refactor: Replace interface{} with any alias and optimize string formatting with fmt.Appendf

- Replace map[string]interface{} with map[string]any in GraphQL, metrics, payment gateway, and webhook handlers
- Replace []byte(fmt.Sprintf()) with fmt.Appendf(nil, ...) for cursor encoding in GraphQL resolvers and tests
- Replace strings.HasPrefix/TrimPrefix with strings.CutPrefix for webhook signature parsing
- Replace stripe.Int64/Bool with new() constructor for Stripe payment parameters
- Rename Error

apps/api-server/internal/graphql/generated.go

@@ -370,6 +370,6 @@ func (e *executableSchema) Exec(ctx context.Context) graphql.ResponseHandler {
 	return nil
 }
 
-func (e *executableSchema) Extensions() map[string]interface{} {
-	return map[string]interface{}{}
+func (e *executableSchema) Extensions() map[string]any {
+	return map[string]any{}
 }

apps/api-server/internal/graphql/resolvers.go

@@ -54,8 +54,8 @@ func strPtr(s string) *string { return new(s) }
 func buildConnectionPageInfo(offset, count int, total int64) *PageInfo {
 	var startCursor, endCursor *string
 	if count > 0 {
-		startCursor = strPtr(base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%d", offset+1))))
-		endCursor = strPtr(base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%d", offset+count))))
+		startCursor = strPtr(base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "%d", offset+1)))
+		endCursor = strPtr(base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "%d", offset+count)))
 	}
 	return &PageInfo{
 		HasNextPage:     int64(offset+count) < total,
@@ -104,7 +104,7 @@ func (r *Resolver) Subscribers(ctx context.Context, first *int, after *string, f
 		s := sub // avoid loop-variable capture
 		edges[i] = &SubscriberEdge{
 			Node:   &s,
-			Cursor: base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%d", offset+i+1))),
+			Cursor: base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "%d", offset+i+1)),
 		}
 	}
 
@@ -143,7 +143,7 @@ func (r *Resolver) UsageEvents(ctx context.Context, first *int, after *string, i
 	for i, event := range events {
 		edges[i] = &UsageEventEdge{
 			Node:   event,
-			Cursor: base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%d", offset+i+1))),
+			Cursor: base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "%d", offset+i+1)),
 		}
 	}
 
@@ -225,7 +225,7 @@ func (r *Resolver) Invoices(ctx context.Context, first *int, after *string, imsi
 	for i, inv := range invoices {
 		edges[i] = &InvoiceEdge{
 			Node:   inv,
-			Cursor: base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%d", offset+i+1))),
+			Cursor: base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "%d", offset+i+1)),
 		}
 	}
 
@@ -271,7 +271,7 @@ func (r *Resolver) Alerts(ctx context.Context, first *int, after *string, subscr
 	for i, alert := range alerts {
 		edges[i] = &AlertEdge{
 			Node:   alert,
-			Cursor: base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%d", offset+i+1))),
+			Cursor: base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "%d", offset+i+1)),
 		}
 	}
 

apps/api-server/internal/graphql/resolvers_test.go

@@ -118,7 +118,7 @@ func TestResolverRoot_Methods(t *testing.T) {
 // Helper functions for testing (these should match the implementations in resolvers.go)
 
 func encodeCursor(offset int) string {
-	return base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("cursor:%d", offset)))
+	return base64.StdEncoding.EncodeToString(fmt.Appendf(nil, "cursor:%d", offset))
 }
 
 func decodeCursor(cursor string) (int, error) {

apps/api-server/internal/handlers/subscriber.go

@@ -264,7 +264,8 @@ func (h *SubscriberHandler) TerminateSubscriber(c *gin.Context) {
 }
 
