split cart and checkout and checkout vs payments

cmd/checkout/amqp-order-handler.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	amqp "github.com/rabbitmq/amqp091-go"
+)
+
+type AmqpOrderHandler struct {
+	conn  *amqp.Connection
+	queue *amqp.Queue
+}
+
+func NewAmqpOrderHandler(conn *amqp.Connection) *AmqpOrderHandler {
+	return &AmqpOrderHandler{
+		conn: conn,
+	}
+}
+
+func (h *AmqpOrderHandler) DefineQueue() error {
+	ch, err := h.conn.Channel()
+	if err != nil {
+		return fmt.Errorf("failed to open a channel: %w", err)
+	}
+	defer ch.Close()
+
+	queue, err := ch.QueueDeclare(
+		"order-queue", // name
+		false,
+		false,
+		false,
+		false,
+		nil,
+	)
+	if err != nil {
+		return fmt.Errorf("failed to declare an exchange: %w", err)
+	}
+	h.queue = &queue
+	return nil
+}
+
+func (h *AmqpOrderHandler) OrderCompleted(body []byte) error {
+	ch, err := h.conn.Channel()
+	if err != nil {
+		return fmt.Errorf("failed to open a channel: %w", err)
+	}
+	defer ch.Close()
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	return ch.PublishWithContext(ctx,
+		"",           // exchange
+		h.queue.Name, // routing key
+		false,        // mandatory
+		false,        // immediate
+		amqp.Publishing{
+			//DeliveryMode: amqp.,
+			ContentType: "application/json",
+			Body:        body,
+		})
+
+}

cmd/checkout/checkout_builder.go

@@ -0,0 +1,208 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"git.k6n.net/go-cart-actor/pkg/cart"
+	"git.k6n.net/go-cart-actor/pkg/checkout"
+	adyenCheckout "github.com/adyen/adyen-go-api-library/v21/src/checkout"
+	"github.com/adyen/adyen-go-api-library/v21/src/common"
+)
+
+// CheckoutMeta carries the external / URL metadata required to build a
+// Klarna CheckoutOrder from a CartGrain snapshot. It deliberately excludes
+// any Klarna-specific response fields (HTML snippet, client token, etc.).
+type CheckoutMeta struct {
+	SiteUrl string
+	// Terms        string
+	// Checkout     string
+	// Confirmation string
+	ClientIp string
+	Country  string
+	Currency string // optional override (defaults to "SEK" if empty)
+	Locale   string // optional override (defaults to "sv-se" if empty)
+}
+
+// BuildCheckoutOrderPayload converts the current cart grain + meta information
+// into a CheckoutOrder domain struct and returns its JSON-serialized payload
+// (to send to Klarna) alongside the structured CheckoutOrder object.
+//
+// This function is PURE: it does not perform any network I/O or mutate the
+// grain. The caller is responsible for:
+//
+//  1. Choosing whether to create or update the Klarna order.
+//  2. Invoking KlarnaClient.CreateOrder / UpdateOrder with the returned payload.
+//  3. Applying an InitializeCheckout mutation (or equivalent) with the
+//     resulting Klarna order id + status.
+//
+// If you later need to support different tax rates per line, you can extend
+// CartItem / Delivery to expose that data and propagate it here.
+func BuildCheckoutOrderPayload(grain *checkout.CheckoutGrain, meta *CheckoutMeta) ([]byte, *CheckoutOrder, error) {
+	if grain == nil {
+		return nil, nil, fmt.Errorf("nil grain")
+	}
+	if meta == nil {
+		return nil, nil, fmt.Errorf("nil checkout meta")
+	}
+
+	currency := meta.Currency
+	if currency == "" {
+		currency = "SEK"
+	}
+	locale := meta.Locale
+	if locale == "" {
+		locale = "sv-se"
+	}
+	country := meta.Country
+	if country == "" {
+		country = "SE" // sensible default; adjust if multi-country support changes
+	}
+
+	lines := make([]*Line, 0, len(grain.CartState.Items)+len(grain.Deliveries))
+
+	// Item lines
+	for _, it := range grain.CartState.Items {
+		if it == nil {
+			continue
+		}
+		lines = append(lines, &Line{
+			Type:           "physical",
+			Reference:      it.Sku,
+			Name:           it.Meta.Name,
+			Quantity:       int(it.Quantity),
+			UnitPrice:      int(it.Price.IncVat),
+			TaxRate:        it.Tax, // TODO: derive if variable tax rates are introduced
+			QuantityUnit:   "st",
+			TotalAmount:    int(it.TotalPrice.IncVat),
+			TotalTaxAmount: int(it.TotalPrice.TotalVat()),
+			ImageURL:       fmt.Sprintf("https://www.elgiganten.se%s", it.Meta.Image),
+		})
+	}
+
+	total := cart.NewPrice()
+	total.Add(*grain.CartState.TotalPrice)
+
+	// Delivery lines
+	for _, d := range grain.Deliveries {
+		if d == nil || d.Price.IncVat <= 0 {
+			continue
+		}
+		//total.Add(d.Price)
+		lines = append(lines, &Line{
+			Type:           "shipping_fee",
+			Reference:      d.Provider,
+			Name:           "Delivery",
+			Quantity:       1,
+			UnitPrice:      int(d.Price.IncVat),
+			TaxRate:        2500,
+			QuantityUnit:   "st",
+			TotalAmount:    int(d.Price.IncVat),
+			TotalTaxAmount: int(d.Price.TotalVat()),
+		})
+	}
+
+	order := &CheckoutOrder{
+		PurchaseCountry:    country,
+		PurchaseCurrency:   currency,
+		Locale:             locale,
+		OrderAmount:        int(total.IncVat),
+		OrderTaxAmount:     int(total.TotalVat()),
+		OrderLines:         lines,
+		MerchantReference1: grain.Id.String(),
+		MerchantURLS: &CheckoutMerchantURLS{
+			Terms:        fmt.Sprintf("%s/terms", meta.SiteUrl),
+			Checkout:     fmt.Sprintf("%s/checkout?order_id={checkout.order.id}", meta.SiteUrl),
+			Confirmation: fmt.Sprintf("%s/confirmation/{checkout.order.id}", meta.SiteUrl),
+			Notification: "https://cart.k6n.net/notification",
+			Validation:   "https://cart.k6n.net/validate",
+			Push:         "https://cart.k6n.net/push?order_id={checkout.order.id}",
+		},
+	}
+
+	payload, err := json.Marshal(order)
+	if err != nil {
+		return nil, nil, fmt.Errorf("marshal checkout order: %w", err)
+	}
+
+	return payload, order, nil
+}
+
+func GetCheckoutMetaFromRequest(r *http.Request) *CheckoutMeta {
+	host := getOriginalHost(r)
+	country := getCountryFromHost(host)
+	return &CheckoutMeta{
+		ClientIp: getClientIp(r),
+		SiteUrl:  fmt.Sprintf("https://%s", host),
+		Country:  country,
+		Currency: getCurrency(country),
+		Locale:   getLocale(country),
+	}
+}
+
+func BuildAdyenCheckoutSession(grain *checkout.CheckoutGrain, meta *CheckoutMeta) (*adyenCheckout.CreateCheckoutSessionRequest, error) {
+	if grain == nil {
+		return nil, fmt.Errorf("nil grain")
+	}
+	if meta == nil {
+		return nil, fmt.Errorf("nil checkout meta")
+	}
+
+	currency := meta.Currency
+	if currency == "" {
+		currency = "SEK"
+	}
+	country := meta.Country
+	if country == "" {
+		country = "SE"
+	}
+
+	lineItems := make([]adyenCheckout.LineItem, 0, len(grain.CartState.Items)+len(grain.Deliveries))
+
+	// Item lines
+	for _, it := range grain.CartState.Items {
+		if it == nil {
+			continue
+		}
+		lineItems = append(lineItems, adyenCheckout.LineItem{
+			Quantity:           common.PtrInt64(int64(it.Quantity)),
+			AmountIncludingTax: common.PtrInt64(it.TotalPrice.IncVat),
+			Description:        common.PtrString(it.Meta.Name),
+			AmountExcludingTax: common.PtrInt64(it.TotalPrice.ValueExVat()),
+			TaxAmount:          common.PtrInt64(it.TotalPrice.TotalVat()),
+			TaxPercentage:      common.PtrInt64(int64(it.Tax)),
+		})
+	}
+	total := cart.NewPrice()
+	total.Add(*grain.CartState.TotalPrice)
+
+	// Delivery lines
+	for _, d := range grain.Deliveries {
+		if d == nil || d.Price.IncVat <= 0 {
+			continue
+		}
+		lineItems = append(lineItems, adyenCheckout.LineItem{
+			Quantity:           common.PtrInt64(1),
+			AmountIncludingTax: common.PtrInt64(d.Price.IncVat),
+			Description:        common.PtrString("Delivery"),
+			AmountExcludingTax: common.PtrInt64(d.Price.ValueExVat()),
+			TaxPercentage:      common.PtrInt64(25),
+		})
+	}
+
+	return &adyenCheckout.CreateCheckoutSessionRequest{
+		Reference: grain.Id.String(),
+		Amount: adyenCheckout.Amount{
+			Value:    total.IncVat,
+			Currency: currency,
+		},
+		CountryCode:     common.PtrString(country),
+		MerchantAccount: "ElgigantenECOM",
+		Channel:         common.PtrString("Web"),
+		ShopperIP:       common.PtrString(meta.ClientIp),
+		ReturnUrl:       fmt.Sprintf("%s/adyen-return", meta.SiteUrl),
+		LineItems:       lineItems,
+	}, nil
+
+}

