class RegionalForm

system.routing.yml in drupal/core/modules/system/system.routing.yml

drupal/core/modules/system/system.routing.yml

class RegionalForm extends SystemConfigFormBase {

  /**
   * The country manager.
   *
   * @var \Drupal\Core\Locale\CountryManagerInterface
   */
  protected $countryManager;

  /**
   * Constructs a RegionalForm object.
   *
   * @param \Drupal\Core\Config\ConfigFactory $config_factory
   *   The factory for configuration objects.
   * @param \Drupal\Core\Config\Context\ContextInterface $context
   *   The configuration context used for this configuration object.
   * @param \Drupal\Core\Locale\CountryManagerInterface $country_manager
   *   The country manager.
   */
  public function __construct(ConfigFactory $config_factory, ContextInterface $context, CountryManagerInterface $country_manager) {
    parent::__construct($config_factory, $context);
    $this->countryManager = $country_manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container
      ->get('config.factory'), $container
      ->get('config.context.free'), $container
      ->get('country_manager'));
  }

  /**
   * {@inheritdoc}
   */
  public function getFormID() {
    return 'system_regional_settings';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, array &$form_state) {
    $countries = $this->countryManager
      ->getList();
    $system_timezone = $this->configFactory
      ->get('system.timezone');
    $system_date = $this->configFactory
      ->get('system.date');

    // Date settings:
    $zones = system_time_zones();
    $form['locale'] = array(
      '#type' => 'details',
      '#title' => t('Locale'),
    );
    $form['locale']['site_default_country'] = array(
      '#type' => 'select',
      '#title' => t('Default country'),
      '#empty_value' => '',
      '#default_value' => $system_date
        ->get('country.default'),
      '#options' => $countries,
      '#attributes' => array(
        'class' => array(
          'country-detect',
        ),
      ),
    );
    $form['locale']['date_first_day'] = array(
      '#type' => 'select',
      '#title' => t('First day of week'),
      '#default_value' => $system_date
        ->get('first_day'),
      '#options' => array(
        0 => t('Sunday'),
        1 => t('Monday'),
        2 => t('Tuesday'),
        3 => t('Wednesday'),
        4 => t('Thursday'),
        5 => t('Friday'),
        6 => t('Saturday'),
      ),
    );
    $form['timezone'] = array(
      '#type' => 'details',
      '#title' => t('Time zones'),
    );
    $form['timezone']['date_default_timezone'] = array(
      '#type' => 'select',
      '#title' => t('Default time zone'),
      '#default_value' => $system_timezone
        ->get('default') ?: date_default_timezone_get(),
      '#options' => $zones,
    );
    $configurable_timezones = $system_timezone
      ->get('user.configurable');
    $form['timezone']['configurable_timezones'] = array(
      '#type' => 'checkbox',
      '#title' => t('Users may set their own time zone.'),
      '#default_value' => $configurable_timezones,
    );
    $form['timezone']['configurable_timezones_wrapper'] = array(
      '#type' => 'container',
      '#states' => array(
        // Hide the user configured timezone settings when users are forced to use
        // the default setting.
        'invisible' => array(
          'input[name="configurable_timezones"]' => array(
            'checked' => FALSE,
          ),
        ),
      ),
    );
    $form['timezone']['configurable_timezones_wrapper']['empty_timezone_message'] = array(
      '#type' => 'checkbox',
      '#title' => t('Remind users at login if their time zone is not set.'),
      '#default_value' => $system_timezone
        ->get('user.warn'),
      '#description' => t('Only applied if users may set their own time zone.'),
    );
    $form['timezone']['configurable_timezones_wrapper']['user_default_timezone'] = array(
      '#type' => 'radios',
      '#title' => t('Time zone for new users'),
      '#default_value' => $system_timezone
        ->get('user.default'),
      '#options' => array(
        DRUPAL_USER_TIMEZONE_DEFAULT => t('Default time zone.'),
        DRUPAL_USER_TIMEZONE_EMPTY => t('Empty time zone.'),
        DRUPAL_USER_TIMEZONE_SELECT => t('Users may set their own time zone at registration.'),
      ),
      '#description' => t('Only applied if users may set their own time zone.'),
    );
    return parent::buildForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, array &$form_state) {
    $this->configFactory
      ->get('system.date')
      ->set('country.default', $form_state['values']['site_default_country'])
      ->set('first_day', $form_state['values']['date_first_day'])
      ->save();
    $this->configFactory
      ->get('system.timezone')
      ->set('default', $form_state['values']['date_default_timezone'])
      ->set('user.configurable', $form_state['values']['configurable_timezones'])
      ->set('user.warn', $form_state['values']['empty_timezone_message'])
      ->set('user.default', $form_state['values']['user_default_timezone'])
      ->save();
    parent::submitForm($form, $form_state);
  }

}