var (
	// ClientCertExpiry is the expiry time of a client certificate
	ClientCertExpiry ExpiryMetric = noopExpiry{}
	// ClientCertRotationAge is the age of a certificate that has just been rotated.
	ClientCertRotationAge DurationMetric = noopDuration{}
	// RequestLatency is the latency metric that rest clients will update.
	RequestLatency LatencyMetric = noopLatency{}
	// RateLimiterLatency is the client side rate limiter latency metric.
	RateLimiterLatency LatencyMetric = noopLatency{}
	// RequestResult is the result metric that rest clients will update.
	RequestResult ResultMetric = noopResult{}
)

type DurationMetric interface {
	Observe(duration time.Duration)
}

type ExpiryMetric interface {
	Set(expiry *time.Time)
}

type LatencyMetric interface {
	Observe(verb string, u url.URL, latency time.Duration)
}

type RegisterOpts struct {
	ClientCertExpiry      ExpiryMetric
	ClientCertRotationAge DurationMetric
	RequestLatency        LatencyMetric
	RateLimiterLatency    LatencyMetric
	RequestResult         ResultMetric
}

type ResultMetric interface {
	Increment(code string, method string, host string)
}