Function formatBriefTimestamp

src/utils/formatBriefTimestamp.ts:16–51

(
  isoString: string,
  now: Date = new Date(),
)

 * `now` is injectable for tests.
 */
export function formatBriefTimestamp(
  isoString: string,
  now: Date = new Date(),
): string {
  const d = new Date(isoString)
  if (Number.isNaN(d.getTime())) {
    return ''
  }

  const locale = getLocale()
  const dayDiff = startOfDay(now) - startOfDay(d)
  const daysAgo = Math.round(dayDiff / 86_400_000)

  if (daysAgo === 0) {
    return d.toLocaleTimeString(locale, {
      hour: 'numeric',
      minute: '2-digit',
    })
  }

  if (daysAgo > 0 && daysAgo < 7) {
    return d.toLocaleString(locale, {
      weekday: 'long',
      hour: 'numeric',
      minute: '2-digit',
    })
  }

  return d.toLocaleString(locale, {
    weekday: 'long',
    month: 'short',
    day: 'numeric',
    hour: 'numeric',
    minute: '2-digit',
  })
}

/**
 * Derive a BCP 47 locale tag from POSIX env vars.