const UTC_DATE_FMT: Intl.DateTimeFormatOptions = {
  year: 'numeric',
  month: 'numeric',
  day: 'numeric',
  hour: '2-digit',
  minute: '2-digit',
  hour12: false,
  timeZone: 'UTC',
}

/** Backend unix nanoseconds (UTC+0) → localized date string with UTC suffix. */
export function formatUnixNano(ns: number | undefined | null): string | null {
  if (!ns || ns <= 0) return null
  const ms = Math.floor(ns / 1_000_000)
  const date = new Date(ms)
  if (Number.isNaN(date.getTime())) return null
  return `${date.toLocaleString('zh-TW', UTC_DATE_FMT)} UTC`
}

/** Threads / API posted_at (ISO or parseable string) → date label. */
export function formatPostedAt(raw: string | undefined | null): string | null {
  const value = raw?.trim()
  if (!value) return null
  const parsed = new Date(value)
  if (!Number.isNaN(parsed.getTime())) {
    return parsed.toLocaleString('zh-TW', UTC_DATE_FMT) + ' UTC'
  }
  if (/^\d{4}[-/]/.test(value)) return value
  return value
}

/** Scan post publish time. Do not fall back to crawl入库 time. */
export function formatScanPostDate(post: {
  posted_at?: string
}): string | null {
  return formatPostedAt(post.posted_at)
}