import (
	"context"
	"sync"

	"go.opentelemetry.io/otel/attribute"
	api "go.opentelemetry.io/otel/metric"

	"istio.io/istio/pkg/log"
)

type gauge struct {
	baseMetric
	g api.Float64ObservableGauge

	// attributeSets stores a map of attributes -> values, for gauges.
	attributeSetsMutex *sync.RWMutex
	attributeSets      map[attribute.Set]*gaugeValues
	currentGaugeSet    *gaugeValues
}

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),
		api.WithFloat64Callback(func(ctx context.Context, observer api.Float64Observer) error {
			dm.mu.RLock()
			defer dm.mu.RUnlock()
			for kv, compute := range dm.attrs {