class ThemeInitialization

class ThemeInitialization implements ThemeInitializationInterface {
    
    /**
     * The theme handler.
     *
     * @var \Drupal\Core\Extension\ThemeHandlerInterface
     */
    protected $themeHandler;
    
    /**
     * The cache backend to use for the active theme.
     *
     * @var \Drupal\Core\Cache\CacheBackendInterface
     */
    protected $cache;
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * The extensions that might be attaching assets.
     *
     * @var array
     */
    protected $extensions;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * Constructs a new ThemeInitialization object.
     *
     * @param string $root
     *   The app root.
     * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
     *   The theme handler.
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache
     *   The cache backend.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler to use to load modules.
     */
    public function __construct($root, ThemeHandlerInterface $theme_handler, CacheBackendInterface $cache, ModuleHandlerInterface $module_handler) {
        $this->root = $root;
        $this->themeHandler = $theme_handler;
        $this->cache = $cache;
        $this->moduleHandler = $module_handler;
    }
    
    /**
     * {@inheritdoc}
     */
    public function initTheme($theme_name) {
        $active_theme = $this->getActiveThemeByName($theme_name);
        $this->loadActiveTheme($active_theme);
        return $active_theme;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getActiveThemeByName($theme_name) {
        if ($cached = $this->cache
            ->get('theme.active_theme.' . $theme_name)) {
            return $cached->data;
        }
        $themes = $this->themeHandler
            ->listInfo();
        // If no theme could be negotiated, or if the negotiated theme is not within
        // the list of installed themes, fall back to the default theme output of
        // core and modules (like Stark, but without a theme extension at all). This
        // is possible, because loadActiveTheme() always loads the Twig theme
        // engine. This is desired, because missing or malformed theme configuration
        // should not leave the application in a broken state. By falling back to
        // default output, the user is able to reconfigure the theme through the UI.
        // Lastly, tests are expected to operate with no theme by default, so as to
        // only assert the original theme output of modules (unless a test manually
        // installs a specific theme).
        if (empty($themes) || !$theme_name || !isset($themes[$theme_name])) {
            $theme_name = 'core';
            // /core/core.info.yml does not actually exist, but is required because
            // Extension expects a pathname.
            $active_theme = $this->getActiveTheme(new Extension($this->root, 'theme', 'core/core.info.yml'));
            // Early-return and do not set state, because the initialized $theme_name
            // differs from the original $theme_name.
            return $active_theme;
        }
        // Find all our ancestor themes and put them in an array.
        $base_themes = [];
        $ancestor = $theme_name;
        while ($ancestor && isset($themes[$ancestor]->base_theme)) {
            $ancestor = $themes[$ancestor]->base_theme;
            if (!$this->themeHandler
                ->themeExists($ancestor)) {
                throw new MissingThemeDependencyException(sprintf('Base theme %s has not been installed.', $ancestor), $ancestor);
            }
            $base_themes[] = $themes[$ancestor];
        }
        $active_theme = $this->getActiveTheme($themes[$theme_name], $base_themes);
        $this->cache
            ->set('theme.active_theme.' . $theme_name, $active_theme);
        return $active_theme;
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadActiveTheme(ActiveTheme $active_theme) {
        // Initialize the theme.
        if ($active_theme->getEngine()) {
            // Include the engine.
            include_once $this->root . '/' . $active_theme->getOwner();
            foreach (array_reverse($active_theme->getBaseThemeExtensions()) as $base) {
                $base->load();
            }
            $active_theme->getExtension()
                ->load();
        }
        else {
            // Include non-engine theme files
            foreach (array_reverse($active_theme->getBaseThemeExtensions()) as $base) {
                // Include the theme file or the engine.
                if ($base->owner) {
                    include_once $this->root . '/' . $base->owner;
                }
            }
            // And our theme gets one too.
            if ($active_theme->getOwner()) {
                include_once $this->root . '/' . $active_theme->getOwner();
            }
        }
        // Always include Twig as the default theme engine.
        include_once $this->root . '/core/themes/engines/twig/twig.engine';
    }
    
    /**
     * {@inheritdoc}
     */
    public function getActiveTheme(Extension $theme, array $base_themes = []) {
        $theme_path = $theme->getPath();
        $values['path'] = $theme_path;
        $values['name'] = $theme->getName();
        // Use the logo declared in this themes info file, otherwise use logo.svg
        // from the themes root.
        if (!empty($theme->info['logo'])) {
            $values['logo'] = $theme->getPath() . '/' . $theme->info['logo'];
        }
        else {
            $values['logo'] = $theme->getPath() . '/logo.svg';
        }
        // Prepare libraries overrides from this theme and ancestor themes. This
        // allows child themes to easily remove CSS files from base themes and
        // modules.
        $values['libraries_override'] = [];
        // Get libraries overrides declared by base themes.
        foreach (array_reverse($base_themes) as $base) {
            if (!empty($base->info['libraries-override'])) {
                foreach ($base->info['libraries-override'] as $library => $override) {
                    $values['libraries_override'][$base->getPath()][$library] = $override;
                }
            }
        }
        // Add libraries overrides declared by this theme.
        if (!empty($theme->info['libraries-override'])) {
            foreach ($theme->info['libraries-override'] as $library => $override) {
                $values['libraries_override'][$theme->getPath()][$library] = $override;
            }
        }
        // Get libraries extensions declared by base themes.
        foreach ($base_themes as $base) {
            if (!empty($base->info['libraries-extend'])) {
                foreach ($base->info['libraries-extend'] as $library => $extend) {
                    if (isset($values['libraries_extend'][$library])) {
                        // Merge if libraries-extend has already been defined for this
                        // library.
                        $values['libraries_extend'][$library] = array_merge($values['libraries_extend'][$library], $extend);
                    }
                    else {
                        $values['libraries_extend'][$library] = $extend;
                    }
                }
            }
        }
        // Add libraries extensions declared by this theme.
        if (!empty($theme->info['libraries-extend'])) {
            foreach ($theme->info['libraries-extend'] as $library => $extend) {
                if (isset($values['libraries_extend'][$library])) {
                    // Merge if libraries-extend has already been defined for this
                    // library.
                    $values['libraries_extend'][$library] = array_merge($values['libraries_extend'][$library], $extend);
                }
                else {
                    $values['libraries_extend'][$library] = $extend;
                }
            }
        }
        // Do basically the same as the above for libraries
        $values['libraries'] = [];
        // Grab libraries from base theme
        foreach ($base_themes as $base) {
            if (!empty($base->libraries)) {
                foreach ($base->libraries as $library) {
                    $values['libraries'][] = $library;
                }
            }
        }
        // Add libraries used by this theme.
        if (!empty($theme->libraries)) {
            foreach ($theme->libraries as $library) {
                $values['libraries'][] = $library;
            }
        }
        $values['engine'] = $theme->engine ?? NULL;
        $values['owner'] = $theme->owner ?? NULL;
        $values['extension'] = $theme;
        $base_active_themes = [];
        foreach ($base_themes as $base_theme) {
            $base_active_themes[$base_theme->getName()] = $base_theme;
        }
        $values['base_theme_extensions'] = $base_active_themes;
        if (!empty($theme->info['regions'])) {
            $values['regions'] = $theme->info['regions'];
        }
        return new ActiveTheme($values);
    }
    
    /**
     * Gets all extensions.
     *
     * @return array
     */
    protected function getExtensions() {
        if (!isset($this->extensions)) {
            $this->extensions = array_merge($this->moduleHandler
                ->getModuleList(), $this->themeHandler
                ->listInfo());
        }
        return $this->extensions;
    }

}