/** Formatting for display. Uses `Intl`, so no dependency and no locale data. */

const RELATIVE = new Intl.RelativeTimeFormat(undefined, { numeric: "auto" });
const ABSOLUTE = new Intl.DateTimeFormat(undefined, {
  dateStyle: "medium",
  timeStyle: "short",
});

/** Largest unit first, so the first one that fits is the one to use. */
const UNITS: [Intl.RelativeTimeFormatUnit, number][] = [
  ["year", 365 * 24 * 60 * 60],
  ["month", 30 * 24 * 60 * 60],
  ["week", 7 * 24 * 60 * 60],
  ["day", 24 * 60 * 60],
  ["hour", 60 * 60],
  ["minute", 60],
];

/**
 * "3 days ago", for a committer time in seconds since the epoch.
 *
 * Commit dates are usually read as "how long ago", not as a date — the exact
 * timestamp goes in the `title` and the `datetime` attribute instead.
 */
export function relativeTime(seconds: number, now = Date.now()): string {
  const elapsed = seconds - Math.floor(now / 1000);

  for (const [unit, size] of UNITS) {
    if (Math.abs(elapsed) >= size) {
      return RELATIVE.format(Math.round(elapsed / size), unit);
    }
  }

  return RELATIVE.format(Math.round(elapsed), "second");
}

/** The full timestamp, for the tooltip. */
export function absoluteTime(seconds: number): string {
  return ABSOLUTE.format(new Date(seconds * 1000));
}

/** A machine-readable timestamp for `<time datetime>`. */
export function isoTime(seconds: number): string {
  return new Date(seconds * 1000).toISOString();
}

/** The short form of a commit id, as git itself abbreviates it. */
export function shortId(id: string): string {
  return id.slice(0, 7);
}