/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

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

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.NumericDocValues;
import org.apache.lucene.index.SortedNumericDocValues;
import org.apache.lucene.search.DiversifiedTopDocsCollector;
import org.apache.lucene.search.DiversifiedTopDocsCollector.ScoreDocKey;
import org.apache.lucene.search.TopDocsCollector;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.index.fielddata.AbstractNumericDocValues;
import org.elasticsearch.search.aggregations.Aggregator;
import org.elasticsearch.search.aggregations.AggregatorFactories;
import org.elasticsearch.search.aggregations.bucket.DeferringBucketCollector;
import org.elasticsearch.search.aggregations.support.AggregationContext;
import org.elasticsearch.search.aggregations.support.ValuesSource;
import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;

import java.io.IOException;
import java.util.Map;
import java.util.function.Consumer;

public class DiversifiedNumericSamplerAggregator extends SamplerAggregator {

    private ValuesSource.Numeric valuesSource;
    private int maxDocsPerValue;

    DiversifiedNumericSamplerAggregator(
        String name,
        int shardSize,
        AggregatorFactories factories,
        AggregationContext context,
        Aggregator parent,
        Map<String, Object> metadata,
        ValuesSourceConfig valuesSourceConfig,
        int maxDocsPerValue
    ) throws IOException {
        super(name, shardSize, factories, context, parent, metadata);
        assert valuesSourceConfig.hasValues();
        this.valuesSource = (ValuesSource.Numeric) valuesSourceConfig.getValuesSource();
        this.maxDocsPerValue = maxDocsPerValue;
    }

    @Override
    public DeferringBucketCollector buildDeferringCollector() {
        bdd = new DiverseDocsDeferringCollector(this::addRequestCircuitBreakerBytes);
        return bdd;
    }

    /**
     * A {@link DeferringBucketCollector} that identifies top scoring documents
     * but de-duped by a key then passes only these on to nested collectors.
     * This implementation is only for use with a single bucket aggregation.
     */
    class DiverseDocsDeferringCollector extends BestDocsDeferringCollector {
        DiverseDocsDeferringCollector(Consumer<Long> circuitBreakerConsumer) {
            super(shardSize, bigArrays(), circuitBreakerConsumer);
        }

        @Override
        protected TopDocsCollector<ScoreDocKey> createTopDocsCollector(int size) {
            // Make sure we do not allow size > maxDoc, to prevent accidental OOM
            int minMaxDocsPerValue = Math.min(maxDocsPerValue, searcher().getIndexReader().maxDoc());
            return new ValuesDiversifiedTopDocsCollector(size, minMaxDocsPerValue);
        }

        @Override
        protected long getPriorityQueueSlotSize() {
            return SCOREDOCKEY_SIZE;
        }

        // This class extends the DiversifiedTopDocsCollector and provides
        // a lookup from elasticsearch's ValuesSource
        class ValuesDiversifiedTopDocsCollector extends DiversifiedTopDocsCollector {

            private SortedNumericDocValues values;

            ValuesDiversifiedTopDocsCollector(int numHits, int maxHitsPerKey) {
                super(numHits, maxHitsPerKey);
            }

            @Override
            protected NumericDocValues getKeys(LeafReaderContext context) {
                try {
                    values = valuesSource.longValues(context);
                } catch (IOException e) {
                    throw new ElasticsearchException("Error reading values", e);
                }
                return new AbstractNumericDocValues() {

                    @Override
                    public boolean advanceExact(int target) throws IOException {
                        if (values.advanceExact(target)) {
                            if (values.docValueCount() > 1) {
                                throw new IllegalArgumentException(
                                        "Sample diversifying key must be a single valued-field");
                            }
                            return true;
                        } else {
                            return false;
                        }
                    }

                    @Override
                    public int docID() {
                        return values.docID();
                    }

                    @Override
                    public long longValue() throws IOException {
                        return values.nextValue();
                    }
                };
            }

        }

    }

}
