theme.inc

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

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

/**
 * Mark content as read.
 */
define('MARK_READ', 0);

/**
 * Mark content as being new.
 */
define('MARK_NEW', 1);

/**
 * Mark content as being updated.
 */
define('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).
 */
define('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).
 */
define('RESPONSIVE_PRIORITY_LOW', 'priority-low');

/**
 * @} End of "Content markers".
 */

/**
 * Determines if a theme is available to use.
 *
 * @param $theme
 *   Either the name of a theme or a full theme object.
 *
 * @return
 *   Boolean TRUE if the theme is enabled or is the site administration theme;
 *   FALSE otherwise.
 */
function backdrop_theme_access($theme) {
  if (is_object($theme)) {
    return _backdrop_theme_access($theme);
  }
  else {
    $themes = list_themes();
    return isset($themes[$theme]) && _backdrop_theme_access($themes[$theme]);
  }
}

/**
 * Helper function for determining access to a theme.
 *
 * @see backdrop_theme_access()
 */
function _backdrop_theme_access($theme) {
  $admin_theme = config_get('system.core', 'admin_theme');
  return !empty($theme->status) || ($admin_theme && $theme->name == $admin_theme);
}

/**
 * Initializes the theme system by loading the theme.
 */
function backdrop_theme_initialize() {
  global $theme, $theme_key;

  // If $theme is already set, assume the others are set, too, and do nothing
  if (isset($theme)) {
    return;
  }

  backdrop_bootstrap(BACKDROP_BOOTSTRAP_DATABASE);
  $themes = list_themes();

  // Load the default theme.
  $theme = config_get('system.core', 'theme_default');

  // Allow modules to override the theme. Validation has already been performed
  // inside menu_get_custom_theme(), so we do not need to check it again here.
  $custom_theme = function_exists('menu_get_custom_theme') ? menu_get_custom_theme() : NULL;
  $theme = !empty($custom_theme) ? $custom_theme : $theme;

  // Store the identifier for retrieving theme settings with.
  $theme_key = $theme;

  // Find all our ancestor themes and put them in an array.
  $base_themes = array();
  $ancestor = $theme;
  while ($ancestor && isset($themes[$ancestor]->base_theme)) {
    $ancestor = $themes[$ancestor]->base_theme;
    $base_themes[] = $themes[$ancestor];
  }
  _backdrop_theme_initialize($themes[$theme], array_reverse($base_themes));

  // Themes can have alter functions, so reset the backdrop_alter() cache.
  backdrop_static_reset('backdrop_alter');

  // Provide the page with information about the theme that's used, so that a
  // later Ajax request can be rendered using the same theme.
  // @see ajax_base_page_theme()
  $setting['ajaxPageState'] = array(
    'theme' => $theme_key,
    'theme_token' => backdrop_get_token($theme_key),
  );
  backdrop_add_js($setting, 'setting');
}

/**
 * Initializes the theme system given already loaded information.
 *
 * This function is useful to initialize a theme when no database is present.
 *
 * @param stdClass $theme
 *   An object with the following information:
 *   - filename: The .info file for this theme. The 'path' to the theme will be
 *     in this file's directory.
 *   - owner: The path to the .theme file or the .engine file to load for the
 *     theme.
 *   - stylesheet: (optional) The primary stylesheet for the theme.
 *   - engine: (optional) The name of theme engine to use.
 * @param array $base_themes
 *   An optional array of objects that represent the 'base theme' if the theme
 *   is meant to be derivative of another theme. It requires the same
 *   information as the $theme object. It should be in 'oldest first' order,
 *   meaning the top level of the chain will be first.
 * @param string $registry_callback
 *   The callback to invoke to set the theme registry.
 */
function _backdrop_theme_initialize($theme, $base_themes = array(), $registry_callback = '_theme_load_registry') {
  global $theme_info, $base_theme_info, $theme_engine, $theme_path;
  $theme_info = $theme;
  $base_theme_info = $base_themes;

  $theme_path = dirname($theme->filename);

