class ThemeManager

class ThemeManager implements ThemeManagerInterface {
    
    /**
     * The theme negotiator.
     *
     * @var \Drupal\Core\Theme\ThemeNegotiatorInterface
     */
    protected $themeNegotiator;
    
    /**
     * The theme registry used to render an output.
     *
     * @var \Drupal\Core\Theme\Registry
     */
    protected $themeRegistry;
    
    /**
     * Contains the current active theme.
     *
     * @var \Drupal\Core\Theme\ActiveTheme
     */
    protected $activeTheme;
    
    /**
     * The theme initialization.
     *
     * @var \Drupal\Core\Theme\ThemeInitializationInterface
     */
    protected $themeInitialization;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * Constructs a new ThemeManager object.
     *
     * @param string $root
     *   The app root.
     * @param \Drupal\Core\Theme\ThemeNegotiatorInterface $theme_negotiator
     *   The theme negotiator.
     * @param \Drupal\Core\Theme\ThemeInitializationInterface $theme_initialization
     *   The theme initialization.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     */
    public function __construct($root, ThemeNegotiatorInterface $theme_negotiator, ThemeInitializationInterface $theme_initialization, ModuleHandlerInterface $module_handler) {
        $this->root = $root;
        $this->themeNegotiator = $theme_negotiator;
        $this->themeInitialization = $theme_initialization;
        $this->moduleHandler = $module_handler;
    }
    
    /**
     * Sets the theme registry.
     *
     * @param \Drupal\Core\Theme\Registry $theme_registry
     *   The theme registry.
     *
     * @return $this
     */
    public function setThemeRegistry(Registry $theme_registry) {
        $this->themeRegistry = $theme_registry;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getActiveTheme(RouteMatchInterface $route_match = NULL) {
        if (!isset($this->activeTheme)) {
            $this->initTheme($route_match);
        }
        return $this->activeTheme;
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasActiveTheme() {
        return isset($this->activeTheme);
    }
    
