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{}
	// ExecPluginPolicyCalls is the number of plugin policy check calls, partitioned
	// by {"allowed", "denied"}
	ExecPluginPolicyCalls PolicyCallsMetric = noopPolicy{}
	// 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{}
	// TransportCAReloads is the metric that counts the number of times a CA reload is attempted
	TransportCAReloads TransportCAReloadsMetric = noopTransportCAReloads{}
	// TransportCertRotationGCCalls counts the number of times a cert rotation goroutine
	// cancel func is called via GC cleanup
	TransportCertRotationGCCalls TransportCertRotationGCCallsMetric = noopTransportCertRotationGCCalls{}
	// TransportCacheGCCalls counts the number of times a GC cleanup attempts
	// to delete a transport cache entry, partitioned by result: deleted, skipped.
	TransportCacheGCCalls TransportCacheGCCallsMetric = noopTransportCacheGCCalls{}
)

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 PolicyCallsMetric interface {
	// Increment increments a counter per status { "allowed", "denied" }
	Increment(status string)
}

type RegisterOpts struct {
	ClientCertExpiry             ExpiryMetric
	ClientCertRotationAge        DurationMetric
	RequestLatency               LatencyMetric
	ResolverLatency              ResolverLatencyMetric
	RequestSize                  SizeMetric
	ResponseSize                 SizeMetric
	RateLimiterLatency           LatencyMetric
	RequestResult                ResultMetric
	ExecPluginCalls              CallsMetric
	ExecPluginPolicyCalls        PolicyCallsMetric
	RequestRetry                 RetryMetric
	TransportCacheEntries        TransportCacheMetric
	TransportCreateCalls         TransportCreateCallsMetric
	TransportCAReloads           TransportCAReloadsMetric
	TransportCertRotationGCCalls TransportCertRotationGCCallsMetric
	TransportCacheGCCalls        TransportCacheGCCallsMetric
}

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 TransportCAReloadsMetric interface {
	Increment(result, reason string)
}

type TransportCacheGCCallsMetric interface {
	Increment(result string)
}

type TransportCacheMetric interface {
	Observe(value int)
}

type TransportCertRotationGCCallsMetric interface {
	Increment()
}

type TransportCreateCallsMetric interface {
	Increment(result string)
}