export const base64 = {
  encode: text => {
    const textRegex = /([^\u0000-\u00ff])/; // eslint-disable-line
    if (textRegex.test(text)) {
      throw new Error("Can't base64 encode non-ASCII characters.");
    }

    const digits =
      'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_';

    let i = 0,
      cur,
      prev,
      byteNum,
      result = [];

    while (i < text.length) {
      cur = text.charCodeAt(i);
      byteNum = i % 3;

      switch (byteNum) {
        case 0: //first byte
          result.push(digits.charAt(cur >> 2));
          break;

        case 1: //second byte
          result.push(digits.charAt(((prev & 3) << 4) | (cur >> 4)));
          break;

        case 2: //third byte
          result.push(digits.charAt(((prev & 0x0f) << 2) | (cur >> 6)));
          result.push(digits.charAt(cur & 0x3f));
          break;
      }

      prev = cur;
      i++;
    }

    if (byteNum == 0) {
      result.push(digits.charAt((prev & 3) << 4));
      result.push('==');
    } else if (byteNum == 1) {
      result.push(digits.charAt((prev & 0x0f) << 2));
      result.push('=');
    }

    return result.join('');
  },
  decode: text => {
    text = text.replace(/\s/g, '');
    const textRegex = /^[a-z0-9\-_\s]+\={0,2}$/i; // eslint-disable-line
    if (!textRegex.test(text) || text.length % 4 > 0) {
      throw new Error('Not a base64-encoded string.');
    }

    //local variables
    const digits =
      'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
    let cur,
      prev,
      digitNum,
      i = 0,
      result = [];

    text = text.replace(/=/g, '');

    while (i < text.length) {
      cur = digits.indexOf(text.charAt(i));
      digitNum = i % 4;

      switch (digitNum) {
        //case 0: first digit - do nothing, not enough info to work with

        case 1: //second digit
          result.push(String.fromCharCode((prev << 2) | (cur >> 4)));
          break;

        case 2: //third digit
          result.push(String.fromCharCode(((prev & 0x0f) << 4) | (cur >> 2)));
          break;

        case 3: //fourth digit
          result.push(String.fromCharCode(((prev & 3) << 6) | cur));
          break;
      }

      prev = cur;
      i++;
    }

    return result.join('');
  }
};