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Please note, a newer package azure-messaging-eventhubs for Azure Event Hubs is available at https://search.maven.org/artifact/com.azure/azure-messaging-eventhubs as of February 2020. While this package will continue to receive critical bug fixes, we strongly encourage you to upgrade. Read the migration guide at https://aka.ms/azsdk/java/migrate/eh for more details.

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

package com.microsoft.azure.eventhubs.impl;

import com.microsoft.azure.eventhubs.ConnectionStringBuilder;
import com.microsoft.azure.eventhubs.RetryPolicy;

import java.time.Duration;

/**
 * RetryPolicy implementation where the delay between retries will grow in an exponential manner.
 * RetryPolicy can be set on the client operations using {@link ConnectionStringBuilder}.
 * RetryIntervals will be computed using a retryFactor which is a function of deltaBackOff (MaximumBackoff - MinimumBackoff) and MaximumRetryCount
 */
public final class RetryExponential extends RetryPolicy {
    private final Duration minimumBackoff;
    private final Duration maximumBackoff;
    private final int maximumRetryCount;
    private final double retryFactor;

    public RetryExponential(final Duration minimumBackoff, final Duration maximumBackoff, final int maximumRetryCount, final String name) {
        super(name);

        this.minimumBackoff = minimumBackoff;
        this.maximumBackoff = maximumBackoff;
        this.maximumRetryCount = maximumRetryCount;
        this.retryFactor = this.computeRetryFactor();
    }

    @Override
    protected Duration onGetNextRetryInterval(final String clientId, final Exception lastException, final Duration remainingTime, final int baseWaitTimeSecs) {
        int currentRetryCount = this.getRetryCount(clientId);

        if (currentRetryCount >= this.maximumRetryCount) {
            return null;
        }

        if (!RetryPolicy.isRetryableException(lastException)) {
            return null;
        }

        double nextRetryInterval = Math.pow(this.retryFactor, (double) currentRetryCount);
        long nextRetryIntervalSeconds = (long) nextRetryInterval;
        long nextRetryIntervalNano = (long) ((nextRetryInterval - (double) nextRetryIntervalSeconds) * 1000000000);
        if (remainingTime.getSeconds() < Math.max(nextRetryInterval, ClientConstants.TIMER_TOLERANCE.getSeconds())) {
            return null;
        }

        Duration retryAfter = this.minimumBackoff.plus(Duration.ofSeconds(nextRetryIntervalSeconds, nextRetryIntervalNano));
        retryAfter = retryAfter.plus(Duration.ofSeconds(baseWaitTimeSecs));

        return retryAfter;
    }

    private double computeRetryFactor() {
        long deltaBackoff = this.maximumBackoff.minus(this.minimumBackoff).getSeconds();
        if (deltaBackoff <= 0 || this.maximumRetryCount <= 0) {
            return 0;
        }

        return (Math.log(deltaBackoff) / Math.log(this.maximumRetryCount));
    }
}