 // ErrorResponse represents an API error response
-type ErrorResponse struct {
+type SubscriberErrorResponse struct {
 	Error   string `json:"error"`
+	Code    string `json:"code"`
 	Details string `json:"details,omitempty"`
 }

apps/api-server/internal/metrics/timeseries.go

@@ -79,7 +79,7 @@ func (ts *TimeSeriesStorage) StoreUsageMetrics(ctx context.Context, metrics Usag
 			"subscriber_id": metrics.SubscriberID,
 			"imsi":          metrics.IMSI,
 		},
-		map[string]interface{}{
+		map[string]any{
 			"data_up":       metrics.DataUp,
 			"data_down":     metrics.DataDown,
 			"voice_seconds": metrics.VoiceSeconds,
@@ -96,7 +96,7 @@ func (ts *TimeSeriesStorage) StoreSystemMetrics(ctx context.Context, metrics Sys
 	point := influxdb2.NewPoint(
 		"system",
 		map[string]string{},
-		map[string]interface{}{
+		map[string]any{
 			"active_sessions": metrics.ActiveSessions,
 			"cpu_usage":       metrics.CPUUsage,
 			"memory_usage":    metrics.MemoryUsage,
@@ -119,7 +119,7 @@ func (ts *TimeSeriesStorage) StoreChargingMetrics(ctx context.Context, metrics C
 			"currency":       metrics.Currency,
 			"status":         metrics.Status,
 		},
-		map[string]interface{}{
+		map[string]any{
 			"balance": metrics.Balance,
 			"amount":  metrics.Amount,
 		},
@@ -136,7 +136,7 @@ func (ts *TimeSeriesStorage) StorePacketMetrics(ctx context.Context, subscriberI
 		map[string]string{
 			"subscriber_id": subscriberID,
 		},
-		map[string]interface{}{
+		map[string]any{
 			"packets_processed": packetsProcessed,
 			"packets_dropped":   packetsDropped,
 			"bytes_processed":   bytesProcessed,
@@ -295,7 +295,7 @@ func (ts *TimeSeriesStorage) GetChargingHistory(ctx context.Context, subscriberI
 }
 
 // GetTopDataUsers retrieves top data users for a time period
-func (ts *TimeSeriesStorage) GetTopDataUsers(ctx context.Context, start, end time.Time, limit int) ([]map[string]interface{}, error) {
+func (ts *TimeSeriesStorage) GetTopDataUsers(ctx context.Context, start, end time.Time, limit int) ([]map[string]any, error) {
 	query := fmt.Sprintf(`
 		from(bucket: "%s")
 		|> range(start: %s, stop: %s)
@@ -312,10 +312,10 @@ func (ts *TimeSeriesStorage) GetTopDataUsers(ctx context.Context, start, end tim
 		return nil, fmt.Errorf("failed to query top data users: %w", err)
 	}
 
-	var users []map[string]interface{}
+	var users []map[string]any
 	for result.Next() {
 		record := result.Record()
-		user := map[string]interface{}{
+		user := map[string]any{
 			"subscriber_id": record.ValueByKey("subscriber_id"),
 			"total_data":    record.ValueByKey("total_data"),
 			"data_up":       record.ValueByKey("data_up"),

apps/api-server/internal/payment/gateway.go

@@ -179,7 +179,7 @@ func (s *StripeGateway) ProcessPayment(ctx context.Context, req *PaymentRequest)
 		return nil, fmt.Errorf("failed to create payment intent: %w", err)
 	}
 
-	intent, ok := intentResp.(map[string]interface{})
+	intent, ok := intentResp.(map[string]any)
 	if !ok {
 		return nil, fmt.Errorf("invalid payment intent response")
 	}
@@ -188,7 +188,7 @@ func (s *StripeGateway) ProcessPayment(ctx context.Context, req *PaymentRequest)
 
 	var failureReason *string
 	if status == PaymentStatusFailed {
-		if lastPaymentError, ok := intent["last_payment_error"].(map[string]interface{}); ok {
+		if lastPaymentError, ok := intent["last_payment_error"].(map[string]any); ok {
 			if message, ok := lastPaymentError["message"].(string); ok {
 				failureReason = &message
 			}
@@ -197,8 +197,8 @@ func (s *StripeGateway) ProcessPayment(ctx context.Context, req *PaymentRequest)
 
 	var redirectURL *string
 	if status == PaymentStatusPending {
-		if nextAction, ok := intent["next_action"].(map[string]interface{}); ok {
-			if url, ok := nextAction["redirect_to_url"].(map[string]interface{}); ok {
+		if nextAction, ok := intent["next_action"].(map[string]any); ok {
+			if url, ok := nextAction["redirect_to_url"].(map[string]any); ok {
 				if redirect, ok := url["url"].(string); ok {
 					redirectURL = &redirect
 				}
@@ -220,7 +220,7 @@ func (s *StripeGateway) ProcessPayment(ctx context.Context, req *PaymentRequest)
 