cmd/checkout/checkout_server.go

@@ -0,0 +1,226 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"git.k6n.net/go-cart-actor/pkg/cart"
+	"git.k6n.net/go-cart-actor/pkg/checkout"
+	messages "git.k6n.net/go-cart-actor/proto/checkout"
+
+	"github.com/matst80/go-redis-inventory/pkg/inventory"
+	amqp "github.com/rabbitmq/amqp091-go"
+)
+
+var tpl = `<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>s10r testing - checkout</title>
+  </head>
+
+  <body>
+    %s
+  </body>
+</html>
+`
+
+func getLocationId(item *cart.CartItem) inventory.LocationID {
+	if item.StoreId == nil || *item.StoreId == "" {
+		return "se"
+	}
+	return inventory.LocationID(*item.StoreId)
+}
+
+func getInventoryRequests(items []*cart.CartItem) []inventory.ReserveRequest {
+	var requests []inventory.ReserveRequest
+	for _, item := range items {
+		if item == nil {
+			continue
+		}
+		requests = append(requests, inventory.ReserveRequest{
+			InventoryReference: &inventory.InventoryReference{
+				SKU:        inventory.SKU(item.Sku),
+				LocationID: getLocationId(item),
+			},
+			Quantity: uint32(item.Quantity),
+		})
+	}
+	return requests
+}
+
+func (a *App) getGrainFromOrder(ctx context.Context, order *CheckoutOrder) (*checkout.CheckoutGrain, error) {
+	cartId, ok := cart.ParseCartId(order.MerchantReference1)
+	if !ok {
+		return nil, fmt.Errorf("invalid cart id in order reference: %s", order.MerchantReference1)
+	}
+	grain, err := a.pool.Get(ctx, uint64(cartId))
+	if err != nil {
+		return nil, fmt.Errorf("failed to get cart grain: %w", err)
+	}
+	return grain, nil
+}
+
+func (a *App) HandleCheckoutRequests(amqpUrl string, mux *http.ServeMux, inventoryService inventory.InventoryService) {
+	conn, err := amqp.Dial(amqpUrl)
+	if err != nil {
+		log.Fatalf("failed to connect to RabbitMQ: %v", err)
+	}
+
+	orderHandler := NewAmqpOrderHandler(conn)
+	orderHandler.DefineQueue()
+
+	mux.HandleFunc("/push", func(w http.ResponseWriter, r *http.Request) {
+		log.Printf("Klarna order confirmation push, method: %s", r.Method)
+		if r.Method != http.MethodPost {
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		orderId := r.URL.Query().Get("order_id")
+		log.Printf("Order confirmation push: %s", orderId)
+
+		order, err := a.klarnaClient.GetOrder(r.Context(), orderId)
+
+		if err != nil {
+			log.Printf("Error creating request: %v\n", err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		grain, err := a.getGrainFromOrder(r.Context(), order)
+		if err != nil {
+			logger.ErrorContext(r.Context(), "Unable to get grain from klarna order", "error", err.Error())
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		if inventoryService != nil {
+			inventoryRequests := getInventoryRequests(grain.CartState.Items)
+			err = inventoryService.ReserveInventory(r.Context(), inventoryRequests...)
+
+			if err != nil {
+				logger.WarnContext(r.Context(), "placeorder inventory reservation failed")
+				w.WriteHeader(http.StatusNotAcceptable)
+				return
+			}
+			a.pool.Apply(r.Context(), uint64(grain.Id), &messages.InventoryReserved{
+				Id:     grain.Id.String(),
+				Status: "success",
+			})
+		}
+
+		// err = confirmOrder(r.Context(), order, orderHandler)
+		// if err != nil {
+		// 	log.Printf("Error confirming order: %v\n", err)
+		// 	w.WriteHeader(http.StatusInternalServerError)
+		// 	return
+		// }
+
+		// err = triggerOrderCompleted(r.Context(), a.server, order)
+		// if err != nil {
+		// 	log.Printf("Error processing cart message: %v\n", err)
+		// 	w.WriteHeader(http.StatusInternalServerError)
+		// 	return
+		// }
+		err = a.klarnaClient.AcknowledgeOrder(r.Context(), orderId)
+		if err != nil {
+			log.Printf("Error acknowledging order: %v\n", err)
+		}
+
+		w.WriteHeader(http.StatusOK)
+	})
+
+	mux.HandleFunc("GET /checkout", a.server.CheckoutHandler(func(order *CheckoutOrder, w http.ResponseWriter) error {
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Header().Set("Permissions-Policy", "payment=(self \"https://js.stripe.com\" \"https://m.stripe.network\" \"https://js.playground.kustom.co\")")
+		w.WriteHeader(http.StatusOK)
+		_, err := fmt.Fprintf(w, tpl, order.HTMLSnippet)
+		return err
+	}))
+
+	mux.HandleFunc("GET /confirmation/{order_id}", func(w http.ResponseWriter, r *http.Request) {
+
+		orderId := r.PathValue("order_id")
+		order, err := a.klarnaClient.GetOrder(r.Context(), orderId)
+
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			return
+		}
+
+		// Apply ConfirmationViewed mutation
+		cartId, ok := cart.ParseCartId(order.MerchantReference1)
+		if ok {
+			a.pool.Apply(r.Context(), uint64(cartId), &messages.ConfirmationViewed{})
+		}
+
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		if order.Status == "checkout_complete" {
+			http.SetCookie(w, &http.Cookie{
+				Name:     "cartid",
+				Value:    "",
+				Path:     "/",
+				Secure:   true,
+				HttpOnly: true,
+				Expires:  time.Unix(0, 0),
+				SameSite: http.SameSiteLaxMode,
+			})
+		}
+
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprintf(w, tpl, order.HTMLSnippet)
+	})
+	mux.HandleFunc("/notification", func(w http.ResponseWriter, r *http.Request) {
+		log.Printf("Klarna order notification, method: %s", r.Method)
+		logger.InfoContext(r.Context(), "Klarna order notification received", "method", r.Method)
+		if r.Method != "POST" {
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		order := &CheckoutOrder{}
+		err := json.NewDecoder(r.Body).Decode(order)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+		}
+		log.Printf("Klarna order notification: %s", order.ID)
+		logger.InfoContext(r.Context(), "Klarna order notification received", "order_id", order.ID)
+
+		w.WriteHeader(http.StatusOK)
+	})
+	mux.HandleFunc("POST /validate", func(w http.ResponseWriter, r *http.Request) {
+		log.Printf("Klarna order validation, method: %s", r.Method)
+		if r.Method != "POST" {
+			w.WriteHeader(http.StatusMethodNotAllowed)
+			return
+		}
+		order := &CheckoutOrder{}
+		err := json.NewDecoder(r.Body).Decode(order)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+		}
+		logger.InfoContext(r.Context(), "Klarna order validation received", "order_id", order.ID, "cart_id", order.MerchantReference1)
+		grain, err := a.getGrainFromOrder(r.Context(), order)
+		if err != nil {
+			logger.ErrorContext(r.Context(), "Unable to get grain from klarna order", "error", err.Error())
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		if inventoryService != nil {
+			inventoryRequests := getInventoryRequests(grain.CartState.Items)
+			_, err = inventoryService.ReservationCheck(r.Context(), inventoryRequests...)
+			if err != nil {
+				logger.WarnContext(r.Context(), "placeorder inventory check failed")
+				w.WriteHeader(http.StatusNotAcceptable)
+				return
+			}
+		}
+
+		w.WriteHeader(http.StatusOK)
+	})
+}

