public/js/util/getProductionOffice.js

import moment from 'moment';

function isBetween({value, lower, upper}) {
  return value >= lower && value <= upper;
}

function getTimezoneOffset() {
  const offset = moment().utcOffset();

  if (isBetween({value: offset, lower: 480, upper: 660})) {
    return 'SYD';
  }

  if (isBetween({value: offset, lower: -560, upper: -400})) {
    return 'SFO';
  }

  if (isBetween({value: offset, lower: -400, upper: -240})) {
    return 'NYC';
  }

  return 'LON';
}

export default function getProductionOffice() {
  const timezoneProductionOfficeMap = {
    SYD: 'AUS',
    SFO: 'US',
    NYC: 'US',
    LON: 'UK'
  };

  return timezoneProductionOfficeMap[getTimezoneOffset()];
}