(function () {
  var WAIT_MS = 8000;   // durata avviso e blocco dei click ripetuti (alza se serve)
  var busy = false;

  function isDownload(url) {
    return /\/slingshot\/node\/content\//.test(url) && /[?&]a=true/.test(url);
  }

  function banner(msg) {
    var el = document.getElementById("dl-banner");
    if (!el) {
      el = document.createElement("div");
      el.id = "dl-banner";
      el.style.cssText = "position:fixed;top:12px;left:50%;transform:translateX(-50%);" +
        "background:#333;color:#fff;padding:10px 20px;border-radius:4px;" +
        "font:14px sans-serif;z-index:100000;box-shadow:0 2px 8px rgba(0,0,0,.4)";
      document.body.appendChild(el);
    }
    el.textContent = msg;
    el.style.display = "block";
  }

  function startDownload(url) {
    if (busy) { return; }
    busy = true;
    document.body.style.cursor = "progress";
    banner("Downloading ... attendere");

    var a = document.createElement("a");
    a.href = url;
    a.style.display = "none";
    document.body.appendChild(a);
    a.click();
    document.body.removeChild(a);

    setTimeout(function () {
      busy = false;
      document.body.style.cursor = "";
      var el = document.getElementById("dl-banner");
      if (el) { el.style.display = "none"; }
    }, WAIT_MS);
  }

  var origOpen = XMLHttpRequest.prototype.open;
  var origSend = XMLHttpRequest.prototype.send;

  XMLHttpRequest.prototype.open = function (method, url) {
    this.__dlUrl = (String(method).toUpperCase() === "GET" && isDownload(String(url))) ? String(url) : null;
    return origOpen.apply(this, arguments);
  };

  XMLHttpRequest.prototype.send = function () {
    if (this.__dlUrl) { startDownload(this.__dlUrl); return; }
    return origSend.apply(this, arguments);
  };
})();