cmd/checkout/k8s-host-discovery.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"log"
+
+	"git.k6n.net/go-cart-actor/pkg/actor"
+	"git.k6n.net/go-cart-actor/pkg/checkout"
+	"git.k6n.net/go-cart-actor/pkg/discovery"
+	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+)
+
+func GetDiscovery() discovery.Discovery {
+	if podIp == "" {
+		return nil
+	}
+
+	config, kerr := rest.InClusterConfig()
+
+	if kerr != nil {
+		log.Fatalf("Error creating kubernetes client: %v\n", kerr)
+	}
+	client, err := kubernetes.NewForConfig(config)
+	if err != nil {
+		log.Fatalf("Error creating client: %v\n", err)
+	}
+	timeout := int64(30)
+	return discovery.NewK8sDiscovery(client, v1.ListOptions{
+		LabelSelector:  "actor-pool=checkout",
+		TimeoutSeconds: &timeout,
+	})
+}
+
+func UseDiscovery(pool actor.GrainPool[*checkout.CheckoutGrain]) {
+
+	go func(hw discovery.Discovery) {
+		if hw == nil {
+			log.Print("No discovery service available")
+			return
+		}
+		ch, err := hw.Watch()
+		if err != nil {
+			log.Printf("Discovery error: %v", err)
+			return
+		}
+		for evt := range ch {
+			if evt.Host == "" {
+				continue
+			}
+			switch evt.IsReady {
+			case false:
+				if pool.IsKnown(evt.Host) {
+					log.Printf("Host %s is not ready, removing", evt.Host)
+					pool.RemoveHost(evt.Host)
+				}
+			default:
+				if !pool.IsKnown(evt.Host) {
+					log.Printf("Discovered host %s", evt.Host)
+					pool.AddRemoteHost(evt.Host)
+				}
+			}
+		}
+	}(GetDiscovery())
+}

