feat(api): daily challenge api (#61346)

Co-authored-by: Huyen Nguyen <25715018+huyenltnguyen@users.noreply.github.com>

api/src/daily-coding-challenge/utils/helpers.ts

@@ -0,0 +1,39 @@
+import { toZonedTime } from 'date-fns-tz';
+
+/**
+ * @returns Now US Central time.
+ */
+export function getNowUsCentral() {
+  return toZonedTime(new Date(), 'America/Chicago');
+}
+
+/**
+ * Returns a Date object set to UTC midnight of the given date.
+ * @param date - Date Object.
+ * @returns UTC midnight of the given date.
+ */
+export function getUtcMidnight(date: Date): Date {
+  return new Date(
+    Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate())
+  );
+}
+
+/**
+ * Parses a date string in the format "YYYY-MM-DD" and returns a Date object set to UTC midnight.
+ * Returns null if the input is not in the correct format.
+ * @param dateStr - Date string in "YYYY-MM-DD" format.
+ * @returns Date object set to UTC midnight or null if invalid.
+ */
+export function dateStringToUtcMidnight(dateStr: string): Date | null {
+  if (!/^\d{4}-\d{2}-\d{2}$/.test(dateStr)) {
+    return null;
+  }
+
+  const [year, month, day] = dateStr.split('-').map(Number) as [
+    number,
+    number,
+    number
+  ];
+
+  return new Date(Date.UTC(year, month - 1, day));
+}