Scheduler: T1327394 — fix appointments display for DST

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

@@ -1,3 +1,6 @@
+import { dateUtils } from '@ts/core/utils/m_date';
+
+import timeZoneUtils from '../../../m_utils_time_zone';
 import { splitIntervalByDay } from '../../common/split_interval_by_days';
 import type { CellInterval, DateInterval } from '../../types';
 
@@ -9,6 +12,8 @@ interface Options {
   skippedDays: number[];
 }
 
+const toMs = dateUtils.dateToMilliseconds;
+
 const filterBySkippedDays = <T extends DateInterval>(
   intervals: T[],
   skippedDays: number[],
@@ -17,6 +22,18 @@ const filterBySkippedDays = <T extends DateInterval>(
   return !skippedDays.includes(weekday);
 });
 
+const adjustDayIntervalMinForMidnightDST = (
+  dayIntervalMin: number,
+  startDayHour: number,
+): number => {
+  const date = timeZoneUtils.createDateFromUTCWithLocalOffset(new Date(dayIntervalMin));
+  const isMidnightDST = startDayHour === 0 && timeZoneUtils.isLocalTimeMidnightDST(date);
+
+  return isMidnightDST
+    ? dayIntervalMin + date.getHours() * toMs('hour')
+    : dayIntervalMin;
+};
+
 export const getMinutesCellIntervals = ({
   intervals,
   startDayHour,
@@ -30,7 +47,11 @@ export const getMinutesCellIntervals = ({
 
   let columnIndex = 0;
   filterBySkippedDays(dayIntervals, skippedDays).forEach((dayInterval) => {
-    const date = new Date(dayInterval.min);
+    const firstAvailableDayTime = adjustDayIntervalMinForMidnightDST(
+      dayInterval.min,
+      startDayHour,
+    );
+    const date = new Date(firstAvailableDayTime);
     while (date.getTime() < dayInterval.max) {
       const min = date.getTime();
       let max = date.setUTCMinutes(date.getUTCMinutes() + durationMinutes);

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

@@ -0,0 +1,48 @@
+/**
+ * @timezone Africa/Cairo
+ */
+
+import {
+  describe, expect, it,
+} from '@jest/globals';
+
+import { getWeekIntervals } from './get_week_intervals';
+
+describe('getWeekIntervals', () => {
+  it('T1327394: should not add a timeline cell before the first available local time on midnight DST', () => {
+    const intervals = getWeekIntervals({
+      startDayHour: 0,
+      endDayHour: 24,
+      min: Date.UTC(2026, 3, 24, 1),
+      max: Date.UTC(2026, 3, 25),
+      skippedDays: [],
+    }, 60, 0, true);
+
+    expect(intervals.cells[0]).toEqual({
+      min: Date.UTC(2026, 3, 24, 1),
+      max: Date.UTC(2026, 3, 24, 2),
+      rowIndex: 0,
+      columnIndex: 0,
+      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,
+    });
+  });
+});