/*
 * 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.metrics;

import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.search.DocValueFormat;
import org.elasticsearch.search.aggregations.AggregationReduceContext;
import org.elasticsearch.search.aggregations.AggregatorReducer;
import org.elasticsearch.search.aggregations.InternalAggregation;
import org.elasticsearch.search.aggregations.support.SamplingContext;
import org.elasticsearch.xcontent.XContentBuilder;

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

public class InternalMedianAbsoluteDeviation extends InternalNumericMetricsAggregation.SingleValue implements MedianAbsoluteDeviation {

    public static double computeMedianAbsoluteDeviation(TDigestState valuesSketch) {
        if (valuesSketch.size() == 0) {
            return Double.NaN;
        } else {
            final double approximateMedian = valuesSketch.quantile(0.5);
            try (TDigestState approximatedDeviationsSketch = TDigestState.createUsingParamsFrom(valuesSketch)) {
                valuesSketch.centroids().forEach(centroid -> {
                    final double deviation = Math.abs(approximateMedian - centroid.mean());
                    approximatedDeviationsSketch.add(deviation, centroid.count());
                });

                return approximatedDeviationsSketch.quantile(0.5);
            }
        }
    }

    private final TDigestState valuesSketch;
    private final double medianAbsoluteDeviation;

    InternalMedianAbsoluteDeviation(String name, Map<String, Object> metadata, DocValueFormat format, TDigestState valuesSketch) {
        super(name, Objects.requireNonNull(format), metadata);
        this.valuesSketch = Objects.requireNonNull(valuesSketch);
        this.medianAbsoluteDeviation = computeMedianAbsoluteDeviation(this.valuesSketch);
    }

    public InternalMedianAbsoluteDeviation(StreamInput in) throws IOException {
        super(in);
        valuesSketch = TDigestState.read(in);
        medianAbsoluteDeviation = in.readDouble();
    }

    @Override
    protected void doWriteTo(StreamOutput out) throws IOException {
        out.writeNamedWriteable(format);
        TDigestState.write(valuesSketch, out);
        out.writeDouble(medianAbsoluteDeviation);
    }

    static InternalMedianAbsoluteDeviation empty(
        String name,
        Map<String, Object> metadata,
        DocValueFormat format,
        double compression,
        TDigestExecutionHint executionHint
    ) {
        return new InternalMedianAbsoluteDeviation(
            name,
            metadata,
            format,
            TDigestState.createWithoutCircuitBreaking(compression, executionHint)
        );
    }

    @Override
    protected AggregatorReducer getLeaderReducer(AggregationReduceContext reduceContext, int size) {
        return new AggregatorReducer() {
            final TDigestState valueMerged = TDigestState.createUsingParamsFrom(valuesSketch);

            @Override
            public void accept(InternalAggregation aggregation) {
                valueMerged.add(((InternalMedianAbsoluteDeviation) aggregation).valuesSketch);
            }

            @Override
            public InternalAggregation get() {
                return new InternalMedianAbsoluteDeviation(name, metadata, format, valueMerged);
            }
        };
    }

    @Override
    public InternalAggregation finalizeSampling(SamplingContext samplingContext) {
        return this;
    }

    @Override
    public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
        final boolean anyResults = valuesSketch.size() > 0;
        final Double mad = anyResults ? getMedianAbsoluteDeviation() : null;

        builder.field(CommonFields.VALUE.getPreferredName(), mad);
        if (format != DocValueFormat.RAW && anyResults) {
            builder.field(CommonFields.VALUE_AS_STRING.getPreferredName(), format.format(mad).toString());
        }

        return builder;
    }

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

    @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;
        InternalMedianAbsoluteDeviation other = (InternalMedianAbsoluteDeviation) obj;
        return Objects.equals(valuesSketch, other.valuesSketch);
    }

    @Override
    public String getWriteableName() {
        return MedianAbsoluteDeviationAggregationBuilder.NAME;
    }

    TDigestState getValuesSketch() {
        return valuesSketch;
    }

    @Override
    public double value() {
        return getMedianAbsoluteDeviation();
    }

    @Override
    public double getMedianAbsoluteDeviation() {
        return medianAbsoluteDeviation;
    }
}