class ThemeHandler

class ThemeHandler implements ThemeHandlerInterface {
    
    /**
     * A list of all currently available themes.
     *
     * @var array
     */
    protected $list;
    
    /**
     * The config factory to get the installed themes.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * An extension discovery instance.
     *
     * @var \Drupal\Core\Extension\ThemeExtensionList
     */
    protected $themeList;
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * Constructs a new ThemeHandler.
     *
     * @param string $root
     *   The app root.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory to get the installed themes.
     * @param \Drupal\Core\Extension\ThemeExtensionList $theme_list
     *   An extension discovery instance.
     */
    public function __construct($root, ConfigFactoryInterface $config_factory, ThemeExtensionList $theme_list) {
        $this->root = $root;
        $this->configFactory = $config_factory;
        $this->themeList = $theme_list;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDefault() {
        return $this->configFactory
            ->get('system.theme')
            ->get('default');
    }
    
    /**
     * {@inheritdoc}
     */
    public function listInfo() {
        if (!isset($this->list)) {
            $this->list = [];
            $installed_themes = $this->configFactory
                ->get('core.extension')
                ->get('theme');
            if (!empty($installed_themes)) {
                $installed_themes = array_intersect_key($this->themeList
                    ->getList(), $installed_themes);
                array_map([
                    $this,
                    'addTheme',
                ], $installed_themes);
            }
        }
        return $this->list;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addTheme(Extension $theme) {
        // Register the namespaces of installed themes.
        // @todo Implement proper theme registration
        // https://www.drupal.org/project/drupal/issues/2941757
        \Drupal::service('class_loader')->addPsr4('Drupal\\' . $theme->getName() . '\\', $this->root . '/' . $theme->getPath() . '/src');
        if (!empty($theme->info['libraries'])) {
            foreach ($theme->info['libraries'] as $library => $name) {
                $theme->libraries[$library] = $name;
            }
        }
        if (isset($theme->info['engine'])) {
            $theme->engine = $theme->info['engine'];
        }
        if (isset($theme->info['base theme'])) {
            $theme->base_theme = $theme->info['base theme'];
        }
        $this->list[$theme->getName()] = $theme;
    }
    
    /**
     * {@inheritdoc}
     */
    public function refreshInfo() {
        $installed = $this->configFactory
            ->get('core.extension')
            ->get('theme');
        // Only refresh the info if a theme has been installed. Modules are
        // installed before themes by the installer and this method is called during
        // module installation.
        if (empty($installed) && empty($this->list)) {
            return;
        }
        $this->reset();
    }
    
    /**
     * {@inheritdoc}
     */
    public function reset() {
        $this->themeList
            ->reset();
        $this->list = NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function rebuildThemeData() {
        return $this->themeList
            ->reset()
            ->getList();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getBaseThemes(array $themes, $theme) {
        return $this->themeList
            ->getBaseThemes($themes, $theme);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getName($theme) {
        return $this->themeList
            ->getName($theme);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getThemeDirectories() {
        $dirs = [];
        foreach ($this->listInfo() as $name => $theme) {
            $dirs[$name] = $this->root . '/' . $theme->getPath();
        }
        return $dirs;
    }
    
    /**
     * {@inheritdoc}
     */
    public function themeExists($theme) {
        $themes = $this->listInfo();
        return isset($themes[$theme]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTheme($name) {
        $themes = $this->listInfo();
        if (isset($themes[$name])) {
            return $themes[$name];
        }
        throw new UnknownExtensionException(sprintf('The theme %s does not exist.', $name));
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasUi($name) {
        $themes = $this->listInfo();
        if (isset($themes[$name])) {
            if (!empty($themes[$name]->info['hidden'])) {
                $theme_config = $this->configFactory
                    ->get('system.theme');
                return $name == $theme_config->get('default') || $name == $theme_config->get('admin');
            }
            return TRUE;
        }
        return FALSE;
    }

}