clock

type Clock interface {
	Now() time.Time
	Since(time.Time) time.Duration
	After(d time.Duration) <-chan time.Time
	NewTimer(d time.Duration) Timer
	Sleep(d time.Duration)
	Tick(d time.Duration) <-chan time.Time
}

type RealClock struct{}

type Timer interface {
	C() <-chan time.Time
	Stop() bool
	Reset(d time.Duration) bool
}