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// Package backoff provides stateless methods of calculating durations based on
// a number of attempts made.
//
// Copyright © 2016 Trevor N. Suarez (Rican7)
package backoff
import (
"math"
"time"
)
// Algorithm defines a function that calculates a time.Duration based on
// the given retry attempt number.
type Algorithm func(attempt uint) time.Duration
// Incremental creates a Algorithm that increments the initial duration
// by the given increment for each attempt.
func Incremental(initial, increment time.Duration) Algorithm {
return func(attempt uint) time.Duration {
return initial + (increment * time.Duration(attempt))
}
}
// Linear creates a Algorithm that linearly multiplies the factor
// duration by the attempt number for each attempt.
func Linear(factor time.Duration) Algorithm {
return func(attempt uint) time.Duration {
return (factor * time.Duration(attempt))
}
}
// Exponential creates a Algorithm that multiplies the factor duration by
// an exponentially increasing factor for each attempt, where the factor is
// calculated as the given base raised to the attempt number.
func Exponential(factor time.Duration, base float64) Algorithm {
return func(attempt uint) time.Duration {
return (factor * time.Duration(math.Pow(base, float64(attempt))))
}
}
// BinaryExponential creates a Algorithm that multiplies the factor
// duration by an exponentially increasing factor for each attempt, where the
// factor is calculated as `2` raised to the attempt number (2^attempt).
func BinaryExponential(factor time.Duration) Algorithm {
return Exponential(factor, 2)
}
// Fibonacci creates a Algorithm that multiplies the factor duration by
// an increasing factor for each attempt, where the factor is the Nth number in
// the Fibonacci sequence.
func Fibonacci(factor time.Duration) Algorithm {
return func(attempt uint) time.Duration {
return (factor * time.Duration(fibonacciNumber(attempt)))
}
}
// fibonacciNumber calculates the Fibonacci sequence number for the given
// sequence position.
func fibonacciNumber(n uint) uint {
if n == 0 || n == 1 {
return n
}
return fibonacciNumber(n-1) + fibonacciNumber(n-2)
}
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