theme.inc

<?php

/**
 * @file
 * The theme system, which controls the output of Drupal.
 *
 * The theme system allows for nearly all output of the Drupal system to be
 * customized by user themes.
 */

use Drupal\Component\Serialization\Json;
use Drupal\Component\Utility\Html;
use Drupal\Component\Utility\SafeMarkup;
use Drupal\Component\Utility\String;
use Drupal\Component\Utility\Unicode;
use Drupal\Component\Utility\UrlHelper;
use Drupal\Component\Utility\Xss;
use Drupal\Core\Config\Config;
use Drupal\Core\Config\StorageException;
use Drupal\Core\Extension\Extension;
use Drupal\Core\Extension\ExtensionNameLengthException;
use Drupal\Core\Template\Attribute;
use Drupal\Core\Theme\ThemeSettings;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Render\Element;
use Symfony\Component\HttpFoundation\Request;

/**
 * @defgroup content_flags Content markers
 * @{
 * Markers used by mark.html.twig and node_mark() to designate content.
 *
 * @see mark.html.twig
 * @see node_mark()
 */

/**
 * Mark content as read.
 */
const MARK_READ = 0;

/**
 * Mark content as being new.
 */
const MARK_NEW = 1;

/**
 * Mark content as being updated.
 */
const MARK_UPDATED = 2;

/**
 * A responsive table class; hide table cell on narrow devices.
 *
 * Indicates that a column has medium priority and thus can be hidden on narrow
 * width devices and shown on medium+ width devices (i.e. tablets and desktops).
 */
const RESPONSIVE_PRIORITY_MEDIUM = 'priority-medium';

/**
 * A responsive table class; only show table cell on wide devices.
 *
 * Indicates that a column has low priority and thus can be hidden on narrow
 * and medium viewports and shown on wide devices (i.e. desktops).
 */
const RESPONSIVE_PRIORITY_LOW = 'priority-low';

/**
 * @} End of "defgroup content_flags".
 */

/**
 * Determines if a theme is available to use.
 *
 * @param string|\Drupal\Core\Extension\Extension $theme
 *   Either the name of a theme or a full theme object.
 *
 * @return bool
 *   Boolean TRUE if the theme is installed or is the site administration theme;
 *   FALSE otherwise.
 *
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
 *   Use \Drupal::service('access_check.theme')->checkAccess().
 *
 * @see \Drupal\Core\Theme\ThemeAccessCheck::checkAccess().
 */
function drupal_theme_access($theme) {
  if ($theme instanceof Extension) {
    $theme = $theme->getName();
  }
  return \Drupal::service('access_check.theme')->checkAccess($theme);
}

/**
 * Gets the theme registry.
 *
 * @param bool $complete
 *   Optional boolean to indicate whether to return the complete theme registry
 *   array or an instance of the Drupal\Core\Utility\ThemeRegistry class.
 *   If TRUE, the complete theme registry array will be returned. This is useful
 *   if you want to foreach over the whole registry, use array_* functions or
 *   inspect it in a debugger. If FALSE, an instance of the
 *   Drupal\Core\Utility\ThemeRegistry class will be returned, this provides an
 *   ArrayObject which allows it to be accessed with array syntax and isset(),
 *   and should be more lightweight than the full registry. Defaults to TRUE.
 *
 * @return
 *   The complete theme registry array, or an instance of the
 *   Drupal\Core\Utility\ThemeRegistry class.
 */
function theme_get_registry($complete = TRUE) {
  $theme_registry = \Drupal::service('theme.registry');
  if ($complete) {
    return $theme_registry->get();
  }
  else {
    return $theme_registry->getRuntime();
  }
}

/**
 * Forces the system to rebuild the theme registry.
 *
 * This function should be called when modules are added to the system, or when
 * a dynamic system needs to add more theme hooks.
 */
function drupal_theme_rebuild() {
  \Drupal::service('theme.registry')->reset();
}

