[calendar] fix: prevent excessive fetching on client reload and refactor calendarfetcherutils.js (#3976)

The bottom line of this PR is, that it fixes an issue and simplifies the
code by dealing with the TODOs in the code.

For review, I suggest looking at each commit individually. If there are
too many changes for a PR, let me know and I'll split it up
:slightly_smiling_face:

## 1. [fix(calendar): prevent excessive fetching with smart refresh
strategy](8892cd3)

- Add lastFetch timestamp tracking to CalendarFetcher
- Add shouldRefetch() method with configurable minimum interval
(default: 3 minutes)
- When reusing existing fetcher: fetch if data is stale (>3 min),
otherwise broadcast cached events
- Prevents double broadcasts to consuming modules while maintaining
fresh data
- Balances rate limit prevention (Issue
#3971) with data
freshness on user reload
- Prevents excessive fetching during rapid reloads (e.g., Fully Kiosk
screensaver use case)
- Allows fresh calendar data when enough time has passed since last
fetch

## 2. [refactor(calendar): simplify event exclusion
logic](d507aba)

- Extract filtering logic from `shouldEventBeExcluded` into new helper
`checkEventAgainstFilter`
- Simplify the main loop in `shouldEventBeExcluded

It resolves a TODO from the comments in the code:
* `This seems like an overly complicated way to exclude events based on
the title.`

## 3. [refactor(calendar): extract recurring event expansion
logic](d510160)

This change separates the expansion of recurring events from the main
filtering loop into a new helper function 'expandRecurringEvent'.

It resolves two TODOs from the comments in the code:
- `This should be a separate function`
- `This should create an event per moment so we can change anything we
want`

This improves code readability, reduces complexity in 'filterEvents',
and allows for cleaner handling of individual recurrence instances.

## 4. [refactor(calendar): simplify recurring event
handling](b04f716)

- Simplify 'getMomentsFromRecurringEvent' using modern syntax
- Improve handling of full-day events across different timezones


## 5. [test(calendar): fix UNTIL date in fullday_until.ics
fixture](1d762b2)

The issue was with the UNTIL date being May 4th while DTSTART was May
5th. This created an invalid recurrence rule where the end date came
before the start date.

The fix only adjusts the UNTIL date from May 4th to May 5th, so it
matches the start date.

Author: KristjanESPERANTO

CHANGELOG.md

@@ -40,6 +40,7 @@ planned for 2026-01-01
 - [gitignore] cleanup/simplify .gitignore (#3952, #3954, #3968, #3969)
 - [compliments] refactor: optimize `loadComplimentFile` method and add unit tests(#3969)
 - [core] chore: simplify Wayland start script (#3974)
+- [calendar] refactor: simplify recurring event handling and event exclusion logic (#3976)
 
 ### Fixed
 
@@ -52,6 +53,7 @@ planned for 2026-01-01
 - [weather] fixed windy icon not showing up in pirateweather (#3957)
 - [compliments] fixed duplicate query param "?" when constructing refresh url (#3967)
 - [compliments] fixed compliments remote file minimum delay to be 15 minutes (#3970)
+- [calendar] prevent excessive fetching with smart refresh strategy (#3976)
 
 ### Updated
 

modules/default/calendar/calendarfetcher.js

@@ -38,6 +38,7 @@ class CalendarFetcher {
 		this.events = [];
 		this.reloadTimer = null;
 		this.serverErrorCount = 0;
+		this.lastFetch = null;
 		this.fetchFailedCallback = () => {};
 		this.eventsReceivedCallback = () => {};
 	}
@@ -165,6 +166,7 @@ class CalendarFetcher {
 						maximumEntries: this.maximumEntries,
 						maximumNumberOfDays: this.maximumNumberOfDays
 					});
+					this.lastFetch = Date.now();
 					this.broadcastEvents();
 				} catch (error) {
 					Log.error(`${this.url} - iCal parsing failed: ${error.message}`);
@@ -179,6 +181,19 @@ class CalendarFetcher {
 		this.scheduleNextFetch(nextDelay);
 	}
 
+	/**
+	 * Check if enough time has passed since the last fetch to warrant a new one.
+	 * Uses reloadInterval as the threshold to respect user's configured fetchInterval.
+	 * @returns {boolean} True if a new fetch should be performed
+	 */
+	shouldRefetch () {
+		if (!this.lastFetch) {
+			return true;
+		}
+		const timeSinceLastFetch = Date.now() - this.lastFetch;
+		return timeSinceLastFetch >= this.reloadInterval;
+	}
+
 	/**
 	 * Broadcasts the current events to listeners
 	 */