/**
* Shared date utilities — pure functions, no DOM or Node APIs.
* Used by both server (src/) and viewer (viewer/) via re-export.
*/
/**
* Convert a UTC ISO timestamp to a YYYY-MM-DD date key in a given timezone.
* @param isoTimestamp - UTC timestamp (e.g. "2026-02-12T03:32:40.563Z")
* @param tzOffsetMinutes - Timezone offset in minutes from Date.getTimezoneOffset()
* (e.g. 480 for PST/UTC-8, -60 for CET/UTC+1)
* @returns YYYY-MM-DD string in the target timezone, or null if invalid
*/
export function utcToLocalDateKey(isoTimestamp: string, tzOffsetMinutes: number): string | null {
const ms = Date.parse(isoTimestamp);
if (isNaN(ms)) return null;
const d = new Date(ms - tzOffsetMinutes * 60_000);
return d.toISOString().slice(0, 10);
}
/**
* Format a Date as YYYY-MM-DD in the runtime's local timezone.
* Returns null for invalid dates.
*/
export function getLocalDateKey(date: Date): string | null {
if (!(date instanceof Date) || isNaN(date.getTime())) return null;
const year = date.getFullYear();
const month = String(date.getMonth() + 1).padStart(2, '0');
const day = String(date.getDate()).padStart(2, '0');
return `${year}-${month}-${day}`;
}