  // Prepare stylesheets from this theme as well as all ancestor themes.
  // We work it this way so that we can have child themes override parent
  // theme stylesheets.
  $final_stylesheets = array();

  // Grab stylesheets from base theme.
  foreach ($base_themes as $base) {
    if (!empty($base->stylesheets)) {
      foreach ($base->stylesheets as $media => $stylesheets) {
        foreach ($stylesheets as $name => $stylesheet) {
          $final_stylesheets[$media][$name] = $stylesheet;
        }
      }
    }
  }

  // Add stylesheets used by this theme.
  if (!empty($theme->stylesheets)) {
    foreach ($theme->stylesheets as $media => $stylesheets) {
      foreach ($stylesheets as $name => $stylesheet) {
        $final_stylesheets[$media][$name] = $stylesheet;
      }
    }
  }

  // And now add the stylesheets properly.
  foreach ($final_stylesheets as $media => $stylesheets) {
    foreach ($stylesheets as $stylesheet) {
      backdrop_add_css($stylesheet, array('group' => CSS_THEME, 'every_page' => TRUE, 'media' => $media));
    }
  }

  // Do basically the same as the above for scripts.
  $final_scripts = array();

  // Grab scripts from base theme.
  foreach ($base_themes as $base) {
    if (!empty($base->scripts)) {
      foreach ($base->scripts as $key => $value) {
        if (is_string($value)) {
          // Empty scope defaults to 'header'.
          $final_scripts['header'][$key] = $value;
        }
        else {
          foreach ($value as $name => $script) {
            $final_scripts[$key][$name] = $script;
          }
        }
      }
    }
  }

  // Add scripts used by this theme.
  if (!empty($theme->scripts)) {
    foreach ($theme->scripts as $key => $value) {
      if (is_string($value)) {
        // Empty scope defaults to 'header'.
        $final_scripts['header'][$key] = $value;
      }
      else {
        foreach ($value as $name => $script) {
          $final_scripts[$key][$name] = $script;
        }
      }
    }
  }

  // Add scripts used by this theme.
  foreach ($final_scripts as $scope => $scripts) {
    foreach ($scripts as $script) {
      backdrop_add_js($script, array('group' => JS_THEME, 'every_page' => TRUE, 'scope' => $scope));
    }
  }

  $theme_engine = NULL;

  // Initialize the theme.
  if (isset($theme->engine)) {
    // Include the engine.
    include_once BACKDROP_ROOT . '/' . $theme->owner;

    $theme_engine = $theme->engine;
    if (function_exists($theme_engine . '_init')) {
      foreach ($base_themes as $base) {
        call_user_func($theme_engine . '_init', $base);
      }
      call_user_func($theme_engine . '_init', $theme);
    }
  }
  else {
    // include non-engine theme files
    foreach ($base_themes as $base) {
      // Include the theme file or the engine.
      if (!empty($base->owner)) {
        include_once BACKDROP_ROOT . '/' . $base->owner;
      }
    }
    // and our theme gets one too.
    if (!empty($theme->owner)) {
      include_once BACKDROP_ROOT . '/' . $theme->owner;
    }
  }

  if (isset($registry_callback)) {
    _theme_registry_callback($registry_callback, array($theme, $base_themes, $theme_engine));
  }
}

/**
 * Gets the theme registry.
 *
 * @param $complete
 *   Optional boolean to indicate whether to return the complete theme registry
 *   array or an instance of the ThemeRegistry class. If TRUE, the complete
 *   theme registry array will be returned. This is useful if you want to
 *   foreach over the whole registry, use array_* functions or inspect it in a
 *   debugger. If FALSE, an instance of the ThemeRegistry class will be
 *   returned, this provides an ArrayObject which allows it to be accessed
 *   with array syntax and  isset(), and should be more lightweight
 *   than the full registry. Defaults to TRUE.
 *
 * @return array
 *   The complete theme registry array, or an instance of the ThemeRegistry
 *   class.
 */
function theme_get_registry($complete = TRUE) {
  // Use the advanced backdrop_static() pattern, since this is called very often.
  static $backdrop_static_fast;
  if (!isset($backdrop_static_fast)) {
    $backdrop_static_fast['registry'] = &backdrop_static('theme_get_registry');
  }
  $theme_registry = &$backdrop_static_fast['registry'];

