feat(order): name the fields an order still lacks for a checkout

missingCheckoutFields returns which of email, invoiceAddress and
delivery an order lacks, so the checkout can answer 400 before it
creates a PayPal order.

Refs libretech/mp#71

src/checkout/order-state.ts

@@ -8,3 +8,20 @@ export type OrderLockState = {
  * so the customer can no longer change its contact details, addresses, delivery method or cart.
  */
 export const isLockedForCustomer = (order: OrderLockState): boolean => Boolean(order.paymentAuthorised);
+
+/** The fields of an order a checkout needs: the contact and address steps of the shop's checkout, and a delivery method. */
+export type CheckoutFields = {
+	email?: string | null;
+	invoiceAddress?: string | null;
+	/** The populated delivery method, or null. */
+	delivery?: unknown;
+};
+
+/** The names of the fields the order still lacks for a checkout, in this order: email, invoiceAddress, delivery. [] if none. */
+export const missingCheckoutFields = (order: CheckoutFields): string[] => {
+	const missing: string[] = [];
+	if (typeof order.email !== "string" || order.email.trim() === "") missing.push("email");
+	if (typeof order.invoiceAddress !== "string" || order.invoiceAddress.trim() === "") missing.push("invoiceAddress");
+	if (order.delivery === null || order.delivery === undefined) missing.push("delivery");
+	return missing;
+};

tests/unit/order-state.test.ts

@@ -1,6 +1,6 @@
 import { test } from "node:test";
 import assert from "node:assert/strict";
-import { isLockedForCustomer } from "../../src/checkout/order-state.ts";
+import { isLockedForCustomer, missingCheckoutFields } from "../../src/checkout/order-state.ts";
 
 // Shaped like the row PUT /orders/:uuid/cart reads with strapi.db.query("api::order.order").findOne before it updates.
 const order = (overrides = {}) => ({
@@ -21,6 +21,36 @@ test("an order is open for the customer until its payment is authorised", () =>
 });
 
 test("an order is locked once its payment is authorised", () => {
-	// what capturePayment writes once PayPal reports the capture COMPLETED
+	// what capturePayment writes once the capture is verified (src/checkout/capture-payment.ts)
+	assert.equal(isLockedForCustomer(order({ paymentAuthorised: true, paymentStatus: "captured" })), true);
+	// what it wrote before
 	assert.equal(isLockedForCustomer(order({ paymentAuthorised: true, paymentStatus: "authorised" })), true);
 });
+
+// Shaped like the row POST /orders/:uuid/checkout reads (strapi.db.query findOne with orderDefaultParams), after both checkout steps.
+const readyForCheckout = (overrides = {}) =>
+	order({
+		invoiceAddress: "Erika Mustermann\nMusterstraße 1\n70190 Stuttgart",
+		deliveryAddress: "Erika Mustermann\nMusterstraße 1\n70190 Stuttgart",
+		delivery: { id: 1, name: "DHL", price: 4.95 },
+		...overrides
+	});
+
+test("an order that went through both checkout steps lacks nothing for the checkout", () => {
+	assert.deepEqual(missingCheckoutFields(readyForCheckout()), []);
+});
+
+test("names the email, invoice address and delivery method an order still lacks for the checkout", () => {
+	// a new order: POST /orders creates it empty
+	assert.deepEqual(missingCheckoutFields({ email: null, invoiceAddress: null, delivery: null }), ["email", "invoiceAddress", "delivery"]);
+	assert.deepEqual(missingCheckoutFields({}), ["email", "invoiceAddress", "delivery"]);
+	// after step 1 alone
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ invoiceAddress: null, deliveryAddress: null, delivery: null })), [
+		"invoiceAddress",
+		"delivery"
+	]);
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ email: "  " })), ["email"]);
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ invoiceAddress: "" })), ["invoiceAddress"]);
+	// a delivery method that was deleted is populated as null
+	assert.deepEqual(missingCheckoutFields(readyForCheckout({ delivery: null })), ["delivery"]);
+});