utils.ts

/**
 * Decodes base64-encoded strings.
 * Copied from the core library.
 */
export function base64urldecode(data: string): string {
  if (!data) {
    return data;
  }
  const padding = 4 - (data.length % 4);
  switch (padding) {
    case 2:
      data += '==';
      break;
    case 3:
      data += '=';
      break;
  }
  const b64Data = data.replace(/-/g, '+').replace(/_/g, '/');
  return base64decode(b64Data);
}

const b64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

function base64decode(encodedData: string): string {
  //  discuss at: http://locutus.io/php/base64_decode/
  // original by: Tyler Akins (http://rumkin.com)
  // improved by: Thunder.m
  // improved by: Kevin van Zonneveld (http://kvz.io)
  // improved by: Kevin van Zonneveld (http://kvz.io)
  //    input by: Aman Gupta
  //    input by: Brett Zamir (http://brett-zamir.me)
  // bugfixed by: Onno Marsman (https://twitter.com/onnomarsman)
  // bugfixed by: Pellentesque Malesuada
  // bugfixed by: Kevin van Zonneveld (http://kvz.io)
  // improved by: Indigo744
  //   example 1: base64_decode('S2V2aW4gdmFuIFpvbm5ldmVsZA==')
  //   returns 1: 'Kevin van Zonneveld'
  //   example 2: base64_decode('YQ==')
  //   returns 2: 'a'
  //   example 3: base64_decode('4pyTIMOgIGxhIG1vZGU=')
  //   returns 3: '✓ à la mode'

  // decodeUTF8string()
  // Internal function to decode properly UTF8 string
  // Adapted from Solution #1 at https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding
  const decodeUTF8string = function (str: string) {
    // Going backwards: from bytestream, to percent-encoding, to original string.
    return decodeURIComponent(
      str
        .split('')
        .map(function (c) {
          return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
        })
        .join('')
    );
  };

  let o1,
    o2,
    o3,
    h1,
    h2,
    h3,
    h4,
    bits,
    i = 0,
    ac = 0,
    dec = '';
  const tmpArr: Array<string> = [];

  if (!encodedData) {
    return encodedData;
  }

  encodedData += '';

  do {
    // unpack four hexets into three octets using index points in b64
    h1 = b64.indexOf(encodedData.charAt(i++));
    h2 = b64.indexOf(encodedData.charAt(i++));
    h3 = b64.indexOf(encodedData.charAt(i++));
    h4 = b64.indexOf(encodedData.charAt(i++));

    bits = (h1 << 18) | (h2 << 12) | (h3 << 6) | h4;

    o1 = (bits >> 16) & 0xff;
    o2 = (bits >> 8) & 0xff;
    o3 = bits & 0xff;

    if (h3 === 64) {
      tmpArr[ac++] = String.fromCharCode(o1);
    } else if (h4 === 64) {
      tmpArr[ac++] = String.fromCharCode(o1, o2);
    } else {
      tmpArr[ac++] = String.fromCharCode(o1, o2, o3);
    }
  } while (i < encodedData.length);

  dec = tmpArr.join('');

  return decodeUTF8string(dec.replace(/\0+$/, ''));
}