Поправил графики

frontend/admin/js/schedule-period.js

@@ -0,0 +1,43 @@
+export function preferredScheduleSemester(semesters, date) {
+    const items = (semesters || [])
+        .filter(semester => semester?.startDate && semester?.endDate);
+    const current = items.find(semester =>
+        semester.startDate <= date && semester.endDate >= date
+    );
+    if (current) return current;
+
+    const upcoming = items
+        .filter(semester => semester.startDate > date)
+        .sort((first, second) => first.startDate.localeCompare(second.startDate));
+    if (upcoming.length) return upcoming[0];
+
+    return items
+        .filter(semester => semester.endDate < date)
+        .sort((first, second) => second.endDate.localeCompare(first.endDate))[0] || null;
+}
+
+export function defaultSchedulePeriod(semesters, date, durationDays = 14) {
+    const semester = preferredScheduleSemester(semesters, date);
+    const startDate = semester && (date < semester.startDate || date > semester.endDate)
+        ? semester.startDate
+        : date;
+    const calculatedEnd = addIsoDays(startDate, Math.max(1, durationDays) - 1);
+    return {
+        semester,
+        startDate,
+        endDate: semester && calculatedEnd > semester.endDate
+            ? semester.endDate
+            : calculatedEnd
+    };
+}
+
+function addIsoDays(value, days) {
+    const [year, month, day] = String(value).split('-').map(Number);
+    const date = new Date(year, month - 1, day);
+    date.setDate(date.getDate() + days);
+    return [
+        date.getFullYear(),
+        String(date.getMonth() + 1).padStart(2, '0'),
+        String(date.getDate()).padStart(2, '0')
+    ].join('-');
+}