 // RefundPayment refunds a payment via Stripe
 func (s *StripeGateway) RefundPayment(ctx context.Context, transactionID string, amount float64) (*RefundResponse, error) {
-	refundData := map[string]interface{}{
+	refundData := map[string]any{
 		"payment_intent": transactionID,
 		"amount":         int64(amount * 100), // Stripe uses cents
 	}
@@ -230,7 +230,7 @@ func (s *StripeGateway) RefundPayment(ctx context.Context, transactionID string,
 		return nil, fmt.Errorf("failed to create refund: %w", err)
 	}
 
-	refund, ok := refundResp.(map[string]interface{})
+	refund, ok := refundResp.(map[string]any)
 	if !ok {
 		return nil, fmt.Errorf("invalid refund response")
 	}
@@ -262,7 +262,7 @@ func (s *StripeGateway) GetPaymentStatus(ctx context.Context, transactionID stri
 		return nil, fmt.Errorf("failed to get payment intent: %w", err)
 	}
 
-	intent, ok := intentResp.(map[string]interface{})
+	intent, ok := intentResp.(map[string]any)
 	if !ok {
 		return nil, fmt.Errorf("invalid payment intent response")
 	}
@@ -273,12 +273,12 @@ func (s *StripeGateway) GetPaymentStatus(ctx context.Context, transactionID stri
 		return nil, fmt.Errorf("failed to get refunds: %w", err)
 	}
 
-	refundsData, _ := refundsResp.(map[string]interface{})
-	refundsList, _ := refundsData["data"].([]interface{})
+	refundsData, _ := refundsResp.(map[string]any)
+	refundsList, _ := refundsData["data"].([]any)
 
 	refunds := make([]RefundInfo, len(refundsList))
 	for i, refundInterface := range refundsList {
-		refund, _ := refundInterface.(map[string]interface{})
+		refund, _ := refundInterface.(map[string]any)
 		createdAt, _ := time.Parse(time.RFC3339, refund["created"].(string))
 		refunds[i] = RefundInfo{
 			RefundID:  refund["id"].(string),
@@ -291,7 +291,7 @@ func (s *StripeGateway) GetPaymentStatus(ctx context.Context, transactionID stri
 	createdAt, _ := time.Parse(time.RFC3339, intent["created"].(string))
 
 	var failureReason *string
-	if lastPaymentError, ok := intent["last_payment_error"].(map[string]interface{}); ok {
+	if lastPaymentError, ok := intent["last_payment_error"].(map[string]any); ok {
 		if message, ok := lastPaymentError["message"].(string); ok {
 			failureReason = &message
 		}
@@ -311,7 +311,7 @@ func (s *StripeGateway) GetPaymentStatus(ctx context.Context, transactionID stri
 
 // CreatePaymentMethod creates a payment method in Stripe
 func (s *StripeGateway) CreatePaymentMethod(ctx context.Context, req *CreatePaymentMethodRequest) (*PaymentMethod, error) {
-	pmData := map[string]interface{}{
+	pmData := map[string]any{
 		"type": s.mapPaymentMethodType(req.Type),
 		"card": map[string]string{
 			"token": req.Token,
@@ -324,13 +324,13 @@ func (s *StripeGateway) CreatePaymentMethod(ctx context.Context, req *CreatePaym
 		return nil, fmt.Errorf("failed to create payment method: %w", err)
 	}
 
-	pm, ok := pmResp.(map[string]interface{})
+	pm, ok := pmResp.(map[string]any)
 	if !ok {
 		return nil, fmt.Errorf("invalid payment method response")
 	}
 
 	// Attach payment method to customer
-	attachData := map[string]interface{}{
+	attachData := map[string]any{
 		"customer": req.CustomerID,
 	}
 	_, err = s.makeStripeRequest(ctx, "POST", "/v1/payment_methods/"+pm["id"].(string)+"/attach", attachData)
@@ -340,7 +340,7 @@ func (s *StripeGateway) CreatePaymentMethod(ctx context.Context, req *CreatePaym
 
