTo(right);
}
};
/** Returns byte size of the underlying FST. */
@Override
public long ramBytesUsed() {
return (fst == null) ? 0 : fst.ramBytesUsed();
}
@Override
public Collection getChildResources() {
if (fst == null) {
return Collections.emptyList();
} else {
return Collections.singleton(Accountables.namedAccountable("fst", fst));
}
}
@Override
public long getCount() {
return count;
}
}