/**
 * Returns a list of all currently available themes.
 *
 * Retrieved from the database, if available and the site is not in maintenance
 * mode; otherwise compiled freshly from the filesystem.
 *
 * @param $refresh
 *   Whether to reload the list of themes from the database. Defaults to FALSE.
 *
 * @return array
 *   An associative array of the currently available themes.
 *
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
 *   Use \Drupal::service('theme_handler')->listInfo().
 *
 * @see \Drupal\Core\Extension\ThemeHandler::listInfo().
 */
function list_themes($refresh = FALSE) {
  /** @var \Drupal\Core\Extension\ThemeHandler $theme_handler */
  $theme_handler = \Drupal::service('theme_handler');

  if ($refresh) {
    $theme_handler->reset();
    system_list_reset();
  }

  return $theme_handler->listInfo();
}

/**
 * Allows themes and/or theme engines to discover overridden theme functions.
 *
 * @param $cache
 *   The existing cache of theme hooks to test against.
 * @param $prefixes
 *   An array of prefixes to test, in reverse order of importance.
 *
 * @return $implementations
 *   The functions found, suitable for returning from hook_theme;
 */
function drupal_find_theme_functions($cache, $prefixes) {
  $implementations = array();
  $functions = get_defined_functions();

  foreach ($cache as $hook => $info) {
    foreach ($prefixes as $prefix) {
      // Find theme functions that implement possible "suggestion" variants of
      // registered theme hooks and add those as new registered theme hooks.
      // The 'pattern' key defines a common prefix that all suggestions must
      // start with. The default is the name of the hook followed by '__'. An
      // 'base hook' key is added to each entry made for a found suggestion,
      // so that common functionality can be implemented for all suggestions of
      // the same base hook. To keep things simple, deep hierarchy of
      // suggestions is not supported: each suggestion's 'base hook' key
      // refers to a base hook, not to another suggestion, and all suggestions
      // are found using the base hook's pattern, not a pattern from an
      // intermediary suggestion.
      $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
      if (!isset($info['base hook']) && !empty($pattern)) {
        $matches = preg_grep('/^' . $prefix . '_' . $pattern . '/', $functions['user']);
        if ($matches) {
          foreach ($matches as $match) {
            $new_hook = substr($match, strlen($prefix) + 1);
            $arg_name = isset($info['variables']) ? 'variables' : 'render element';
            $implementations[$new_hook] = array(
              'function' => $match,
              $arg_name => $info[$arg_name],
              'base hook' => $hook,
            );
          }
        }
      }
      // Find theme functions that implement registered theme hooks and include
      // that in what is returned so that the registry knows that the theme has
      // this implementation.
      if (function_exists($prefix . '_' . $hook)) {
        $implementations[$hook] = array(
          'function' => $prefix . '_' . $hook,
        );
      }
    }
  }

  return $implementations;
}

/**
 * Allows themes and/or theme engines to easily discover overridden templates.
 *
 * @param $cache
 *   The existing cache of theme hooks to test against.
 * @param $extension
 *   The extension that these templates will have.
 * @param $path
 *   The path to search.
 */
function drupal_find_theme_templates($cache, $extension, $path) {
  $implementations = array();

  // Collect paths to all sub-themes grouped by base themes. These will be
  // used for filtering. This allows base themes to have sub-themes in its
  // folder hierarchy without affecting the base themes template discovery.
  $theme_paths = array();
  foreach (list_themes() as $theme_info) {
    if (!empty($theme_info->base_theme)) {
      $theme_paths[$theme_info->base_theme][$theme_info->getName()] = $theme_info->getPath();
    }
  }
  foreach ($theme_paths as $basetheme => $subthemes) {
    foreach ($subthemes as $subtheme => $subtheme_path) {
      if (isset($theme_paths[$subtheme])) {
        $theme_paths[$basetheme] = array_merge($theme_paths[$basetheme], $theme_paths[$subtheme]);
      }
    }
  }
  $theme = \Drupal::theme()->getActiveTheme()->getName();
  $subtheme_paths = isset($theme_paths[$theme]) ? $theme_paths[$theme] : array();

