Code:

class user_authorization {
    function set_username($user) {
    $this->username = $user;
    $this->username = trim($this->username);
    $this->username = str_replace(' ', '', $this->username);
    }

    function set_password($pass) {
    $this->password = $pass;
    }

    function set_login_cookies($remember) {
        if($remember) {
        setcookie('username', $this->username, time()+60*60*24*30, '/');
        setcookie('password', $this->password, time()+60*60*24*30, '/');
        } else {
        setcookie('username', $this->username, -1, '/');
        setcookie('password', $this->password, -1, '/');
        }
    }

    function validate() {
    global $db;

        if(!empty($this->username) && !empty($this->password)) {
        $user_row = $db->fetch_row("SELECT * FROM users WHERE username = '$this->username' AND password = '$this->password'");

        $username_db = $user_row['username'];
        $password_db = $user_row['password'];

            if(strcasecmp($this->username, $username_db) == 0 && strcasecmp($this->password, $password_db) == 0 && !empty($this->username) && !empty($this->password)) {
            $this->user_id = $user_row['id'];
            $this->logged_in = 1;
            $this->username_format = $user_row['username_format'];

                $row_super_admin = $db->fetch_row("SELECT * FROM groups_users WHERE name = 'Super Administrator' AND user_id = '$this->user_id'");
                if(empty($row_super_admin['0'])) {
                $this->super_admin = 0;

                    $result_admin_mods = $db->query("SELECT * FROM modules_admin ORDER BY module ASC");
                    while($row_admin_mods = $db->fetch_array($result_admin_mods)) {
                    $groups_admin = $db->fetch_row("SELECT groups FROM modules_admin WHERE id = '" . $row_admin_mods['id'] . "'");
                    $groups_admin = $groups_admin['0'];

                    $groups_admin_array = explode(':', $groups_admin); 
                        $x = 0;
                        while(!empty($groups_admin_array[$x])) {
                        $user_groups = $db->fetch_row("SELECT * FROM users WHERE id = '$this->user_id'");
                        $user_groups = $user_groups['groups'];

                        $user_groups_array = explode(':', $user_groups);
                            if(in_array($groups_admin_array[$x], $user_groups_array)) {
                            $this->admin = 1;
                            }
                        $x++;
                        }
                    }

                    if(empty($this->admin)) {
                    $this->admin = 0;
                    }
                } else {
                $this->admin = 1;
                $this->super_admin = 1;
                }

            return 1;
            } else {
            $this->super_admin = 0;
            $this->logged_in = 0;
            $this->user_id = '1';
            $this->admin = 0;

            return 0;
            }
        } else {
        $this->super_admin = 0;
        $this->logged_in = 0;
        $this->user_id = '1';
        $this->admin = 0;

        return 0;
        }
    }
    
    function validation_mode() {
    global $user, $pass, $remember, $HTTP_COOKIE_VARS;
             $pass = md5($pass);
        if(!empty($user) && !empty($pass)) {
        $this->set_username($user);
        $this->set_password($pass);

            if($this->validate()) {
            $this->set_login_cookies($remember);
            }
        } else {
        $this->set_username($HTTP_COOKIE_VARS['username']);
        $this->set_password($HTTP_COOKIE_VARS['password']);

        $this->validate();
        }
    }
}

$user_authorization = new user_authorization;

$user_authorization->validation_mode();

$user_id = $user_authorization->user_id;

$admin = $user_authorization->admin;

$super_admin = $user_authorization->super_admin;

$username = $user_authorization->username;

$username_format = $user_authorization->username_format;

$logged_in = $user_authorization->logged_in;