const tehranParts = new Intl.DateTimeFormat('en-CA', {
  timeZone: 'Asia/Tehran',
  year: 'numeric',
  month: '2-digit',
  day: '2-digit',
  hour: '2-digit',
  minute: '2-digit',
  second: '2-digit',
  hourCycle: 'h23',
});

function parts(value: Date) {
  return Object.fromEntries(
    tehranParts
      .formatToParts(value)
      .filter((part) => part.type !== 'literal')
      .map((part) => [part.type, Number(part.value)]),
  );
}

function tehranOffset(value: Date) {
  const local = parts(value);
  return (
    Date.UTC(local.year, local.month - 1, local.day, local.hour, local.minute, local.second) - value.getTime()
  );
}

export function millisecondsUntilTehranMidnight(now = new Date()): number {
  const local = parts(now);
  const targetAsUTC = Date.UTC(local.year, local.month - 1, local.day + 1);
  let target = new Date(targetAsUTC - tehranOffset(now));
  target = new Date(targetAsUTC - tehranOffset(target));
  return Math.max(0, target.getTime() - now.getTime());
}