  // Initialize the theme, if this is called early in the bootstrap, or after
  // static variables have been reset.
  if (!is_array($theme_registry)) {
    backdrop_theme_initialize();
    $theme_registry = array();
  }

  $key = (int) $complete;

  if (!isset($theme_registry[$key])) {
    list($callback, $arguments) = _theme_registry_callback();
    if (!$complete) {
      $arguments[] = FALSE;
    }
    $theme_registry[$key] = call_user_func_array($callback, $arguments);
  }

  return $theme_registry[$key];
}

/**
 * Sets the callback that will be used by theme_get_registry().
 *
 * @param $callback
 *   The name of the callback function.
 * @param $arguments
 *   The arguments to pass to the function.
 *
 * @return array
 *   The currently set theme registry callback and arguments.
 */
function _theme_registry_callback($callback = NULL, array $arguments = array()) {
  static $stored;
  if (isset($callback)) {
    $stored = array($callback, $arguments);
  }
  return $stored;
}

/**
 * Gets the theme_registry cache; if it doesn't exist, builds it.
 *
 * @param $theme
 *   The loaded $theme object as returned by list_themes().
 * @param $base_themes
 *   An array of loaded $theme objects representing the ancestor themes in
 *   oldest first order.
 * @param $theme_engine
 *   The name of the theme engine.
 * @param $complete
 *   Whether to load the complete theme registry or an instance of the
 *   ThemeRegistry class.
 *
 * @return
 *   The theme registry array, or an instance of the ThemeRegistry class.
 */
function _theme_load_registry($theme, $base_themes = NULL, $theme_engine = NULL, $complete = TRUE) {
  if ($complete) {
    // Check the theme registry cache; if it exists, use it.
    $cached = cache()->get("theme_registry:$theme->name");
    if (isset($cached->data)) {
      $registry = $cached->data;
    }
    else {
      // If not, build one and cache it.
      $registry = _theme_build_registry($theme, $base_themes, $theme_engine);
      // Only persist this registry if all modules are loaded. This assures a
      // complete set of theme hooks.
      if (module_load_all(NULL)) {
        _theme_save_registry($theme, $registry);
      }
    }
    return $registry;
  }
  else {
    return new ThemeRegistry('theme_registry:runtime:' . $theme->name, 'cache');
  }
}

/**
 * Writes the theme_registry cache into the database.
 */
function _theme_save_registry($theme, $registry) {
  cache()->set("theme_registry:$theme->name", $registry);
}

/**
 * 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 backdrop_theme_rebuild() {
  backdrop_static_reset('theme_get_registry');
  cache()->deletePrefix('theme_registry');
}

/**
 * Builds the run-time theme registry.
 *
 * Extends BackdropCacheArray to allow the theme registry to be accessed as a
 * complete registry, while internally caching only the parts of the registry
 * that are actually in use on the site. On cache misses the complete
 * theme registry is loaded and used to update the run-time cache.
 */
class ThemeRegistry Extends BackdropCacheArray {

  /**
   * Whether the partial registry can be persisted to the cache.
   *
   * This is only allowed if all modules and the request method is GET. theme()
   * should be very rarely called on POST requests and this avoids polluting
   * the runtime cache.
   */
  protected $persistable;

  /**
   * The complete theme registry array.
   */
  protected $completeRegistry;

  function __construct($cid, $bin) {
    $this->cid = $cid;
    $this->bin = $bin;
    $this->persistable = module_load_all(NULL) && $_SERVER['REQUEST_METHOD'] == 'GET';

    if ($this->persistable && $cached = cache($this->bin)->get($this->cid)) {
      $data = $cached->data;
    }
    else {
      // If there is no runtime cache stored, fetch the full theme registry,
      // but then initialize each value to NULL. This allows offsetExists()
      // to function correctly on non-registered theme hooks without triggering
      // a call to resolveCacheMiss().
      $data = $this->initializeRegistry();
      if ($this->persistable) {
        $this->set($data);
      }
    }
    $this->storage = $data;
  }

