function get_random_code(){
    // 675O-7OAF-3LLV-H0CK
    $code = '';
    $letters_numbers = array_merge( range('A', 'Z'), range(0,9) );
    $letters = range('A', 'Z');

    for($i=0; $i < 20; $i++){
        if($i < 3)
            $code .= $letters[array_rand($letters)];
        else if($i % 5)
            $code .= $letters_numbers[array_rand($letters_numbers)];
        else
            $code .= '-';
    }

    $code = substr($code, 1);
    return $code;
}