function gcke(n) {
  const cs = document.cookie.split(';');
  for (let i=0; i<cs.length; i++) {
    let c = cs[i].trim();
    if (c.startsWith(n + '=')) {
      return c.substring(n.length + 1);
    }
  }
  return null;
}

if ('BroadcastChannel' in self) {
    const chn = window.location.hostname;
    if (!chn.includes('devlocal')) {
        const bc = new BroadcastChannel('esup_' + chn);
        let isAlpha = true;
        bc.addEventListener('message', (msg) => {
            if (msg.data === 'multiple-tabs' && isAlpha) {
                bc.postMessage('already-open');
            }
            if (msg.data === 'already-open') {
                let cc = (gcke("tabCheck_" + chn) === null);
                if (isAlpha && cc) {
                    isAlpha = false;
                    document.cookie = "tabCheck_" + chn + "=true; max-age=300";
                    alert('WARNING: You are using this application in multiple tabs.  This is not supported and WILL result in corrupted data.');
                }
                
            }
        });
        bc.postMessage('multiple-tabs');
    }
}