class ThemeExperimentalConfirmForm

class ThemeExperimentalConfirmForm extends ConfirmFormBase {
    
    /**
     * An extension discovery instance.
     *
     * @var \Drupal\Core\Extension\ThemeExtensionList
     */
    protected $themeList;
    
    /**
     * The theme installer service.
     *
     * @var \Drupal\Core\Extension\ThemeInstallerInterface
     */
    protected $themeInstaller;
    
    /**
     * Constructs a ThemeExperimentalConfirmForm object.
     *
     * @param \Drupal\Core\Extension\ThemeExtensionList $theme_list
     *   The theme extension list.
     * @param \Drupal\Core\Extension\ThemeInstallerInterface $theme_installer
     *   The theme installer.
     */
    public function __construct(ThemeExtensionList $theme_list, ThemeInstallerInterface $theme_installer) {
        $this->themeList = $theme_list;
        $this->themeInstaller = $theme_installer;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('extension.list.theme'), $container->get('theme_installer'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getQuestion() {
        return $this->t('Are you sure you wish to install an experimental theme?');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCancelUrl() {
        return new Url('system.themes_page');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConfirmText() {
        return $this->t('Continue');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDescription() {
        return $this->t('Would you like to continue with the above?');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'system_themes_experimental_confirm_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $theme = $form_state->getBuildInfo()['args'][0] ? $form_state->getBuildInfo()['args'][0] : NULL;
        $all_themes = $this->themeList
            ->getList();
        if (!isset($all_themes[$theme])) {
            return $this->redirect('system.themes_page');
        }
        $this->messenger()
            ->addWarning($this->t('Experimental themes are provided for testing purposes only. Use at your own risk.'));
        $dependencies = array_keys($all_themes[$theme]->requires);
        $themes = array_merge([
            $theme,
        ], $dependencies);
        $is_experimental = function ($theme) use ($all_themes) {
            return isset($all_themes[$theme]) && $all_themes[$theme]->isExperimental();
        };
        $get_label = function ($theme) use ($all_themes) {
            return $all_themes[$theme]->info['name'];
        };
        $items = [];
        if (!empty($dependencies)) {
            // Display a list of required themes that have to be installed as well.
            $items[] = $this->formatPlural(count($dependencies), 'You must enable the @required theme to install @theme.', 'You must enable the @required themes to install @theme.', [
                '@theme' => $get_label($theme),
                // It is safe to implode this because theme names are not translated
                // markup and so will not be double-escaped.
'@required' => implode(', ', array_map($get_label, $dependencies)),
            ]);
        }
        // Add the list of experimental themes after any other messages.
        $items[] = $this->t('The following themes are experimental: @themes', [
            '@themes' => implode(', ', array_map($get_label, array_filter($themes, $is_experimental))),
        ]);
        $form['message'] = [
            '#theme' => 'item_list',
            '#items' => $items,
        ];
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $args = $form_state->getBuildInfo()['args'];
        $theme = $args[0] ?? NULL;
        $set_default = $args[1] ?? FALSE;
        $themes = $this->themeList
            ->getList();
        $config = $this->configFactory()
            ->getEditable('system.theme');
        try {
            if ($this->themeInstaller
                ->install([
                $theme,
            ])) {
                if ($set_default) {
                    // Set the default theme.
                    $config->set('default', $theme)
                        ->save();
                    // The status message depends on whether an admin theme is currently
                    // in use: an empty string 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('Please 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 {
                    $this->messenger()
                        ->addStatus($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));
        }
        $form_state->setRedirectUrl($this->getCancelUrl());
    }

}