// 下面是64个基本的编码
const base64EncodeChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
const base64DecodeChars = [-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1];

/**
 * @description: base64加密
 * @param {string} str
 * @return {string}
 * @example encode(123) // MTIz
 */
function encode(str = '') {
  str = String(str);
  var out, i, len;
  var c1, c2, c3;
  len = str.length;
  i = 0;
  out = '';
  while (i < len) {
    c1 = str.charCodeAt(i++) & 0xff;
    if (i === len) {
      out += base64EncodeChars.charAt(c1 >> 2);
      out += base64EncodeChars.charAt((c1 & 0x3) << 4);
      out += '==';
      break;
    }
    c2 = str.charCodeAt(i++);
    if (i === len) {
      out += base64EncodeChars.charAt(c1 >> 2);
      out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xf0) >> 4));
      out += base64EncodeChars.charAt((c2 & 0xf) << 2);
      out += '=';
      break;
    }
    c3 = str.charCodeAt(i++);
    out += base64EncodeChars.charAt(c1 >> 2);
    out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xf0) >> 4));
    out += base64EncodeChars.charAt(((c2 & 0xf) << 2) | ((c3 & 0xc0) >> 6));
    out += base64EncodeChars.charAt(c3 & 0x3f);
  }
  return out;
}

/**
 * @description: base64解密
 * @param {string} str
 * @return {string}
 * @example decode('MTIz') // 123
 */
function decode(str = '') {
  var c1, c2, c3, c4;
  var i, len, out;
  len = str.length;
  i = 0;
  out = '';
  while (i < len) {
    do {
      c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
    } while (i < len && c1 === -1);
    if (c1 === -1) {
      break;
    }
    do {
      c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
    } while (i < len && c2 === -1);
    if (c2 === -1) {
      break;
    }
    out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
    do {
      c3 = str.charCodeAt(i++) & 0xff;
      if (c3 === 61) {
        return out;
      }
      c3 = base64DecodeChars[c3];
    } while (i < len && c3 === -1);
    if (c3 === -1) {
      break;
    }
    out += String.fromCharCode(((c2 & 0xf) << 4) | ((c3 & 0x3c) >> 2));

    do {
      c4 = str.charCodeAt(i++) & 0xff;
      if (c4 === 61) {
        return out;
      }
      c4 = base64DecodeChars[c4];
    } while (i < len && c4 === -1);
    if (c4 === -1) {
      break;
    }
    out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
  }
  return out;
}

const base64 = {
  encode,
  decode,
};

export default base64;