fix: guard date-formatting utilities against invalid input

src/utils/__tests__/dateUtils.test.ts

@@ -0,0 +1,104 @@
+import { describe, it, expect } from 'vitest';
+import { isValidDate, formatDate, formatShortDate, formatTime, formatRelative } from '../dateUtils';
+
+describe('isValidDate', () => {
+  it('returns true for valid Date objects', () => {
+    expect(isValidDate(new Date('2024-01-15'))).toBe(true);
+  });
+
+  it('returns true for valid date strings', () => {
+    expect(isValidDate('2024-01-15')).toBe(true);
+  });
+
+  it('returns true for valid timestamps', () => {
+    expect(isValidDate(1705276800000)).toBe(true);
+  });
+
+  it('returns false for invalid date strings', () => {
+    expect(isValidDate('not-a-date')).toBe(false);
+  });
+
+  it('returns false for empty strings', () => {
+    expect(isValidDate('')).toBe(false);
+  });
+
+  it('returns false for random non-date strings', () => {
+    expect(isValidDate('hello world')).toBe(false);
+  });
+});
+
+describe('formatDate', () => {
+  it('formats a valid date', () => {
+    const result = formatDate(new Date('2024-01-15'), 'en-US');
+    expect(result).toBe('January 15, 2024');
+  });
+
+  it('formats a valid date string', () => {
+    const result = formatDate('2024-01-15', 'en-US');
+    expect(result).toBe('January 15, 2024');
+  });
+
+  it('returns empty string for invalid input by default', () => {
+    expect(formatDate('not-a-date', 'en-US')).toBe('');
+  });
+
+  it('returns custom fallback for invalid input', () => {
+    expect(formatDate('not-a-date', 'en-US', undefined, 'N/A')).toBe('N/A');
+  });
+
+  it('returns empty string for null-like inputs', () => {
+    expect(formatDate('')).toBe('');
+  });
+});
+
+describe('formatShortDate', () => {
+  it('formats a valid date in short format', () => {
+    const result = formatShortDate(new Date('2024-01-15'), 'en-US');
+    expect(result).toBe('Jan 15, 2024');
+  });
+
+  it('returns empty string for invalid input', () => {
+    expect(formatShortDate('not-a-date', 'en-US')).toBe('');
+  });
+
+  it('returns custom fallback for invalid input', () => {
+    expect(formatShortDate('not-a-date', 'en-US', '--')).toBe('--');
+  });
+});
+
+describe('formatTime', () => {
+  it('formats a valid date to time', () => {
+    const result = formatTime(new Date('2024-01-15T14:30:00'), 'en-US');
+    expect(result).toMatch(/\d{1,2}:\d{2}\s?(AM|PM)/);
+  });
+
+  it('returns empty string for invalid input', () => {
+    expect(formatTime('not-a-date', 'en-US')).toBe('');
+  });
+
+  it('returns custom fallback for invalid input', () => {
+    expect(formatTime('invalid', 'en-US', 'N/A')).toBe('N/A');
+  });
+});
+
+describe('formatRelative', () => {
+  it('returns relative time for a valid date', () => {
+    const now = new Date();
+    const fiveMinutesAgo = new Date(now.getTime() - 5 * 60 * 1000);
+    const result = formatRelative(fiveMinutesAgo, 'en-US');
+    expect(result).toBe('5 minutes ago');
+  });
+
+  it('returns "now" for a very recent date', () => {
+    const result = formatRelative(new Date(), 'en-US');
+    expect(result).toMatch(/seconds? ago|now/);
+  });
+
+  it('returns empty string for invalid input', () => {
+    expect(formatRelative('not-a-date', 'en-US')).toBe('');
+  });
+
+  it('returns custom fallback for invalid input', () => {
+    expect(formatRelative('garbage', 'en-US', 'unknown')).toBe('unknown');
+  });
+});

src/utils/dateUtils.ts

@@ -5,23 +5,40 @@
 
 import { getDateTimeFormat, getRelativeTimeFormat } from './intlCache';
 
+export function isValidDate(date: Date | string | number): boolean {
+  const parsed = new Date(date);
+  return !Number.isNaN(parsed.getTime());
+}
+
 export function formatDate(
   date: Date | string | number,
   locale?: string,
   options: Intl.DateTimeFormatOptions = { year: 'numeric', month: 'long', day: 'numeric' },
+  fallback = '',
 ): string {
+  if (!isValidDate(date)) return fallback;
   return getDateTimeFormat(locale, options).format(new Date(date));
 }
 
-export function formatShortDate(date: Date | string | number, locale?: string): string {
-  return formatDate(date, locale, { year: 'numeric', month: 'short', day: 'numeric' });
+export function formatShortDate(
+  date: Date | string | number,
+  locale?: string,
+  fallback = '',
+): string {
+  return formatDate(date, locale, { year: 'numeric', month: 'short', day: 'numeric' }, fallback);
 }
 
-export function formatTime(date: Date | string | number, locale?: string): string {
+export function formatTime(date: Date | string | number, locale?: string, fallback = ''): string {
+  if (!isValidDate(date)) return fallback;
   return getDateTimeFormat(locale, { hour: '2-digit', minute: '2-digit' }).format(new Date(date));
 }
 
-export function formatRelative(date: Date | string | number, locale?: string): string {
+export function formatRelative(
+  date: Date | string | number,
+  locale?: string,
+  fallback = '',
+): string {
+  if (!isValidDate(date)) return fallback;
   const diff = Math.round((new Date(date).getTime() - Date.now()) / 1000);
   const rtf = getRelativeTimeFormat(locale, { numeric: 'auto' });