/*
 * 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", the "GNU Affero General Public License v3.0 only", 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", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */
package org.elasticsearch.search.aggregations.bucket.terms;

import org.apache.lucene.util.CollectionUtil;
import org.elasticsearch.common.Randomness;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.util.SetBackedScalingCuckooFilter;
import org.elasticsearch.search.DocValueFormat;
import org.elasticsearch.search.aggregations.AggregationErrors;
import org.elasticsearch.search.aggregations.AggregationReduceContext;
import org.elasticsearch.search.aggregations.AggregatorReducer;
import org.elasticsearch.search.aggregations.BucketOrder;
import org.elasticsearch.search.aggregations.InternalAggregation;
import org.elasticsearch.search.aggregations.InternalAggregations;
import org.elasticsearch.search.aggregations.support.SamplingContext;
import org.elasticsearch.xcontent.XContentBuilder;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;

public abstract class InternalMappedRareTerms<A extends InternalRareTerms<A, B>, B extends InternalRareTerms.Bucket<B>> extends
    InternalRareTerms<A, B> {

    protected DocValueFormat format;
    protected List<B> buckets;

    final SetBackedScalingCuckooFilter filter;

    InternalMappedRareTerms(
        String name,
        BucketOrder order,
        Map<String, Object> metadata,
        DocValueFormat format,
        List<B> buckets,
        long maxDocCount,
        SetBackedScalingCuckooFilter filter
    ) {
        super(name, order, maxDocCount, metadata);
        this.format = format;
        this.buckets = buckets;
        this.filter = filter;
    }

    SetBackedScalingCuckooFilter getFilter() {
        return filter;
    }

    /**
     * Read from a stream.
     */
    InternalMappedRareTerms(StreamInput in, Bucket.Reader<B> bucketReader) throws IOException {
        super(in);
        format = in.readNamedWriteable(DocValueFormat.class);
        buckets = in.readCollectionAsList(stream -> bucketReader.read(stream, format));
        filter = new SetBackedScalingCuckooFilter(in, Randomness.get());
    }

    @Override
    protected void writeTermTypeInfoTo(StreamOutput out) throws IOException {
        out.writeNamedWriteable(format);
        out.writeCollection(buckets);
        filter.writeTo(out);
    }

    @Override
    protected AggregatorReducer getLeaderReducer(AggregationReduceContext reduceContext, int size) {
        return new AggregatorReducer() {
            final Map<Object, List<B>> buckets = new HashMap<>();
            InternalRareTerms<A, B> referenceTerms = null;
            SetBackedScalingCuckooFilter filter = null;

            @Override
            public void accept(InternalAggregation aggregation) {
                // Unmapped rare terms don't have a cuckoo filter so we'll skip all this work
                // and save some type casting headaches later.
                if (aggregation.canLeadReduction() == false) {
                    return;
                }

                @SuppressWarnings("unchecked")
                InternalRareTerms<A, B> terms = (InternalRareTerms<A, B>) aggregation;
                if (referenceTerms == null && aggregation.getClass().equals(UnmappedRareTerms.class) == false) {
                    referenceTerms = terms;
                }
                if (referenceTerms != null
                    && referenceTerms.getClass().equals(terms.getClass()) == false
                    && terms.getClass().equals(UnmappedRareTerms.class) == false) {
                    // control gets into this loop when the same field name against which the query is executed
                    // is of different types in different indices.
                    throw AggregationErrors.reduceTypeMismatch(referenceTerms.getName(), Optional.empty());
                }
                for (B bucket : terms.getBuckets()) {
                    List<B> bucketList = buckets.computeIfAbsent(bucket.getKey(), k -> new ArrayList<>());
                    bucketList.add(bucket);
                }

                SetBackedScalingCuckooFilter otherFilter = ((InternalMappedRareTerms) aggregation).getFilter();
                if (filter == null) {
                    filter = new SetBackedScalingCuckooFilter(otherFilter.getThreshold(), otherFilter.getRng(), otherFilter.getFpp());
                }
                filter.merge(otherFilter);
            }

            @Override
            public InternalAggregation get() {
                final List<B> rare = new ArrayList<>();
                for (List<B> sameTermBuckets : buckets.values()) {
                    final B b = reduceBucket(sameTermBuckets, reduceContext);
                    if ((b.getDocCount() <= maxDocCount && containsTerm(filter, b) == false)) {
                        rare.add(b);
                        reduceContext.consumeBucketsAndMaybeBreak(1);
                    } else if (b.getDocCount() > maxDocCount) {
                        // this term has gone over threshold while merging, so add it to the filter.
                        // Note this may happen during incremental reductions too
                        addToFilter(filter, b);
                    }
                }
                CollectionUtil.introSort(rare, order.comparator());
                return createWithFilter(name, rare, filter);
            }
        };
    }

    private B reduceBucket(List<B> buckets, AggregationReduceContext context) {
        assert buckets.isEmpty() == false;
        long docCount = 0;
        for (B bucket : buckets) {
            docCount += bucket.docCount;
        }
        final List<InternalAggregations> aggregations = new BucketAggregationList<>(buckets);
        final InternalAggregations aggs = InternalAggregations.reduce(aggregations, context);
        return createBucket(docCount, aggs, buckets.get(0));
    }

    @Override
    public A finalizeSampling(SamplingContext samplingContext) {
        final List<B> originalBuckets = getBuckets();
        final List<B> buckets = new ArrayList<>(originalBuckets.size());
        for (B bucket : originalBuckets) {
            buckets.add(
                createBucket(
                    samplingContext.scaleUp(bucket.getDocCount()),
                    InternalAggregations.finalizeSampling(bucket.aggregations, samplingContext),
                    bucket
                )
            );
        }
        return createWithFilter(name, buckets, filter);
    }

    public abstract boolean containsTerm(SetBackedScalingCuckooFilter filter, B bucket);

    public abstract void addToFilter(SetBackedScalingCuckooFilter filter, B bucket);

    @Override
    public List<B> getBuckets() {
        return buckets;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || getClass() != obj.getClass()) return false;
        if (super.equals(obj) == false) return false;
        InternalMappedRareTerms<?, ?> that = (InternalMappedRareTerms<?, ?>) obj;
        return Objects.equals(buckets, that.buckets) && Objects.equals(format, that.format) && Objects.equals(filter, that.filter);
    }

    @Override
    public int hashCode() {
        return Objects.hash(super.hashCode(), buckets, format, filter);
    }

    @Override
    public final XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
        return doXContentCommon(builder, params, buckets);
    }
}