class ThemeController

class ThemeController extends ControllerBase {
  
  /**
   * The theme handler service.
   *
   * @var \Drupal\Core\Extension\ThemeHandlerInterface
   */
  protected $themeHandler;
  
  /**
   * An extension discovery instance.
   *
   * @var \Drupal\Core\Extension\ThemeExtensionList
   */
  protected $themeList;
  
  /**
   * The theme installer service.
   *
   * @var \Drupal\Core\Extension\ThemeInstallerInterface
   */
  protected $themeInstaller;
  
  /**
   * Constructs a new ThemeController.
   *
   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
   *   The theme handler.
   * @param \Drupal\Core\Extension\ThemeExtensionList $theme_list
   *   The theme extension list.
   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
   *   The config factory.
   * @param \Drupal\Core\Extension\ThemeInstallerInterface $theme_installer
   *   The theme installer.
   */
  public function __construct(ThemeHandlerInterface $theme_handler, ThemeExtensionList $theme_list, ConfigFactoryInterface $config_factory, ThemeInstallerInterface $theme_installer) {
    $this->themeHandler = $theme_handler;
    $this->themeList = $theme_list;
    $this->configFactory = $config_factory;
    $this->themeInstaller = $theme_installer;
  }
  
  /**
   * Uninstalls a theme.
   *
   * @param string $theme
   *   The theme name.
   *
   * @return \Symfony\Component\HttpFoundation\RedirectResponse
   *   Redirects back to the appearance admin page.
   */
  public function uninstall(#[MapQueryParameter] string $theme) {
    $config = $this->config('system.theme');
    // Get current list of themes.
    $themes = $this->themeHandler
      ->listInfo();
    // Check if the specified theme is one recognized by the system.
    if (!empty($themes[$theme])) {
      // Do not uninstall the default or admin theme.
      if ($theme === $config->get('default') || $theme === $config->get('admin')) {
        $this->messenger()
          ->addError($this->t('%theme is the default theme and cannot be uninstalled.', [
          '%theme' => $themes[$theme]->info['name'],
        ]));
      }
      else {
        $this->themeInstaller
          ->uninstall([
          $theme,
        ]);
        $this->messenger()
          ->addStatus($this->t('The %theme theme has been uninstalled.', [
          '%theme' => $themes[$theme]->info['name'],
        ]));
      }
    }
    else {
      $this->messenger()
        ->addError($this->t('The %theme theme was not found.', [
        '%theme' => $theme,
      ]));
    }
    return $this->redirect('system.themes_page');
  }
  
  /**
   * Installs a theme.
   *
   * @param string $theme
   *   The theme name.
   *
   * @return \Symfony\Component\HttpFoundation\RedirectResponse|array
   *   Redirects back to the appearance admin page or the confirmation form
   *   if an experimental theme will be installed.
   */
  public function install(#[MapQueryParameter] string $theme) {
    // Display confirmation form in case of experimental theme.
    if ($this->willInstallExperimentalTheme($theme)) {
      return $this->formBuilder()
        ->getForm(ThemeExperimentalConfirmForm::class, $theme);
    }
    try {
      if ($this->themeInstaller
        ->install([
        $theme,
      ])) {
        $themes = $this->themeHandler
          ->listInfo();
        $this->messenger()
          ->addStatus($this->t('The %theme theme has been installed.', [
          '%theme' => $themes[$theme]->info['name'],
        ]));
      }
      else {
        $this->messenger()
          ->addError($this->t('The %theme theme was not found.', [
          '%theme' => $theme,
        ]));
      }
    } catch (PreExistingConfigException $e) {
      $config_objects = $e->flattenConfigObjects($e->getConfigObjects());
      $this->messenger()
        ->addError($this->formatPlural(count($config_objects), 'Unable to install @extension, %config_names already exists in active configuration.', 'Unable to install @extension, %config_names already exist in active configuration.', [
        '%config_names' => implode(', ', $config_objects),
        '@extension' => $theme,
      ]));
    } catch (UnmetDependenciesException $e) {
      $this->messenger()
        ->addError($e->getTranslatedMessage($this->getStringTranslation(), $theme));
    } catch (MissingDependencyException) {
      $this->messenger()
        ->addError($this->t('Unable to install @theme due to missing module dependencies.', [
        '@theme' => $theme,
      ]));
    }
    return $this->redirect('system.themes_page');
  }
  
  /**
   * Checks if the given theme requires the installation of experimental themes.
   *
   * @param string $theme
   *   The name of the theme to check.
   *
   * @return bool
   *   Whether experimental themes will be installed.
   */
  protected function willInstallExperimentalTheme($theme) {
    $all_themes = $this->themeList
      ->getList();
    $dependencies = array_keys($all_themes[$theme]->requires);
    $themes_to_enable = array_merge([
      $theme,
    ], $dependencies);
    foreach ($themes_to_enable as $name) {
      if (isset($all_themes[$name]) && $all_themes[$name]->isExperimental() && $all_themes[$name]->status === 0) {
        return TRUE;
      }
    }
    return FALSE;
  }
  
  /**
   * Set the default theme.
   *
   * @param string $theme
   *   The theme name.
   *
   * @return \Symfony\Component\HttpFoundation\RedirectResponse|array
   *   Redirects back to the appearance admin page or the confirmation form
   *   if an experimental theme will be installed.
   */
  public function setDefaultTheme(#[MapQueryParameter] string $theme) {
    $config = $this->configFactory
      ->getEditable('system.theme');
    // Get current list of themes.
    $themes = $this->themeHandler
      ->listInfo();
    // Display confirmation form if an experimental theme is being installed.
    if ($this->willInstallExperimentalTheme($theme)) {
      return $this->formBuilder()
        ->getForm(ThemeExperimentalConfirmForm::class, $theme, TRUE);
    }
    // Check if the specified theme is one recognized by the system.
    // Or try to install the theme.
    if (isset($themes[$theme]) || $this->themeInstaller
      ->install([
      $theme,
    ])) {
      $themes = $this->themeHandler
        ->listInfo();
      // Set the default theme.
      $config->set('default', $theme)
        ->save();
      // The status message depends on whether an admin theme is currently in
      // use: a value of 0 means the admin theme is set to be the default
      // theme.
      $admin_theme = $config->get('admin');
      if (!empty($admin_theme) && $admin_theme != $theme) {
        $this->messenger()
          ->addStatus($this->t('Note that the administration theme is still set to the %admin_theme theme; consequently, the theme on this page remains unchanged. All non-administrative sections of the site, however, will show the selected %selected_theme theme by default.', [
          '%admin_theme' => $themes[$admin_theme]->info['name'],
          '%selected_theme' => $themes[$theme]->info['name'],
        ]));
      }
      else {
        $this->messenger()
          ->addStatus($this->t('%theme is now the default theme.', [
          '%theme' => $themes[$theme]->info['name'],
        ]));
      }
    }
    else {
      $this->messenger()
        ->addError($this->t('The %theme theme was not found.', [
        '%theme' => $theme,
      ]));
    }
    return $this->redirect('system.themes_page');
  }

}