    /**
     * {@inheritdoc}
     */
    public function resetActiveTheme() {
        $this->activeTheme = NULL;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setActiveTheme(ActiveTheme $active_theme) {
        $this->activeTheme = $active_theme;
        if ($active_theme) {
            $this->themeInitialization
                ->loadActiveTheme($active_theme);
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render($hook, array $variables) {
        static $default_attributes;
        $active_theme = $this->getActiveTheme();
        // If called before all modules are loaded, we do not necessarily have a
        // full theme registry to work with, and therefore cannot process the theme
        // request properly. See also \Drupal\Core\Theme\Registry::get().
        if (!$this->moduleHandler
            ->isLoaded() && !defined('MAINTENANCE_MODE')) {
            throw new \Exception('The theme implementations may not be rendered until all modules are loaded.');
        }
        $theme_registry = $this->themeRegistry
            ->getRuntime();
        // If an array of hook candidates were passed, use the first one that has an
        // implementation.
        if (is_array($hook)) {
            foreach ($hook as $candidate) {
                if ($theme_registry->has($candidate)) {
                    break;
                }
            }
            $hook = $candidate;
        }
        // Save the original theme hook, so it can be supplied to theme variable
        // preprocess callbacks.
        $original_hook = $hook;
        // If there's no implementation, check for more generic fallbacks.
        // If there's still no implementation, log an error and return an empty
        // string.
        if (!$theme_registry->has($hook)) {
            // Iteratively strip everything after the last '__' delimiter, until an
            // implementation is found.
            while ($pos = strrpos($hook, '__')) {
                $hook = substr($hook, 0, $pos);
                if ($theme_registry->has($hook)) {
                    break;
                }
            }
            if (!$theme_registry->has($hook)) {
                // Only log a message when not trying theme suggestions ($hook being an
                // array).
                if (!isset($candidate)) {
                    \Drupal::logger('theme')->warning('Theme hook %hook not found.', [
                        '%hook' => $hook,
                    ]);
                }
                // There is no theme implementation for the hook passed. Return FALSE so
                // the function calling
                // \Drupal\Core\Theme\ThemeManagerInterface::render() can differentiate
                // between a hook that exists and renders an empty string, and a hook
                // that is not implemented.
                return FALSE;
            }
        }
        $info = $theme_registry->get($hook);
        // If a renderable array is passed as $variables, then set $variables to
        // the arguments expected by the theme function.
        if (isset($variables['#theme']) || isset($variables['#theme_wrappers'])) {
            $element = $variables;
            $variables = [];
            if (isset($info['variables'])) {
                foreach (array_keys($info['variables']) as $name) {
                    if (isset($element["#{$name}"]) || array_key_exists("#{$name}", $element)) {
                        $variables[$name] = $element["#{$name}"];
                    }
                }
            }
            else {
                $variables[$info['render element']] = $element;
                // Give a hint to render engines to prevent infinite recursion.
                $variables[$info['render element']]['#render_children'] = TRUE;
            }
        }
        // Merge in argument defaults.
        if (!empty($info['variables'])) {
            $variables += $info['variables'];
        }
        elseif (!empty($info['render element'])) {
            $variables += [
                $info['render element'] => [],
            ];
        }
        // Supply original caller info.
        $variables += [
            'theme_hook_original' => $original_hook,
        ];
        // Set base hook for later use. For example if '#theme' => 'node__article'
        // is called, we run hook_theme_suggestions_node_alter() rather than
        // hook_theme_suggestions_node__article_alter(), and also pass in the base
        // hook as the last parameter to the suggestions alter hooks.
        if (isset($info['base hook'])) {
            $base_theme_hook = $info['base hook'];
        }
        else {
            $base_theme_hook = $hook;
        }
        // Invoke hook_theme_suggestions_HOOK().
        $suggestions = $this->moduleHandler
            ->invokeAll('theme_suggestions_' . $base_theme_hook, [
            $variables,
        ]);
        // If the theme implementation was invoked with a direct theme suggestion
        // like '#theme' => 'node__article', add it to the suggestions array before
        // invoking suggestion alter hooks.
        if (isset($info['base hook'])) {
            $suggestions[] = $hook;
        }
        // Invoke hook_theme_suggestions_alter() and
        // hook_theme_suggestions_HOOK_alter().
        $hooks = [
            'theme_suggestions',
            'theme_suggestions_' . $base_theme_hook,
        ];
        $this->moduleHandler
            ->alter($hooks, $suggestions, $variables, $base_theme_hook);
        $this->alter($hooks, $suggestions, $variables, $base_theme_hook);
        // Check if each suggestion exists in the theme registry, and if so,
        // use it instead of the base hook. For example, a function may use
        // '#theme' => 'node', but a module can add 'node__article' as a suggestion
        // via hook_theme_suggestions_HOOK_alter(), enabling a theme to have
        // an alternate template file for article nodes.
        foreach (array_reverse($suggestions) as $suggestion) {
            if ($theme_registry->has($suggestion)) {
                $info = $theme_registry->get($suggestion);
                break;
            }
        }
        // Include a file if the theme function or variable preprocessor is held
        // elsewhere.
        if (!empty($info['includes'])) {
            foreach ($info['includes'] as $include_file) {
                include_once $this->root . '/' . $include_file;
            }
        }
        // Invoke the variable preprocessors, if any.
        if (isset($info['base hook'])) {
            $base_hook = $info['base hook'];
            $base_hook_info = $theme_registry->get($base_hook);
            // Include files required by the base hook, since its variable
            // preprocessors might reside there.
            if (!empty($base_hook_info['includes'])) {
                foreach ($base_hook_info['includes'] as $include_file) {
                    include_once $this->root . '/' . $include_file;
                }
            }
            if (isset($base_hook_info['preprocess functions'])) {
                // Set a variable for the 'theme_hook_suggestion'. This is used to
                // maintain backwards compatibility with template engines.
                $theme_hook_suggestion = $hook;
            }
        }
        if (isset($info['preprocess functions'])) {
            foreach ($info['preprocess functions'] as $preprocessor_function) {
                if (function_exists($preprocessor_function)) {
                    $preprocessor_function($variables, $hook, $info);
                }
            }
            // Allow theme preprocess functions to set $variables['#attached'] and
            // $variables['#cache'] and use them like the corresponding element
            // properties on render arrays. In Drupal 8, this is the (only) officially
            // supported method of attaching bubbleable metadata from preprocess
            // functions. Assets attached here should be associated with the template
            // that we are preprocessing variables for.
            $preprocess_bubbleable = [];
            foreach ([
                '#attached',
                '#cache',
            ] as $key) {
                if (isset($variables[$key])) {
                    $preprocess_bubbleable[$key] = $variables[$key];
                }
            }
            // We do not allow preprocess functions to define cacheable elements.
            unset($preprocess_bubbleable['#cache']['keys']);
            if ($preprocess_bubbleable) {
                // @todo Inject the Renderer in https://www.drupal.org/node/2529438.
                \Drupal::service('renderer')->render($preprocess_bubbleable);
            }
        }
        // Generate the output using either a function or a template.
        $output = '';
        if (isset($info['function'])) {
            if (function_exists($info['function'])) {
                // Theme functions do not render via the theme engine, so the output is
                // not autoescaped. However, we can only presume that the theme function
                // has been written correctly and that the markup is safe.
                $output = Markup::create($info['function']($variables));
            }
        }
        else {
            $render_function = 'twig_render_template';
            $extension = '.html.twig';
            // The theme engine may use a different extension and a different
            // renderer.
            $theme_engine = $active_theme->getEngine();
            if (isset($theme_engine)) {
                if ($info['type'] != 'module') {
                    if (function_exists($theme_engine . '_render_template')) {
                        $render_function = $theme_engine . '_render_template';
                    }
                    $extension_function = $theme_engine . '_extension';
                    if (function_exists($extension_function)) {
                        $extension = $extension_function();
                    }
                }
            }
            // In some cases, a template implementation may not have had
            // template_preprocess() run (for example, if the default implementation
            // is a function, but a template overrides that default implementation).
            // In these cases, a template should still be able to expect to have
            // access to the variables provided by template_preprocess(), so we add
            // them here if they don't already exist. We don't want the overhead of
            // running template_preprocess() twice, so we use the 'directory' variable
            // to determine if it has already run, which while not completely
            // intuitive, is reasonably safe, and allows us to save on the overhead of
            // adding some new variable to track that.
            if (!isset($variables['directory'])) {
                $default_template_variables = [];
                template_preprocess($default_template_variables, $hook, $info);
                $variables += $default_template_variables;
            }
            if (!isset($default_attributes)) {
                $default_attributes = new Attribute();
            }
            foreach ([
                'attributes',
                'title_attributes',
                'content_attributes',
            ] as $key) {
                if (isset($variables[$key]) && !$variables[$key] instanceof Attribute) {
                    if ($variables[$key]) {
                        $variables[$key] = new Attribute($variables[$key]);
                    }
                    else {
                        // Create empty attributes.
                        $variables[$key] = clone $default_attributes;
                    }
                }
            }
            // Render the output using the template file.
            $template_file = $info['template'] . $extension;
            if (isset($info['path'])) {
                $template_file = $info['path'] . '/' . $template_file;
            }
            // Add the theme suggestions to the variables array just before rendering
            // the template for backwards compatibility with template engines.
            $variables['theme_hook_suggestions'] = $suggestions;
            // For backwards compatibility, pass 'theme_hook_suggestion' on to the
            // template engine. This is only set when calling a direct suggestion like
            // '#theme' => 'menu__shortcut_default' when the template exists in the
            // current theme.
            if (isset($theme_hook_suggestion)) {
                $variables['theme_hook_suggestion'] = $theme_hook_suggestion;
            }
            $output = $render_function($template_file, $variables);
        }
        return $output instanceof MarkupInterface ? $output : (string) $output;
    }
    
