refactor: split app into modular src architecture

src/utils/date.js

@@ -0,0 +1,25 @@
+export function makeId(prefix) {
+  return `${prefix}_${Date.now()}_${Math.random().toString(36).slice(2, 8)}`;
+}
+
+export function todayYMD() {
+  const now = new Date();
+  return `${now.getFullYear()}-${`${now.getMonth() + 1}`.padStart(2, '0')}-${`${now.getDate()}`.padStart(2, '0')}`;
+}
+
+export function parseYMD(value) {
+  if (!value || !/^\d{4}-\d{2}-\d{2}$/.test(value)) return null;
+  const d = new Date(`${value}T00:00:00`);
+  return Number.isNaN(d.getTime()) ? null : d;
+}
+
+export function findActiveTripId(trips) {
+  const today = parseYMD(todayYMD());
+  if (!today) return null;
+  const active = trips.find((trip) => {
+    const start = parseYMD(trip.startDate);
+    const end = parseYMD(trip.endDate);
+    return !!start && !!end && today >= start && today <= end;
+  });
+  return active?.id || null;
+}