class TwigExtension

class TwigExtension extends \Twig_Extension {
    
    /**
     * The URL generator.
     *
     * @var \Drupal\Core\Routing\UrlGeneratorInterface
     */
    protected $urlGenerator;
    
    /**
     * The renderer.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * The theme manager.
     *
     * @var \Drupal\Core\Theme\ThemeManagerInterface
     */
    protected $themeManager;
    
    /**
     * The date formatter.
     *
     * @var \Drupal\Core\Datetime\DateFormatterInterface
     */
    protected $dateFormatter;
    
    /**
     * Constructs \Drupal\Core\Template\TwigExtension.
     *
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer.
     * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
     *   The URL generator.
     * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
     *   The theme manager.
     * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
     *   The date formatter.
     */
    public function __construct(RendererInterface $renderer, UrlGeneratorInterface $url_generator, ThemeManagerInterface $theme_manager, DateFormatterInterface $date_formatter) {
        $this->renderer = $renderer;
        $this->urlGenerator = $url_generator;
        $this->themeManager = $theme_manager;
        $this->dateFormatter = $date_formatter;
    }
    
    /**
     * Sets the URL generator.
     *
     * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
     *   The URL generator.
     *
     * @return $this
     *
     * @deprecated in drupal:8.0.0 and is removed from drupal:9.0.0.
     */
    public function setGenerators(UrlGeneratorInterface $url_generator) {
        return $this->setUrlGenerator($url_generator);
    }
    
    /**
     * Sets the URL generator.
     *
     * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
     *   The URL generator.
     *
     * @return $this
     *
     * @deprecated in drupal:8.3.0 and is removed from drupal:9.0.0.
     */
    public function setUrlGenerator(UrlGeneratorInterface $url_generator) {
        $this->urlGenerator = $url_generator;
        return $this;
    }
    
    /**
     * Sets the theme manager.
     *
     * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
     *   The theme manager.
     *
     * @return $this
     *
     * @deprecated in drupal:8.3.0 and is removed from drupal:9.0.0.
     */
    public function setThemeManager(ThemeManagerInterface $theme_manager) {
        $this->themeManager = $theme_manager;
        return $this;
    }
    
    /**
     * Sets the date formatter.
     *
     * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
     *   The date formatter.
     *
     * @return $this
     *
     * @deprecated in drupal:8.3.0 and is removed from drupal:9.0.0.
     */
    public function setDateFormatter(DateFormatterInterface $date_formatter) {
        $this->dateFormatter = $date_formatter;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFunctions() {
        return [
            // This function will receive a renderable array, if an array is detected.
new \Twig_SimpleFunction('render_var', [
                $this,
                'renderVar',
            ]),
            // The url and path function are defined in close parallel to those found
            // in \Symfony\Bridge\Twig\Extension\RoutingExtension
new \Twig_SimpleFunction('url', [
                $this,
                'getUrl',
            ], [
                'is_safe_callback' => [
                    $this,
                    'isUrlGenerationSafe',
                ],
            ]),
            new \Twig_SimpleFunction('path', [
                $this,
                'getPath',
            ], [
                'is_safe_callback' => [
                    $this,
                    'isUrlGenerationSafe',
                ],
            ]),
            new \Twig_SimpleFunction('link', [
                $this,
                'getLink',
            ]),
            new \Twig_SimpleFunction('file_url', function ($uri) {
                return file_url_transform_relative(file_create_url($uri));
            }),
            new \Twig_SimpleFunction('attach_library', [
                $this,
                'attachLibrary',
            ]),
            new \Twig_SimpleFunction('active_theme_path', [
                $this,
                'getActiveThemePath',
            ]),
            new \Twig_SimpleFunction('active_theme', [
                $this,
                'getActiveTheme',
            ]),
            new \Twig_SimpleFunction('create_attribute', [
                $this,
                'createAttribute',
            ]),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFilters() {
        return [
            // Translation filters.
new \Twig_SimpleFilter('t', 't', [
                'is_safe' => [
                    'html',
                ],
            ]),
            new \Twig_SimpleFilter('trans', 't', [
                'is_safe' => [
                    'html',
                ],
            ]),
            // The "raw" filter is not detectable when parsing "trans" tags. To detect
            // which prefix must be used for translation (@, !, %), we must clone the
            // "raw" filter and give it identifiable names. These filters should only
            // be used in "trans" tags.
            // @see TwigNodeTrans::compileString()
new \Twig_SimpleFilter('placeholder', [
                $this,
                'escapePlaceholder',
            ], [
                'is_safe' => [
                    'html',
                ],
                'needs_environment' => TRUE,
            ]),
            // Replace twig's escape filter with our own.
new \Twig_SimpleFilter('drupal_escape', [
                $this,
                'escapeFilter',
            ], [
                'needs_environment' => TRUE,
                'is_safe_callback' => 'twig_escape_filter_is_safe',
            ]),
            // Implements safe joining.
            // @todo Make that the default for |join? Upstream issue:
            //   https://github.com/fabpot/Twig/issues/1420
new \Twig_SimpleFilter('safe_join', [
                $this,
                'safeJoin',
            ], [
                'needs_environment' => TRUE,
                'is_safe' => [
                    'html',
                ],
            ]),
            // Array filters.
new \Twig_SimpleFilter('without', [
                $this,
                'withoutFilter',
            ]),
            // CSS class and ID filters.
new \Twig_SimpleFilter('clean_class', '\\Drupal\\Component\\Utility\\Html::getClass'),
            new \Twig_SimpleFilter('clean_id', '\\Drupal\\Component\\Utility\\Html::getId'),
            // This filter will render a renderable array to use the string results.
new \Twig_SimpleFilter('render', [
                $this,
                'renderVar',
            ]),
            new \Twig_SimpleFilter('format_date', [
                $this->dateFormatter,
                'format',
            ]),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getNodeVisitors() {
        // The node visitor is needed to wrap all variables with
        // render_var -> TwigExtension->renderVar() function.
        return [
            new TwigNodeVisitor(),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTokenParsers() {
        return [
            new TwigTransTokenParser(),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getName() {
        return 'drupal_core';
    }
    
