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Java library for Azure Service Bus. Please note, a newer package com.azure:azure-messaging-servicebus for Azure Service Bus is available as of December 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/sb for more details.

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/*
 * Copyright (c) Microsoft. All rights reserved.
 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
 */
package com.microsoft.azure.servicebus.primitives;

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
 *  @since 1.0
 */
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;
		}	

		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));
	}
}