(function () {
  var _open = XMLHttpRequest.prototype.open;
  XMLHttpRequest.prototype.open = open;

  var _setRequestHeader = XMLHttpRequest.prototype.setRequestHeader;
  XMLHttpRequest.prototype.setRequestHeader = setRequestHeader;

  var currentValue = 0;
  setInterval(increment, 10000);

  function open () {
    var ret = _open.apply(this, arguments);

    this.setRequestHeader('x-distil-blocks', 'bot-' + currentValue);
    this.setRequestHeader('access-control-request-headers', '');

    return ret;
  }
  function setRequestHeader (key, value) {
    if (key.toLowerCase() === 'access-control-request-headers') {
      arguments[1] = value + ', x-distil-blocks';
    }
    return _setRequestHeader.apply(this, arguments);
  }
  function increment () {
    currentValue++;
  }
}());