    /**
     * Generates a URL path given a route name and parameters.
     *
     * @param $name
     *   The name of the route.
     * @param array $parameters
     *   An associative array of route parameters names and values.
     * @param array $options
     *   (optional) An associative array of additional options. The 'absolute'
     *   option is forced to be FALSE.
     *
     * @return string
     *   The generated URL path (relative URL) for the given route.
     *
     * @see \Drupal\Core\Routing\UrlGeneratorInterface::generateFromRoute()
     */
    public function getPath($name, $parameters = [], $options = []) {
        assert($this->urlGenerator instanceof UrlGeneratorInterface, "The URL generator hasn't been set up. Any configuration YAML file with a service directive dealing with the Twig configuration can cause this, most likely found in a recently installed or changed module.");
        $options['absolute'] = FALSE;
        return $this->urlGenerator
            ->generateFromRoute($name, $parameters, $options);
    }
    
    /**
     * Generates an absolute URL given a route name and parameters.
     *
     * @param $name
     *   The name of the route.
     * @param array $parameters
     *   An associative array of route parameter names and values.
     * @param array $options
     *   (optional) An associative array of additional options. The 'absolute'
     *   option is forced to be TRUE.
     *
     * @return array
     *   A render array with generated absolute URL for the given route.
     *
     * @todo Add an option for scheme-relative URLs.
     */
    public function getUrl($name, $parameters = [], $options = []) {
        assert($this->urlGenerator instanceof UrlGeneratorInterface, "The URL generator hasn't been set up. Any configuration YAML file with a service directive dealing with the Twig configuration can cause this, most likely found in a recently installed or changed module.");
        // Generate URL.
        $options['absolute'] = TRUE;
        $generated_url = $this->urlGenerator
            ->generateFromRoute($name, $parameters, $options, TRUE);
        // Return as render array, so we can bubble the bubbleable metadata.
        $build = [
            '#markup' => $generated_url->getGeneratedUrl(),
        ];
        $generated_url->applyTo($build);
        return $build;
    }
    
