Scheduler: fix recurrence appointment display date according DST (T1305659) (#31307)

Author: Ambrozy

packages/devextreme/js/__internal/scheduler/__tests__/recurrence.DST.test.ts

@@ -0,0 +1,123 @@
+import {
+  describe, expect, it,
+} from '@jest/globals';
+
+import { createScheduler } from './__mock__/create_scheduler';
+import { setupSchedulerTestEnvironment } from './__mock__/m_mock_scheduler';
+import type { AppointmentModel } from './__mock__/model/appointment';
+
+const ChicagoDST = [new Date('2025-03-08T00:00:00.000Z'), new Date('2025-11-01T00:00:00.000Z')]; // +1, -1
+const SydneyDST = [new Date('2025-04-07T00:00:00.000Z'), new Date('2025-10-04T00:00:00.000Z')]; // -1, +1
+const BelgradeDST = [new Date('2025-03-29T00:00:00.000Z'), new Date('2025-10-25T00:00:00.000Z')]; // +1, -1
+const dailyAppointment = {
+  startDate: new Date('2025-01-07T13:00:00.000Z'),
+  endDate: new Date('2025-01-07T14:00:00.000Z'),
+  startDateTimeZone: 'America/Chicago',
+  endDateTimeZone: 'America/Chicago',
+  recurrenceRule: 'FREQ=DAILY',
+};
+const views = [{ type: 'week', intervalCount: 2 }];
+
+const getDisplayDates = (appointments: AppointmentModel[]): string[] => appointments
+  .map((appointment) => appointment.getDisplayDate());
+const reduceDates = (texts: string[]): string[] => texts
+  .reduce<string[]>((result, time) => {
+    if (result.at(-1) !== time) {
+      result.push(time);
+    }
+
+    return result;
+  }, []);
+
+/*
+ * NOTE:
+ * display date = source date - source time zone offset + target time zone offset
+ *
+ * Chicago: UTC-6h, UTC-5h, UTC-6h
+ * Sydney: UTC+11h, UTC+10h, UTC+11h
+ * Belgrade: UTC+1h, UTC+2h, UTC+1h
+ *
+ * Chicago to Chicago: should keep the same display date
+ * Chicago to Sydney:   +17h, +16h, +15h, +16h, +17h
+ * Chicago to Belgrade:  +7h,  +6h,  +7h,  +6h,  +7h
+ */
+describe('Recurrence appointments', () => {
+  it('should change dates according to DST in target (Chicago) and appointment timezones (T1305659)', async () => {
+    setupSchedulerTestEnvironment();
+    const { POM, scheduler } = await createScheduler({
+      timeZone: 'America/Chicago',
+      dataSource: [dailyAppointment],
+      views,
+      currentView: 'week',
+      currentDate: ChicagoDST[0],
+    });
+
+    const getDates = () => getDisplayDates(POM.getAppointments());
+
+    const dates = getDates();
+    scheduler.option('currentDate', ChicagoDST[1]);
+    dates.push(...getDates());
+
+    expect(reduceDates(dates)).toEqual([
+      '7:00 AM - 8:00 AM',
+    ]);
+  });
+
+  it('should change dates according to DST in target (Sydney) and appointment timezones (T1305659)', async () => {
+    setupSchedulerTestEnvironment();
+    const { POM, scheduler } = await createScheduler({
+      timeZone: 'Australia/Sydney',
+      dataSource: [dailyAppointment],
+      views,
+      currentView: 'week',
+      currentDate: ChicagoDST[0],
+    });
+
+    const getDates = () => getDisplayDates(POM.getAppointments());
+
+    const dates = getDates();
+    scheduler.option('currentDate', SydneyDST[0]);
+    dates.push(...getDates());
+    scheduler.option('currentDate', SydneyDST[1]);
+    dates.push(...getDates());
+    scheduler.option('currentDate', ChicagoDST[1]);
+    dates.push(...getDates());
+
+    expect(reduceDates(dates)).toEqual([
+      '12:00 AM - 1:00 AM',
+      '11:00 PM - 12:00 AM',
+      '10:00 PM - 11:00 PM',
+      '11:00 PM - 12:00 AM',
+      '12:00 AM - 1:00 AM',
+    ]);
+  });
+
+  it('should change dates according to DST in target (Belgrade) and appointment timezones (T1305659)', async () => {
+    setupSchedulerTestEnvironment();
+    const { POM, scheduler } = await createScheduler({
+      timeZone: 'Europe/Belgrade',
+      dataSource: [dailyAppointment],
+      views,
+      currentView: 'week',
+      currentDate: ChicagoDST[0],
+    });
+
+    const getDates = () => getDisplayDates(POM.getAppointments());
+
+    const dates = getDates();
+    scheduler.option('currentDate', BelgradeDST[0]);
+    dates.push(...getDates());
+    scheduler.option('currentDate', BelgradeDST[1]);
+    dates.push(...getDates());
+    scheduler.option('currentDate', ChicagoDST[1]);
+    dates.push(...getDates());
+
+    expect(reduceDates(dates)).toEqual([
+      '2:00 PM - 3:00 PM',
+      '1:00 PM - 2:00 PM',
+      '2:00 PM - 3:00 PM',
+      '1:00 PM - 2:00 PM',
+      '2:00 PM - 3:00 PM',
+    ]);
+  });
+});