fix(calendar): correct multi-day slice day counts (#4232)

While reviewing #4208, I had a bit of a headache figuring out the
`sliceMultiDay` logic. I cleaned that part up to make it easier to
follow and structurally clearer. In doing so, I noticed the previous
calculation was wrong in two edge cases:

- events crossing a DST change were not split by the actual calendar
days they touched
- events ending exactly at 00:00 were incorrectly counted as an
additional day

These cases are easy to miss because they are rare and only show up in
specific time windows or timezone transitions.

The logic now splits multi-day events by the calendar days they actually
cover and handles the boundary cases correctly.

Author: KristjanESPERANTO

defaultmodules/calendar/calendar.js

@@ -465,6 +465,20 @@ Module.register("calendar", {
 		return moment(timestamp, "x").tz(moment.tz.guess());
 	},
 
+	/**
+	 * Sets the relative day flags (today, yesterday, ...) on an event based on its day.
+	 * @param {object} event The event to flag.
+	 * @param {moment.Moment} dayMoment The day the event belongs to.
+	 * @param {moment.Moment} now The current moment.
+	 */
+	setRelativeDayFlags (event, dayMoment, now) {
+		event.today = dayMoment.isSame(now, "d");
+		event.dayBeforeYesterday = dayMoment.isSame(now.clone().subtract(2, "days"), "d");
+		event.yesterday = dayMoment.isSame(now.clone().subtract(1, "days"), "d");
+		event.tomorrow = dayMoment.isSame(now.clone().add(1, "days"), "d");
+		event.dayAfterTomorrow = dayMoment.isSame(now.clone().add(2, "days"), "d");
+	},
+
 	/**
 	 * Creates the sorted list of all events.
 	 * @param {boolean} limitNumberOfEntries Whether to filter returned events for display.
@@ -503,43 +517,36 @@ Module.register("calendar", {
 				}
 
 				event.url = calendarUrl;
-				event.today = eventStartDateMoment.isSame(now, "d");
-				event.dayBeforeYesterday = eventStartDateMoment.isSame(now.clone().subtract(2, "days"), "d");
-				event.yesterday = eventStartDateMoment.isSame(now.clone().subtract(1, "days"), "d");
-				event.tomorrow = eventStartDateMoment.isSame(now.clone().add(1, "days"), "d");
-				event.dayAfterTomorrow = eventStartDateMoment.isSame(now.clone().add(2, "days"), "d");
+				this.setRelativeDayFlags(event, eventStartDateMoment, now);
 
 				/*
-				 * if sliceMultiDayEvents is set to true, multiday events (events exceeding at least one midnight) are sliced into days,
-				 * otherwise, esp. in dateheaders mode it is not clear how long these events are.
+				 * If sliceMultiDayEvents is enabled, an event spanning several calendar days is split into one entry per day.
+				 * Otherwise, esp. in dateheaders mode, it is not clear how long these events are.
+				 * dayCount is the number of calendar days the event touches (an end exactly at midnight does not add a day).
 				 */
-				const maxCount = eventEndDateMoment.diff(eventStartDateMoment, "days");
-				if (this.config.sliceMultiDayEvents && maxCount > 1) {
+				const eventStartDay = eventStartDateMoment.clone().startOf("day");
+				const eventEndDay = eventEndDateMoment.clone().startOf("day");
+				const endsAtMidnight = !eventEndDateMoment.isAfter(eventEndDay);
+				const dayCount = eventEndDay.diff(eventStartDay, "days") + (endsAtMidnight ? 0 : 1);
+				if (this.config.sliceMultiDayEvents && dayCount > 1) {
 					const splitEvents = [];
-					let midnight
-						= eventStartDateMoment
-							.clone()
-							.startOf("day")
-							.add(1, "day")
-							.endOf("day");
-					let count = 1;
-					while (eventEndDateMoment.isAfter(midnight)) {
-						const thisEvent = JSON.parse(JSON.stringify(event)); // clone object
-						thisEvent.today = this.timestampToMoment(thisEvent.startDate).isSame(now, "d");
-						thisEvent.tomorrow = this.timestampToMoment(thisEvent.startDate).isSame(now.clone().add(1, "days"), "d");
-						thisEvent.endDate = midnight.clone().subtract(1, "day").format("x");
-						thisEvent.title += ` (${count}/${maxCount})`;
-						splitEvents.push(thisEvent);
-
-						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
+					// Each slice covers one day: it starts at the event start (first slice) or midnight,
+					// and ends at the event end (last slice) or one millisecond before the next midnight.
+					let sliceStart = eventStartDateMoment.clone();
+
+					for (let dayNumber = 1; dayNumber <= dayCount; dayNumber++) {
+						const isLastSlice = dayNumber === dayCount;
+						const nextMidnight = sliceStart.clone().startOf("day").add(1, "day");
+
+						const slice = JSON.parse(JSON.stringify(event)); // clone object
+						slice.startDate = sliceStart.format("x");
+						slice.endDate = isLastSlice ? event.endDate : nextMidnight.clone().subtract(1, "millisecond").format("x");
+						slice.title = `${event.title} (${dayNumber}/${dayCount})`;
+						this.setRelativeDayFlags(slice, sliceStart, now);
+						splitEvents.push(slice);
+
+						sliceStart = nextMidnight;
 					}
-					// Last day
-					event.title += ` (${count}/${maxCount})`;
-					event.today += this.timestampToMoment(event.startDate).isSame(now, "d");
-					event.tomorrow = this.timestampToMoment(event.startDate).isSame(now.clone().add(1, "days"), "d");
-					splitEvents.push(event);
 