 	// Set as default if requested
 	if req.IsDefault {
-		customerData := map[string]interface{}{
+		customerData := map[string]any{
 			"invoice_settings": map[string]string{
 				"default_payment_method": pm["id"].(string),
 			},
@@ -351,7 +351,7 @@ func (s *StripeGateway) CreatePaymentMethod(ctx context.Context, req *CreatePaym
 		}
 	}
 
-	card, _ := pm["card"].(map[string]interface{})
+	card, _ := pm["card"].(map[string]any)
 	createdAt, _ := time.Parse(time.RFC3339, pm["created"].(string))
 
 	return &PaymentMethod{
@@ -388,10 +388,10 @@ func (s *StripeGateway) ValidateWebhook(ctx context.Context, signature string, b
 	var timestamp, v1Signature string
 	for _, part := range parts {
 		part = strings.TrimSpace(part)
-		if strings.HasPrefix(part, "t=") {
-			timestamp = strings.TrimPrefix(part, "t=")
-		} else if strings.HasPrefix(part, "v1=") {
-			v1Signature = strings.TrimPrefix(part, "v1=")
+		if after, ok := strings.CutPrefix(part, "t="); ok {
+			timestamp = after
+		} else if after, ok := strings.CutPrefix(part, "v1="); ok {
+			v1Signature = after
 		}
 	}
 
@@ -406,7 +406,7 @@ func (s *StripeGateway) ValidateWebhook(ctx context.Context, signature string, b
 }
 
 // Helper methods
-func (s *StripeGateway) makeStripeRequest(ctx context.Context, method, path string, data interface{}) (interface{}, error) {
+func (s *StripeGateway) makeStripeRequest(ctx context.Context, method, path string, data any) (any, error) {
 	url := "https://api.stripe.com" + path
 
 	var body io.Reader
@@ -439,9 +439,9 @@ func (s *StripeGateway) makeStripeRequest(ctx context.Context, method, path stri
 	}
 
 	if resp.StatusCode >= 400 {
-		var errorResp map[string]interface{}
+		var errorResp map[string]any
 		if err := json.Unmarshal(respBody, &errorResp); err == nil {
-			if errorMsg, ok := errorResp["error"].(map[string]interface{}); ok {
+			if errorMsg, ok := errorResp["error"].(map[string]any); ok {
 				if message, ok := errorMsg["message"].(string); ok {
 					return nil, fmt.Errorf("stripe error: %s", message)
 				}
@@ -450,7 +450,7 @@ func (s *StripeGateway) makeStripeRequest(ctx context.Context, method, path stri
 		return nil, fmt.Errorf("stripe error: %s", string(respBody))
 	}
 
-	var result interface{}
+	var result any
 	if err := json.Unmarshal(respBody, &result); err != nil {
 		return nil, fmt.Errorf("failed to unmarshal response: %w", err)
 	}

apps/api-server/internal/payment/gateways/stripe.go

@@ -42,7 +42,7 @@ func NewStripeGateway(secretKey, webhookSecret string) *StripeGateway {
 func (g *StripeGateway) ProcessPayment(ctx context.Context, req *PaymentRequest) (*PaymentResponse, error) {
 	// Create payment intent
 	params := &stripe.PaymentIntentParams{
-		Amount:   stripe.Int64(int64(req.Amount * 100)), // Convert to cents
+		Amount:   new(int64(req.Amount * 100)), // Convert to cents
 		Currency: stripe.String(string(req.Currency)),
 		Metadata: map[string]string{
 			"subscriber_id": fmt.Sprintf("%d", req.SubscriberID),
@@ -132,7 +132,7 @@ func (g *StripeGateway) ProcessRefund(ctx context.Context, transactionID string,
 	}
 
 	if amount > 0 {
-		params.Amount = stripe.Int64(int64(amount * 100)) // Convert to cents
+		params.Amount = new(int64(amount * 100)) // Convert to cents
 	}
 
 	refund, err := refund.New(params)
@@ -185,10 +185,10 @@ func (g *StripeGateway) CreateInvoice(ctx context.Context, customerID string, it
 	for _, item := range items {
 		itemParams := &stripe.InvoiceItemParams{
 			Customer:    stripe.String(customerID),
-			Amount:      stripe.Int64(int64(item.Amount * 100)),
+			Amount:      new(int64(item.Amount * 100)),
 			Currency:    stripe.String(string(item.Currency)),
 			Description: stripe.String(item.Description),
-			Quantity:    stripe.Int64(int64(item.Quantity)),
+			Quantity:    new(int64(item.Quantity)),
 		}
 
