feat: event system metrics (#96)

event/event.go

@@ -71,6 +71,7 @@ func (e *EventBus) Subscribe(eventType EventType) (EventSubscriberId, <-chan Eve
 	}
 	evtTypeSubs := e.subscribers[eventType]
 	evtTypeSubs[subId] = evtCh
+	metricSubscribers.WithLabelValues(string(eventType)).Inc()
 	return subId, evtCh
 }
 
@@ -96,6 +97,7 @@ func (e *EventBus) Unsubscribe(eventType EventType, subId EventSubscriberId) {
 	if evtTypeSubs, ok := e.subscribers[eventType]; ok {
 		delete(evtTypeSubs, subId)
 	}
+	metricSubscribers.WithLabelValues(string(eventType)).Dec()
 }
 
 // Publish allows a producer to send an event of a particular type to all subscribers
@@ -110,4 +112,5 @@ func (e *EventBus) Publish(eventType EventType, evt Event) {
 			subCh <- evt
 		}
 	}
+	metricEventsTotal.WithLabelValues(string(eventType)).Inc()
 }

event/metrics.go

@@ -0,0 +1,37 @@
+// Copyright 2024 Blink Labs Software
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package event
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	metricEventsTotal = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "event_total",
+			Help: "total events by type",
+		},
+		[]string{"type"},
+	)
+	metricSubscribers = promauto.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "event_subscribers",
+			Help: "subscribers by event type",
+		},
+		[]string{"type"},
+	)
+)