cmd/checkout/klarna-client.go

@@ -0,0 +1,142 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+
+	"github.com/google/uuid"
+)
+
+type KlarnaClient struct {
+	Url      string
+	UserName string
+	Password string
+	client   *http.Client
+}
+
+func NewKlarnaClient(url, userName, password string) *KlarnaClient {
+	return &KlarnaClient{
+		Url:      url,
+		UserName: userName,
+		Password: password,
+		client:   &http.Client{},
+	}
+}
+
+const (
+	KlarnaPlaygroundUrl = "https://api.playground.klarna.com"
+)
+
+func (k *KlarnaClient) GetOrder(ctx context.Context, orderId string) (*CheckoutOrder, error) {
+	req, err := http.NewRequest("GET", k.Url+"/checkout/v3/orders/"+orderId, nil)
+	if err != nil {
+		return nil, err
+	}
+	spanCtx, span := tracer.Start(ctx, "Get klarna order")
+	defer span.End()
+	req = req.WithContext(spanCtx)
+	req.Header.Add("Content-Type", "application/json")
+	req.SetBasicAuth(k.UserName, k.Password)
+
+	res, err := k.client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	return k.getOrderResponse(res)
+}
+
+func (k *KlarnaClient) getOrderResponse(res *http.Response) (*CheckoutOrder, error) {
+	var err error
+	var klarnaOrderResponse CheckoutOrder
+	if res.StatusCode >= 200 && res.StatusCode <= 299 {
+		err = json.NewDecoder(res.Body).Decode(&klarnaOrderResponse)
+		if err != nil {
+			return nil, err
+		}
+		return &klarnaOrderResponse, nil
+	}
+	body, err := io.ReadAll(res.Body)
+	if err == nil {
+		log.Println(string(body))
+	}
+
+	return nil, fmt.Errorf("%s", res.Status)
+}
+
+func (k *KlarnaClient) CreateOrder(ctx context.Context, reader io.Reader) (*CheckoutOrder, error) {
+	//bytes.NewReader(reply.Payload)
+	req, err := http.NewRequest("POST", k.Url+"/checkout/v3/orders", reader)
+	if err != nil {
+		return nil, err
+	}
+	spanCtx, span := tracer.Start(ctx, "Create klarna order")
+	defer span.End()
+	req = req.WithContext(spanCtx)
+	req.Header.Add("Content-Type", "application/json")
+	req.SetBasicAuth(k.UserName, k.Password)
+
+	res, err := http.DefaultClient.Do(req)
+	if nil != err {
+		return nil, err
+	}
+	defer res.Body.Close()
+	return k.getOrderResponse(res)
+}
+
+func (k *KlarnaClient) UpdateOrder(ctx context.Context, orderId string, reader io.Reader) (*CheckoutOrder, error) {
+	//bytes.NewReader(reply.Payload)
+	req, err := http.NewRequest("POST", fmt.Sprintf("%s/checkout/v3/orders/%s", k.Url, orderId), reader)
+	if err != nil {
+		return nil, err
+	}
+
+	spanCtx, span := tracer.Start(ctx, "Update klarna order")
+	defer span.End()
+	req = req.WithContext(spanCtx)
+	req.Header.Add("Content-Type", "application/json")
+	req.SetBasicAuth(k.UserName, k.Password)
+
+	res, err := http.DefaultClient.Do(req)
+	if nil != err {
+		return nil, err
+	}
+	defer res.Body.Close()
+	return k.getOrderResponse(res)
+}
+
+func (k *KlarnaClient) AbortOrder(ctx context.Context, orderId string) error {
+	req, err := http.NewRequest("POST", fmt.Sprintf("%s/checkout/v3/orders/%s/abort", k.Url, orderId), nil)
+	if err != nil {
+		return err
+	}
+	spanCtx, span := tracer.Start(ctx, "Abort klarna order")
+	defer span.End()
+	req = req.WithContext(spanCtx)
+	req.SetBasicAuth(k.UserName, k.Password)
+
+	_, err = http.DefaultClient.Do(req)
+	return err
+}
+
+// ordermanagement/v1/orders/{order_id}/acknowledge
+func (k *KlarnaClient) AcknowledgeOrder(ctx context.Context, orderId string) error {
+	req, err := http.NewRequest("POST", fmt.Sprintf("%s/ordermanagement/v1/orders/%s/acknowledge", k.Url, orderId), nil)
+	if err != nil {
+		return err
+	}
+	spanCtx, span := tracer.Start(ctx, "Acknowledge klarna order")
+	defer span.End()
+	req = req.WithContext(spanCtx)
+	id := uuid.New()
+
+	req.SetBasicAuth(k.UserName, k.Password)
+	req.Header.Add("Klarna-Idempotency-Key", id.String())
+
+	_, err = http.DefaultClient.Do(req)
+	return err
+}