  // Escape the periods in the extension.
  $regex = '/' . str_replace('.', '\.', $extension) . '$/';
  // Get a listing of all template files in the path to search.
  $files = file_scan_directory($path, $regex, array('key' => 'filename'));

  // Find templates that implement registered theme hooks and include that in
  // what is returned so that the registry knows that the theme has this
  // implementation.
  foreach ($files as $template => $file) {
    // Ignore sub-theme templates for the current theme.
    if (strpos($file->uri, str_replace($subtheme_paths, '', $file->uri)) !== 0) {
      continue;
    }
    // Remove the extension from the filename.
    $template = str_replace($extension, '', $template);
    // Transform - in filenames to _ to match function naming scheme
    // for the purposes of searching.
    $hook = strtr($template, '-', '_');
    if (isset($cache[$hook])) {
      $implementations[$hook] = array(
        'template' => $template,
        'path' => dirname($file->uri),
      );
    }

    // Match templates based on the 'template' filename.
    foreach ($cache as $hook => $info) {
      if (isset($info['template'])) {
        $template_candidates = array($info['template'], str_replace($info['theme path'] . '/templates/', '', $info['template']));
        if (in_array($template, $template_candidates)) {
          $implementations[$hook] = array(
            'template' => $template,
            'path' => dirname($file->uri),
          );
        }
      }
    }
  }

  // Find templates that implement possible "suggestion" variants of registered
  // theme hooks and add those as new registered theme hooks. See
  // drupal_find_theme_functions() for more information about suggestions and
  // the use of 'pattern' and 'base hook'.
  $patterns = array_keys($files);
  foreach ($cache as $hook => $info) {
    $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
    if (!isset($info['base hook']) && !empty($pattern)) {
      // Transform _ in pattern to - to match file naming scheme
      // for the purposes of searching.
      $pattern = strtr($pattern, '_', '-');

      $matches = preg_grep('/^' . $pattern . '/', $patterns);
      if ($matches) {
        foreach ($matches as $match) {
          $file = $match;
          // Remove the extension from the filename.
          $file = str_replace($extension, '', $file);
          // Put the underscores back in for the hook name and register this
          // pattern.
          $arg_name = isset($info['variables']) ? 'variables' : 'render element';
          $implementations[strtr($file, '-', '_')] = array(
            'template' => $file,
            'path' => dirname($files[$match]->uri),
            $arg_name => $info[$arg_name],
            'base hook' => $hook,
          );
        }
      }
    }
  }
  return $implementations;
}

/**
 * Retrieves a setting for the current theme or for a given theme.
 *
 * The final setting is obtained from the last value found in the following
 * sources:
 * - the saved values from the global theme settings form
 * - the saved values from the theme's settings form
 * To only retrieve the default global theme setting, an empty string should be
 * given for $theme.
 *
 * @param $setting_name
 *   The name of the setting to be retrieved.
 * @param $theme
 *   The name of a given theme; defaults to the current theme.
 *
 * @return
 *   The value of the requested setting, NULL if the setting does not exist.
 */
function theme_get_setting($setting_name, $theme = NULL) {
  /** @var \Drupal\Core\Theme\ThemeSettings[] $cache */
  $cache = &drupal_static(__FUNCTION__, array());

  // If no key is given, use the current theme if we can determine it.
  if (!isset($theme)) {
    $theme = \Drupal::theme()->getActiveTheme()->getName();
  }

  if (empty($cache[$theme])) {
    // Create a theme settings object.
    $cache[$theme] = new ThemeSettings($theme);
    // Get the global settings from configuration.
    $cache[$theme]->setData(\Drupal::config('system.theme.global')->get());

    $themes = \Drupal::service('theme_handler')->listInfo();
    if (isset($themes[$theme])) {
      $theme_object = $themes[$theme];

