// Copyright 2016 Michal Witkowski. All Rights Reserved.
// See LICENSE for licensing terms.

package grpc_retry

import (
	"time"

	"github.com/grpc-ecosystem/go-grpc-middleware/util/backoffutils"
)

// BackoffLinear is very simple: it waits for a fixed period of time between calls.
func BackoffLinear(waitBetween time.Duration) BackoffFunc {
	return func(attempt uint) time.Duration {
		return waitBetween
	}
}

// BackoffLinearWithJitter waits a set period of time, allowing for jitter (fractional adjustment).
//
// For example waitBetween=1s and jitter=0.10 can generate waits between 900ms and 1100ms.
func BackoffLinearWithJitter(waitBetween time.Duration, jitterFraction float64) BackoffFunc {
	return func(attempt uint) time.Duration {
		return backoffutils.JitterUp(waitBetween, jitterFraction)
	}
}

// BackoffExponential produces increasing intervals for each attempt.
//
// The scalar is multiplied times 2 raised to the current attempt. So the first
// retry with a scalar of 100ms is 100ms, while the 5th attempt would be 1.6s.
func BackoffExponential(scalar time.Duration) BackoffFunc {
	return func(attempt uint) time.Duration {
		return scalar * time.Duration(backoffutils.ExponentBase2(attempt))
	}
}

// BackoffExponentialWithJitter creates an exponential backoff like
// BackoffExponential does, but adds jitter.
func BackoffExponentialWithJitter(scalar time.Duration, jitterFraction float64) BackoffFunc {
	return func(attempt uint) time.Duration {
		return backoffutils.JitterUp(scalar*time.Duration(backoffutils.ExponentBase2(attempt)), jitterFraction)
	}
}