cmd/checkout/klarna-types.go

@@ -0,0 +1,169 @@
+package main
+
+type (
+	LineType string
+
+	// CheckoutOrder type is the request structure to create a new order from the Checkout API
+	CheckoutOrder struct {
+		ID                     string                `json:"order_id,omitempty"`
+		PurchaseCountry        string                `json:"purchase_country"`
+		PurchaseCurrency       string                `json:"purchase_currency"`
+		Locale                 string                `json:"locale"`
+		Status                 string                `json:"status,omitempty"`
+		BillingAddress         *Address              `json:"billing_address,omitempty"`
+		ShippingAddress        *Address              `json:"shipping_address,omitempty"`
+		OrderAmount            int                   `json:"order_amount"`
+		OrderTaxAmount         int                   `json:"order_tax_amount"`
+		OrderLines             []*Line               `json:"order_lines"`
+		Customer               *CheckoutCustomer     `json:"customer,omitempty"`
+		MerchantURLS           *CheckoutMerchantURLS `json:"merchant_urls"`
+		HTMLSnippet            string                `json:"html_snippet,omitempty"`
+		MerchantReference1     string                `json:"merchant_reference1,omitempty"`
+		MerchantReference2     string                `json:"merchant_reference2,omitempty"`
+		StartedAt              string                `json:"started_at,omitempty"`
+		CompletedAt            string                `json:"completed_at,omitempty"`
+		LastModifiedAt         string                `json:"last_modified_at,omitempty"`
+		Options                *CheckoutOptions      `json:"options,omitempty"`
+		Attachment             *Attachment           `json:"attachment,omitempty"`
+		ExternalPaymentMethods []*PaymentProvider    `json:"external_payment_methods,omitempty"`
+		ExternalCheckouts      []*PaymentProvider    `json:"external_checkouts,omitempty"`
+		ShippingCountries      []string              `json:"shipping_countries,omitempty"`
+		ShippingOptions        []*ShippingOption     `json:"shipping_options,omitempty"`
+		MerchantData           string                `json:"merchant_data,omitempty"`
+		GUI                    *GUI                  `json:"gui,omitempty"`
+		MerchantRequested      *AdditionalCheckBox   `json:"merchant_requested,omitempty"`
+		SelectedShippingOption *ShippingOption       `json:"selected_shipping_option,omitempty"`
+		ErrorCode              string                `json:"error_code,omitempty"`
+		ErrorMessages          []string              `json:"error_messages,omitempty"`
+	}
+
+	// GUI type wraps the GUI options
+	GUI struct {
+		Options []string `json:"options,omitempty"`
+	}
+
+	// ShippingOption type is part of the CheckoutOrder structure, represent the shipping options field
+	ShippingOption struct {
+		ID             string `json:"id"`
+		Name           string `json:"name"`
+		Description    string `json:"description,omitempty"`
+		Promo          string `json:"promo,omitempty"`
+		Price          int    `json:"price"`
+		TaxAmount      int    `json:"tax_amount"`
+		TaxRate        int    `json:"tax_rate"`
+		Preselected    bool   `json:"preselected,omitempty"`
+		ShippingMethod string `json:"shipping_method,omitempty"`
+	}
+
+	// PaymentProvider type is part of the CheckoutOrder structure, represent the ExternalPaymentMethods and
+	// ExternalCheckouts field
+	PaymentProvider struct {
+		Name        string   `json:"name"`
+		RedirectURL string   `json:"redirect_url"`
+		ImageURL    string   `json:"image_url,omitempty"`
+		Fee         int      `json:"fee,omitempty"`
+		Description string   `json:"description,omitempty"`
+		Countries   []string `json:"countries,omitempty"`
+	}
+
+	Attachment struct {
+		ContentType string `json:"content_type"`
+		Body        string `json:"body"`
+	}
+
+	CheckoutOptions struct {
+		AcquiringChannel               string              `json:"acquiring_channel,omitempty"`
+		AllowSeparateShippingAddress   bool                `json:"allow_separate_shipping_address,omitempty"`
+		ColorButton                    string              `json:"color_button,omitempty"`
+		ColorButtonText                string              `json:"color_button_text,omitempty"`
+		ColorCheckbox                  string              `json:"color_checkbox,omitempty"`
+		ColorCheckboxCheckmark         string              `json:"color_checkbox_checkmark,omitempty"`
+		ColorHeader                    string              `json:"color_header,omitempty"`
+		ColorLink                      string              `json:"color_link,omitempty"`
+		DateOfBirthMandatory           bool                `json:"date_of_birth_mandatory,omitempty"`
+		ShippingDetails                string              `json:"shipping_details,omitempty"`
+		TitleMandatory                 bool                `json:"title_mandatory,omitempty"`
+		AdditionalCheckbox             *AdditionalCheckBox `json:"additional_checkbox"`
+		RadiusBorder                   string              `json:"radius_border,omitempty"`
+		ShowSubtotalDetail             bool                `json:"show_subtotal_detail,omitempty"`
+		RequireValidateCallbackSuccess bool                `json:"require_validate_callback_success,omitempty"`
+		AllowGlobalBillingCountries    bool                `json:"allow_global_billing_countries,omitempty"`
+	}
+
+	AdditionalCheckBox struct {
+		Text     string `json:"text"`
+		Checked  bool   `json:"checked"`
+		Required bool   `json:"required"`
+	}
+
+	CheckoutMerchantURLS struct {
+		// URL of merchant terms and conditions. Should be different than checkout, confirmation and push URLs.
+		// (max 2000 characters)
+		Terms string `json:"terms"`
+
+		// URL of merchant checkout page. Should be different than terms, confirmation and push URLs.
+		// (max 2000 characters)
+		Checkout string `json:"checkout"`
+
+		// URL of merchant confirmation page. Should be different than checkout and confirmation URLs.
+		// (max 2000 characters)
+		Confirmation string `json:"confirmation"`
+
+		// URL that will be requested when an order is completed. Should be different than checkout and
+		// confirmation URLs. (max 2000 characters)
+		Push string `json:"push"`
+		// URL that will be requested for final merchant validation. (must be https, max 2000 characters)
+		Validation string `json:"validation,omitempty"`
+
+		// URL for shipping option update. (must be https, max 2000 characters)
+		ShippingOptionUpdate string `json:"shipping_option_update,omitempty"`
+
+		// URL for shipping, tax and purchase currency updates. Will be called on address changes.
+		// (must be https, max 2000 characters)
+		AddressUpdate string `json:"address_update,omitempty"`
+
+		// URL for notifications on pending orders. (max 2000 characters)
+		Notification string `json:"notification,omitempty"`
+
+		// URL for shipping, tax and purchase currency updates. Will be called on purchase country changes.
+		// (must be https, max 2000 characters)
+		CountryChange string `json:"country_change,omitempty"`
+	}
+
+	CheckoutCustomer struct {
+		// DateOfBirth in string representation 2006-01-02
+		DateOfBirth string `json:"date_of_birth"`
+	}
+
+	// Address type define the address object (json serializable) being used for the API to represent billing &
+	// shipping addresses
+	Address struct {
+		GivenName      string `json:"given_name,omitempty"`
+		FamilyName     string `json:"family_name,omitempty"`
+		Email          string `json:"email,omitempty"`
+		Title          string `json:"title,omitempty"`
+		StreetAddress  string `json:"street_address,omitempty"`
+		StreetAddress2 string `json:"street_address2,omitempty"`
+		PostalCode     string `json:"postal_code,omitempty"`
+		City           string `json:"city,omitempty"`
+		Region         string `json:"region,omitempty"`
+		Phone          string `json:"phone,omitempty"`
+		Country        string `json:"country,omitempty"`
+	}
+
+	Line struct {
+		Type                string `json:"type,omitempty"`
+		Reference           string `json:"reference,omitempty"`
+		Name                string `json:"name"`
+		Quantity            int    `json:"quantity"`
+		QuantityUnit        string `json:"quantity_unit,omitempty"`
+		UnitPrice           int    `json:"unit_price"`
+		TaxRate             int    `json:"tax_rate"`
+		TotalAmount         int    `json:"total_amount"`
+		TotalDiscountAmount int    `json:"total_discount_amount,omitempty"`
+		TotalTaxAmount      int    `json:"total_tax_amount"`
+		MerchantData        string `json:"merchant_data,omitempty"`
+		ProductURL          string `json:"product_url,omitempty"`
+		ImageURL            string `json:"image_url,omitempty"`
+	}
+)