      // Retrieve configured theme-specific settings, if any.
      try {
        if ($theme_settings = \Drupal::config($theme . '.settings')->get()) {
          $cache[$theme]->merge($theme_settings);
        }
      }
      catch (StorageException $e) {
      }

      // If the theme does not support a particular feature, override the global
      // setting and set the value to NULL.
      if (!empty($theme_object->info['features'])) {
        foreach (_system_default_theme_features() as $feature) {
          if (!in_array($feature, $theme_object->info['features'])) {
            $cache[$theme]->set('features.' . $feature, NULL);
          }
        }
      }

      // Generate the path to the logo image.
      if ($cache[$theme]->get('features.logo')) {
        $logo_path = $cache[$theme]->get('logo.path');
        if ($cache[$theme]->get('logo.use_default')) {
          $cache[$theme]->set('logo.url', file_create_url($theme_object->getPath() . '/logo.png'));
        }
        elseif ($logo_path) {
          $cache[$theme]->set('logo.url', file_create_url($logo_path));
        }
      }

      // Generate the path to the favicon.
      if ($cache[$theme]->get('features.favicon')) {
        $favicon_path = $cache[$theme]->get('favicon.path');
        if ($cache[$theme]->get('favicon.use_default')) {
          if (file_exists($favicon = $theme_object->getPath() . '/favicon.ico')) {
            $cache[$theme]->set('favicon.url', file_create_url($favicon));
          }
          else {
            $cache[$theme]->set('favicon.url', file_create_url('core/misc/favicon.ico'));
          }
        }
        elseif ($favicon_path) {
          $cache[$theme]->set('favicon.url', file_create_url($favicon_path));
        }
        else {
          $cache[$theme]->set('features.favicon', FALSE);
        }
      }
    }
  }

  return $cache[$theme]->get($setting_name);
}

/**
 * Converts theme settings to configuration.
 *
 * @see system_theme_settings_submit()
 *
 * @param array $theme_settings
 *   An array of theme settings from system setting form or a Drupal 7 variable.
 * @param Config $config
 *   The configuration object to update.
 *
 * @return
 *   The Config object with updated data.
 */
function theme_settings_convert_to_config(array $theme_settings, Config $config) {
  foreach ($theme_settings as $key => $value) {
    if ($key == 'default_logo') {
      $config->set('logo.use_default', $value);
    }
    else if ($key == 'logo_path') {
      $config->set('logo.path', $value);
    }
    else if ($key == 'default_favicon') {
      $config->set('favicon.use_default', $value);
    }
    else if ($key == 'favicon_path') {
      $config->set('favicon.path', $value);
    }
    else if ($key == 'favicon_mimetype') {
      $config->set('favicon.mimetype', $value);
    }
    else if (substr($key, 0, 7) == 'toggle_') {
      $config->set('features.' . Unicode::substr($key, 7), $value);
    }
    else if (!in_array($key, array('theme', 'logo_upload'))) {
      $config->set($key, $value);
    }
  }
  return $config;
}

/**
 * @addtogroup themeable
 * @{
 */

/**
 * Prepares variables for time templates.
 *
 * Default template: time.html.twig.
 *
 * @param array $variables
 *   An associative array possibly containing:
 *   - attributes['timestamp']:
 *   - timestamp:
 *   - text:
 */
function template_preprocess_time(&$variables) {
  // Format the 'datetime' attribute based on the timestamp.
  // @see http://www.w3.org/TR/html5-author/the-time-element.html#attr-time-datetime
  if (!isset($variables['attributes']['datetime']) && isset($variables['timestamp'])) {
    $variables['attributes']['datetime'] = format_date($variables['timestamp'], 'html_datetime', '', 'UTC');
  }

  // If no text was provided, try to auto-generate it.
  if (!isset($variables['text'])) {
    // Format and use a human-readable version of the timestamp, if any.
    if (isset($variables['timestamp'])) {
      $variables['text'] = format_date($variables['timestamp']);
      $variables['html'] = FALSE;
    }
    // Otherwise, use the literal datetime attribute.
    elseif (isset($variables['attributes']['datetime'])) {
      $variables['text'] = $variables['attributes']['datetime'];
      $variables['html'] = FALSE;
    }
  }
}

