"citadel_server_root_cert_expiry_timestamp",
		"The unix timestamp, in seconds, when Citadel root cert will expire. "+
			"A negative time indicates the cert is expired.",
	)
	rootCertExpirySeconds = monitoring.NewDerivedGauge(
		"citadel_server_root_cert_expiry_seconds",
		"The time remaining, in seconds, before the root certificate will expire. "+
			"A negative value indicates the cert is expired.",
	)

	numFileSecretFailures = monitoring.NewSum(
		"num_file_secret_failures_total",
		"Number of times secret generation failed for files",
	)

	certExpirySeconds = monitoring.NewDerivedGauge(
		"cert_expiry_seconds",
		"The time remaining, in seconds, before the certificate chain will expire. "+
			"A negative value indicates the cert is expired.",
	)

	if dm != nil {
		return dm
	}
	return newGauge(o)
}

// NewDerivedGauge creates a new Gauge Metric. That means that data collected by the new
// Metric will export only the last recorded value.
// Unlike NewGauge, the DerivedGauge accepts functions which are called to get the current value.
func NewDerivedGauge(name, description string) DerivedMetric {
	knownMetrics.register(MetricDefinition{
		Name:        name,

	"istio.io/istio/pkg/slices"
)

type derivedGauge struct {
	mu    sync.RWMutex
	attrs map[attribute.Set]func() float64

	name string
}

var _ DerivedMetric = &derivedGauge{}

func newDerivedGauge(name, description string) DerivedMetric {
	dm := &derivedGauge{
		name:  name,
		attrs: map[attribute.Set]func() float64{},
	}
	_, err := meter().Float64ObservableGauge(name,
		api.WithDescription(description),

)

type monitor struct {
	monitoringServer *http.Server
}

const (
	metricsPath = "/metrics"
	versionPath = "/version"
)

var (
	serverStart = time.Now()

	_ = monitoring.NewDerivedGauge(
		"istiod_uptime_seconds",
		"Current istiod server uptime in seconds",
	).ValueFrom(func() float64 {
		return time.Since(serverStart).Seconds()
	})

	versionTag   = monitoring.CreateLabel("version")

}

var (
	testDerivedGauge = monitoring.NewDerivedGauge(
		"test_derived_gauge",
		"Testing derived gauge functionality",
	).ValueFrom(func() float64 {
		return 17.76
	})

	testDerivedGaugeLabels = monitoring.NewDerivedGauge(
		"test_derived_gauge_labels",
		"Testing derived gauge functionality",
	)
)