    /**
     * Initializes the active theme for a given route match.
     *
     * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
     *   The current route match.
     */
    protected function initTheme(RouteMatchInterface $route_match = NULL) {
        // Determine the active theme for the theme negotiator service. This includes
        // the default theme as well as really specific ones like the ajax base theme.
        if (!$route_match) {
            $route_match = \Drupal::routeMatch();
        }
        if ($route_match instanceof StackedRouteMatchInterface) {
            $route_match = $route_match->getMasterRouteMatch();
        }
        $theme = $this->themeNegotiator
            ->determineActiveTheme($route_match);
        $this->activeTheme = $this->themeInitialization
            ->initTheme($theme);
    }
    
    /**
     * {@inheritdoc}
     *
     * @todo Should we cache some of these information?
     */
    public function alterForTheme(ActiveTheme $theme, $type, &$data, &$context1 = NULL, &$context2 = NULL) {
        // Most of the time, $type is passed as a string, so for performance,
        // normalize it to that. When passed as an array, usually the first item in
        // the array is a generic type, and additional items in the array are more
        // specific variants of it, as in the case of array('form', 'form_FORM_ID').
        if (is_array($type)) {
            $extra_types = $type;
            $type = array_shift($extra_types);
            // Allow if statements in this function to use the faster isset() rather
            // than !empty() both when $type is passed as a string, or as an array with
            // one item.
            if (empty($extra_types)) {
                unset($extra_types);
            }
        }
        $theme_keys = array_keys($theme->getBaseThemeExtensions());
        $theme_keys[] = $theme->getName();
        $functions = [];
        foreach ($theme_keys as $theme_key) {
            $function = $theme_key . '_' . $type . '_alter';
            if (function_exists($function)) {
                $functions[] = $function;
            }
            if (isset($extra_types)) {
                foreach ($extra_types as $extra_type) {
                    $function = $theme_key . '_' . $extra_type . '_alter';
                    if (function_exists($function)) {
                        $functions[] = $function;
                    }
                }
            }
        }
        foreach ($functions as $function) {
            $function($data, $context1, $context2);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function alter($type, &$data, &$context1 = NULL, &$context2 = NULL) {
        $theme = $this->getActiveTheme();
        $this->alterForTheme($theme, $type, $data, $context1, $context2);
    }

}