/**
 * Prepares variables for datetime form element templates.
 *
 * The datetime form element serves as a wrapper around the date element type,
 * which creates a date and a time component for a date.
 *
 * Default template: datetime-form.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #value, #options, #description, #required,
 *     #attributes.
 *
 * @see form_process_datetime()
 */
function template_preprocess_datetime_form(&$variables) {
  $element = $variables['element'];

  $variables['attributes'] = array();
  if (isset($element['#id'])) {
    $variables['attributes']['id'] = $element['#id'];
  }
  if (!empty($element['#attributes']['class'])) {
    $variables['attributes']['class'] = (array) $element['#attributes']['class'];
  }

  $variables['content'] = $element;
}

/**
 * Prepares variables for datetime form wrapper templates.
 *
 * Default template: datetime-wrapper.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: An associative array containing the properties of the element.
 *     Properties used: #title, #children, #required, #attributes.
 */
function template_preprocess_datetime_wrapper(&$variables) {
  $element = $variables['element'];

  if (!empty($element['#title'])) {
    $variables['title'] = $element['#title'];
  }

  if (!empty($element['#description'])) {
    $variables['description'] = $element['#description'];
  }

  $variables['required'] = FALSE;
  // For required datetime fields a 'form-required' class is appended to the
  // label attributes.
  if (!empty($element['#required'])) {
    $variables['required'] = TRUE;
  }
  $variables['content'] = $element['#children'];
}

/**
 * Prepares variables for status message templates.
 *
 * Default template: status-messages.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - display: (optional) May have a value of 'status' or 'error' when only
 *     displaying messages of that specific type.
 */
function template_preprocess_status_messages(&$variables) {
  $variables['message_list'] = drupal_get_messages($variables['display']);
  $variables['status_headings'] = array(
    'status' => t('Status message'),
    'error' => t('Error message'),
    'warning' => t('Warning message'),
  );
}

/**
 * Prepares variables for links templates.
 *
 * Default template: links.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - links: An associative array of links to be themed. The key for each link
 *     is used as its CSS class. Each link should be itself an array, with the
 *     following elements:
 *     - title: The link text.
 *     - url: (optional) The url object to link to. If omitted, no a tag is
 *       printed out.
 *     - html: (optional) Whether or not 'title' is HTML. If set, the title
 *       will not be passed through
 *       \Drupal\Component\Utility\String::checkPlain().
 *     - attributes: (optional) Attributes for the anchor, or for the <span>
 *       tag used in its place if no 'href' is supplied. If element 'class' is
 *       included, it must be an array of one or more class names.
 *     If the 'href' element is supplied, the entire link array is passed to
 *     l() as its $options parameter.
 *   - attributes: A keyed array of attributes for the UL containing the
 *     list of links.
 *   - set_active_class: (optional) Whether each link should compare the
 *     route_name + route_parameters or href (path), language and query options
 *     to the current URL, to determine whether the link is "active". If so, an
 *     "active" class will be applied to the list item containing the link, as
 *     well as the link itself. It is important to use this sparingly since it
 *     is usually unnecessary and requires extra processing.
 *     For anonymous users, the "active" class will be calculated on the server,
 *     because most sites serve each anonymous user the same cached page anyway.
 *     For authenticated users, the "active" class will be calculated on the
 *     client (through JavaScript), only data- attributes are added to list
 *     items and contained links, to prevent breaking the render cache. The
 *     JavaScript is added in system_page_attachments().
 *   - heading: (optional) A heading to precede the links. May be an
 *     associative array or a string. If it's an array, it can have the
 *     following elements:
 *     - text: The heading text.
 *     - level: The heading level (e.g. 'h2', 'h3').
 *     - attributes: (optional) An array of the CSS attributes for the heading.
 *     When using a string it will be used as the text of the heading and the
 *     level will default to 'h2'. Headings should be used on navigation menus
 *     and any list of links that consistently appears on multiple pages. To
 *     make the heading invisible use the 'visually-hidden' CSS class. Do not
 *     use 'display:none', which removes it from screen readers and assistive
 *     technology. Headings allow screen reader and keyboard only users to
 *     navigate to or skip the links. See
 *     http://juicystudio.com/article/screen-readers-display-none.php and
 *     http://www.w3.org/TR/WCAG-TECHS/H42.html for more information.
 *
 * Unfortunately links templates duplicate the "active" class handling of l()
 * and LinkGenerator::generate() because it needs to be able to set the "active"
 * class not on the links themselves ("a" tags), but on the list items ("li"
 * tags) that contain the links. This is necessary for CSS to be able to style
 * list items differently when the link is active, since CSS does not yet allow
 * one to style list items only if it contains a certain element with a certain
 * class. I.e. we cannot yet convert this jQuery selector to a CSS selector:
 *   jQuery('li:has("a.active")')
 *
 * @see \Drupal\Core\Utility\LinkGenerator
 * @see \Drupal\Core\Utility\LinkGenerator::generate()
 * @see system_page_attachments()
 */
function template_preprocess_links(&$variables) {
  $links = $variables['links'];
  $heading = &$variables['heading'];

