Function timeZoneGetter

packages/common/src/i18n/format_date.ts:465–505

* Returns a date formatter that transforms a date and an offset into a timezone with ISO8601 or * GMT format depending on the width (eg: short = +0430, short:GMT = GMT+4, long = GMT+04:30, * extended = +04:30)

(width: ZoneWidth)

 * extended = +04:30)
 */
function timeZoneGetter(width: ZoneWidth): DateFormatter {
  return function (date: Date, locale: string, offset: number) {
    const zone = -1 * offset;
    const minusSign = getLocaleNumberSymbol(locale, NumberSymbol.MinusSign);
    const hours = zone > 0 ? Math.floor(zone / 60) : Math.ceil(zone / 60);
    switch (width) {
      case ZoneWidth.Short:
        return (
          (zone >= 0 ? '+' : '') +
          padNumber(hours, 2, minusSign) +
          padNumber(Math.abs(zone % 60), 2, minusSign)
        );
      case ZoneWidth.ShortGMT:
        return 'GMT' + (zone >= 0 ? '+' : '') + padNumber(hours, 1, minusSign);
      case ZoneWidth.Long:
        return (
          'GMT' +
          (zone >= 0 ? '+' : '') +
          padNumber(hours, 2, minusSign) +
          ':' +
          padNumber(Math.abs(zone % 60), 2, minusSign)
        );
      case ZoneWidth.Extended:
        if (offset === 0) {
          return 'Z';
        } else {
          return (
            (zone >= 0 ? '+' : '') +
            padNumber(hours, 2, minusSign) +
            ':' +
            padNumber(Math.abs(zone % 60), 2, minusSign)
          );
        }
      default:
        throw new RuntimeError(
          RuntimeErrorCode.UNKNOWN_ZONE_WIDTH,
          ngDevMode && `Unknown zone width "${width}"`,
        );
    }
  };
}

const JANUARY = 0;
const THURSDAY = 4;