FIX: Decimal point truncation (#223)

Amounts like $45.80 were being displayed as $45.8. Which doesn't look
correct for currency.

Bug Report: https://meta.discourse.org/t/316007

assets/javascripts/discourse/helpers/format-currency.js

@@ -1,40 +1,36 @@
-import Helper from "@ember/component/helper";
+import { helper } from "@ember/component/helper";
 
-export default Helper.helper(function (params) {
+export function formatCurrency([currency, amount]) {
   let currencySign;
 
-  switch (params[0]) {
+  switch (currency.toUpperCase()) {
     case "EUR":
-    case "eur":
       currencySign = "€";
       break;
     case "GBP":
-    case "gbp":
       currencySign = "£";
       break;
     case "INR":
-    case "inr":
       currencySign = "₹";
       break;
     case "BRL":
-    case "brl":
       currencySign = "R$";
       break;
     case "DKK":
-    case "dkk":
       currencySign = "DKK";
       break;
     case "SGD":
-    case "sgd":
       currencySign = "S$";
       break;
     case "ZAR":
-    case "zar":
       currencySign = "R";
       break;
     default:
       currencySign = "$";
   }
 
-  return currencySign + params[1];
+  let formattedAmount = parseFloat(amount).toFixed(2);
-});
+  return currencySign + formattedAmount;
+}
+
+export default helper(formatCurrency);

test/javascripts/helpers/format-currency-test.js

@@ -0,0 +1,17 @@
+import { setupTest } from "ember-qunit";
+import { module, test } from "qunit";
+import { formatCurrency } from "discourse/plugins/discourse-subscriptions/discourse/helpers/format-currency";
+
+module("Unit | Helper | format-currency", function (hooks) {
+  setupTest(hooks);
+
+  test("it formats USD correctly", function (assert) {
+    let result = formatCurrency(["USD", 338.2]);
+    assert.equal(result, "$338.20", "Formats USD correctly");
+  });
+
+  test("it rounds correctly", function (assert) {
+    let result = formatCurrency(["USD", 338.289]);
+    assert.equal(result, "$338.29", "Rounds correctly");
+  });
+});