fix: exclude timed EXDATE instances crossing UTC midnight due to DST

[KristjanESPERANTO]

While implementing expandRecurringEvent in MagicMirror I noticed a subtle bug: recurring timed events with an EXDATE weren't always excluded correctly.

The culprit is a DST edge case — when an event's local time crosses UTC midnight (e.g. 16:00 PST = 00:00 UTC the next day), the date-only key from generateDateKey() ("2023-11-09") matches neither key stored by the parser ("2023-11-08" local date, or "2023-11-09T00:00:00.000Z" full ISO string).

The fix adds a fallback to the full ISO string lookup, consistent with the dual-key storage already in the parser.

Includes a regression test with a weekly 16:00 America/Los_Angeles event and an EXDATE on the first occurrence after the PDT→PST switch.

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of excluded recurring event instances (EXDATE) by expanding lookup to cover additional key formats, ensuring events are properly excluded even during daylight saving time transitions.

• Tests

  • Added test cases validating EXDATE exclusion during UTC midnight crossings caused by DST changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📝 Walkthrough

Walkthrough

The pull request extends EXDATE exclusion logic to check both a generated dateKey and ISO string representation (date.toISOString()) for non-full-day recurring events, and adds test coverage for EXDATE handling across DST boundaries.

Changes

Cohort / File(s)	Summary
EXDATE Lookup Enhancement node-ical.js	Added dual-key EXDATE lookup for non-full-day recurring events: now checks both event.exdate[dateKey] and event.exdate[date.toISOString()] to broaden exclusion coverage.
EXDATE DST Test Cases test/expand-recurring-event.test.js	Added two test cases validating EXDATE exclusion for weekly recurring events with times when EXDATE dates cross UTC midnight due to DST transitions (PST/PDT), ensuring correct instance exclusion while preserving adjacent occurrences.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• fix(parser): change exdate from array to plain object #423: Directly related — both modify how EXDATEs are represented and looked up by key, with this PR adding ISO string key checking to match the keyed representation introduced there.
• Add expandRecurringEvent API for Recurring Event Expansion #430: Directly related — both touch EXDATE lookup logic in node-ical.js; the retrieved PR implemented generateDateKey while this PR extends the dual-key lookup strategy.
• fix: correct EXDATE matching for full-day recurring events #456: Related — both modify EXDATE matching in recurrence expansion to handle timezone/ISO string variants across DST boundaries.

Poem

🐰 A rabbit hopped through dates so fine,
But timezones made the schedule malign,
ISO strings we now consult with glee,
Dual keys for exceptions—now decree!
DST no longer dims our sight,
Each excluded event, perfectly right! 🕐

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely describes the main bug fix: adding support for EXDATE exclusion of timed events that cross UTC midnight due to DST transitions. It directly reflects the core change in node-ical.js and the regression test added.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[KristjanESPERANTO]

The "1 configuration not found" CodeQL warning is a pre-existing issue unrelated to this PR — commit 54bef15 renamed the language from javascript to javascript-typescript, leaving stale baseline results on master. This will resolve itself on the next push to master.

Coderabbit seems satisfied. In my view, this can be merged 🙂

[KristjanESPERANTO]

@jens-maus Thanks for the quick merges! A new release would be nice since this blocks my efforts implementing expandRecurringEvent in MagicMirror 🙂