    /**
     * Gets a rendered link from a url object.
     *
     * @param string $text
     *   The link text for the anchor tag as a translated string.
     * @param \Drupal\Core\Url|string $url
     *   The URL object or string used for the link.
     * @param array|\Drupal\Core\Template\Attribute $attributes
     *   An optional array or Attribute object of link attributes.
     *
     * @return array
     *   A render array representing a link to the given URL.
     */
    public function getLink($text, $url, $attributes = []) {
        assert(is_string($url) || $url instanceof Url, '$url must be a string or object of type \\Drupal\\Core\\Url');
        assert(is_array($attributes) || $attributes instanceof Attribute, '$attributes, if set, must be an array or object of type \\Drupal\\Core\\Template\\Attribute');
        if (!$url instanceof Url) {
            $url = Url::fromUri($url);
        }
        // The twig extension should not modify the original URL object, this
        // ensures consistent rendering.
        // @see https://www.drupal.org/node/2842399
        $url = clone $url;
        if ($attributes) {
            if ($attributes instanceof Attribute) {
                $attributes = $attributes->toArray();
            }
            $url->mergeOptions([
                'attributes' => $attributes,
            ]);
        }
        // The text has been processed by twig already, convert it to a safe object
        // for the render system.
        if ($text instanceof \Twig_Markup) {
            $text = Markup::create($text);
        }
        $build = [
            '#type' => 'link',
            '#title' => $text,
            '#url' => $url,
        ];
        return $build;
    }
    
    /**
     * Gets the name of the active theme.
     *
     * @return string
     *   The name of the active theme.
     */
    public function getActiveTheme() {
        return $this->themeManager
            ->getActiveTheme()
            ->getName();
    }
    
    /**
     * Gets the path of the active theme.
     *
     * @return string
     *   The path to the active theme.
     */
    public function getActiveThemePath() {
        return $this->themeManager
            ->getActiveTheme()
            ->getPath();
    }
    
    /**
     * Determines at compile time whether the generated URL will be safe.
     *
     * Saves the unneeded automatic escaping for performance reasons.
     *
     * The URL generation process percent encodes non-alphanumeric characters.
     * Thus, the only character within a URL that must be escaped in HTML is the
     * ampersand ("&") which separates query params. Thus we cannot mark
     * the generated URL as always safe, but only when we are sure there won't be
     * multiple query params. This is the case when there are none or only one
     * constant parameter given. For instance, we know beforehand this will not
     * need to be escaped:
     * - path('route')
     * - path('route', {'param': 'value'})
     * But the following may need to be escaped:
     * - path('route', var)
     * - path('route', {'param': ['val1', 'val2'] }) // a sub-array
     * - path('route', {'param1': 'value1', 'param2': 'value2'})
     * If param1 and param2 reference placeholders in the route, it would not
     * need to be escaped, but we don't know that in advance.
     *
     * @param \Twig_Node $args_node
     *   The arguments of the path/url functions.
     *
     * @return array
     *   An array with the contexts the URL is safe
     */
    public function isUrlGenerationSafe(\Twig_Node $args_node) {
        // Support named arguments.
        $parameter_node = $args_node->hasNode('parameters') ? $args_node->getNode('parameters') : ($args_node->hasNode(1) ? $args_node->getNode(1) : NULL);
        if (!isset($parameter_node) || $parameter_node instanceof \Twig_Node_Expression_Array && count($parameter_node) <= 2 && (!$parameter_node->hasNode(1) || $parameter_node->getNode(1) instanceof \Twig_Node_Expression_Constant)) {
            return [
                'html',
            ];
        }
        return [];
    }
    
    /**
     * Attaches an asset library to the template, and hence to the response.
     *
     * Allows Twig templates to attach asset libraries using
     * @code
     * {{ attach_library('extension/library_name') }}
     * @endcode
     *
     * @param string $library
     *   An asset library.
     */
    public function attachLibrary($library) {
        assert(is_string($library), 'Argument must be a string.');
        // Use Renderer::render() on a temporary render array to get additional
        // bubbleable metadata on the render stack.
        $template_attached = [
            '#attached' => [
                'library' => [
                    $library,
                ],
            ],
        ];
        $this->renderer
            ->render($template_attached);
    }
    
    /**
     * Provides a placeholder wrapper around ::escapeFilter.
     *
     * @param \Twig_Environment $env
     *   A Twig_Environment instance.
     * @param mixed $string
     *   The value to be escaped.
     *
     * @return string|null
     *   The escaped, rendered output, or NULL if there is no valid output.
     */
    public function escapePlaceholder(\Twig_Environment $env, $string) {
        $return = $this->escapeFilter($env, $string);
        return $return ? '<em class="placeholder">' . $return . '</em>' : NULL;
    }
    
