FA-77284 / Calendar recurrence rules / Member archive

Closed-form final date of a COUNT-limited weekly BYDAY series: full weeks · case 04

When the remaining count is a multiple of the weekday count, the end date is one week early.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

For FREQ=WEEKLY;INTERVAL;BYDAY;WKST;COUNT starting at dtstart (weeks begin on wkst, days of the first week before dtstart are skipped, active weeks every interval weeks from the dtstart week), compute the date of the final instance arithmetically, without expanding. count < 1 returns None. The result must equal the last element of the full expansion.

Why this case matters

Recurring calendar series are expanded into concrete instances for display, reminders and conflict checks.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
WKST=WE interval 2	`"2024-07-11"`	`"2024-07-25"`	Failed

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