/*
 * generates a passphrase
 * 
 * uses window.crypto.getRandomValues() if it's supported by current browsers
 * otherwise uses a fallback to Math.floor() which is not cryptographically strong
 * 
 * implementation by Aaron Toponce:
 *   https://pthree.org/2014/06/25/cryptographically-secure-passphrases-in-d-note/
 */
export default function(length){
  var text = "";
  var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
  var random_array = new Uint32Array(length);

  // Make some attempt at preferring a strong CSPRNG first
  if (window.crypto && window.crypto.getRandomValues) {
    // Desktop Chrome 11.0, Firefox 21.0, Opera 15.0, Safari 3.1
    // Mobile Chrome 23, Firefox 21.0, iOS 6
    window.crypto.getRandomValues(random_array);
  }
  else if (window.msCrypto && window.msCrypto.getRandomValues) {
    // IE 11
    window.msCrypto.getRandomValues(random_array);
  }
  else {
    // Android browser, IE Mobile, Opera Mobile, older desktop browsers
    for(var i=length; i--;) {
      random_array[i] = Math.floor(Math.random() * Math.pow(2, 32));
    }
  }

  for(var j=length; j--;) {
    text += possible.charAt(Math.floor(random_array[j] % possible.length));
  }

  return text;
}