/**
 * Current UTC offset in hours for an IANA timezone, using the environment's
 * locale rules (accounts for DST at `reference`, default "now").
 */
export function getIANATimezoneOffsetHours(
  ianaTimezone: string,
  reference: Date = new Date()
): number {
  const utcDate = new Date(reference.toLocaleString("en-US", { timeZone: "UTC" }));
  const tzDate = new Date(
    reference.toLocaleString("en-US", { timeZone: ianaTimezone })
  );
  return (tzDate.getTime() - utcDate.getTime()) / 3600000;
}