// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

'use strict';

/* This is a Base64 Polyfill adapted from
 * https://github.com/davidchambers/Base64.js/blob/0.3.0/,
 * which has a "do whatever you want" license,
 * https://github.com/davidchambers/Base64.js/blob/0.3.0/LICENSE.
 */
(function(global) {
  var chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz' +
      '0123456789+/=';

  function InvalidCharacterError(message) {
    this.message = message;
  }
  InvalidCharacterError.prototype = new Error;
  InvalidCharacterError.prototype.name = 'InvalidCharacterError';

  // encoder
  // [https://gist.github.com/999166] by [https://github.com/nignag]
  global.btoa = function(input) {
    var str = String(input);
    for (
        // Initialize result and counter.
        var block, charCode, idx = 0, map = chars, output = '';
        // If the next str index does not exist:
        //   change the mapping table to "="
        //   check if d has no fractional digits
        str.charAt(idx | 0) || (map = '=', idx % 1);
        // "8 - idx % 1 * 8" generates the sequence 2, 4, 6, 8.
        output += map.charAt(63 & block >> 8 - idx % 1 * 8)) {
      charCode = str.charCodeAt(idx += 3 / 4);
      if (charCode > 0xFF) {
        throw new InvalidCharacterError(
            '\'btoa\' failed: The string to be encoded contains characters ' +
            'outside of the Latin1 range.');
      }
      block = block << 8 | charCode;
    }
    return output;
  };

  // decoder
  // [https://gist.github.com/1020396] by [https://github.com/atk]
  global.atob = function(input) {
    var str = String(input).replace(/=+$/, '');
    if (str.length % 4 == 1) {
      throw new InvalidCharacterError(
          '\'atob\' failed: The string to be decoded is not ' +
          'correctly encoded.');
    }
    for (
        // Initialize result and counters.
        var bc = 0, bs, buffer, idx = 0, output = '';
        // Get next character.
        buffer = str.charAt(idx++);
        // Character found in table? initialize bit storage and add its
        // ascii value;
        ~buffer && (bs = bc % 4 ? bs * 64 + buffer : buffer,
            // And if not first of each 4 characters,
            // convert the first 8 bits to one ascii character.
            bc++ % 4) ? output += String.fromCharCode(
                  255 & bs >> (-2 * bc & 6)) : 0) {
      // Try to find character in table (0-63, not found => -1).
      buffer = chars.indexOf(buffer);
    }
    return output;
  };

})(this);