Fix: Incorrect bill splits for some currencies

src/components/MoneyRequestConfirmationList.js

@@ -138,9 +138,11 @@ class MoneyRequestConfirmationList extends Component {
      * @returns {Array}
      */
     getParticipantsWithAmount(participants) {
+        const iouAmount = IOUUtils.calculateAmount(participants, this.props.iouAmount, this.props.iou.selectedCurrencyCode);
+
         return OptionsListUtils.getIOUConfirmationOptionsFromParticipants(
             participants,
-            this.props.numberFormat(IOUUtils.calculateAmount(participants, this.props.iouAmount) / 100, {
+            this.props.numberFormat(iouAmount / 100, {
                 style: 'currency',
                 currency: this.props.iou.selectedCurrencyCode,
             }),
@@ -172,9 +174,10 @@ class MoneyRequestConfirmationList extends Component {
             const formattedUnselectedParticipants = this.getParticipantsWithoutAmount(unselectedParticipants);
             const formattedParticipants = _.union(formattedSelectedParticipants, formattedUnselectedParticipants);
 
+            const myIOUAmount = IOUUtils.calculateAmount(selectedParticipants, this.props.iouAmount, this.props.iou.selectedCurrencyCode, true);
             const formattedMyPersonalDetails = OptionsListUtils.getIOUConfirmationOptionsFromMyPersonalDetail(
                 this.props.currentUserPersonalDetails,
-                this.props.numberFormat(IOUUtils.calculateAmount(selectedParticipants, this.props.iouAmount, true) / 100, {
+                this.props.numberFormat(myIOUAmount / 100, {
                     style: 'currency',
                     currency: this.props.iou.selectedCurrencyCode,
                 }),

src/libs/IOUUtils.js

@@ -1,31 +1,75 @@
 import _ from 'underscore';
+import Onyx from 'react-native-onyx';
+import lodashGet from 'lodash/get';
 import CONST from '../CONST';
+import ONYXKEYS from '../ONYXKEYS';
+
+let currencyList = {};
+Onyx.connect({
+    key: ONYXKEYS.CURRENCY_LIST,
+    callback: (val) => {
+        if (_.isEmpty(val)) {
+            return;
+        }
+
+        currencyList = val;
+    },
+});
+
+/**
+ * Returns the number of digits after the decimal separator for a specific currency.
+ * For currencies that have decimal places > 2, floor to 2 instead:
+ * https://github.com/Expensify/App/issues/15878#issuecomment-1496291464
+ *
+ * @param {String} currency - IOU currency
+ * @returns {Number}
+ */
+function getCurrencyDecimals(currency = CONST.CURRENCY.USD) {
+    const decimals = lodashGet(currencyList, [currency, 'decimals']);
+    return _.isUndefined(decimals) ? 2 : Math.min(decimals, 2);
+}
+
+/**
+ * Returns the currency's minor unit quantity
+ * e.g. Cent in USD
+ *
+ * @param {String} currency - IOU currency
+ * @returns {Number}
+ */
+function getCurrencyUnit(currency = CONST.CURRENCY.USD) {
+    return 10 ** getCurrencyDecimals(currency);
+}
 
 /**
  * Calculates the amount per user given a list of participants
  * @param {Array} participants - List of logins for the participants in the chat. It should not include the current user's login.
  * @param {Number} total - IOU total amount
+ * @param {String} currency - IOU currency
  * @param {Boolean} isDefaultUser - Whether we are calculating the amount for the current user
  * @returns {Number}
  */
-function calculateAmount(participants, total, isDefaultUser = false) {
+function calculateAmount(participants, total, currency, isDefaultUser = false) {
     // Convert to cents before working with iouAmount to avoid
     // javascript subtraction with decimal problem -- when dealing with decimals,
     // because they are encoded as IEEE 754 floating point numbers, some of the decimal
     // numbers cannot be represented with perfect accuracy.
-    // Cents is temporary and there must be support for other currencies in the future
-    const iouAmount = Math.round(parseFloat(total * 100));
+    // Currencies that do not have minor units (i.e. no decimal place) are also supported.
+    // https://github.com/Expensify/App/issues/15878
+    const currencyUnit = getCurrencyUnit(currency);
+    const iouAmount = Math.round(parseFloat(total * currencyUnit));
+
     const totalParticipants = participants.length + 1;
     const amountPerPerson = Math.round(iouAmount / totalParticipants);
 
