// Timestamps are rendered by the server in UTC, next to a <time> element's
// machine-readable value. Rewrite those elements' hover titles so they show the
// reader's own local time instead.

const LOCAL_TIME_FORMAT = new Intl.DateTimeFormat("en-GB", {
  day: "numeric",
  month: "short",
  year: "numeric",
  hour: "2-digit",
  minute: "2-digit",
  hourCycle: "h23",
})

// Only absolute timestamps carry a zone to convert from: a date-only value would
// be read as UTC midnight and shift to the previous day for most readers.
const ABSOLUTE_TIMESTAMP = /T\d{2}:\d{2}(:\d{2})?(\.\d+)?(Z|[+-]\d{2}:\d{2})$/

const localizeTimestamps = () => {
  document.querySelectorAll("time[datetime]").forEach((element) => {
    const value = element.getAttribute("datetime")

    if (!ABSOLUTE_TIMESTAMP.test(value)) return

    const timestamp = new Date(value)

    if (!Number.isNaN(timestamp.getTime())) {
      element.title = LOCAL_TIME_FORMAT.format(timestamp)
    }
  })
}

document.addEventListener("turbo:load", localizeTimestamps)