cmd/checkout/main.go

@@ -0,0 +1,252 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"os/signal"
+	"strings"
+	"time"
+
+	"git.k6n.net/go-cart-actor/pkg/actor"
+	"git.k6n.net/go-cart-actor/pkg/cart"
+	"git.k6n.net/go-cart-actor/pkg/checkout"
+	"git.k6n.net/go-cart-actor/pkg/proxy"
+	"github.com/adyen/adyen-go-api-library/v21/src/adyen"
+	"github.com/adyen/adyen-go-api-library/v21/src/common"
+	"github.com/gogo/protobuf/proto"
+	"github.com/matst80/go-redis-inventory/pkg/inventory"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/redis/go-redis/v9"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+)
+
+var (
+	grainSpawns = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "checkout_grain_spawned_total",
+		Help: "The total number of spawned checkout grains",
+	})
+)
+
+func init() {
+	os.Mkdir("data", 0755)
+}
+
+type App struct {
+	pool         *actor.SimpleGrainPool[checkout.CheckoutGrain]
+	server       *CheckoutPoolServer
+	klarnaClient *KlarnaClient
+	cartClient   *CartClient // For internal communication to cart
+}
+
+var podIp = os.Getenv("POD_IP")
+var name = os.Getenv("POD_NAME")
+var amqpUrl = os.Getenv("AMQP_URL")
+var redisAddress = os.Getenv("REDIS_ADDRESS")
+var redisPassword = os.Getenv("REDIS_PASSWORD")
+var cartInternalUrl = os.Getenv("CART_INTERNAL_URL") // e.g., http://cart-service:8081
+
+func getCountryFromHost(host string) string {
+	if strings.Contains(strings.ToLower(host), "-no") {
+		return "no"
+	}
+	if strings.Contains(strings.ToLower(host), "-se") {
+		return "se"
+	}
+	return ""
+}
+
+type CartClient struct {
+	httpClient *http.Client
+	baseUrl    string
+}
+
+func NewCartClient(baseUrl string) *CartClient {
+	return &CartClient{
+		httpClient: &http.Client{Timeout: 10 * time.Second},
+		baseUrl:    baseUrl,
+	}
+}
+
+func (c *CartClient) ApplyMutation(cartId cart.CartId, mutation proto.Message) error {
+	url := fmt.Sprintf("%s/internal/cart/%s/mutation", c.baseUrl, cartId.String())
+	data, err := proto.Marshal(mutation)
+	if err != nil {
+		return err
+	}
+	req, err := http.NewRequest("POST", url, bytes.NewReader(data))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/protobuf")
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("cart mutation failed: %s", resp.Status)
+	}
+	return nil
+}
+
+func main() {
+
+	controlPlaneConfig := actor.DefaultServerConfig()
+
+	reg := checkout.NewCheckoutMutationRegistry(checkout.NewCheckoutMutationContext())
+	reg.RegisterProcessor(
+		actor.NewMutationProcessor(func(ctx context.Context, g *checkout.CheckoutGrain) error {
+			g.Version++
+			return nil
+		}),
+	)
+	rdb := redis.NewClient(&redis.Options{
+		Addr:     redisAddress,
+		Password: redisPassword,
+		DB:       0,
+	})
+	inventoryService, err := inventory.NewRedisInventoryService(rdb)
+	if err != nil {
+		log.Fatalf("Error creating inventory service: %v\n", err)
+	}
+
+	diskStorage := actor.NewDiskStorage[checkout.CheckoutGrain]("data", reg)
+
+	poolConfig := actor.GrainPoolConfig[checkout.CheckoutGrain]{
+		MutationRegistry: reg,
+		Storage:          diskStorage,
+		Spawn: func(ctx context.Context, id uint64) (actor.Grain[checkout.CheckoutGrain], error) {
+			_, span := tracer.Start(ctx, fmt.Sprintf("Spawn checkout id %d", id))
+			defer span.End()
+			grainSpawns.Inc()
+
+			ret := checkout.NewCheckoutGrain(id, 0, 0, time.Now(), nil) // version to be set later
+			return ret, nil
+		},
+		Destroy: func(grain actor.Grain[checkout.CheckoutGrain]) error {
+			return nil
+		},
+		SpawnHost: func(host string) (actor.Host, error) {
+			return proxy.NewRemoteHost[checkout.CheckoutGrain](host)
+		},
+		TTL:      1 * time.Hour, // Longer TTL for checkout
+		PoolSize: 65535,
+		Hostname: podIp,
+	}
+
+	pool, err := actor.NewSimpleGrainPool(poolConfig)
+	if err != nil {
+		log.Fatalf("Error creating checkout pool: %v\n", err)
+	}
+
+	adyenClient := adyen.NewClient(&common.Config{
+		ApiKey:      os.Getenv("ADYEN_API_KEY"),
+		Environment: common.TestEnv,
+	})
+
+	klarnaClient := NewKlarnaClient(KlarnaPlaygroundUrl, os.Getenv("KLARNA_API_USERNAME"), os.Getenv("KLARNA_API_PASSWORD"))
+
+	cartClient := NewCartClient(cartInternalUrl)
+
+	syncedServer := NewCheckoutPoolServer(pool, fmt.Sprintf("%s, %s", name, podIp), klarnaClient, cartClient, adyenClient)
+
+	app := &App{
+		pool:         pool,
+		server:       syncedServer,
+		klarnaClient: klarnaClient,
+		cartClient:   cartClient,
+	}
+
+	mux := http.NewServeMux()
+	debugMux := http.NewServeMux()
+
+	if amqpUrl == "" {
+		log.Printf("no connection to amqp defined")
+	} else {
+		app.HandleCheckoutRequests(amqpUrl, mux, inventoryService)
+	}
+
+	grpcSrv, err := actor.NewControlServer[*checkout.CheckoutGrain](controlPlaneConfig, pool)
+	if err != nil {
+		log.Fatalf("Error starting control plane gRPC server: %v\n", err)
+	}
+	defer grpcSrv.GracefulStop()
+
+	UseDiscovery(pool)
+
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
+	defer stop()
+
+	otelShutdown, err := setupOTelSDK(ctx)
+	if err != nil {
+		log.Fatalf("Unable to start otel %v", err)
+	}
+
+	syncedServer.Serve(mux)
+
+	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
+		grainCount, capacity := app.pool.LocalUsage()
+		if grainCount >= capacity {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte("grain pool at capacity"))
+			return
+		}
+		if !pool.IsHealthy() {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte("control plane not healthy"))
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("ok"))
+	})
+	mux.HandleFunc("/readyz", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("ok"))
+	})
+	mux.HandleFunc("/livez", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("ok"))
+	})
+
+	mux.HandleFunc("/version", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte("1.0.0"))
+	})
+
+	srv := &http.Server{
+		Addr:         ":8080",
+		BaseContext:  func(net.Listener) context.Context { return ctx },
+		ReadTimeout:  10 * time.Second,
+		WriteTimeout: 20 * time.Second,
+		Handler:      otelhttp.NewHandler(mux, "/"),
+	}
+
+	defer func() {
+		fmt.Println("Shutting down due to signal")
+		otelShutdown(context.Background())
+		diskStorage.Close()
+		pool.Close()
+	}()
+
+	srvErr := make(chan error, 1)
+	go func() {
+		srvErr <- srv.ListenAndServe()
+	}()
+
+	log.Print("Checkout server started at port 8080")
+
+	go http.ListenAndServe(":8081", debugMux)
+
+	select {
+	case err = <-srvErr:
+		log.Fatalf("Unable to start server: %v", err)
+	case <-ctx.Done():
+		stop()
+	}
+}