  if (!empty($links)) {
    // Prepend the heading to the list, if any.
    if (!empty($heading)) {
      // Convert a string heading into an array, using a H2 tag by default.
      if (is_string($heading)) {
        $heading = array('text' => $heading);
      }
      // Merge in default array properties into $heading.
      $heading += array(
        'level' => 'h2',
        'attributes' => array(),
      );
      // Convert the attributes array into an Attribute object.
      $heading['attributes'] = new Attribute($heading['attributes']);
      $heading['text'] = String::checkPlain($heading['text']);
    }

    $variables['links'] = array();
    foreach ($links as $key => $link) {
      $item = array();
      $link += array(
        'ajax' => NULL,
        'url' => NULL,
      );

      $li_attributes = array();
      $keys = ['title', 'url'];
      $link_element = array(
        '#type' => 'link',
        '#title' => $link['title'],
        '#options' => array_diff_key($link, array_combine($keys, $keys)),
        '#url' => $link['url'],
        '#ajax' => $link['ajax'],
      );

      // Handle links and ensure that the active class is added on the LIs, but
      // only if the 'set_active_class' option is not empty.
      if (isset($link['url'])) {
        if (!empty($variables['set_active_class'])) {

          // Also enable set_active_class for the contained link.
          $link_element['#options']['set_active_class'] = TRUE;

          if (!empty($link['language'])) {
            $li_attributes['hreflang'] = $link['language']->getId();
          }

          // Add a "data-drupal-link-query" attribute to let the
          // drupal.active-link library know the query in a standardized manner.
          if (!empty($link['query'])) {
            $query = $link['query'];
            ksort($query);
            $li_attributes['data-drupal-link-query'] = Json::encode($query);
          }

          /** @var \Drupal\Core\Url $url */
          $url = $link['url'];
          if ($url->isRouted()) {
            // Add a "data-drupal-link-system-path" attribute to let the
            // drupal.active-link library know the path in a standardized manner.
            $system_path = $url->getInternalPath();
            // @todo System path is deprecated - use the route name and parameters.
            // Special case for the front page.
            $li_attributes['data-drupal-link-system-path'] = $system_path == '' ? '<front>' : $system_path;
          }
        }

        $item['link'] = $link_element;
      }

      // Handle title-only text items.
      $text = (!empty($link['html']) ? $link['title'] : String::checkPlain($link['title']));
      $item['text'] = $text;
      if (isset($link['attributes'])) {
        $item['text_attributes'] = new Attribute($link['attributes']);
      }

      // Handle list item attributes.
      $item['attributes'] = new Attribute($li_attributes);

      // Add the item to the list of links.
      $variables['links'][$key] = $item;
    }
  }
}

