50 lines
1.8 KiB
TypeScript
50 lines
1.8 KiB
TypeScript
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/**
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* Display form of a journal entry's `date:` frontmatter. Client-safe (no `fs`),
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* shared by the /journal index and the entry header so both show the same thing.
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*
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* The value is typed by hand, so it is read as a calendar date, not an instant:
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*
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* - `2026-03-15` (optionally followed by a time) is formatted in UTC. `new Date()`
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* reads a date-only ISO string as UTC midnight, and formatting that in the
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* server's or browser's timezone showed Mar 14 west of Greenwich.
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* - `2026-03` shows month and year — `new Date('2026-03')` invented the 1st.
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* - Anything else (`15.03.2026`, `March 2026`, `Spring 2026`, an impossible
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* `2026-02-30`) is shown as written instead of "Invalid Date" or a guessed day.
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*/
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const DAY = /^(\d{4})-(\d{2})-(\d{2})(?=$|[T\s])/;
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const MONTH = /^(\d{4})-(\d{2})$/;
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export function formatJournalDate(raw: string | undefined, locale: string): string | null {
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const value = raw?.trim();
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if (!value) return null;
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const day = DAY.exec(value);
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if (day) {
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const [y, m, d] = [Number(day[1]), Number(day[2]), Number(day[3])];
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const date = new Date(Date.UTC(y, m - 1, d));
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// Date.UTC rolls 2026-02-30 over into March; refuse instead of moving it.
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if (date.getUTCFullYear() !== y || date.getUTCMonth() !== m - 1 || date.getUTCDate() !== d) {
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return value;
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}
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return date.toLocaleDateString(locale, {
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timeZone: 'UTC',
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year: 'numeric',
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month: 'short',
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day: 'numeric',
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});
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}
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const month = MONTH.exec(value);
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if (month) {
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const [y, m] = [Number(month[1]), Number(month[2])];
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if (m < 1 || m > 12) return value;
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return new Date(Date.UTC(y, m - 1, 1)).toLocaleDateString(locale, {
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timeZone: 'UTC',
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year: 'numeric',
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month: 'long',
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});
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}
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return value;
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}
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