Fix race conditions caused by missing await in calls, clean up code slightly (#147)

* Fix race conditions due to missing `await` in calls

* Format code with Prettier

* Refactor user switching component to use `useRef` instead of `createRef` for better performance

* Use `const` instead of `var`

* Format code with Prettier

---------

Co-authored-by: IsaacCheng9 <[email protected]>

Author: IsaacCheng9

client/src/components/user_switching.jsx

@@ -1,10 +1,9 @@
-import React from "react";
+import React, { useRef } from "react";
 import "../styles/user_switching.css";
-import { createRef } from "react";
 
 function UserSwitching(props) {
   let group = props.group;
-  let selectRef = createRef();
+  let selectRef = useRef();
 
   function handleChange() {
     // Get the selected user

server/app.js

@@ -20,7 +20,7 @@ app.use(debtsRouter);
 // !IMPORTANT: Create .env file with password
 const password = process.env.PASSWORD || "changePasswordHere";
 let devUrl = `mongodb+srv://admin:${password}@fairsplit.fjvgxmg.mongodb.net/?retryWrites=true&w=majority`;
-var mongoDB = process.env.MONGODB_URI || devUrl;
+const mongoDB = process.env.MONGODB_URI || devUrl;
 // Set up the Mongoose connection.
 mongoose
   .connect(mongoDB)

server/controllers/debt_controller.js

@@ -68,7 +68,7 @@ exports.settleDebt = async (request, response) => {
     );
     // Recalculate debts to minimise the number of transactions, as this
     // settlement may have changed the optimal strategy.
-    helpers.simplifyDebts();
+    await helpers.simplifyDebts();
     response.send(
       `Debt from '${request.body.from}' to '${request.body.to}' partially\
         settled and reduced successfully.`,
@@ -91,7 +91,7 @@ exports.settleDebt = async (request, response) => {
     );
     // Recalculate debts to minimise the number of transactions, as this
     // settlement may have changed the optimal strategy.
-    helpers.simplifyDebts();
+    await helpers.simplifyDebts();
     response.send(
       `Debt from '${request.body.from}' to '${request.body.to}' fully\
         settled and deleted successfully.`,
@@ -111,7 +111,7 @@ exports.deleteDebtBetweenUsers = async (request, response) => {
   });
   // Now that we've deleted the debt, there may be a better way of allocating
   // the debt, so recalculate debts to minimise the number of transactions.
-  helpers.simplifyDebts();
+  await helpers.simplifyDebts();
   response.send(
     `Debt from '${request.params.from}' to '${request.params.to}' deleted\
       successfully.`,

server/controllers/expense_controller.js

@@ -5,7 +5,7 @@ const expenseModel = require("../models/expense");
 exports.addExpense = async (request, response) => {
   // Check that the sum of amounts owed matches the total expense amount.
   let currentSum = 0;
-  for (borrower of request.body.borrowers) {
+  for (const borrower of request.body.borrowers) {
     if (borrower[1] <= 0) {
       return response.status(400).json({
         error: "The amount owed must be a positive number.",
@@ -30,7 +30,7 @@ exports.addExpense = async (request, response) => {
   });
 
   // Loop through each borrower and create/update debts accordingly.
-  for (borrowerInfo of request.body.borrowers) {
+  for (const borrowerInfo of request.body.borrowers) {
     const borrower = borrowerInfo[0];
     // The amount they owe must be handled before this to account for different
     // methods of splitting the expense (e.g. specific amounts, by percentage,
@@ -41,7 +41,7 @@ exports.addExpense = async (request, response) => {
 
   // Recalculate debts to minimise the number of transactions, as this
   // settlement may have changed the optimal strategy.
-  helpers.simplifyDebts();
+  await helpers.simplifyDebts();
   response.status(201).json(expense);
 };
 

server/controllers/helpers/index.js

@@ -112,14 +112,17 @@ exports.simplifyDebts = async function () {
   }
 
   // Create a new set of optimised debts to store the simplified debts.
-  optimisedDebtModel.deleteMany({});
+  await optimisedDebtModel.deleteMany({});
   // Create transactions until the min-heaps are empty to reach a zero-state.
   while (!minHeapDebt.empty() && !minHeapCredit.empty()) {
     const smallestDebt = minHeapDebt.pop();
     const smallestCredit = minHeapCredit.pop();
     // Create a new optimised debt.
-    transactionAmount = Math.min(smallestDebt.amount, smallestCredit.amount);
-    optimisedDebtModel.create({
+    const transactionAmount = Math.min(
+      smallestDebt.amount,
+      smallestCredit.amount,
+    );
+    await optimisedDebtModel.create({
       from: smallestDebt.username,
       to: smallestCredit.username,
       amount: transactionAmount,