 					for (const splitEvent of splitEvents) {
 						if (this.timestampToMoment(splitEvent.endDate).isAfter(now) && this.timestampToMoment(splitEvent.endDate).isSameOrBefore(future)) {

tests/configs/modules/calendar/sliceMultiDayEventsEndsMidnight.js

@@ -0,0 +1,33 @@
+const config = {
+	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,
+				maximumEntries: 100,
+				showEnd: true,
+				sliceMultiDayEvents: true,
+				calendars: [
+					{
+						maximumEntries: 100,
+						url: "http://localhost:8080/tests/mocks/calendar_test_slice_multiday_ends_midnight.ics"
+					}
+				]
+			}
+		}
+	]
+};
+
+/*************** DO NOT EDIT THE LINE BELOW ***************/
+if (typeof module !== "undefined") {
+	module.exports = config;
+}

tests/electron/modules/calendar_spec.js

@@ -179,6 +179,20 @@ describe("Calendar module", () => {
 			await helpers.startApplication("tests/configs/modules/calendar/sliceMultiDayEvents.js", "01 Sept 2024 10:38:00 GMT+02:00", [], "Europe/Berlin");
 			await expect(doTestCount()).resolves.toBe(6);
 		});
+
+		it("counts all touched dates across DST, not just elapsed 24h blocks", async () => {
+			// Event runs from 2024-10-25 to 2024-10-28 in Europe/Berlin, crossing the DST change.
+			// It touches 4 calendar dates: Fri, Sat, Sun, Mon.
+			await startCalendarShowEndScenario("slice_multiday_timed_start_midnight", "25 Oct 2024 06:00:00 GMT", "Europe/Berlin");
+			await expect(doTestCount()).resolves.toBe(4);
+		});
+
+		it("does not create an extra slice when an event ends exactly at 00:00", async () => {
+			// Event runs Fri 12:00 -> Mon 00:00. It should cover Fri, Sat, Sun only; Monday is not touched.
+			await helpers.startApplication("tests/configs/modules/calendar/sliceMultiDayEventsEndsMidnight.js", "25 Oct 2024 06:00:00 GMT", [], "GMT");
+			await expect(doTestCount()).resolves.toBe(3);
+			await expect(doTestTableContent(".calendar .event", ".title", "(3/3)", last)).resolves.toBe(true);
+		});
 	});
 
 	describe("sliceMultiDayEvents slice start time", () => {

tests/mocks/calendar_test_slice_multiday_ends_midnight.ics

@@ -0,0 +1,16 @@
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//MagicMirror//slice regression//EN
+CALSCALE:GREGORIAN
+METHOD:PUBLISH
+BEGIN:VEVENT
+DTSTART:20241025T120000Z
+DTEND:20241028T000000Z
+DTSTAMP:20241024T153358Z
+UID:slice-midnight-end-regression@magicmirror.test
+SEQUENCE:0
+STATUS:CONFIRMED
+SUMMARY:Slice
+TRANSP:OPAQUE
+END:VEVENT
+END:VCALENDAR