feat: image variants cache panel

internal/infrastructure/useCases/ServeVariant.go

@@ -55,6 +55,18 @@ type ServeVariantUseCase struct {
 	maxSourcePixels int64
 	renderSlots     chan struct{}
 	flights         singleflight.Group
+	tracker         image.VariantUsageTracker
+}
+
+type idleUsageTracker struct{}
+
+func (idleUsageTracker) RecordHit(string, string) {}
+func (idleUsageTracker) RecordRejection()         {}
+func (idleUsageTracker) Flush() error             { return nil }
+
+func (u *ServeVariantUseCase) WithUsageTracker(tracker image.VariantUsageTracker) *ServeVariantUseCase {
+	u.tracker = tracker
+	return u
 }
 
 func NewServeVariantUseCase(variants image.VariantRepository, files image.VariantFileRepository, images image.Repository, storage image.Storage, renderer image.VariantRenderer, limits ServeVariantLimits) *ServeVariantUseCase {
@@ -67,10 +79,19 @@ func NewServeVariantUseCase(variants image.VariantRepository, files image.Varian
 		maxSourceBytes:  limits.MaxSourceBytes,
 		maxSourcePixels: limits.MaxSourcePixels,
 		renderSlots:     make(chan struct{}, max(1, limits.MaxConcurrentRenders)),
+		tracker:         idleUsageTracker{},
 	}
 }
 
 func (u *ServeVariantUseCase) Serve(request ServeVariantRequest) (ServedVariant, error) {
+	served, err := u.serve(request)
+	if errors.Is(err, image.ErrUnknownVariant) || errors.Is(err, image.ErrUnsupportedParameter) {
+		u.tracker.RecordRejection()
+	}
+	return served, err
+}
+
+func (u *ServeVariantUseCase) serve(request ServeVariantRequest) (ServedVariant, error) {
 	if parameter := unsupportedParameter(request.Parameters); parameter != "" {
 		return ServedVariant{}, image.NewUnsupportedParameterError(parameter)
 	}
@@ -134,18 +155,26 @@ func (u *ServeVariantUseCase) serveSource(variant image.Variant, request ServeVa
 	settings := variant.Settings()
 	etag := image.VariantETag(settings, request.StoredName)
 	if image.ETagMatches(request.IfNoneMatch, etag) {
+		u.tracker.RecordHit(variant.Name, request.StoredName)
 		return ServedVariant{NotModified: true, ETag: etag}, nil
 	}
 	fingerprint := settings.Fingerprint()
 	cached, previous, hit, err := u.lookupCached(variant.Name, request.StoredName, fingerprint, etag)
 	if err != nil || hit {
+		if err == nil {
+			u.tracker.RecordHit(variant.Name, request.StoredName)
+		}
 		return cached, err
 	}
 	file, err := u.generated(requestContext(request), variant, request.StoredName, fingerprint, previous)
 	if err != nil {
 		return ServedVariant{}, err
 	}
-	return u.serveFile(file, etag)
+	served, err := u.serveFile(file, etag)
+	if err == nil {
+		u.tracker.RecordHit(variant.Name, request.StoredName)
+	}
+	return served, err
 }
 
 func requestContext(request ServeVariantRequest) context.Context {