const RE_RES = /^(\d\d\d)\s.*/;
const RE_MULTI = /^(\d\d\d)-/;

function parseFtpResponses(prev, cur) {
  let response = '';
  let accumulated = prev.accumulated;

  if (RE_MULTI.test(accumulated)) {
    if (RE_RES.test(cur)) {
      response = accumulated + '\n' + cur;
      accumulated = '';
    } else {
      accumulated = accumulated + '\n' + cur;
    }
  } else if (RE_MULTI.test(cur)) {
    accumulated = cur;
  } else {
    response = cur;
  }

  return { response, accumulated };
}