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+/*
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+ * Licensed to Elasticsearch under one or more contributor
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+ * license agreements. See the NOTICE file distributed with
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+ * this work for additional information regarding copyright
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+ * ownership. Elasticsearch licenses this file to you under
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+ * the Apache License, Version 2.0 (the "License"); you may
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+ * not use this file except in compliance with the License.
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+ * You may obtain a copy of the License at
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+ *
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+ * http://www.apache.org/licenses/LICENSE-2.0
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+ *
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+ * Unless required by applicable law or agreed to in writing,
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+ * software distributed under the License is distributed on an
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+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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+ * KIND, either express or implied. See the License for the
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+ * specific language governing permissions and limitations
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+ * under the License.
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+ */
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+package org.elasticsearch.search.suggest.completion;
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+
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+import org.apache.lucene.analysis.CharArraySet;
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+import org.apache.lucene.index.LeafReaderContext;
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+import org.apache.lucene.search.CollectionTerminatedException;
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+import org.apache.lucene.search.TotalHits;
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+import org.apache.lucene.search.suggest.Lookup;
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+import org.apache.lucene.search.suggest.document.TopSuggestDocs;
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+import org.apache.lucene.search.suggest.document.TopSuggestDocsCollector;
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+import org.apache.lucene.util.PriorityQueue;
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+
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+import java.io.IOException;
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+import java.util.ArrayList;
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+import java.util.Collections;
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+import java.util.HashMap;
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+import java.util.List;
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+import java.util.Map;
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+
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+/**
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+ *
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+ * Custom {@link TopSuggestDocsCollector} that returns top documents from the completion suggester.
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+ * <p>
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+ * TODO: this should be refactored when https://issues.apache.org/jira/browse/LUCENE-8529 is fixed.
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+ * Unlike the parent class, this collector uses the surface form to tie-break suggestions with identical
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+ * scores.
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+ * <p>
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+ * This collector groups suggestions coming from the same document but matching different contexts
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+ * or surface form together. When different contexts or surface forms match the same suggestion form only
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+ * the best one per document (sorted by weight) is kept.
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+ * <p>
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+ * This collector is also able to filter duplicate suggestion coming from different documents.
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+ * In order to keep this feature fast, the de-duplication of suggestions with different contexts is done
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+ * only on the top N*num_contexts (where N is the number of documents to return) suggestions per segment.
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+ * This means that skip_duplicates will visit at most N*num_contexts suggestions per segment to find unique suggestions
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+ * that match the input. If more than N*num_contexts suggestions are duplicated with different contexts this collector
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+ * will not be able to return more than one suggestion even when N is greater than 1.
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+ **/
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+class TopSuggestGroupDocsCollector extends TopSuggestDocsCollector {
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+ private final class SuggestScoreDocPriorityQueue extends PriorityQueue<TopSuggestDocs.SuggestScoreDoc> {
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+ /**
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+ * Creates a new priority queue of the specified size.
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+ */
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+ private SuggestScoreDocPriorityQueue(int size) {
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+ super(size);
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+ }
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+
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+ @Override
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+ protected boolean lessThan(TopSuggestDocs.SuggestScoreDoc a, TopSuggestDocs.SuggestScoreDoc b) {
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+ if (a.score == b.score) {
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+ // tie break by completion key
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+ int cmp = Lookup.CHARSEQUENCE_COMPARATOR.compare(a.key, b.key);
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+ // prefer smaller doc id, in case of a tie
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+ return cmp != 0 ? cmp > 0 : a.doc > b.doc;
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+ }
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+ return a.score < b.score;
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+ }
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+
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+ /**
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+ * Returns the top N results in descending order.
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+ */
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+ public TopSuggestDocs.SuggestScoreDoc[] getResults() {
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+ int size = size();
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+ TopSuggestDocs.SuggestScoreDoc[] res = new TopSuggestDocs.SuggestScoreDoc[size];
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+ for (int i = size - 1; i >= 0; i--) {
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+ res[i] = pop();
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+ }
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+ return res;
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+ }
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+ }
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+
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+
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+ private final SuggestScoreDocPriorityQueue priorityQueue;
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+ private final int num;
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+
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+ /** Only set if we are deduplicating hits: holds all per-segment hits until the end, when we dedup them */
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+ private final List<TopSuggestDocs.SuggestScoreDoc> pendingResults;
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+
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+ /** Only set if we are deduplicating hits: holds all surface forms seen so far in the current segment */
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+ final CharArraySet seenSurfaceForms;
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+
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+ /** Document base offset for the current Leaf */
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+ protected int docBase;
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+
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+ private Map<Integer, List<CharSequence>> docContexts = new HashMap<>();
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+
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+ /**
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+ * Sole constructor
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+ *
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+ * Collects at most <code>num</code> completions
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+ * with corresponding document and weight
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+ */
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+ TopSuggestGroupDocsCollector(int num, boolean skipDuplicates) {
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+ super(1, skipDuplicates);
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+ if (num <= 0) {
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+ throw new IllegalArgumentException("'num' must be > 0");
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+ }
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+ this.num = num;
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+ this.priorityQueue = new SuggestScoreDocPriorityQueue(num);
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+ if (skipDuplicates) {
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+ seenSurfaceForms = new CharArraySet(num, false);
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+ pendingResults = new ArrayList<>();
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+ } else {
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+ seenSurfaceForms = null;
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+ pendingResults = null;
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+ }
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+ }
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+
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+ /**
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+ * Returns the contexts associated with the provided <code>doc</code>.