/**
 * Prepares variables for image templates.
 *
 * Default template: image.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - uri: Either the path of the image file (relative to base_path()) or a
 *     full URL.
 *   - width: The width of the image (if known).
 *   - height: The height of the image (if known).
 *   - alt: The alternative text for text-based browsers. HTML 4 and XHTML 1.0
 *     always require an alt attribute. The HTML 5 draft allows the alt
 *     attribute to be omitted in some cases. Therefore, this variable defaults
 *     to an empty string, but can be set to NULL for the attribute to be
 *     omitted. Usually, neither omission nor an empty string satisfies
 *     accessibility requirements, so it is strongly encouraged for code
 *     calling _theme('image') to pass a meaningful value for this variable.
 *     - http://www.w3.org/TR/REC-html40/struct/objects.html#h-13.8
 *     - http://www.w3.org/TR/xhtml1/dtds.html
 *     - http://dev.w3.org/html5/spec/Overview.html#alt
 *   - title: The title text is displayed when the image is hovered in some
 *     popular browsers.
 *   - attributes: Associative array of attributes to be placed in the img tag.
 *   - srcset: Array of multiple URIs and sizes/multipliers.
 *   - sizes: The sizes attribute for viewport-based selection of images.
 *     - http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content.html#introduction-3:viewport-based-selection-2
 */
function template_preprocess_image(&$variables) {
  if (!empty($variables['uri'])) {
    $variables['attributes']['src'] = file_create_url($variables['uri']);
  }
  // Generate a srcset attribute conforming to the spec at
  // http://www.w3.org/html/wg/drafts/html/master/embedded-content.html#attr-img-srcset
  if (!empty($variables['srcset'])) {
    $srcset = array();
    foreach ($variables['srcset'] as $src) {
      // URI is mandatory.
      $source = file_create_url($src['uri']);
      if (isset($src['width']) && !empty($src['width'])) {
        $source .= ' ' . $src['width'];
      }
      elseif (isset($src['multiplier']) && !empty($src['multiplier'])) {
        $source .= ' ' . $src['multiplier'];
      }
      $srcset[] = $source;
    }
    $variables['attributes']['srcset'] = implode(', ', $srcset);
  }

  foreach (array('width', 'height', 'alt', 'title', 'sizes') as $key) {
    if (isset($variables[$key])) {
      // If the property has already been defined in the attributes,
      // do not override, including NULL.
      if (array_key_exists($key, $variables['attributes'])) {
        continue;
      }
      $variables['attributes'][$key] = $variables[$key];
    }
  }
}