    /**
     * Overrides twig_escape_filter().
     *
     * Replacement function for Twig's escape filter.
     *
     * Note: This function should be kept in sync with
     * theme_render_and_autoescape().
     *
     * @param \Twig_Environment $env
     *   A Twig_Environment instance.
     * @param mixed $arg
     *   The value to be escaped.
     * @param string $strategy
     *   The escaping strategy. Defaults to 'html'.
     * @param string $charset
     *   The charset.
     * @param bool $autoescape
     *   Whether the function is called by the auto-escaping feature (TRUE) or by
     *   the developer (FALSE).
     *
     * @return string|null
     *   The escaped, rendered output, or NULL if there is no valid output.
     *
     * @throws \Exception
     *   When $arg is passed as an object which does not implement __toString(),
     *   RenderableInterface or toString().
     *
     * @todo Refactor this to keep it in sync with theme_render_and_autoescape()
     *   in https://www.drupal.org/node/2575065
     */
    public function escapeFilter(\Twig_Environment $env, $arg, $strategy = 'html', $charset = NULL, $autoescape = FALSE) {
        // Check for a numeric zero int or float.
        if ($arg === 0 || $arg === 0.0) {
            return 0;
        }
        // Return early for NULL and empty arrays.
        if ($arg == NULL) {
            return NULL;
        }
        $this->bubbleArgMetadata($arg);
        // Keep Twig_Markup objects intact to support autoescaping.
        if ($autoescape && ($arg instanceof \Twig_Markup || $arg instanceof MarkupInterface)) {
            return $arg;
        }
        $return = NULL;
        if (is_scalar($arg)) {
            $return = (string) $arg;
        }
        elseif (is_object($arg)) {
            if ($arg instanceof RenderableInterface) {
                $arg = $arg->toRenderable();
            }
            elseif (method_exists($arg, '__toString')) {
                $return = (string) $arg;
            }
            elseif (method_exists($arg, 'toString')) {
                $return = $arg->toString();
            }
            else {
                throw new \Exception('Object of type ' . get_class($arg) . ' cannot be printed.');
            }
        }
        // We have a string or an object converted to a string: Autoescape it!
        if (isset($return)) {
            if ($autoescape && $return instanceof MarkupInterface) {
                return $return;
            }
            // Drupal only supports the HTML escaping strategy, so provide a
            // fallback for other strategies.
            if ($strategy == 'html') {
                return Html::escape($return);
            }
            return twig_escape_filter($env, $return, $strategy, $charset, $autoescape);
        }
        // This is a normal render array, which is safe by definition, with
        // special simple cases already handled.
        // Early return if this element was pre-rendered (no need to re-render).
        if (isset($arg['#printed']) && $arg['#printed'] == TRUE && isset($arg['#markup']) && strlen($arg['#markup']) > 0) {
            return $arg['#markup'];
        }
        $arg['#printed'] = FALSE;
        return $this->renderer
            ->render($arg);
    }
    
    /**
     * Bubbles Twig template argument's cacheability & attachment metadata.
     *
     * For example: a generated link or generated URL object is passed as a Twig
     * template argument, and its bubbleable metadata must be bubbled.
     *
     * @see \Drupal\Core\GeneratedLink
     * @see \Drupal\Core\GeneratedUrl
     *
     * @param mixed $arg
     *   A Twig template argument that is about to be printed.
     *
     * @see \Drupal\Core\Theme\ThemeManager::render()
     * @see \Drupal\Core\Render\RendererInterface::render()
     */
    protected function bubbleArgMetadata($arg) {
        // If it's a renderable, then it'll be up to the generated render array it
        // returns to contain the necessary cacheability & attachment metadata. If
        // it doesn't implement CacheableDependencyInterface or AttachmentsInterface
        // then there is nothing to do here.
        if ($arg instanceof RenderableInterface || !($arg instanceof CacheableDependencyInterface || $arg instanceof AttachmentsInterface)) {
            return;
        }
        $arg_bubbleable = [];
        BubbleableMetadata::createFromObject($arg)->applyTo($arg_bubbleable);
        $this->renderer
            ->render($arg_bubbleable);
    }
    
