fix: fix bug for timelineweek and day views

Author: sjbur

packages/devextreme/js/__internal/scheduler/view_model/generate_view_model/options/get_minutes_cell_intervals.ts

@@ -1,3 +1,4 @@
+import timeZoneUtils from '../../../m_utils_time_zone';
 import { splitIntervalByDay } from '../../common/split_interval_by_days';
 import type { CellInterval, DateInterval } from '../../types';
 
@@ -17,16 +18,16 @@ const filterBySkippedDays = <T extends DateInterval>(
   return !skippedDays.includes(weekday);
 });
 
-const isFirstMidnightDSTInterval = (interval: DateInterval, dayInterval: DateInterval): boolean => {
-  const intervalMin = new Date(interval.min);
-  const dayIntervalMin = new Date(dayInterval.min);
+const getFirstAvailableDayTime = (
+  dayInterval: DateInterval,
+  startDayHour: number,
+): number => {
+  const date = timeZoneUtils.createDateFromUTCWithLocalOffset(new Date(dayInterval.min));
+  const isMidnightDST = startDayHour === 0 && timeZoneUtils.isLocalTimeMidnightDST(date);
 
-  return interval.min > dayInterval.min
-    && intervalMin.getUTCHours() === 1
-    && dayIntervalMin.getUTCHours() === 0
-    && intervalMin.getUTCFullYear() === dayIntervalMin.getUTCFullYear()
-    && intervalMin.getUTCMonth() === dayIntervalMin.getUTCMonth()
-    && intervalMin.getUTCDate() === dayIntervalMin.getUTCDate();
+  return isMidnightDST
+    ? dayInterval.min + date.getHours() * 60 * 60 * 1000
+    : dayInterval.min;
 };
 
 export const getMinutesCellIntervals = ({
@@ -42,10 +43,9 @@ export const getMinutesCellIntervals = ({
 
   let columnIndex = 0;
   filterBySkippedDays(dayIntervals, skippedDays).forEach((dayInterval) => {
-    const isFirstDSTInterval = isFirstMidnightDSTInterval(interval, dayInterval);
-    const intervalMin = isFirstDSTInterval ? interval.min : dayInterval.min;
-    const intervalMax = isFirstDSTInterval
-      ? Math.min(dayInterval.max, interval.max) : dayInterval.max;
+    const firstAvailableDayTime = getFirstAvailableDayTime(dayInterval, startDayHour);
+    const intervalMin = Math.max(firstAvailableDayTime, interval.min);
+    const intervalMax = Math.min(dayInterval.max, interval.max);
     const date = new Date(intervalMin);
     while (date.getTime() < intervalMax) {
       const min = date.getTime();

packages/devextreme/js/__internal/scheduler/view_model/generate_view_model/options/get_week_intervals.cairo.test.ts

@@ -26,4 +26,23 @@ describe('getWeekIntervals', () => {
       cellIndex: 0,
     });
   });
+
+  it('T1327394: should not add a timeline week cell before the first available local time on midnight DST', () => {
+    const intervals = getWeekIntervals({
+      startDayHour: 0,
+      endDayHour: 24,
+      min: Date.UTC(2026, 3, 20),
+      max: Date.UTC(2026, 3, 27),
+      skippedDays: [],
+    }, 60, 0, true);
+
+    expect(intervals.cells.find((cell) => cell.min === Date.UTC(2026, 3, 24))).toBeUndefined();
+    expect(intervals.cells.find((cell) => cell.min === Date.UTC(2026, 3, 24, 1))).toEqual({
+      min: Date.UTC(2026, 3, 24, 1),
+      max: Date.UTC(2026, 3, 24, 2),
+      rowIndex: 0,
+      columnIndex: 96,
+      cellIndex: 96,
+    });
+  });
 });