fix(calendar): sliced multi-day events start at 00:00, not 23:59

With `sliceMultiDayEvents: true`, every slice after the first was given the
following day's `endOf("day")` (23:59:59.999) as its `startDate`, so slices
2..n rendered a start time of 23:59 instead of the next day's 00:00.

Set the next slice's start to `startOf("day")` of that day.

Adds an electron regression test (scenario `slice_multiday_timed_start_midnight`
with a timed event spanning several midnights): every rendered slice time cell
must contain a 00:00 start and never 23:59. Fails without the fix.

Closes #4206

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
(cherry picked from commit 890db2b)

Author: ago1776

defaultmodules/calendar/calendar.js

@@ -531,7 +531,7 @@ Module.register("calendar", {
 						thisEvent.title += ` (${count}/${maxCount})`;
 						splitEvents.push(thisEvent);
 
-						event.startDate = midnight.format("x");
+						event.startDate = midnight.clone().startOf("day").format("x"); // start next slice at 00:00, not 23:59
 						count += 1;
 						midnight = midnight.clone().add(1, "day").endOf("day"); // next day
 					}

tests/configs/modules/calendar/calendarShowEndConfigs.js

@@ -347,6 +347,32 @@ const calendarShowEndConfigs = {
 				}
 			}
 		]
+	},
+	slice_multiday_timed_start_midnight: {
+		address: "0.0.0.0",
+		ipWhitelist: [],
+		timeFormat: 24,
+		modules: [
+			{
+				module: "calendar",
+				position: "bottom_bar",
+				config: {
+					fade: false,
+					urgency: 0,
+					dateFormat: "Do.MMM, HH:mm",
+					fullDayEventDateFormat: "Do.MMM",
+					timeFormat: "absolute",
+					getRelative: 0,
+					sliceMultiDayEvents: true,
+					calendars: [
+						{
+							maximumEntries: 100,
+							url: "http://localhost:8080/tests/mocks/calendar_test_slice_multiday_timed.ics"
+						}
+					]
+				}
+			}
+		]
 	}
 };
 

tests/electron/modules/calendar_spec.js

@@ -181,6 +181,20 @@ describe("Calendar module", () => {
 		});
 	});
 
+	describe("sliceMultiDayEvents slice start time", () => {
+		it("sliced sub-events start at 00:00, not 23:59", async () => {
+			// Timed event Fri 25 Oct 12:00 -> Mon 28 Oct 08:00 (UTC) is sliced across
+			// several midnights. Every slice after the first must start at 00:00 of its
+			// day. Regression for the bug where they started at 23:59 instead.
+			await startCalendarShowEndScenario("slice_multiday_timed_start_midnight", "25 Oct 2024 06:00:00 GMT", "GMT");
+			const firstTimeCell = global.page.locator(".calendar .event .time").locator(`nth=${first}`);
+			await firstTimeCell.waitFor({ state: "visible" });
+			const times = await global.page.locator(".calendar .event .time").allTextContents();
+			expect(times.some((time) => time.includes("00:00"))).toBe(true);
+			expect(times.every((time) => !time.includes("23:59"))).toBe(true);
+		});
+	});
+
 	describe("germany timezone", () => {
 		it("Issue #unknown fullday timezone East of UTC edge", async () => {
 			await helpers.startApplication("tests/configs/modules/calendar/germany_at_end_of_day_repeating.js", "01 Oct 2024 10:38:00 GMT+02:00", [], "Europe/Berlin");

tests/mocks/calendar_test_slice_multiday_timed.ics

@@ -0,0 +1,16 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//MagicMirror//slice regression//EN
+CALSCALE:GREGORIAN
+METHOD:PUBLISH
+BEGIN:VEVENT
+DTSTART:20241025T120000Z
+DTEND:20241028T080000Z
+DTSTAMP:20241024T153358Z
+UID:slice-midnight-regression@magicmirror.test
+SEQUENCE:0
+STATUS:CONFIRMED
+SUMMARY:Timed multi-day slice
+TRANSP:OPAQUE
+END:VEVENT
+END:VCALENDAR