    /**
     * Wrapper around render() for twig printed output.
     *
     * If an object is passed which does not implement __toString(),
     * RenderableInterface or toString() then an exception is thrown;
     * Other objects are casted to string. However in the case that the
     * object is an instance of a Twig_Markup object it is returned directly
     * to support auto escaping.
     *
     * If an array is passed it is rendered via render() and scalar values are
     * returned directly.
     *
     * @param mixed $arg
     *   String, Object or Render Array.
     *
     * @throws \Exception
     *   When $arg is passed as an object which does not implement __toString(),
     *   RenderableInterface or toString().
     *
     * @return mixed
     *   The rendered output or an Twig_Markup object.
     *
     * @see render
     * @see TwigNodeVisitor
     */
    public function renderVar($arg) {
        // Check for a numeric zero int or float.
        if ($arg === 0 || $arg === 0.0) {
            return 0;
        }
        // Return early for NULL and empty arrays.
        if ($arg == NULL) {
            return NULL;
        }
        // Optimize for scalars as it is likely they come from the escape filter.
        if (is_scalar($arg)) {
            return $arg;
        }
        if (is_object($arg)) {
            $this->bubbleArgMetadata($arg);
            if ($arg instanceof RenderableInterface) {
                $arg = $arg->toRenderable();
            }
            elseif (method_exists($arg, '__toString')) {
                return (string) $arg;
            }
            elseif (method_exists($arg, 'toString')) {
                return $arg->toString();
            }
            else {
                throw new \Exception('Object of type ' . get_class($arg) . ' cannot be printed.');
            }
        }
        // This is a render array, with special simple cases already handled.
        // Early return if this element was pre-rendered (no need to re-render).
        if (isset($arg['#printed']) && $arg['#printed'] == TRUE && isset($arg['#markup']) && strlen($arg['#markup']) > 0) {
            return $arg['#markup'];
        }
        $arg['#printed'] = FALSE;
        return $this->renderer
            ->render($arg);
    }
    
    /**
     * Joins several strings together safely.
     *
     * @param \Twig_Environment $env
     *   A Twig_Environment instance.
     * @param mixed[]|\Traversable|null $value
     *   The pieces to join.
     * @param string $glue
     *   The delimiter with which to join the string. Defaults to an empty string.
     *   This value is expected to be safe for output and user provided data
     *   should never be used as a glue.
     *
     * @return string
     *   The strings joined together.
     */
    public function safeJoin(\Twig_Environment $env, $value, $glue = '') {
        if ($value instanceof \Traversable) {
            $value = iterator_to_array($value, FALSE);
        }
        return implode($glue, array_map(function ($item) use ($env) {
            // If $item is not marked safe then it will be escaped.
            return $this->escapeFilter($env, $item, 'html', NULL, TRUE);
        }, (array) $value));
    }
    
    /**
     * Creates an Attribute object.
     *
     * @param array $attributes
     *   (optional) An associative array of key-value pairs to be converted to
     *   HTML attributes.
     *
     * @return \Drupal\Core\Template\Attribute
     *   An attributes object that has the given attributes.
     */
    public function createAttribute(array $attributes = []) {
        return new Attribute($attributes);
    }
    
    /**
     * Removes child elements from a copy of the original array.
     *
     * Creates a copy of the renderable array and removes child elements by key
     * specified through filter's arguments. The copy can be printed without these
     * elements. The original renderable array is still available and can be used
     * to print child elements in their entirety in the twig template.
     *
     * @param array|object $element
     *   The parent renderable array to exclude the child items.
     * @param string[]|string ...
     *   The string keys of $element to prevent printing. Arguments can include
     *   string keys directly, or arrays of string keys to hide.
     *
     * @return array
     *   The filtered renderable array.
     */
    public function withoutFilter($element) {
        if ($element instanceof \ArrayAccess) {
            $filtered_element = clone $element;
        }
        else {
            $filtered_element = $element;
        }
        $args = func_get_args();
        unset($args[0]);
        // Since the remaining arguments can be a mix of arrays and strings, we use
        // some native PHP iterator classes to allow us to recursively iterate over
        // everything in a single pass.
        $iterator = new \RecursiveIteratorIterator(new \RecursiveArrayIterator($args));
        foreach ($iterator as $key) {
            unset($filtered_element[$key]);
        }
        return $filtered_element;
    }

}