Test the checkout code; publish images only for releases (#5)

- src/checkout/ (PayPal order request, pricing, VAT) and src/logging/format.ts
  hold the checkout's pure code, moved out of PayPalApi, the product service
  and config without a behaviour change.
- npm test runs node:test on the TypeScript sources (type stripping), with no
  dependencies: 21 tests, 13 pin today's output, 8 describe the correct
  behaviour for the known defects of libretech/mp#67
  and are marked todo.
- CI: the tests run in the image's base (node:22.14.0-alpine) for every pull
  request, push to main and release tag. The image is built for pull requests
  and built and published only for v* tags; main no longer publishes :main
  and :sha-* images.

Refs libretech/mp#71

Co-authored-by: Michael Czechowski <mail@librete.ch>

src/checkout/paypal-order.ts

@@ -0,0 +1,124 @@
+import type { Order } from "../../types";
+import { calculateTotalProductPrice } from "./pricing";
+import { vatIncludedDecimal } from "./vat";
+
+// The PayPal order that PayPalApi.createSessionOrThrow creates, built without the PayPal SDK so it can be unit tested.
+// String literals stand in for the SDK enums, with the values of @paypal/paypal-server-sdk 0.6.1.
+
+export type PayPalMoney = {
+	currencyCode: string;
+	value: string;
+};
+
+export type PayPalOrderItem = {
+	name: string;
+	unitAmount: PayPalMoney;
+	tax: PayPalMoney;
+	quantity: string;
+};
+
+export type PayPalOrderRequest = {
+	/** CheckoutPaymentIntent.Capture */
+	intent: "CAPTURE";
+	purchaseUnits: {
+		referenceId: string;
+		amount: PayPalMoney & {
+			breakdown: {
+				itemTotal: PayPalMoney;
+				taxTotal: PayPalMoney;
+				shipping: PayPalMoney | undefined;
+			};
+		};
+		shipping: {
+			name: { fullName: string };
+			address: { addressLine1: string; postalCode: string; adminArea2: string; countryCode: string };
+		};
+		customId: string;
+		invoiceId: string;
+	}[];
+	applicationContext: {
+		returnUrl: string;
+		cancelUrl: string;
+		/** OrderApplicationContextShippingPreference.SetProvidedAddress */
+		shippingPreference: "SET_PROVIDED_ADDRESS";
+	};
+};
+
+/**
+ * The part of PayPalApi.createSessionOrThrow that runs before its try block, so nothing thrown here is logged there.
+ * Rejects an order without a total, then computes one item per cart line. The items are not sent to PayPal, but computing
+ * them throws a TypeError for a cart line without a product.
+ */
+export const buildPayPalOrderItems = (order: Order): PayPalOrderItem[] => {
+	if (!order.total) throw new Error("Cart is empty or has no total");
+
+	return order.cart.map((item) => {
+		const totalProductPrice = calculateTotalProductPrice(item.product);
+		const amount = totalProductPrice / vatIncludedDecimal;
+		const tax = totalProductPrice - amount;
+
+		return {
+			name: item.product.name,
+			unitAmount: {
+				currencyCode: "EUR",
+				value: amount.toFixed(2)
+			},
+			tax: {
+				currencyCode: "EUR",
+				value: tax.toFixed(2)
+			},
+			quantity: item.count.toString()
+		};
+	});
+};
+
+/**
+ * The order request body PayPalApi.createSessionOrThrow sends. It is built inside that try block, so whatever throws here is logged there.
+ */
+export const buildPayPalOrderRequest = (returnUrl: string, order: Order): PayPalOrderRequest => ({
+	intent: "CAPTURE",
+	purchaseUnits: [
+		{
+			// items: computed by buildPayPalOrderItems, but not sent
+			referenceId: order.uuid,
+			amount: {
+				currencyCode: "EUR",
+				value: order.total.toFixed(2),
+				breakdown: {
+					itemTotal: {
+						currencyCode: "EUR",
+						value: (Math.round((order.subtotal / vatIncludedDecimal) * 100) / 100).toFixed(2)
+					},
+					taxTotal: {
+						currencyCode: "EUR",
+						value: order.VAT.toFixed(2)
+					},
+					shipping: order.delivery
+						? {
+								currencyCode: "EUR",
+								value: order.delivery.price.toFixed(2)
+							}
+						: undefined
+				}
+			},
+			shipping: {
+				name: {
+					fullName: order.deliveryAddress.split("\n")[0]
+				},
+				address: {
+					addressLine1: order.deliveryAddress.split("\n")[1],
+					postalCode: order.deliveryAddress.split("\n")[2].slice(0, 5),
+					adminArea2: order.deliveryAddress.split("\n")[2].slice(6),
+					countryCode: "DE"
+				}
+			},
+			customId: order.uuid,
+			invoiceId: order.invoiceNumber
+		}
+	],
+	applicationContext: {
+		returnUrl: returnUrl,
+		cancelUrl: returnUrl,
+		shippingPreference: "SET_PROVIDED_ADDRESS"
+	}
+});

src/checkout/pricing.ts

@@ -0,0 +1,5 @@
+import type { Product } from "../../types";
+
+export const calculateTotalProductPrice = (product: Partial<Product>): number => {
+	return (product?.cover?.price ?? 0) + (product?.pages?.price ?? 0) + (product?.ruling?.price ?? 0);
+};

src/checkout/vat.ts

@@ -0,0 +1,4 @@
+// TODO: Should be retrieved from DepotApi
+export const vatIncludedDecimal = 1.19;
+// TODO: Should be retrieved from DepotApi
+export const vatDecimal = 0.19;