 		_, err := invoiceitem.New(itemParams)
@@ -200,7 +200,7 @@ func (g *StripeGateway) CreateInvoice(ctx context.Context, customerID string, it
 	// Create the invoice
 	params := &stripe.InvoiceParams{
 		Customer:    stripe.String(customerID),
-		AutoAdvance: stripe.Bool(true),
+		AutoAdvance: new(true),
 	}
 
 	inv, err := invoice.New(params)

apps/api-server/internal/payment/webhook.go

@@ -15,12 +15,12 @@ import (
 
 // WebhookEvent represents a payment webhook event
 type WebhookEvent struct {
-	ID       string                 `json:"id"`
-	Type     string                 `json:"type"`
-	Object   string                 `json:"object"`
-	Created  int64                  `json:"created"`
-	Livemode bool                   `json:"livemode"`
-	Data     map[string]interface{} `json:"data"`
+	ID       string         `json:"id"`
+	Type     string         `json:"type"`
+	Object   string         `json:"object"`
+	Created  int64          `json:"created"`
+	Livemode bool           `json:"livemode"`
+	Data     map[string]any `json:"data"`
 }
 
 // WebhookHandler handles payment webhooks
@@ -97,7 +97,7 @@ func (wh *WebhookHandler) HandleStripeWebhook(c *gin.Context) {
 
 // handlePaymentSucceeded handles successful payment events
 func (wh *WebhookHandler) handlePaymentSucceeded(ctx context.Context, event WebhookEvent) error {
-	paymentIntent, ok := event.Data["object"].(map[string]interface{})
+	paymentIntent, ok := event.Data["object"].(map[string]any)
 	if !ok {
 		return fmt.Errorf("invalid payment intent object")
 	}
@@ -145,7 +145,7 @@ func (wh *WebhookHandler) handlePaymentSucceeded(ctx context.Context, event Webh
 
 // handlePaymentFailed handles failed payment events
 func (wh *WebhookHandler) handlePaymentFailed(ctx context.Context, event WebhookEvent) error {
-	paymentIntent, ok := event.Data["object"].(map[string]interface{})
+	paymentIntent, ok := event.Data["object"].(map[string]any)
 	if !ok {
 		return fmt.Errorf("invalid payment intent object")
 	}
@@ -166,7 +166,7 @@ func (wh *WebhookHandler) handlePaymentFailed(ctx context.Context, event Webhook
 	transaction.UpdatedAt = time.Now()
 
 	// Add failure reason if available
-	if lastPaymentError, ok := paymentIntent["last_payment_error"].(map[string]interface{}); ok {
+	if lastPaymentError, ok := paymentIntent["last_payment_error"].(map[string]any); ok {
 		if message, ok := lastPaymentError["message"].(string); ok {
 			transaction.Description += " - Failed: " + message
 		}
@@ -199,7 +199,7 @@ func (wh *WebhookHandler) handlePaymentFailed(ctx context.Context, event Webhook
 
 // handlePaymentCanceled handles canceled payment events
 func (wh *WebhookHandler) handlePaymentCanceled(ctx context.Context, event WebhookEvent) error {
-	paymentIntent, ok := event.Data["object"].(map[string]interface{})
+	paymentIntent, ok := event.Data["object"].(map[string]any)
 	if !ok {
 		return fmt.Errorf("invalid payment intent object")
 	}
@@ -230,7 +230,7 @@ func (wh *WebhookHandler) handlePaymentCanceled(ctx context.Context, event Webho
 
 // handleDisputeCreated handles dispute events
 func (wh *WebhookHandler) handleDisputeCreated(ctx context.Context, event WebhookEvent) error {
-	dispute, ok := event.Data["object"].(map[string]interface{})
+	dispute, ok := event.Data["object"].(map[string]any)
 	if !ok {
 		return fmt.Errorf("invalid dispute object")
 	}