Fix race conditions due to missing await in calls

Author: IsaacCheng9

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 +112,14 @@ 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,