feat: Updated purchase page

adminsite/lib/paddle.ts

@@ -15,3 +15,62 @@ export function initPaddle(): Promise<Paddle | undefined> {
     }
     return cached;
 }
+
+export interface PricedLine {
+    priceId: string;
+    /* Already localised and currency-formatted by Paddle, e.g. "£39.00". The line
+     * total for the quantity, not the unit price. */
+    total: string;
+    unit: string;
+}
+
+export interface PricePreview {
+    currency: string;
+    /* Grand total, formatted. */
+    total: string;
+    lines: Record<string, PricedLine>;
+}
+
+/*
+ * previewPrices asks Paddle for the real localised prices of a set of line items,
+ * so the order summary shows what the customer will actually pay rather than a
+ * hardcoded number that would drift from the dashboard.
+ *
+ * It returns null when Paddle is unavailable or a price cannot be previewed (an
+ * unconfigured sandbox price, an ad blocker). The caller falls back to showing
+ * the line items without amounts rather than a wrong total — the real figure
+ * still appears in the checkout overlay, which is the authority.
+ */
+export async function previewPrices(
+    items: { priceId: string; quantity: number }[],
+): Promise<PricePreview | null> {
+    if (items.length === 0) return { currency: "", total: "", lines: {} };
+    const paddle = await initPaddle();
+    if (!paddle) return null;
+    try {
+        const res = await paddle.PricePreview({
+            items: items.map((i) => ({ priceId: i.priceId, quantity: i.quantity })),
+        });
+        const currency = res.data.currencyCode;
+        const lines: Record<string, PricedLine> = {};
+        // Paddle gives per-line totals but no grand total, so sum the raw minor
+        // units and format once. The checkout overlay is the authority; this is
+        // the honest preview beside it.
+        let subtotalMinor = 0;
+        for (const li of res.data.details.lineItems) {
+            lines[li.price.id] = {
+                priceId: li.price.id,
+                total: li.formattedTotals.subtotal,
+                unit: li.formattedUnitTotals.subtotal,
+            };
+            subtotalMinor += Number.parseInt(li.totals.subtotal, 10) || 0;
+        }
+        const total = new Intl.NumberFormat(undefined, {
+            style: "currency",
+            currency,
+        }).format(subtotalMinor / 100);
+        return { currency, total, lines };
+    } catch {
+        return null;
+    }
+}