Hide Chinese name

/**
 *  Only the first and last characters of the string are reserved , Hide intermediate use * Instead of （ Only the first one is displayed when there are two characters ）
 * @param string $user_name  full name 
 * @return string  Formatted name 
 */
function substr_cut($user_name){
    $strlen     = mb_strlen($user_name, 'utf-8');
    $firstStr     = mb_substr($user_name, 0, 1, 'utf-8');
    $lastStr     = mb_substr($user_name, -1, 1, 'utf-8');
    return $strlen == 2 ? $firstStr . str_repeat('*', mb_strlen($user_name, 'utf-8') - 1) : $firstStr . str_repeat("*", $strlen - 2) . $lastStr;
}