/**
 * Prepares variables for table templates.
 *
 * Default template: table.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - header: An array containing the table headers. Each element of the array
 *     can be either a localized string or an associative array with the
 *     following keys:
 *     - data: The localized title of the table column.
 *     - field: The database field represented in the table column (required
 *       if user is to be able to sort on this column).
 *     - sort: A default sort order for this column ("asc" or "desc"). Only
 *       one column should be given a default sort order because table sorting
 *       only applies to one column at a time.
 *     - class: An array of values for the 'class' attribute. In particular,
 *       the least important columns that can be hidden on narrow and medium
 *       width screens should have a 'priority-low' class, referenced with the
 *       RESPONSIVE_PRIORITY_LOW constant. Columns that should be shown on
 *       medium+ wide screens should be marked up with a class of
 *       'priority-medium', referenced by with the RESPONSIVE_PRIORITY_MEDIUM
 *       constant. Themes may hide columns with one of these two classes on
 *       narrow viewports to save horizontal space.
 *     - Any HTML attributes, such as "colspan", to apply to the column header
 *       cell.
 *   - rows: An array of table rows. Every row is an array of cells, or an
 *     associative array with the following keys:
 *     - data: An array of cells.
 *     - Any HTML attributes, such as "class", to apply to the table row.
 *     - no_striping: A Boolean indicating that the row should receive no
 *       'even / odd' styling. Defaults to FALSE.
 *     Each cell can be either a string or an associative array with the
 *     following keys:
 *     - data: The string to display in the table cell.
 *     - header: Indicates this cell is a header.
 *     - Any HTML attributes, such as "colspan", to apply to the table cell.
 *     Here's an example for $rows:
 *     @code
 *     $rows = array(
 *       // Simple row
 *       array(
 *         'Cell 1', 'Cell 2', 'Cell 3'
 *       ),
 *       // Row with attributes on the row and some of its cells.
 *       array(
 *         'data' => array('Cell 1', array('data' => 'Cell 2', 'colspan' => 2)), 'class' => array('funky')
 *       ),
 *     );
 *     @endcode
 *   - footer: An array of table rows which will be printed within a <tfoot>
 *     tag, in the same format as the rows element (see above).
 *   - attributes: An array of HTML attributes to apply to the table tag.
 *   - caption: A localized string to use for the <caption> tag.
 *   - colgroups: An array of column groups. Each element of the array can be
 *     either:
 *     - An array of columns, each of which is an associative array of HTML
 *       attributes applied to the COL element.
 *     - An array of attributes applied to the COLGROUP element, which must
 *       include a "data" attribute. To add attributes to COL elements, set the
 *       "data" attribute with an array of columns, each of which is an
 *       associative array of HTML attributes.
 *     Here's an example for $colgroup:
 *     @code
 *     $colgroup = array(
 *       // COLGROUP with one COL element.
 *       array(
 *         array(
 *           'class' => array('funky'), // Attribute for the COL element.
 *         ),
 *       ),
 *       // Colgroup with attributes and inner COL elements.
 *       array(
 *         'data' => array(
 *           array(
 *             'class' => array('funky'), // Attribute for the COL element.
 *           ),
 *         ),
 *         'class' => array('jazzy'), // Attribute for the COLGROUP element.
 *       ),
 *     );
 *     @endcode
 *     These optional tags are used to group and set properties on columns
 *     within a table. For example, one may easily group three columns and
 *     apply same background style to all.
 *   - sticky: Use a "sticky" table header.
 *   - empty: The message to display in an extra row if table does not have any
 *     rows.
 */
function template_preprocess_table(&$variables) {
  $is_sticky = !empty($variables['sticky']);
  $is_responsive = !empty($variables['responsive']);

  // Format the table columns:
  if (!empty($variables['colgroups'])) {
    foreach ($variables['colgroups'] as &$colgroup) {
      // Check if we're dealing with a simple or complex column
      if (isset($colgroup['data'])) {
        $cols = $colgroup['data'];
        unset($colgroup['data']);
        $colgroup_attributes = $colgroup;
      }
      else {
        $cols = $colgroup;
        $colgroup_attributes = array();
      }
      $colgroup = array();
      $colgroup['attributes'] = new Attribute($colgroup_attributes);
      $colgroup['cols'] = array();

      // Build columns.
      if (is_array($cols) && !empty($cols)) {
        foreach ($cols as $col_key => $col) {
          $colgroup['cols'][$col_key]['attributes'] = new Attribute($col);
        }
      }
    }
  }

  // Build an associative array of responsive classes keyed by column.
  $responsive_classes = array();

  // Format the table header:
  $ts = array();
  $header_columns = 0;
  if (!empty($variables['header'])) {
    $ts = tablesort_init($variables['header']);

    // Use a separate index with responsive classes as headers
    // may be associative.
    $responsive_index = -1;
    foreach ($variables['header'] as $col_key => $cell) {
      // Increase the responsive index.
      $responsive_index++;

      if (!is_array($cell)) {
        $header_columns++;
        $cell_content = $cell;
        $cell_attributes = new Attribute();
        $is_header = TRUE;
      }
      else {
        if (isset($cell['colspan'])) {
          $header_columns += $cell['colspan'];
        }
        else {
          $header_columns++;
        }
        $cell_content = '';
        if (isset($cell['data'])) {
          $cell_content = $cell['data'];
          unset($cell['data']);
        }