  /**
   * Initializes the full theme registry.
   *
   * @return
   *   An array with the keys of the full theme registry, but the values
   *   initialized to NULL.
   */
  function initializeRegistry() {
    $this->completeRegistry = theme_get_registry();

    return array_fill_keys(array_keys($this->completeRegistry), NULL);
  }

  public function offsetExists($offset) {
    // Since the theme registry allows for theme hooks to be requested that
    // are not registered, just check the existence of the key in the registry.
    // Use array_key_exists() here since a NULL value indicates that the theme
    // hook exists but has not yet been requested.
    return array_key_exists($offset, $this->storage);
  }

  public function offsetGet($offset) {
    // If the offset is set but empty, it is a registered theme hook that has
    // not yet been requested. Offsets that do not exist at all were not
    // registered in hook_theme().
    if (isset($this->storage[$offset])) {
      return $this->storage[$offset];
    }
    elseif (array_key_exists($offset, $this->storage)) {
      return $this->resolveCacheMiss($offset);
    }
    return NULL;
  }

  public function resolveCacheMiss($offset) {
    if (!isset($this->completeRegistry)) {
      $this->completeRegistry = theme_get_registry();
    }
    $this->storage[$offset] = $this->completeRegistry[$offset];
    if ($this->persistable) {
      $this->persist($offset);
    }
    return $this->storage[$offset];
  }

  public function set($data, $lock = TRUE) {
    $lock_name = $this->cid . ':' . $this->bin;
    if (!$lock || lock_acquire($lock_name)) {
      if ($cached = cache($this->bin)->get($this->cid)) {
        // Use array merge instead of union so that filled in values in $data
        // overwrite empty values in the current cache.
        $data = array_merge($cached->data, $data);
      }
      else {
        $registry = $this->initializeRegistry();
        $data = array_merge($registry, $data);
      }
      cache($this->bin)->set($this->cid, $data);
      if ($lock) {
        lock_release($lock_name);
      }
    }
  }
}

/**
 * Process a single implementation of hook_theme().
 *
 * @param $cache
 *   The theme registry that will eventually be cached; It is an associative
 *   array keyed by theme hooks, whose values are associative arrays describing
 *   the hook:
 *   - 'type': The passed-in $type.
 *   - 'theme path': The passed-in $path.
 *   - 'function': The name of the function generating output for this theme
 *     hook. Either defined explicitly in hook_theme() or, if neither 'function'
 *     nor 'template' is defined, then the default theme function name is used.
 *     The default theme function name is the theme hook prefixed by either
 *     'theme_' for modules or '$name_' for everything else. If 'function' is
 *     defined, 'template' is not used.
 *   - 'template': The filename of the template generating output for this
 *     theme hook. The template is in the directory defined by the 'path' key of
 *     hook_theme() or defaults to $path.
 *   - 'variables': The variables for this theme hook as defined in
 *     hook_theme(). If there is more than one implementation and 'variables' is
 *     not specified in a later one, then the previous definition is kept.
 *   - 'render element': The renderable element for this theme hook as defined
 *     in hook_theme(). If there is more than one implementation and
 *     'render element' is not specified in a later one, then the previous
 *     definition is kept.
 *   - 'preprocess functions': See theme() for detailed documentation.
 * @param $name
 *   The name of the module, theme engine, base theme engine, theme or base
 *   theme implementing hook_theme().
 * @param $type
 *   One of 'module', 'theme_engine', 'base_theme_engine', 'theme', or
 *   'base_theme'. Unlike regular hooks that can only be implemented by modules,
 *   each of these can implement hook_theme(). _theme_process_registry() is
 *   called in aforementioned order and new entries override older ones. For
 *   example, if a theme hook is both defined by a module and a theme, then the
 *   definition in the theme will be used.
 * @param $theme
 *   The loaded $theme object as returned from list_themes().
 * @param $path
 *   The directory where $name is. For example, modules/system or
 *   themes/bartik.
 *
 * @see theme()
 * @see _theme_build_registry()
 * @see hook_theme()
 * @see list_themes()
 */
function _theme_process_registry(&$cache, $name, $type, $theme, $path) {
  $result = array();

