progress [skip ci]

internal/mojang/uuids_provider.go

@@ -1,6 +1,12 @@
 package mojang
 
-import "context"
+import (
+	"context"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/metric"
+	"go.uber.org/multierr"
+)
 
 type MojangUuidsStorage interface {
 	// The second argument must be returned as a incoming username in case,
@@ -10,13 +16,32 @@ type MojangUuidsStorage interface {
 	StoreMojangUuid(ctx context.Context, username string, uuid string) error
 }
 
+func NewUuidsProviderWithCache(o UuidsProvider, s MojangUuidsStorage) (*UuidsProviderWithCache, error) {
+	metrics, err := newUuidsProviderWithCacheMetrics(otel.GetMeterProvider().Meter(ScopeName))
+	if err != nil {
+		return nil, err
+	}
+
+	return &UuidsProviderWithCache{
+		Provider: o,
+		Storage:  s,
+		metrics:  metrics,
+	}, nil
+}
+
 type UuidsProviderWithCache struct {
 	Provider UuidsProvider
 	Storage  MojangUuidsStorage
+
+	metrics *uuidsProviderWithCacheMetrics
 }
 
 func (p *UuidsProviderWithCache) GetUuid(ctx context.Context, username string) (*ProfileInfo, error) {
-	uuid, foundUsername, err := p.Storage.GetUuidForMojangUsername(ctx, username)
+	var uuid, foundUsername string
+	var err error
+	defer p.recordMetrics(ctx, uuid, foundUsername, err)
+
+	uuid, foundUsername, err = p.Storage.GetUuidForMojangUsername(ctx, username)
 	if err != nil {
 		return nil, err
 	}
@@ -45,3 +70,41 @@ func (p *UuidsProviderWithCache) GetUuid(ctx context.Context, username string) (
 
 	return profile, nil
 }
+
+func (p *UuidsProviderWithCache) recordMetrics(ctx context.Context, uuid string, username string, err error) {
+	if err != nil {
+		return
+	}
+
+	if username != "" {
+		p.metrics.Hits.Add(ctx, 1)
+	} else {
+		p.metrics.Misses.Add(ctx, 1)
+	}
+}
+
+func newUuidsProviderWithCacheMetrics(meter metric.Meter) (*uuidsProviderWithCacheMetrics, error) {
+	m := &uuidsProviderWithCacheMetrics{}
+	var errors, err error
+
+	m.Hits, err = meter.Int64Counter(
+		"uuids.cache.hit",
+		metric.WithDescription(""), // TODO: write description
+		metric.WithUnit("1"),
+	)
+	errors = multierr.Append(errors, err)
+
+	m.Misses, err = meter.Int64Counter(
+		"uuids.cache.miss",
+		metric.WithDescription(""), // TODO: write description
+		metric.WithUnit("1"),
+	)
+	errors = multierr.Append(errors, err)
+
+	return m, errors
+}
+
+type uuidsProviderWithCacheMetrics struct {
+	Hits   metric.Int64Counter
+	Misses metric.Int64Counter
+}