-    if (!isDefaultUser) {
-        return amountPerPerson;
-    }
+    let finalAmount = amountPerPerson;
 
-    const sumAmount = amountPerPerson * totalParticipants;
-    const difference = iouAmount - sumAmount;
+    if (isDefaultUser) {
+        const sumAmount = amountPerPerson * totalParticipants;
+        const difference = iouAmount - sumAmount;
+        finalAmount = iouAmount !== sumAmount ? (amountPerPerson + difference) : amountPerPerson;
+    }
 
-    return iouAmount !== sumAmount ? (amountPerPerson + difference) : amountPerPerson;
+    return (finalAmount * 100) / currencyUnit;
 }
 
 /**
@@ -139,4 +183,6 @@ export {
     updateIOUOwnerAndTotal,
     getIOUReportActions,
     isIOUReportPendingCurrencyConversion,
+    getCurrencyUnit,
+    getCurrencyDecimals,
 };

src/libs/actions/IOU.js

@@ -311,8 +311,8 @@ function createSplitsAndOnyxData(participants, currentUserLogin, amount, comment
     ];
 
     // Loop through participants creating individual chats, iouReports and reportActionIDs as needed
-    const splitAmount = IOUUtils.calculateAmount(participants, amount);
-    const splits = [{email: currentUserEmail, amount: IOUUtils.calculateAmount(participants, amount, true)}];
+    const splitAmount = IOUUtils.calculateAmount(participants, amount, currency, false);
+    const splits = [{email: currentUserEmail, amount: IOUUtils.calculateAmount(participants, amount, currency, true)}];
 
     const hasMultipleParticipants = participants.length > 1;
     _.each(participants, (participant) => {

tests/unit/IOUUtilsTest.js

@@ -1,6 +1,10 @@
+import Onyx from 'react-native-onyx';
 import CONST from '../../src/CONST';
 import * as IOUUtils from '../../src/libs/IOUUtils';
 import * as ReportUtils from '../../src/libs/ReportUtils';
+import ONYXKEYS from '../../src/ONYXKEYS';
+import waitForPromisesToResolve from '../utils/waitForPromisesToResolve';
+import currencyList from './currencyList.json';
 
 let iouReport;
 let reportActions;
@@ -38,27 +42,37 @@ function cancelMoneyRequest(moneyRequestAction, {isOnline} = {}) {
     );
 }
 
-beforeEach(() => {
-    reportActions = [];
-    const chatReportID = ReportUtils.generateReportID();
-    const amount = 1000;
-    const currency = 'USD';
-
-    iouReport = ReportUtils.buildOptimisticIOUReport(
-        ownerEmail,
-        managerEmail,
-        amount,
-        chatReportID,
-        currency,
-        CONST.LOCALES.EN,
-    );
-
-    // The starting point of all tests is the IOUReport containing a single non-pending transaction in USD
-    // All requests in the tests are assumed to be offline, unless isOnline is specified
-    createIOUReportAction('create', amount, currency, {IOUTransactionID: '', isOnline: true});
-});
+function initCurrencyList() {
+    Onyx.init({
+        keys: ONYXKEYS,
+        initialKeyStates: {
+            [ONYXKEYS.CURRENCY_LIST]: currencyList,
+        },
+    });
+    return waitForPromisesToResolve();
+}
 
