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);
      }
    }
  };
}