Method doExecute

/**
 * Internal function to execute the command.
 *
 * @param   InputInterface   $input   The input to inject into the command.
 * @param   OutputInterface  $output  The output to inject into the command.
 *
 * @return  integer  The command exit code
 *
 * @since   4.0.0
 */
protected function doExecute(InputInterface $input, OutputInterface $output) : int
{
    $this->configureIO($input, $output);
    $this->username = $this->getStringFromOption('username', 'Please enter a username');
    $this->ioStyle->title('Add user to group');
    $userId = $this->getUserId($this->username);
    if (empty($userId)) {
        $this->ioStyle->error("The user " . $this->username . " does not exist!");
        return Command::FAILURE;
    }
    // Fetch user
    $user = User::getInstance($userId);
    $this->userGroups = $this->getGroups($user);
    $db = Factory::getDbo();
    $query = $db->getQuery(true)->select($db->quoteName('title'))->from($db->quoteName('#__usergroups'))->where($db->quoteName('id') . ' = :userGroup');
    foreach ($this->userGroups as $userGroup) {
        $query->bind(':userGroup', $userGroup);
        $db->setQuery($query);
        $result = $db->loadResult();
        if (UserHelper::addUserToGroup($user->id, $userGroup)) {
            $this->ioStyle->success("Added '" . $user->username . "' to group '" . $result . "'!");
        } else {
            $this->ioStyle->error("Can't add '" . $user->username . "' to group '" . $result . "'!");
            return Command::FAILURE;
        }
    }
    return Command::SUCCESS;
}