op-service/metrics: Add Event and EventVec metrics

Reusable event metrics modules.

op-service/metrics/event.go

+package metrics
+
+import (
+	"fmt"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+type Event struct {
+	Total    prometheus.Counter
+	LastTime prometheus.Gauge
+}
+
+func (e *Event) Record() {
+	e.Total.Inc()
+	e.LastTime.SetToCurrentTime()
+}
+
+func NewEvent(factory Factory, ns string, name string, displayName string) Event {
+	return Event{
+		Total: factory.NewCounter(prometheus.CounterOpts{
+			Namespace: ns,
+			Name:      fmt.Sprintf("%s_total", name),
+			Help:      fmt.Sprintf("Count of %s events", displayName),
+		}),
+		LastTime: factory.NewGauge(prometheus.GaugeOpts{
+			Namespace: ns,
+			Name:      fmt.Sprintf("last_%s_unix", name),
+			Help:      fmt.Sprintf("Timestamp of last %s event", displayName),
+		}),
+	}
+}
+
+type EventVec struct {
+	Total    prometheus.CounterVec
+	LastTime prometheus.GaugeVec
+}
+
+func (e *EventVec) Record(lvs ...string) {
+	e.Total.WithLabelValues(lvs...).Inc()
+	e.LastTime.WithLabelValues(lvs...).SetToCurrentTime()
+}
+
+func NewEventVec(factory Factory, ns string, name string, displayName string, labelNames []string) EventVec {
+	return EventVec{
+		Total: *factory.NewCounterVec(prometheus.CounterOpts{
+			Namespace: ns,
+			Name:      fmt.Sprintf("%s_total", name),
+			Help:      fmt.Sprintf("Count of %s events", displayName),
+		}, labelNames),
+		LastTime: *factory.NewGaugeVec(prometheus.GaugeOpts{
+			Namespace: ns,
+			Name:      fmt.Sprintf("last_%s_unix", name),
+			Help:      fmt.Sprintf("Timestamp of last %s event", displayName),
+		},
+			labelNames),
+	}
+}