feat(core): add invoice update endpoint with validation

src/index.ts

@@ -50,6 +50,48 @@ app.get("/invoice/:id", (c) => {
   return c.json({ invoice, payments });
 });
 
+// Identity fields (id, invoice_number, customer_id, created_at) are immutable;
+// strictObject rejects them explicitly instead of silently stripping.
+const UpdateInvoice = z
+  .strictObject({
+    status: z.enum(["open", "partially_paid", "paid", "void", "corrupted"]),
+    due_on: z.iso.date(),
+    description: z.string().nullable(),
+    quantity: z.number().int().positive(),
+    unit_price: z.number().int().nonnegative(),
+    amount: z.number().int().nonnegative(),
+    currency: z.string().min(1).transform((s) => s.toUpperCase()),
+  })
+  .partial()
+  .refine((o) => Object.keys(o).length > 0, { error: "provide at least one updatable field" });
+
+app.put("/invoice/:id", async (c) => {
+  const parsed = UpdateInvoice.safeParse(await c.req.json().catch(() => null));
+  if (!parsed.success) return c.json({ error: z.treeifyError(parsed.error) }, 400);
+  const key = c.req.param("id");
+
+  const target = db
+    .query<{ id: string }, [string, string]>(
+      "SELECT id FROM invoices WHERE id = ? OR invoice_number = ? ORDER BY created_at DESC",
+    )
+    .get(key, key);
+  if (!target) return c.json({ error: "invoice not found" }, 404);
+
+  // Keys are whitelisted by the zod schema, so interpolating them is safe
+  const fields = Object.entries(parsed.data);
+  try {
+    db.run(
+      `UPDATE invoices SET ${fields.map(([k]) => `${k} = ?`).join(", ")} WHERE id = ?`,
+      [...fields.map(([, v]) => v), target.id],
+    );
+  } catch (err) {
+    // schema CHECK: any non-corrupted status requires all money/date fields present —
+    // repairing a corrupted invoice means supplying the missing fields in the same PUT
+    return c.json({ error: err instanceof Error ? err.message : String(err) }, 400);
+  }
+  return c.json(db.query("SELECT * FROM invoices WHERE id = ?").get(target.id));
+});
+
 // --- Payments (happy path: pay an invoice, idempotent) -----------------------
 
 const CreatePayment = z.object({