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+ */
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+ public List<CharSequence> getContexts(int doc) {
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+ return docContexts.getOrDefault(doc, Collections.emptyList());
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+ }
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+
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+ @Override
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+ protected boolean doSkipDuplicates() {
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+ return seenSurfaceForms != null;
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+ }
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+
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+ @Override
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+ public int getCountToCollect() {
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+ return num;
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+ }
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+
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+ @Override
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+ protected void doSetNextReader(LeafReaderContext context) throws IOException {
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+ docBase = context.docBase;
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+ if (seenSurfaceForms != null) {
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+ seenSurfaceForms.clear();
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+ // NOTE: this also clears the priorityQueue:
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+ for (TopSuggestDocs.SuggestScoreDoc hit : priorityQueue.getResults()) {
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+ pendingResults.add(hit);
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+ }
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+ }
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+ }
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+
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+ @Override
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+ public void collect(int docID, CharSequence key, CharSequence context, float score) throws IOException {
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+ int globalDoc = docID + docBase;
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+ boolean isDuplicate = docContexts.containsKey(globalDoc);
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+ List<CharSequence> contexts = docContexts.computeIfAbsent(globalDoc, k -> new ArrayList<>());
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+ if (context != null) {
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+ contexts.add(context);
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+ }
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+ if (isDuplicate) {
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+ return;
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+ }
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+ TopSuggestDocs.SuggestScoreDoc current = new TopSuggestDocs.SuggestScoreDoc(globalDoc, key, context, score);
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+ if (current == priorityQueue.insertWithOverflow(current)) {
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+ // if the current SuggestScoreDoc has overflown from pq,
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+ // we can assume all of the successive collections from
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+ // this leaf will be overflown as well
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+ // TODO: reuse the overflow instance?
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+ throw new CollectionTerminatedException();
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+ }
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+ }
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+
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+ @Override
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+ public TopSuggestDocs get() throws IOException {
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+
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+ TopSuggestDocs.SuggestScoreDoc[] suggestScoreDocs;
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+
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+ if (seenSurfaceForms != null) {
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+ // NOTE: this also clears the priorityQueue:
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+ for (TopSuggestDocs.SuggestScoreDoc hit : priorityQueue.getResults()) {
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+ pendingResults.add(hit);
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+ }
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+
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+ // Deduplicate all hits: we already dedup'd efficiently within each segment by
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+ // truncating the FST top paths search, but across segments there may still be dups:
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+ seenSurfaceForms.clear();
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+
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+ // TODO: we could use a priority queue here to make cost O(N * log(num)) instead of O(N * log(N)), where N = O(num *
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+ // numSegments), but typically numSegments is smallish and num is smallish so this won't matter much in practice:
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+
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+ Collections.sort(pendingResults,
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+ (a, b) -> {
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+ // sort by higher score
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+ int cmp = Float.compare(b.score, a.score);
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+ if (cmp == 0) {
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+ // tie break by completion key
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+ cmp = Lookup.CHARSEQUENCE_COMPARATOR.compare(a.key, b.key);
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+ if (cmp == 0) {
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+ // prefer smaller doc id, in case of a tie
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+ cmp = Integer.compare(a.doc, b.doc);
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+ }
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+ }
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+ return cmp;
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+ });
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+
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+ List<TopSuggestDocs.SuggestScoreDoc> hits = new ArrayList<>();
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+
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+ for (TopSuggestDocs.SuggestScoreDoc hit : pendingResults) {
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+ if (seenSurfaceForms.contains(hit.key) == false) {
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+ seenSurfaceForms.add(hit.key);
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+ hits.add(hit);
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+ if (hits.size() == num) {
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+ break;
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+ }
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+ }
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+ }
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+ suggestScoreDocs = hits.toArray(new TopSuggestDocs.SuggestScoreDoc[0]);
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+ } else {
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+ suggestScoreDocs = priorityQueue.getResults();
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+ }
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+
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+ if (suggestScoreDocs.length > 0) {
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+ return new TopSuggestDocs(new TotalHits(suggestScoreDocs.length, TotalHits.Relation.EQUAL_TO), suggestScoreDocs);
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+ } else {
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+ return TopSuggestDocs.EMPTY;
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+ }
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+ }
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+
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+}
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Jim Ferenczi