Safer handling of backend date formats

and add frontend testing

frontend/src/locale/DateTimeFormat.ts

@@ -1,15 +1,36 @@
-import { intlFormat, parseISO } from "date-fns";
+import { fromUnixTime, intlFormat, parseISO } from "date-fns";
 
-const DateTimeFormat = (isoDate: string) =>
-	intlFormat(parseISO(isoDate), {
-		weekday: "long",
-		year: "numeric",
-		month: "numeric",
-		day: "numeric",
-		hour: "numeric",
-		minute: "numeric",
-		second: "numeric",
-		hour12: true,
-	});
+const isUnixTimestamp = (value: unknown): boolean => {
+	if (typeof value !== "number" && typeof value !== "string") return false;
+	const num = Number(value);
+	if (!Number.isFinite(num)) return false;
+	// Check plausible Unix timestamp range: from 1970 to ~year 3000
+	// Support both seconds and milliseconds
+	if (num > 0 && num < 10000000000) return true; // seconds (<= 10 digits)
+	if (num >= 10000000000 && num < 32503680000000) return true; // milliseconds (<= 13 digits)
+	return false;
+};
+
+const DateTimeFormat = (value: string | number): string => {
+	if (typeof value !== "number" && typeof value !== "string") return `${value}`;
+
+	try {
+		const d = isUnixTimestamp(value)
+			? fromUnixTime(+value)
+			: parseISO(`${value}`);
+		return intlFormat(d, {
+			weekday: "long",
+			year: "numeric",
+			month: "numeric",
+			day: "numeric",
+			hour: "numeric",
+			minute: "numeric",
+			second: "numeric",
+			hour12: true,
+		});
+	} catch {
+		return `${value}`;
+	}
+};
 
 export { DateTimeFormat };

frontend/src/locale/IntlProvider.tsx

@@ -30,13 +30,20 @@ const getLocale = (short = false) => {
 	if (short) {
 		return loc.slice(0, 2);
 	}
+	// finally, fallback
+	if (!loc) {
+		loc = "en";
+	}
 	return loc;
 };
 
 const cache = createIntlCache();
 
 const initialMessages = loadMessages(getLocale());
-let intl = createIntl({ locale: getLocale(), messages: initialMessages }, cache);
+let intl = createIntl(
+	{ locale: getLocale(), messages: initialMessages },
+	cache,
+);
 
 const changeLocale = (locale: string): void => {
 	const messages = loadMessages(locale);
@@ -76,4 +83,12 @@ const T = ({
 	);
 };
 
-export { localeOptions, getFlagCodeForLocale, getLocale, createIntl, changeLocale, intl, T };
+export {
+	localeOptions,
+	getFlagCodeForLocale,
+	getLocale,
+	createIntl,
+	changeLocale,
+	intl,
+	T,
+};