cmd/checkout/otel.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
+	"go.opentelemetry.io/otel/log/global"
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/sdk/log"
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/trace"
+)
+
+// setupOTelSDK bootstraps the OpenTelemetry pipeline.
+// If it does not return an error, make sure to call shutdown for proper cleanup.
+func setupOTelSDK(ctx context.Context) (func(context.Context) error, error) {
+	var shutdownFuncs []func(context.Context) error
+	var err error
+
+	// shutdown calls cleanup functions registered via shutdownFuncs.
+	// The errors from the calls are joined.
+	// Each registered cleanup will be invoked once.
+	shutdown := func(ctx context.Context) error {
+		var err error
+		for _, fn := range shutdownFuncs {
+			err = errors.Join(err, fn(ctx))
+		}
+		shutdownFuncs = nil
+		return err
+	}
+
+	// handleErr calls shutdown for cleanup and makes sure that all errors are returned.
+	handleErr := func(inErr error) {
+		err = errors.Join(inErr, shutdown(ctx))
+	}
+
+	// Set up propagator.
+	prop := newPropagator()
+	otel.SetTextMapPropagator(prop)
+
+	// Set up trace provider.
+	tracerProvider, err := newTracerProvider()
+	if err != nil {
+		handleErr(err)
+		return shutdown, err
+	}
+	shutdownFuncs = append(shutdownFuncs, tracerProvider.Shutdown)
+	otel.SetTracerProvider(tracerProvider)
+
+	// Set up meter provider.
+	meterProvider, err := newMeterProvider()
+	if err != nil {
+		handleErr(err)
+		return shutdown, err
+	}
+	shutdownFuncs = append(shutdownFuncs, meterProvider.Shutdown)
+	otel.SetMeterProvider(meterProvider)
+
+	// Set up logger provider.
+	loggerProvider, err := newLoggerProvider()
+	if err != nil {
+		handleErr(err)
+		return shutdown, err
+	}
+	shutdownFuncs = append(shutdownFuncs, loggerProvider.Shutdown)
+	global.SetLoggerProvider(loggerProvider)
+
+	return shutdown, err
+}
+
+func newPropagator() propagation.TextMapPropagator {
+	return propagation.NewCompositeTextMapPropagator(
+		propagation.TraceContext{},
+		propagation.Baggage{},
+	)
+}
+
+func newTracerProvider() (*trace.TracerProvider, error) {
+	traceExporter, err := otlptracegrpc.New(context.Background())
+	if err != nil {
+		return nil, err
+	}
+
+	tracerProvider := trace.NewTracerProvider(
+		trace.WithBatcher(traceExporter,
+			// Default is 5s. Set to 1s for demonstrative purposes.
+			trace.WithBatchTimeout(time.Second)),
+	)
+	return tracerProvider, nil
+}
+
+func newMeterProvider() (*metric.MeterProvider, error) {
+	exporter, err := otlpmetricgrpc.New(context.Background())
+	if err != nil {
+		return nil, err
+	}
+
+	provider := metric.NewMeterProvider(metric.WithReader(metric.NewPeriodicReader(exporter)))
+	return provider, nil
+}
+
+func newLoggerProvider() (*log.LoggerProvider, error) {
+	logExporter, err := otlploggrpc.New(context.Background())
+	if err != nil {
+		return nil, err
+	}
+
+	loggerProvider := log.NewLoggerProvider(
+		log.WithProcessor(log.NewBatchProcessor(logExporter)),
+	)
+	return loggerProvider, nil
+}