  $hook_defaults = array(
    'variables' => TRUE,
    'render element' => TRUE,
    'pattern' => TRUE,
    'base hook' => TRUE,
  );

  // Invoke the hook_theme() implementation, process what is returned, and
  // merge it into $cache.
  $function = $name . '_theme';
  if (function_exists($function)) {
    $result = $function($cache, $type, $theme, $path);
    foreach ($result as $hook => $info) {
      // When a theme or engine overrides a module's theme function
      // $result[$hook] will only contain key/value pairs for information being
      // overridden.  Pull the rest of the information from what was defined by
      // an earlier hook.

      // Fill in the type and path of the module, theme, or engine that
      // implements this theme function.
      $result[$hook]['type'] = $type;
      $result[$hook]['theme path'] = $path;

      // If function and file are omitted, default to standard naming
      // conventions.
      if (!isset($info['template']) && !isset($info['function'])) {
        $result[$hook]['function'] = ($type == 'module' ? 'theme_' : $name . '_') . $hook;
      }

      if (isset($cache[$hook]['includes'])) {
        $result[$hook]['includes'] = $cache[$hook]['includes'];
      }

      // If the theme implementation defines a file, then also use the path
      // that it defined. Otherwise use the default path. This allows
      // system.module to declare theme functions on behalf of core .include
      // files.
      if (isset($info['file'])) {
        $include_file = isset($info['path']) ? $info['path'] : $path;
        $include_file .= '/' . $info['file'];
        include_once BACKDROP_ROOT . '/' . $include_file;
        $result[$hook]['includes'][] = $include_file;
      }

      // If the default keys are not set, use the default values registered
      // by the module.
      if (isset($cache[$hook])) {
        $result[$hook] += array_intersect_key($cache[$hook], $hook_defaults);
      }

      // The following apply only to theme hooks implemented as templates.
      if (isset($info['template'])) {
        // Prepend the current theme path when none is set.
        if (!isset($info['path'])) {
          $result[$hook]['template'] = $path . '/' . $info['template'];
        }
      }

      // Allow variable preprocessors for all theme hooks, whether the hook is
      // implemented as a template or as a function.
      // Check for existing variable preprocessors and ensure they're in the
      // expected format.
      if (!isset($info['preprocess functions']) || !is_array($info['preprocess functions'])) {
        $info['preprocess functions'] = array();
        $prefixes = array();

        if ($type == 'module') {
          // Default variable preprocessor prefix.
          $prefixes[] = 'template';
          // Add all modules so they can intervene with their own variable
          // preprocessors. This allows them to provide variable preprocessors
          // even if they are not the owner of the current hook.
          $prefixes += module_list();
        }
        elseif ($type == 'theme_engine' || $type == 'base_theme_engine') {
          // Theme engines get an extra set that come before the normally
          // named variable preprocessors.
          $prefixes[] = $name . '_engine';
          // The theme engine registers on behalf of the theme using the
          // theme's name.
          $prefixes[] = $theme;
        }
        else {
          // This applies when the theme manually registers their own variable
          // preprocessors.
          $prefixes[] = $name;
        }

        foreach ($prefixes as $prefix) {
          // Only use non-hook-specific variable preprocessors for theme hooks
          // implemented as templates. See theme().
          if (isset($info['template']) && function_exists($prefix . '_preprocess')) {
            $info['preprocess functions'][] = $prefix . '_preprocess';
          }
          if (function_exists($prefix . '_preprocess_' . $hook)) {
            $info['preprocess functions'][] = $prefix . '_preprocess_' . $hook;
          }
        }
      }
      // Check for the override flag and prevent the cached variable
      // preprocessors from being used. This allows themes or theme engines to
      // remove variable preprocessors set earlier in the registry build.
      if (!empty($info['override preprocess functions'])) {
        // Flag not needed inside the registry.
        unset($result[$hook]['override preprocess functions']);
      }
      elseif (isset($cache[$hook]['preprocess functions']) && is_array($cache[$hook]['preprocess functions'])) {
        $info['preprocess functions'] = array_merge($cache[$hook]['preprocess functions'], $info['preprocess functions']);
      }
      $result[$hook]['preprocess functions'] = $info['preprocess functions'];
    }

