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 \Symfony\Component\HttpFoundation\Request $request
     *   A request object containing a theme name and a valid token.
     *
     * @return \Symfony\Component\HttpFoundation\RedirectResponse
     *   Redirects back to the appearance admin page.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
     *   Throws access denied when no theme or token is set in the request or when
     *   the token is invalid.
     */
    public function uninstall(Request $request) {
        $theme = $request->query
            ->get('theme');
        $config = $this->config('system.theme');
        if (isset($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');
        }
        throw new AccessDeniedHttpException();
    }
    
    /**
     * Installs a theme.
     *
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   A request object containing a theme name and a valid token.
     *
     * @return \Symfony\Component\HttpFoundation\RedirectResponse|array
     *   Redirects back to the appearance admin page or the confirmation form
     *   if an experimental theme will be installed.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
     *   Throws access denied when no theme or token is set in the request or when
     *   the token is invalid.
     */
    public function install(Request $request) {
        $theme = $request->query
            ->get('theme');
        if (isset($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 $e) {
                $this->messenger()
                    ->addError($this->t('Unable to install @theme due to missing module dependencies.', [
                    '@theme' => $theme,
                ]));
            }
            return $this->redirect('system.themes_page');
        }
        throw new AccessDeniedHttpException();
    }
    
    /**
     * 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 \Symfony\Component\HttpFoundation\Request $request
     *   A request object containing a 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.
     *
     * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
     *   Throws access denied when no theme is set in the request.
     */
    public function setDefaultTheme(Request $request) {
        $config = $this->configFactory
            ->getEditable('system.theme');
        $theme = $request->query
            ->get('theme');
        if (isset($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');
        }
        throw new AccessDeniedHttpException();
    }

}