function onChange(event) {
  var file = event.target.files[0];
  var reader = new FileReader();
  reader.onload = function(event) {
    let self = this;
    window.crypto.subtle.generateKey({
      name: "AES-CBC",
      length: 128 
    },
    true,
    ["encrypt", "decrypt"])
    .then(function(key){
      var arrayBuffer = self.result;
      var array = new Uint8Array(arrayBuffer);

      var random_iv = window.crypto.getRandomValues(new Uint8Array(16));

      window.crypto.subtle.encrypt({
        name: "AES-CBC",
        iv: random_iv },
        key,
        array)
        .then(function(encrypted){
          var dataView = new DataView(encrypted);
          var blob = new Blob([dataView], { type: file.type });
          
          var fd = new FormData();
          fd.append("fname", file.name);
          fd.append("data", blob, file.name);

          var xhr = new XMLHttpRequest();
          var hex = ivToStr(random_iv);
          xhr.open("post", "/upload/" + hex, true);

          var li = document.createElement("li");
          var name = document.createElement("p");
          name.innerHTML = file.name;
          li.appendChild(name);
          
          var link = document.createElement("a");
          li.appendChild(link);

          var progress = document.createElement("p");
          li.appendChild(progress);
          document.getElementById("uploaded_files").appendChild(li);


          xhr.upload.addEventListener("progress", returnBindedLI(progress, name, link, li));

          xhr.onreadystatechange = function() { 
            if (xhr.readyState == XMLHttpRequest.DONE) {
              window.crypto.subtle.exportKey("jwk", key).then(function(keydata) {
                var curr_name = localStorage.getItem(file.name);
                
                localStorage.setItem(hex, xhr.responseText);

                link.innerHTML = "http://localhost:3000/download/" + hex + "/#" + keydata.k;
                link.setAttribute("href", "http://localhost:3000/download/" + hex + "/#" + keydata.k);

                console.log("Share this link with a friend: http://localhost:3000/download/" + hex + "/#" + keydata.k);
              })
            }
          };

          xhr.send(fd);
        })
        .catch(function(err){
          console.error(err);
        });

      })
    .catch(function(err){
        console.error(err);
    });
    
  };
  reader.readAsArrayBuffer(file);
}

function ivToStr(iv) {
  let hexStr = "";
  for (var i in iv) {
    if (iv[i] < 16) {
      hexStr += "0" + iv[i].toString(16);
    } else {
      hexStr += iv[i].toString(16);
    }
  }
  window.hexStr = hexStr;
  return hexStr;
}

function strToIv(str) {
  var iv = new Uint8Array(16);
  for (var i = 0; i < str.length; i += 2) {
    iv[i/2] = parseInt((str.charAt(i) + str.charAt(i + 1)), 16);
  }

  return iv;
}

function returnBindedLI(a_element, name, link, li) {
  return function updateProgress(e) {
            if (e.lengthComputable) { 
              var percentComplete = Math.floor((e.loaded / e.total) * 100);
              a_element.innerHTML = "Progress: " + percentComplete + "%";

              if (percentComplete === 100) {
                var btn = document.createElement("button");
                btn.innerHTML = "Delete from server";
                btn.addEventListener("click", function() {
                  var segments = link.innerHTML.split("/");
                  var key = segments[segments.length - 2];

                  var xhr = new XMLHttpRequest();
                  xhr.open("post", "/delete/" + key, true);
                  xhr.setRequestHeader("Content-Type", "application/json");
                  if (!localStorage.getItem(key)) return;

                  xhr.send(JSON.stringify({delete_token: localStorage.getItem(key)}));

                  xhr.onreadystatechange = function() {
                    if (xhr.readyState === XMLHttpRequest.DONE) {
                      document.getElementById("uploaded_files").removeChild(li);
                      localStorage.removeItem(key);
                    }

                    if (xhr.status === 200) {
                      console.log("The file was successfully deleted.");
                    } else {
                      console.log("The file has expired, or has already been deleted.");
                    }
                  }
                  
                });
                li.appendChild(btn);
              }
            } 
          }
}