Function getLocale

src/utils/formatBriefTimestamp.ts:58–77

* Derive a BCP 47 locale tag from POSIX env vars. * LC_ALL > LC_TIME > LANG, falls back to undefined (system default). * Converts POSIX format (en_GB.UTF-8) to BCP 47 (en-GB).

()

 * Converts POSIX format (en_GB.UTF-8) to BCP 47 (en-GB).
 */
function getLocale(): string | undefined {
  const raw =
    process.env.LC_ALL || process.env.LC_TIME || process.env.LANG || ''
  if (!raw || raw === 'C' || raw === 'POSIX') {
    return undefined
  }
  // Strip codeset (.UTF-8) and modifier (@euro), replace _ with -
  const base = raw.split('.')[0]!.split('@')[0]!
  if (!base) {
    return undefined
  }
  const tag = base.replaceAll('_', '-')
  // Validate by trying to construct an Intl locale — invalid tags throw
  try {
    new Intl.DateTimeFormat(tag)
    return tag
  } catch {
    return undefined
  }
}

function startOfDay(d: Date): number {
  return new Date(d.getFullYear(), d.getMonth(), d.getDate()).getTime()