class Theme

class Theme extends Updater implements UpdaterInterface {
    
    /**
     * Returns the directory where a theme should be installed.
     *
     * If the theme is already installed, drupal_get_path() will return a valid
     * path and we should install it there. If we're installing a new theme, we
     * always want it to go into /themes, since that's where all the
     * documentation recommends users install their themes, and there's no way
     * that can conflict on a multi-site installation, since the Update manager
     * won't let you install a new theme if it's already found on your system,
     * and if there was a copy in the top-level we'd see it.
     *
     * @return string
     *   The absolute path of the directory.
     */
    public function getInstallDirectory() {
        if ($this->isInstalled() && ($relative_path = drupal_get_path('theme', $this->name))) {
            // The return value of drupal_get_path() is always relative to the site,
            // so prepend DRUPAL_ROOT.
            return DRUPAL_ROOT . '/' . dirname($relative_path);
        }
        else {
            // When installing a new theme, prepend the requested root directory.
            return $this->root . '/' . $this->getRootDirectoryRelativePath();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getRootDirectoryRelativePath() {
        return 'themes';
    }
    
    /**
     * {@inheritdoc}
     */
    public function isInstalled() {
        // Check if the theme exists in the file system, regardless of whether it
        // is enabled or not.
        $themes = \Drupal::state()->get('system.theme.files', []);
        return isset($themes[$this->name]);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function canUpdateDirectory($directory) {
        $info = static::getExtensionInfo($directory);
        return isset($info['type']) && $info['type'] == 'theme';
    }
    
    /**
     * Determines whether this class can update the specified project.
     *
     * @param string $project_name
     *   The project to check.
     *
     * @return bool
     */
    public static function canUpdate($project_name) {
        return (bool) drupal_get_path('theme', $project_name);
    }
    
    /**
     * {@inheritdoc}
     */
    public function postInstall() {
        // Update the theme info.
        clearstatcache();
        \Drupal::service('theme_handler')->rebuildThemeData();
    }
    
    /**
     * {@inheritdoc}
     */
    public function postInstallTasks() {
        // Since this is being called outside of the primary front controller,
        // the base_url needs to be set explicitly to ensure that links are
        // relative to the site root.
        // @todo Simplify with https://www.drupal.org/node/2548095
        $default_options = [
            '#type' => 'link',
            '#options' => [
                'absolute' => TRUE,
                'base_url' => $GLOBALS['base_url'],
            ],
        ];
        return [
            $default_options + [
                '#url' => Url::fromRoute('system.themes_page'),
                '#title' => t('Install newly added themes'),
            ],
            $default_options + [
                '#url' => Url::fromRoute('system.admin'),
                '#title' => t('Administration pages'),
            ],
        ];
    }

}