(feat) Add helper functions to get total bill and balance (#73)

__mocks__/bills.mock.ts

@@ -70,7 +70,6 @@ export const billsSummary = [
           description: 'Mpesa',
           retired: false,
         },
-
         attributes: [
           {
             uuid: '84aacfcc-9788-4f7b-a56a-407d84af1b54',

packages/esm-billing-app/src/helpers/functions.ts

@@ -0,0 +1,32 @@
+import { Payment, LineItem } from '../types';
+
+// amount already paid
+export function calculateTotalAmountTendered(payments: Array<Payment>) {
+  return Array.isArray(payments)
+    ? payments.reduce((totalAmount, item) => {
+        // Ensure that "amount" property is present and numeric
+        if (typeof item.amount === 'number' && item.voided !== true) {
+          return totalAmount + item.amount;
+        }
+        return totalAmount;
+      }, 0)
+    : 0;
+}
+
+// balance
+export function calculateTotalBalance(lineItems: Array<LineItem>, payments: Array<Payment>) {
+  return Math.min(this.calculateTotalAmount(lineItems) - this.calculateTotalAmountTendered(payments));
+}
+
+// total bill
+export function calculateTotalAmount(lineItems: Array<LineItem>) {
+  return Array.isArray(lineItems)
+    ? lineItems.reduce((totalAmount, item) => {
+        // Ensure that "price" and "quantity" properties are present and numeric
+        if (typeof item.price === 'number' && typeof item.quantity === 'number' && item.voided !== true) {
+          return totalAmount + item.price * item.quantity;
+        }
+        return totalAmount;
+      }, 0)
+    : 0;
+}

packages/esm-billing-app/src/helpers/index.ts

@@ -0,0 +1 @@
+export * from './functions';

packages/esm-billing-app/src/types/index.ts

@@ -46,7 +46,7 @@ interface Provider {
   links: ProviderLink[];
 }
 
-interface LineItem {
+export interface LineItem {
   uuid: string;
   display: string;
   voided: boolean;
@@ -103,7 +103,7 @@ interface PaymentInstanceType {
   retired: boolean;
 }
 
-interface Payment {
+export interface Payment {
   uuid: string;
   instanceType: PaymentInstanceType;
   attributes: Attribute[];