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{}
	// ResolverLatency is the latency metric that DNS resolver will update
	ResolverLatency ResolverLatencyMetric = noopResolverLatency{}
	// RequestSize is the request size metric that rest clients will update.
	RequestSize SizeMetric = noopSize{}
	// ResponseSize is the response size metric that rest clients will update.
	ResponseSize SizeMetric = noopSize{}
	// 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{}
	// ExecPluginCalls is the number of calls made to an exec plugin, partitioned by
	// exit code and call status.
	ExecPluginCalls CallsMetric = noopCalls{}
	// RequestRetry is the retry metric that tracks the number of
	// retries sent to the server.
	RequestRetry RetryMetric = noopRetry{}
	// TransportCacheEntries is the metric that tracks the number of entries in the
	// internal transport cache.
	TransportCacheEntries TransportCacheMetric = noopTransportCache{}
	// TransportCreateCalls is the metric that counts the number of times a new transport
	// is created
	TransportCreateCalls TransportCreateCallsMetric = noopTransportCreateCalls{}
)

type CallsMetric interface {
	// Increment increments a counter per exitCode and callStatus.
	Increment(exitCode int, callStatus string)
}

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

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

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

type RegisterOpts struct {
	ClientCertExpiry      ExpiryMetric
	ClientCertRotationAge DurationMetric
	RequestLatency        LatencyMetric
	ResolverLatency       ResolverLatencyMetric
	RequestSize           SizeMetric
	ResponseSize          SizeMetric
	RateLimiterLatency    LatencyMetric
	RequestResult         ResultMetric
	ExecPluginCalls       CallsMetric
	RequestRetry          RetryMetric
	TransportCacheEntries TransportCacheMetric
	TransportCreateCalls  TransportCreateCallsMetric
}

type ResolverLatencyMetric interface {
	Observe(ctx context.Context, host string, latency time.Duration)
}

type ResultMetric interface {
	Increment(ctx context.Context, code string, method string, host string)
}

type RetryMetric interface {
	IncrementRetry(ctx context.Context, code string, method string, host string)
}

type SizeMetric interface {
	Observe(ctx context.Context, verb string, host string, size float64)
}

type TransportCacheMetric interface {
	Observe(value int)
}

type TransportCreateCallsMetric interface {
	Increment(result string)
}