big update i guess

frontend/js/utils.js

@@ -37,6 +37,32 @@ export function toDateInput(d) {
   return `${d.getFullYear()}-${String(d.getMonth()+1).padStart(2,'0')}-${String(d.getDate()).padStart(2,'0')}`;
 }
 
+// Monday-first: returns 0=Mo, 1=Di, ..., 6=So
+export function dayOfWeek(d, weekStartDay = 'monday') {
+  if (weekStartDay === 'sunday') {
+    return d.getDay(); // 0=So, 1=Mo, ..., 6=Sa
+  }
+  return (d.getDay() + 6) % 7; // 0=Mo, 1=Di, ..., 6=So
+}
+
+// Returns the start-of-week date for d
+export function weekStart(d, weekStartDay = 'monday') {
+  const m = new Date(d);
+  m.setDate(m.getDate() - dayOfWeek(m, weekStartDay));
+  m.setHours(0, 0, 0, 0);
+  return m;
+}
+
+// Returns the ISO week number (Monday-based, ISO 8601)
+export function getISOWeekNumber(d) {
+  const date = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
+  // ISO week: weeks start on Monday, week 1 contains the first Thursday
+  const day = date.getUTCDay() || 7; // make Sunday = 7
+  date.setUTCDate(date.getUTCDate() + 4 - day);
+  const yearStart = new Date(Date.UTC(date.getUTCFullYear(), 0, 1));
+  return Math.ceil((((date - yearStart) / 86400000) + 1) / 7);
+}
+
 export function applyTheme(settings) {
   const root = document.documentElement;
   root.style.setProperty('--primary',      settings.primary_color || '#4285f4');