kamilsk/retry

// Package backoff provides stateless methods of calculating durations based on
// a number of attempts made.
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

// Constant creates an Algorithm that returns the initial duration
// by the all time.
func Constant(duration time.Duration) Algorithm {
    return func(uint) time.Duration {
        return duration
    }
}

// Incremental creates an 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 an Algorithm that linearly multiplies the factor
// duration by the attempt number for each attempt.
func Linear(factor time.Duration) Algorithm {
    return Incremental(0, factor)
}

// Exponential creates an 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 an 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 an 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 {
        n := attempt
        if n != 0 {
            var a, b uint = 0, 1
            for i := uint(1); i < attempt; i++ {
                a, b = b, a+b
            }
            n = b
        }
        return factor * time.Duration(n)
    }
}