RegistrationModel::registerNewUser PHP Method

    public static function registerNewUser()
    {
        // clean the input
        $user_name = strip_tags(Request::post('user_name'));
        $user_email = strip_tags(Request::post('user_email'));
        $user_email_repeat = strip_tags(Request::post('user_email_repeat'));
        $user_password_new = Request::post('user_password_new');
        $user_password_repeat = Request::post('user_password_repeat');
        // stop registration flow if registrationInputValidation() returns false (= anything breaks the input check rules)
        $validation_result = self::registrationInputValidation(Request::post('captcha'), $user_name, $user_password_new, $user_password_repeat, $user_email, $user_email_repeat);
        if (!$validation_result) {
            return false;
        }
        // crypt the password with the PHP 5.5's password_hash() function, results in a 60 character hash string.
        // @see php.net/manual/en/function.password-hash.php for more, especially for potential options
        $user_password_hash = password_hash($user_password_new, PASSWORD_DEFAULT);
        // make return a bool variable, so both errors can come up at once if needed
        $return = true;
        // check if username already exists
        if (UserModel::doesUsernameAlreadyExist($user_name)) {
            Session::add('feedback_negative', Text::get('FEEDBACK_USERNAME_ALREADY_TAKEN'));
            $return = false;
        }
        // check if email already exists
        if (UserModel::doesEmailAlreadyExist($user_email)) {
            Session::add('feedback_negative', Text::get('FEEDBACK_USER_EMAIL_ALREADY_TAKEN'));
            $return = false;
        }
        // if Username or Email were false, return false
        if (!$return) {
            return false;
        }
        // generate random hash for email verification (40 char string)
        $user_activation_hash = sha1(uniqid(mt_rand(), true));
        // write user data to database
        if (!self::writeNewUserToDatabase($user_name, $user_password_hash, $user_email, time(), $user_activation_hash)) {
            Session::add('feedback_negative', Text::get('FEEDBACK_ACCOUNT_CREATION_FAILED'));
            return false;
            // no reason not to return false here
        }
        // get user_id of the user that has been created, to keep things clean we DON'T use lastInsertId() here
        $user_id = UserModel::getUserIdByUsername($user_name);
        if (!$user_id) {
            Session::add('feedback_negative', Text::get('FEEDBACK_UNKNOWN_ERROR'));
            return false;
        }
        // send verification email
        if (self::sendVerificationEmail($user_id, $user_email, $user_activation_hash)) {
            Session::add('feedback_positive', Text::get('FEEDBACK_ACCOUNT_SUCCESSFULLY_CREATED'));
            return true;
        }
        // if verification email sending failed: instantly delete the user
        self::rollbackRegistrationByUserId($user_id);
        Session::add('feedback_negative', Text::get('FEEDBACK_VERIFICATION_MAIL_SENDING_FAILED'));
        return false;
    }

 /**
  * Register page action
  * POST-request after form submit
  */
 public function register_action()
 {
     $registration_successful = RegistrationModel::registerNewUser();
     if ($registration_successful) {
         Redirect::to('login/index');
     } else {
         Redirect::to('register/index');
     }
 }