refactor(sync): use options to init metrics

sync/metrics.go

@@ -11,31 +11,40 @@ import (
 var meter = otel.Meter("header/sync")
 
 type metrics struct {
-	totalSynced int64
+	totalSynced      atomic.Int64
+	totalSyncedGauge metric.Float64ObservableGauge
 }
 
-func (s *Syncer[H]) InitMetrics() error {
-	s.metrics = &metrics{}
-
+func newMetrics() *metrics {
 	totalSynced, err := meter.Float64ObservableGauge(
 		"total_synced_headers",
 		metric.WithDescription("total synced headers"),
 	)
 	if err != nil {
-		return err
+		panic(err)
+	}
+
+	m := &metrics{
+		totalSyncedGauge: totalSynced,
 	}
 
 	callback := func(ctx context.Context, observer metric.Observer) error {
-		observer.ObserveFloat64(totalSynced, float64(atomic.LoadInt64(&s.metrics.totalSynced)))
+		observer.ObserveFloat64(totalSynced, float64(m.totalSynced.Load()))
 		return nil
 	}
 	_, err = meter.RegisterCallback(callback, totalSynced)
-	return err
+	if err != nil {
+		panic(err)
+	}
+
+	return m
 }
 
 // recordTotalSynced records the total amount of synced headers.
 func (m *metrics) recordTotalSynced(totalSynced int) {
-	if m != nil {
-		atomic.AddInt64(&m.totalSynced, int64(totalSynced))
+	if m == nil {
+		return
 	}
+
+	m.totalSynced.Store(int64(totalSynced))
 }

sync/options.go

@@ -28,6 +28,8 @@ type Parameters struct {
 	// recencyThreshold describes the time period for which a header is
 	// considered "recent". The default is blockTime + 5 seconds.
 	recencyThreshold time.Duration
+	// metrics is a flag that enables metrics collection.
+	metrics bool
 }
 
 // DefaultParameters returns the default params to configure the syncer.
@@ -44,6 +46,13 @@ func (p *Parameters) Validate() error {
 	return nil
 }
 
+// WithMetrics enables Metrics on Syncer.
+func WithMetrics() Option {
+	return func(p *Parameters) {
+		p.metrics = true
+	}
+}
+
 // WithBlockTime is a functional option that configures the
 // `blockTime` parameter.
 func WithBlockTime(duration time.Duration) Option {

sync/sync.go

@@ -69,10 +69,15 @@ func NewSyncer[H header.Header[H]](
 		return nil, err
 	}
 
+	var metrics *metrics
+	if params.metrics {
+		metrics = newMetrics()
+	}
 	return &Syncer[H]{
 		sub:         sub,
 		store:       syncStore[H]{Store: store},
 		getter:      syncGetter[H]{Getter: getter},
+		metrics:     metrics,
 		triggerSync: make(chan struct{}, 1), // should be buffered
 		Params:      &params,
 	}, nil