41 lines
1.5 KiB
TypeScript
41 lines
1.5 KiB
TypeScript
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// Server-side helper for resolving the calling user's IANA timezone.
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//
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// After Phase 7.1 Plan 01, `session.user.timezone` is a string populated
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// either from the stored `"user".timezone` column or from Better Auth's
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// additionalField `defaultValue` (`process.env.DEFAULT_TIMEZONE || 'UTC'`).
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//
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// This helper:
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// - reads the value off a Better Auth session
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// - validates it against `Intl.supportedValuesOf('timeZone')` (defence in
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// depth — Plan 02 already validates writes, but a corrupt row from
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// before this phase, or a manual SQL edit, must not crash dashboards)
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// - falls back to `process.env.DEFAULT_TIMEZONE || 'UTC'` if invalid
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//
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// Use this in every API route that does day/week/month boundary math.
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export const DEFAULT_TIMEZONE_FALLBACK = (): string =>
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process.env.DEFAULT_TIMEZONE || 'UTC';
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type SessionLike = {
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user?: { timezone?: unknown } | null;
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} | null | undefined;
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function isValidIanaTimezone(tz: unknown): tz is string {
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if (typeof tz !== 'string' || tz.length === 0 || tz.length > 64) return false;
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try {
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return Intl.supportedValuesOf('timeZone').includes(tz);
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} catch {
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return false;
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}
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}
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/**
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* Returns a validated IANA timezone string for the given session.
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* Never throws; always returns a usable string (worst case: 'UTC').
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*/
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export function getUserTimezone(session: SessionLike): string {
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const raw = session?.user?.timezone;
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if (isValidIanaTimezone(raw)) return raw;
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return DEFAULT_TIMEZONE_FALLBACK();
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}
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