date.ts

export type DateParts = { year: string; month: string; day: string };

export function getLocalizedDateParts(locale: string): DateParts {
  const rtf = new Intl.RelativeTimeFormat(locale),
    result: DateParts = { year: '', month: '', day: '' };

  ['year', 'month', 'day'].forEach(part => {
    const parts = rtf.formatToParts(-1, `${part}s` as Intl.RelativeTimeFormatUnit),
      index = parts.findIndex(({ unit }) => unit === part),
      value = parts[index + 1].value;

    result[part as keyof DateParts] = value.trim().substring(0, 1);
  });

  return result;
}

export function getLocalizedDatePattern(locale: string, options: Intl.DateTimeFormatOptions = {}): string {
  const dtf = new Intl.DateTimeFormat(locale, options),
    parts = getLocalizedDateParts(locale);

  return dtf
    .formatToParts(new Date('2022-01-01'))
    .map(part => {
      switch (part.type) {
        case 'day':
          return parts.day.repeat(part.value.length);
        case 'month':
          return parts.month.repeat(part.value.length);
        case 'year':
          return parts.year.repeat(part.value.length);
        default:
          return part.value;
      }
    })
    .join('');
}