cloud-8.x-2.0-beta1/src/Form/Config/CloudAdminSettings.php

<?php

namespace Drupal\cloud\Form\Config;

use Drupal\Core\Form\ConfigFormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Class Cloud Admin Settings.
 */
class CloudAdminSettings extends ConfigFormBase {

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'cloud_admin_settings';
  }

  /**
   * {@inheritdoc}
   */
  protected function getEditableConfigNames() {
    return ['cloud.settings'];
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {

    $config = $this->config('cloud.settings');

    $form['location_map'] = [
      '#type' => 'details',
      '#title' => $this->t('Location Map'),
      '#open' => TRUE,
    ];

    $form['location_map']['cloud_location_map_json_url'] = [
      '#type' => 'url',
      '#title' => $this->t('Location Map JSON URL'),
      '#default_value' => $config->get('cloud_location_map_json_url'),
      '#description' => $this->t('The URL of the geojson file to draw the location map.'),
    ];

    return parent::buildForm($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $config = $this->configFactory()->getEditable('cloud.settings');
    $config->set('cloud_location_map_json_url', $form_state->getValue('cloud_location_map_json_url'));
    $config->save();
    parent::submitForm($form, $form_state);
  }

}