    // Merge the newly created theme hooks into the existing cache.
    $cache = $result + $cache;
  }

  // Let themes have variable preprocessors even if they didn't register a
  // template.
  if ($type == 'theme' || $type == 'base_theme') {
    foreach ($cache as $hook => $info) {
      // Check only if not registered by the theme or engine.
      if (empty($result[$hook])) {
        if (!isset($info['preprocess functions'])) {
          $cache[$hook]['preprocess functions'] = array();
        }
        // Only use non-hook-specific variable preprocessors for theme hooks
        // implemented as templates. See theme().
        if (isset($info['template']) && function_exists($name . '_preprocess')) {
          $cache[$hook]['preprocess functions'][] = $name . '_preprocess';
        }
        if (function_exists($name . '_preprocess_' . $hook)) {
          $cache[$hook]['preprocess functions'][] = $name . '_preprocess_' . $hook;
          $cache[$hook]['theme path'] = $path;
        }
        // Ensure uniqueness.
        $cache[$hook]['preprocess functions'] = array_unique($cache[$hook]['preprocess functions']);
      }
    }
  }
}

/**
 * Builds the theme registry cache.
 *
 * @param $theme
 *   The loaded $theme object as returned by list_themes().
 * @param array $base_themes
 *   An array of loaded $theme objects representing the ancestor themes in
 *   oldest first order.
 * @param string $theme_engine
 *   The name of the theme engine.
 *
 * @return array
 *   The completely built theme registry.
 */
function _theme_build_registry($theme, $base_themes, $theme_engine) {
  $cache = array();
  $modules_loaded = module_load_all(NULL);

  // First, process the theme hooks advertised by modules. This will
  // serve as the basic registry. Since the list of enabled modules is the same
  // regardless of the theme used, this is cached in its own entry to save
  // building it for every theme.
  if ($modules_loaded && $cached = cache()->get('theme_registry:build:modules')) {
    $cache = $cached->data;
  }
  else {
    foreach (module_implements('theme') as $module) {
      _theme_process_registry($cache, $module, 'module', $module, backdrop_get_path('module', $module));
    }
    // Only cache this registry if all modules are loaded.
    if ($modules_loaded) {
      cache()->set('theme_registry:build:modules', $cache);
    }
  }

  // Process each base theme.
  foreach ($base_themes as $base) {
    // If the base theme uses a theme engine, process its hooks.
    $base_path = dirname($base->filename);
    if ($theme_engine) {
      _theme_process_registry($cache, $theme_engine, 'base_theme_engine', $base->name, $base_path);
    }
    _theme_process_registry($cache, $base->name, 'base_theme', $base->name, $base_path);
  }

  // And then the same thing, but for the theme.
  if ($theme_engine) {
    _theme_process_registry($cache, $theme_engine, 'theme_engine', $theme->name, dirname($theme->filename));
  }

  // Finally, hooks provided by the theme itself.
  _theme_process_registry($cache, $theme->name, 'theme', $theme->name, dirname($theme->filename));

  // Let modules alter the registry.
  backdrop_alter('theme_registry', $cache);

  // Optimize the registry to not have empty arrays for functions.
  foreach ($cache as $hook => $info) {
    if (empty($info['preprocess functions'])) {
      unset($cache[$hook]['preprocess functions']);
    }
  }
  return $cache;
}

