build ui for adding and displaying added items

src/utils/calculator.ts

@@ -0,0 +1,47 @@
+import type { Bill, BillItem, ComputedBill, ComputedBillItem } from "../types";
+
+export function findById<T extends { id: string }>(
+  items: T[],
+  id: string,
+): T | undefined {
+  return items.find((item) => item.id === id);
+}
+
+export function computeItem(item: BillItem): ComputedBillItem {
+  return {
+    ...item,
+    finalPrice: item.unitPrice * item.quantity,
+  };
+}
+
+export function computeBill(bill: Bill): ComputedBill {
+  const computedItems = bill.items.map(computeItem);
+
+  const subtotal = computedItems.reduce(
+    (sum, item) => sum + item.finalPrice,
+    0,
+  );
+
+  const taxAmount = (subtotal * bill.taxPercent) / 100;
+  const total = subtotal + taxAmount;
+
+  return {
+    ...bill,
+    items: computedItems,
+    subtotal,
+    taxAmount,
+    total,
+  };
+}
+
+export function formatCurrency(amount: number, currency: string): string {
+  return new Intl.NumberFormat("en-IN", {
+    style: "currency",
+    currency,
+    minimumFractionDigits: 2,
+  }).format(amount);
+}
+
+export function generateId(): string {
+  return Math.random().toString(36).slice(2, 9);
+}