package outpost

import "time"

// Backoff maps a failure count to a retry delay. It is called with the number
// of failures recorded so far, starting at 1.
type Backoff func(failures int) time.Duration

// ExponentialBackoff returns base * 2^(failures-1), capped at max. base must be
// positive.
func ExponentialBackoff(base, max time.Duration) Backoff {
	return func(failures int) time.Duration {
		if failures < 1 {
			failures = 1
		}
		d := base
		for i := 1; i < failures; i++ {
			if d >= max {
				break
			}
			d *= 2
		}
		if d > max {
			d = max
		}
		return d
	}
}