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/*
 * 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.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.InternalAggregation;
import org.elasticsearch.xcontent.XContentBuilder;

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

public class InternalSum extends InternalNumericMetricsAggregation.SingleValue implements Sum {
    private final double sum;

    public InternalSum(String name, double sum, DocValueFormat formatter, Map metadata) {
        super(name, metadata);
        this.sum = sum;
        this.format = formatter;
    }

    /**
     * Read from a stream.
     */
    public InternalSum(StreamInput in) throws IOException {
        super(in);
        format = in.readNamedWriteable(DocValueFormat.class);
        sum = in.readDouble();
    }

    @Override
    protected void doWriteTo(StreamOutput out) throws IOException {
        out.writeNamedWriteable(format);
        out.writeDouble(sum);
    }

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

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

    @Override
    public double getValue() {
        return sum;
    }

    @Override
    public InternalSum reduce(List aggregations, ReduceContext reduceContext) {
        // Compute the sum of double values with Kahan summation algorithm which is more
        // accurate than naive summation.
        CompensatedSum kahanSummation = new CompensatedSum(0, 0);
        for (InternalAggregation aggregation : aggregations) {
            double value = ((InternalSum) aggregation).sum;
            kahanSummation.add(value);
        }
        return new InternalSum(name, kahanSummation.value(), format, getMetadata());
    }

    @Override
    public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
        builder.field(CommonFields.VALUE.getPreferredName(), sum);
        if (format != DocValueFormat.RAW) {
            builder.field(CommonFields.VALUE_AS_STRING.getPreferredName(), format.format(sum).toString());
        }
        return builder;
    }

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

    @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;

        InternalSum that = (InternalSum) obj;
        return Objects.equals(sum, that.sum);
    }
}