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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.
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package org.elasticsearch.search.aggregations.bucket.nested;

import com.carrotsearch.hppc.LongIntHashMap;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.join.BitSetProducer;
import org.apache.lucene.util.BitSet;
import org.elasticsearch.common.ParseField;
import org.elasticsearch.common.lucene.search.Queries;
import org.elasticsearch.index.mapper.ObjectMapper;
import org.elasticsearch.search.aggregations.Aggregator;
import org.elasticsearch.search.aggregations.AggregatorFactories;
import org.elasticsearch.search.aggregations.InternalAggregation;
import org.elasticsearch.search.aggregations.LeafBucketCollector;
import org.elasticsearch.search.aggregations.LeafBucketCollectorBase;
import org.elasticsearch.search.aggregations.bucket.SingleBucketAggregator;
import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
import org.elasticsearch.search.internal.SearchContext;

import java.io.IOException;
import java.util.List;
import java.util.Map;

public class ReverseNestedAggregator extends SingleBucketAggregator {

    static final ParseField PATH_FIELD = new ParseField("path");

    private final Query parentFilter;
    private final BitSetProducer parentBitsetProducer;

    public ReverseNestedAggregator(String name, AggregatorFactories factories, ObjectMapper objectMapper,
            SearchContext context, Aggregator parent, List<PipelineAggregator> pipelineAggregators, Map<String, Object> metaData)
            throws IOException {
        super(name, factories, context, parent, pipelineAggregators, metaData);
        if (objectMapper == null) {
            parentFilter = Queries.newNonNestedFilter();
        } else {
            parentFilter = objectMapper.nestedTypeFilter();
        }
        parentBitsetProducer = context.bitsetFilterCache().getBitSetProducer(parentFilter);
    }

    @Override
    protected LeafBucketCollector getLeafCollector(LeafReaderContext ctx, final LeafBucketCollector sub) throws IOException {
        // In ES if parent is deleted, then also the children are deleted, so the child docs this agg receives
        // must belong to parent docs that is alive. For this reason acceptedDocs can be null here.
        final BitSet parentDocs = parentBitsetProducer.getBitSet(ctx);
        if (parentDocs == null) {
            return LeafBucketCollector.NO_OP_COLLECTOR;
        }
        final LongIntHashMap bucketOrdToLastCollectedParentDoc = new LongIntHashMap(32);
        return new LeafBucketCollectorBase(sub, null) {
            @Override
            public void collect(int childDoc, long bucket) throws IOException {
                // fast forward to retrieve the parentDoc this childDoc belongs to
                final int parentDoc = parentDocs.nextSetBit(childDoc);
                assert childDoc <= parentDoc && parentDoc != DocIdSetIterator.NO_MORE_DOCS;

                int keySlot = bucketOrdToLastCollectedParentDoc.indexOf(bucket);
                if (bucketOrdToLastCollectedParentDoc.indexExists(keySlot)) {
                    int lastCollectedParentDoc = bucketOrdToLastCollectedParentDoc.indexGet(keySlot);
                    if (parentDoc > lastCollectedParentDoc) {
                        collectBucket(sub, parentDoc, bucket);
                        bucketOrdToLastCollectedParentDoc.indexReplace(keySlot, parentDoc);
                    }
                } else {
                    collectBucket(sub, parentDoc, bucket);
                    bucketOrdToLastCollectedParentDoc.indexInsert(keySlot, bucket, parentDoc);
                }
            }
        };
    }

    @Override
    public InternalAggregation buildAggregation(long owningBucketOrdinal) throws IOException {
        return new InternalReverseNested(name, bucketDocCount(owningBucketOrdinal), bucketAggregations(owningBucketOrdinal), pipelineAggregators(),
                metaData());
    }

    @Override
    public InternalAggregation buildEmptyAggregation() {
        return new InternalReverseNested(name, 0, buildEmptySubAggregations(), pipelineAggregators(), metaData());
    }

    Query getParentFilter() {
        return parentFilter;
    }
}
