src/utils/toTimeZone.ts

import { TZDate } from "@date-fns/tz";

/**
 * Convert a {@link Date} or {@link TZDate} instance to the given time zone.
 * Reuses the same instance when it is already a {@link TZDate} using the target
 * time zone to avoid extra allocations.
 */
export function toTimeZone(date: Date, timeZone: string): TZDate {
  if (date instanceof TZDate && date.timeZone === timeZone) {
    return date;
  }
  return new TZDate(date, timeZone);
}