/**
 * List of `zeit.world` nameservers
 */

const nameservers = new Set([
  'california.zeit.world',
  'london.zeit.world',
  'newark.zeit.world',
  'sydney.zeit.world',
  'iowa.zeit.world',
  'dallas.zeit.world',
  'amsterdam.zeit.world',
  'paris.zeit.world',
  'frankfurt.zeit.world',
  'singapore.zeit.world'
]);

/**
 * Given an array of nameservers (ie: as returned
 * by `resolveNs` from Node, assert that they're
 * zeit.world's.
 */
export default function isZeitWorld (ns) {
  return ns.length > 1 && ns.every((host) => {
    return nameservers.has(host);
  });
}