feat: add pdf to the central invoice system

apps/edr-freight-api/src/modules/billing/invoice-settlement.util.ts

@@ -0,0 +1,36 @@
+/**
+ * Shared payment/settlement math for invoices. Both the global
+ * `BillingService.recordPayment` and the warehouse fee invoice flow apply a
+ * payment the same way — accumulate `paidAmount`, derive the outstanding
+ * `balanceAmount`, and decide whether the invoice is now fully settled. Keeping
+ * it here means the two flows can never drift on rounding or the
+ * partial-vs-full threshold.
+ */
+
+/** Round to 2 decimals, avoiding binary float drift. */
+export const round2 = (n: number): number => Math.round(n * 100) / 100;
+
+export interface SettlementResult {
+  /** New cumulative amount paid. */
+  paidAmount: number;
+  /** Remaining balance (0 once fully paid). */
+  balanceAmount: number;
+  /** True once the balance reaches zero. */
+  fullyPaid: boolean;
+}
+
+/**
+ * Apply a single payment of `amount` to an invoice with `totalAmount` already
+ * carrying `currentPaid`. Caller is responsible for validating `amount > 0` and
+ * the invoice being in a payable state.
+ */
+export function applySettlement(
+  totalAmount: number,
+  currentPaid: number,
+  amount: number,
+): SettlementResult {
+  const total = Number(totalAmount);
+  const paidAmount = round2(Number(currentPaid) + Number(amount));
+  const balanceAmount = Math.max(0, round2(total - paidAmount));
+  return { paidAmount, balanceAmount, fullyPaid: paidAmount >= total };
+}