update useBill reset value and calculator sum generic function

src/hooks/useBill.ts

@@ -58,8 +58,8 @@ export function useBill() {
       title: "New Bill",
       currency: Currency.INR,
       createdAt: new Date(),
-      taxPercent: 18,
-      taxType: TaxType.GST,
+      taxPercent: 0,
+      taxType: TaxType.None,
       items: [],
     });
   }, []);

src/utils/calculator.ts

@@ -14,12 +14,16 @@ export function computeItem(item: BillItem): ComputedBillItem {
   };
 }
 
+export function sumBy<T>(items: T[], getValue: (item: T) => number): number {
+  return items.reduce((sum, currentItem) => sum + getValue(currentItem), 0);
+}
+
 export function computeBill(bill: Bill): ComputedBill {
   const computedItems = bill.items.map(computeItem);
 
-  const subtotal = computedItems.reduce(
-    (sum, item) => sum + item.finalPrice,
-    0,
+  const subtotal = sumBy(
+    computedItems,
+    (computedItem) => computedItem.finalPrice,
   );
 
   const taxAmount = (subtotal * bill.taxPercent) / 100;