/**
 * @description: 生成一个uid，全局唯一标识符
 * @param {Number} len uid的长度
 * @param {Number} radix 进制数
 * @return {String}
 * @example getUid(12) // 18djrujZHyaO
 */
export default function getUid(len = 12, radix = 0) {
  const chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.split('');
  const uuid = [];
  let i;
  radix = radix > 0 ? radix : chars.length;
  if (len) {
    // Compact form
    for (i = 0; i < len; i++) uuid[i] = chars[0 | (Math.random() * radix)];
  } else {
    // rfc4122, version 4 form
    let r;
    // rfc4122 requires these characters
    uuid[8] = uuid[13] = uuid[18] = uuid[23] = '-';
    uuid[14] = '4';
    // Fill in random data.  At i==19 set the high bits of clock sequence as
    // per rfc4122, sec. 4.1.5
    for (i = 0; i < 36; i++) {
      if (!uuid[i]) {
        r = 0 | (Math.random() * 16);
        uuid[i] = chars[i == 19 ? (r & 0x3) | 0x8 : r];
      }
    }
  }
  return uuid.join('');
}