 describe('isIOUReportPendingCurrencyConversion', () => {
+    beforeEach(() => {
+        reportActions = [];
+        const chatReportID = ReportUtils.generateReportID();
+        const amount = 1000;
+        const currency = 'USD';
+
+        iouReport = ReportUtils.buildOptimisticIOUReport(
+            ownerEmail,
+            managerEmail,
+            amount,
+            chatReportID,
+            currency,
+            CONST.LOCALES.EN,
+        );
+
+        // The starting point of all tests is the IOUReport containing a single non-pending transaction in USD
+        // All requests in the tests are assumed to be offline, unless isOnline is specified
+        createIOUReportAction('create', amount, currency, {IOUTransactionID: '', isOnline: true});
+    });
+
     test('Requesting money offline in a different currency will show the pending conversion message', () => {
         // Request money offline in AED
         createIOUReportAction('create', 100, 'AED');
@@ -132,3 +146,57 @@ describe('isIOUReportPendingCurrencyConversion', () => {
     });
 });
 
+describe('getCurrencyDecimals', () => {
+    beforeAll(() => initCurrencyList());
+    test('Currency decimals smaller than or equal 2', () => {
+        expect(IOUUtils.getCurrencyDecimals('JPY')).toBe(0);
+        expect(IOUUtils.getCurrencyDecimals('USD')).toBe(2);
+    });
+
+    test('Currency decimals larger than 2 should return 2', () => {
+        // Actual: 3
+        expect(IOUUtils.getCurrencyDecimals('LYD')).toBe(2);
+
+        // Actual: 4
+        expect(IOUUtils.getCurrencyDecimals('UYW')).toBe(2);
+    });
+});
+
+describe('getCurrencyUnit', () => {
+    beforeAll(() => initCurrencyList());
+    test('Currency with decimals smaller than or equal 2', () => {
+        expect(IOUUtils.getCurrencyUnit('JPY')).toBe(1);
+        expect(IOUUtils.getCurrencyUnit('USD')).toBe(100);
+    });
+
+    test('Currency with decimals larger than 2 should be floor to 2', () => {
+        expect(IOUUtils.getCurrencyUnit('LYD')).toBe(100);
+    });
+});
+
+describe('calculateAmount', () => {
+    beforeAll(() => initCurrencyList());
+    test('103 JPY split among 3 participants including the default user should be [35, 34, 34]', () => {
+        const participants = ['tonystark@expensify.com', 'reedrichards@expensify.com'];
+        expect(IOUUtils.calculateAmount(participants, 103, 'JPY', true)).toBe(3500);
+        expect(IOUUtils.calculateAmount(participants, 103, 'JPY')).toBe(3400);
+    });
+
+    test('10 AFN split among 4 participants including the default user should be [1, 3, 3, 3]', () => {
+        const participants = ['tonystark@expensify.com', 'reedrichards@expensify.com', 'suestorm@expensify.com'];
+        expect(IOUUtils.calculateAmount(participants, 10, 'AFN', true)).toBe(100);
+        expect(IOUUtils.calculateAmount(participants, 10, 'AFN')).toBe(300);
+    });
+
+    test('10 BHD split among 3 participants including the default user should be [334, 333, 333]', () => {
+        const participants = ['tonystark@expensify.com', 'reedrichards@expensify.com'];
+        expect(IOUUtils.calculateAmount(participants, 10, 'BHD', true)).toBe(334);
+        expect(IOUUtils.calculateAmount(participants, 10, 'BHD')).toBe(333);
+    });
+
+    test('0.02 USD split among 4 participants including the default user should be [-1, 1, 1, 1]', () => {
+        const participants = ['tonystark@expensify.com', 'reedrichards@expensify.com', 'suestorm@expensify.com'];
+        expect(IOUUtils.calculateAmount(participants, 0.02, 'USD', true)).toBe(-1);
+        expect(IOUUtils.calculateAmount(participants, 0.02, 'USD')).toBe(1);
+    });
+});