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feat(relativeTime): add relativeYearsDe helper for historical letter dates

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The correspondence timeline labels each row with its distance from today
("vor 86 Jahren"). Uses calendar-field math so the anniversary day
flips exactly — an ms-based 365.25d average misses by a day on leap
years. Invalid / future dates return "" so the caller can hide the
label rather than print "vor 0 Jahren".

Refs #305

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Marcel
2026-04-23 14:36:43 +02:00
committed by marcel
parent 70d813ee70
commit a52d481a8e
2 changed files with 48 additions and 1 deletions
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19
frontend/src/lib/relativeTime.ts
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@@ -9,3 +9,22 @@ export function relativeTimeDe(from: Date, now: Date = new Date()): string {
if (minutes < 1440) return m.comment_time_hours({ count: Math.round(minutes / 60) });
return m.comment_time_days({ count: Math.round(minutes / 1440) });
}
// "vor N Jahren" for a historical letter date relative to now. Computed from
// calendar fields (not a constant ms-per-year) so that a letter from exactly
// one year ago reports "vor 1 Jahr" rather than falling on the wrong side of
// a leap-year rounding. Returns "" for invalid or future dates — the caller
// should then hide the relative-time label rather than render a misleading
// "vor 0 Jahren".
export function relativeYearsDe(from: Date, now: Date = new Date()): string {
if (Number.isNaN(from.getTime()) || Number.isNaN(now.getTime())) return '';
if (from.getTime() > now.getTime()) return '';
let years = now.getUTCFullYear() - from.getUTCFullYear();
const beforeAnniversary =
now.getUTCMonth() < from.getUTCMonth() ||
(now.getUTCMonth() === from.getUTCMonth() && now.getUTCDate() < from.getUTCDate());
if (beforeAnniversary) years -= 1;
if (years < 1) return 'vor weniger als 1 Jahr';
if (years === 1) return 'vor 1 Jahr';
return `vor ${years} Jahren`;
}