cmd/checkout/pool-server.go

@@ -0,0 +1,320 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"time"
+
+	"git.k6n.net/go-cart-actor/pkg/actor"
+	"git.k6n.net/go-cart-actor/pkg/cart"
+	"git.k6n.net/go-cart-actor/pkg/checkout"
+	messages "git.k6n.net/go-cart-actor/proto/checkout"
+
+	adyen "github.com/adyen/adyen-go-api-library/v21/src/adyen"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"go.opentelemetry.io/contrib/bridges/otelslog"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/trace"
+)
+
+func getOriginalHost(r *http.Request) string {
+	proxyHost := r.Header.Get("X-Forwarded-Host")
+	if proxyHost != "" {
+		return proxyHost
+	}
+	return r.Host
+}
+
+func getClientIp(r *http.Request) string {
+	ip := r.Header.Get("X-Forwarded-For")
+	if ip == "" {
+		ip = r.RemoteAddr
+	}
+	return ip
+}
+
+func getCurrency(country string) string {
+	if country == "no" {
+		return "NOK"
+	}
+	return "SEK"
+}
+
+func getLocale(country string) string {
+	if country == "no" {
+		return "nb-no"
+	}
+	return "sv-se"
+}
+
+var (
+	grainMutations = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "checkout_grain_mutations_total",
+		Help: "The total number of mutations",
+	})
+	grainLookups = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "checkout_grain_lookups_total",
+		Help: "The total number of lookups",
+	})
+)
+
+type CheckoutPoolServer struct {
+	actor.GrainPool[*checkout.CheckoutGrain]
+	pod_name     string
+	klarnaClient *KlarnaClient
+	adyenClient  *adyen.APIClient
+	cartClient   *CartClient
+}
+
+func NewCheckoutPoolServer(pool actor.GrainPool[*checkout.CheckoutGrain], pod_name string, klarnaClient *KlarnaClient, cartClient *CartClient, adyenClient *adyen.APIClient) *CheckoutPoolServer {
+	srv := &CheckoutPoolServer{
+		GrainPool:    pool,
+		pod_name:     pod_name,
+		klarnaClient: klarnaClient,
+		cartClient:   cartClient,
+		adyenClient:  adyenClient,
+	}
+
+	return srv
+}
+
+func (s *CheckoutPoolServer) ApplyLocal(ctx context.Context, id checkout.CheckoutId, mutation ...proto.Message) (*actor.MutationResult[*checkout.CheckoutGrain], error) {
+	return s.Apply(ctx, uint64(id), mutation...)
+}
+
+func (s *CheckoutPoolServer) GetCheckoutHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
+	grain, err := s.Get(r.Context(), uint64(id))
+	if err != nil {
+		return err
+	}
+
+	return s.WriteResult(w, grain)
+}
+
+func (s *CheckoutPoolServer) WriteResult(w http.ResponseWriter, result any) error {
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Access-Control-Allow-Origin", "*")
+	w.Header().Set("X-Pod-Name", s.pod_name)
+	if result == nil {
+
+		w.WriteHeader(http.StatusInternalServerError)
+
+		return nil
+	}
+	w.WriteHeader(http.StatusOK)
+	enc := json.NewEncoder(w)
+	err := enc.Encode(result)
+	return err
+}
+
+func (s *CheckoutPoolServer) CreateOrUpdateCheckout(r *http.Request, id checkout.CheckoutId) (*CheckoutOrder, error) {
+	// Get cart state from cart service
+	cartGrain, err := s.Get(r.Context(), uint64(id))
+	if err != nil {
+		return nil, err
+	}
+
+	meta := GetCheckoutMetaFromRequest(r)
+
+	payload, _, err := BuildCheckoutOrderPayload(cartGrain, meta)
+	if err != nil {
+		return nil, err
+	}
+
+	grain, err := s.Get(r.Context(), uint64(id))
+	if err != nil {
+		return nil, err
+	}
+
+	if grain.OrderId != nil {
+		return s.klarnaClient.UpdateOrder(r.Context(), *grain.OrderId, bytes.NewReader(payload))
+	} else {
+		return s.klarnaClient.CreateOrder(r.Context(), bytes.NewReader(payload))
+	}
+}
+
+func (s *CheckoutPoolServer) ApplyKlarnaPaymentStarted(ctx context.Context, klarnaOrder *CheckoutOrder, id checkout.CheckoutId) (*actor.MutationResult[*checkout.CheckoutGrain], error) {
+	method := "checkout"
+	return s.ApplyLocal(ctx, id, &messages.PaymentStarted{
+		PaymentId: klarnaOrder.ID,
+		Amount:    int64(klarnaOrder.OrderAmount),
+		Currency:  klarnaOrder.PurchaseCurrency,
+		Provider:  "klarna",
+		Method:    &method,
+		StartedAt: timestamppb.New(time.Now()),
+	})
+}
+
+func (s *CheckoutPoolServer) CheckoutHandler(fn func(order *CheckoutOrder, w http.ResponseWriter) error) func(w http.ResponseWriter, r *http.Request) {
+	return CheckoutIdHandler(s.ProxyHandler(func(w http.ResponseWriter, r *http.Request, checkoutId checkout.CheckoutId) error {
+		orderId := r.URL.Query().Get("order_id")
+		if orderId == "" {
+			order, err := s.CreateOrUpdateCheckout(r, checkoutId)
+			if err != nil {
+				logger.Error("unable to create klarna session", "error", err)
+				return err
+			}
+			s.ApplyKlarnaPaymentStarted(r.Context(), order, checkoutId)
+			return fn(order, w)
+		}
+		order, err := s.klarnaClient.GetOrder(r.Context(), orderId)
+		if err != nil {
+			return err
+		}
+		return fn(order, w)
+	}))
+}
+
+func (s *CheckoutPoolServer) getCartGrain(ctx context.Context, cartId cart.CartId, version int) (*cart.CartGrain, error) {
+	// Call cart service to get grain
+	url := fmt.Sprintf("%s/internal/cart/%s/%d", s.cartClient.baseUrl, cartId.String(), version)
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := s.cartClient.httpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to get cart: %s", resp.Status)
+	}
+	var grain cart.CartGrain
+	err = json.NewDecoder(resp.Body).Decode(&grain)
+	return &grain, err
+}
+
+func CheckoutIdHandler(fn func(checkoutId checkout.CheckoutId, w http.ResponseWriter, r *http.Request) error) func(w http.ResponseWriter, r *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		var id checkout.CheckoutId
+		raw := r.PathValue("id")
+		if raw == "" {
+			id = checkout.CheckoutId(cart.MustNewCartId())
+			w.Header().Set("Set-Checkout-Id", id.String())
+		} else {
+			if parsedId, ok := cart.ParseCartId(raw); !ok {
+				w.WriteHeader(http.StatusBadRequest)
+				w.Write([]byte("checkout id is invalid"))
+				return
+			} else {
+				id = checkout.CheckoutId(parsedId)
+			}
+		}
+
+		err := fn(id, w, r)
+		if err != nil {
+			log.Printf("Server error, not remote error: %v\n", err)
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+		}
+	}
+}
+
+func (s *CheckoutPoolServer) ProxyHandler(fn func(w http.ResponseWriter, r *http.Request, checkoutId checkout.CheckoutId) error) func(checkoutId checkout.CheckoutId, w http.ResponseWriter, r *http.Request) error {
+	return func(checkoutId checkout.CheckoutId, w http.ResponseWriter, r *http.Request) error {
+		if ownerHost, ok := s.OwnerHost(uint64(checkoutId)); ok {
+			ctx, span := tracer.Start(r.Context(), "proxy")
+			defer span.End()
+			span.SetAttributes(attribute.String("checkoutid", checkoutId.String()))
+			hostAttr := attribute.String("other host", ownerHost.Name())
+			span.SetAttributes(hostAttr)
+			logger.InfoContext(ctx, "checkout proxyed", "result", ownerHost.Name())
+			proxyCalls.Add(ctx, 1, metric.WithAttributes(hostAttr))
+			handled, err := ownerHost.Proxy(uint64(checkoutId), w, r, nil)
+
+			grainLookups.Inc()
+			if err == nil && handled {
+				return nil
+			}
+		}
+		_, span := tracer.Start(r.Context(), "own")
+		span.SetAttributes(attribute.String("checkoutid", checkoutId.String()))
+		defer span.End()
+		return fn(w, r, checkoutId)
+	}
+}
+
+var (
+	tracer     = otel.Tracer(name)
+	hmacKey    = os.Getenv("ADYEN_HMAC")
+	meter      = otel.Meter(name)
+	logger     = otelslog.NewLogger(name)
+	proxyCalls metric.Int64Counter
+)
+
+func init() {
+	var err error
+	proxyCalls, err = meter.Int64Counter("proxy.calls",
+		metric.WithDescription("Number of proxy calls"),
+		metric.WithUnit("{calls}"))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Request) {
+	// Similar to cart's, but apply to checkout and then callback to cart
+}
+
+func (s *CheckoutPoolServer) Serve(mux *http.ServeMux) {
+	handleFunc := func(pattern string, handlerFunc func(http.ResponseWriter, *http.Request)) {
+		attr := attribute.String("http.route", pattern)
+		mux.HandleFunc(pattern, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			span := trace.SpanFromContext(r.Context())
+			span.SetName(pattern)
+			span.SetAttributes(attr)
+
+			labeler, _ := otelhttp.LabelerFromContext(r.Context())
+			labeler.Add(attr)
+
+			handlerFunc(w, r)
+		}))
+	}
+
+	handleFunc("/adyen_hook", s.AdyenHookHandler)
+
+	handleFunc("GET /checkout", s.CheckoutHandler(func(order *CheckoutOrder, w http.ResponseWriter) error {
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Header().Set("Permissions-Policy", "payment=(self \"https://js.stripe.com\" \"https://m.stripe.network\" \"https://js.playground.kustom.co\")")
+		w.WriteHeader(http.StatusOK)
+		_, err := fmt.Fprintf(w, tpl, order.HTMLSnippet)
+		return err
+	}))
+
+	handleFunc("GET /confirmation/{order_id}", func(w http.ResponseWriter, r *http.Request) {
+		orderId := r.PathValue("order_id")
+		order, err := s.klarnaClient.GetOrder(r.Context(), orderId)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			return
+		}
+
+		// Apply ConfirmationViewed to checkout
+		checkoutId := checkout.CheckoutId(cart.MustNewCartId()) // Need to resolve from order
+		s.Apply(r.Context(), uint64(checkoutId), &messages.ConfirmationViewed{})
+
+		// Callback to cart
+		cartId := cart.CartId(checkoutId) // Assuming same
+		s.cartClient.ApplyMutation(cartId, &messages.OrderCreated{OrderId: order.ID, Status: order.Status})
+
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprintf(w, tpl, order.HTMLSnippet)
+	})
+}