/**
 * 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
 *   An associative array of the currently available themes. The keys are the
 *   themes' machine names and the values are objects having the following
 *   properties:
 *   - filename: The filepath and name of the .info file.
 *   - name: The machine name of the theme.
 *   - status: 1 for enabled, 0 for disabled themes.
 *   - info: The contents of the .info file.
 *   - stylesheets: A two dimensional array, using the first key for the
 *     media attribute (e.g. 'all'), the second for the name of the file
 *     (e.g. style.css). The value is a complete filepath (e.g.
 *     themes/bartik/style.css). Not set if no stylesheets are defined in the
 *     .info file.
 *   - scripts: An associative array of JavaScripts, using the filename as key
 *     and the complete filepath as value. Not set if no scripts are defined in
 *     the .info file.
 *   - prefix: The base theme engine prefix.
 *   - engine: The machine name of the theme engine.
 *   - base_theme: If this is a sub-theme, the machine name of the base theme
 *     defined in the .info file. Otherwise, the element is not set.
 *   - base_themes: If this is a sub-theme, an associative array of the
 *     base-theme ancestors of this theme, starting with this theme's base
 *     theme, then the base theme's own base theme, etc. Each entry has an
 *     array key equal to the theme's machine name, and a value equal to the
 *     human-readable theme name; if a theme with matching machine name does
 *     not exist in the system, the value will instead be NULL (and since the
 *     system would not know whether that theme itself has a base theme, that
 *     will end the array of base themes). This is not set if the theme is not
 *     a sub-theme.
 *   - sub_themes: An associative array of themes on the system that are
 *     either direct sub-themes (that is, they declare this theme to be
 *     their base theme), direct sub-themes of sub-themes, etc. The keys are
 *     the themes' machine names, and the values are the themes' human-readable
 *     names. This element is not set if there are no themes on the system that
 *     declare this theme as their base theme.
*/
function list_themes($refresh = FALSE) {
  $list = &backdrop_static(__FUNCTION__, array());

  if ($refresh) {
    $list = array();
    system_list_reset();
  }

  if (empty($list)) {
    $list = array();
    $themes = array();
    // Extract from the database only when it is available.
    // Also check that the site is not in the middle of an install or update.
    if (!defined('MAINTENANCE_MODE')) {
      try {
        $themes = system_list('theme');
      }
      catch (Exception $e) {
        // If the database is not available, rebuild the theme data.
        $themes = _system_rebuild_theme_data();
      }
    }
    else {
      // Scan the installation when the database should not be read.
      $themes = _system_rebuild_theme_data();
    }

    foreach ($themes as $theme) {
      foreach ($theme->info['stylesheets'] as $media => $stylesheets) {
        foreach ($stylesheets as $stylesheet => $path) {
          $theme->stylesheets[$media][$stylesheet] = $path;
        }
      }
      foreach ($theme->info['scripts'] as $script => $path) {
        $theme->scripts[$script] = $path;
      }
      if (isset($theme->info['engine'])) {
        $theme->engine = $theme->info['engine'];
      }
      if (isset($theme->info['base theme'])) {
        $theme->base_theme = $theme->info['base theme'];
      }
      // Status is normally retrieved from the database. Add zero values when
      // read from the installation directory to prevent notices.
      if (!isset($theme->status)) {
        $theme->status = 0;
      }
      $list[$theme->name] = $theme;
    }
  }

  return $list;
}

/**
 * Find all the base themes for the specified theme.
 *
 * Themes can inherit templates and function implementations from earlier themes.
 *
 * @param $themes
 *   An array of available themes.
 * @param $key
 *   The name of the theme whose base we are looking for.
 * @param $used_keys
 *   A recursion parameter preventing endless loops.
 * @return
 *   Returns an array of all of the theme's ancestors; the first element's value
 *   will be NULL if an error occurred.
 */
function backdrop_find_base_themes($themes, $key, $used_keys = array()) {
  $base_key = $themes[$key]->info['base theme'];
  // Does the base theme exist?
  if (!isset($themes[$base_key])) {
    return array($base_key => NULL);
  }

  $current_base_theme = array($base_key => $themes[$base_key]->info['name']);

  // Is the base theme itself a child of another theme?
  if (isset($themes[$base_key]->info['base theme'])) {
    // Do we already know the base themes of this theme?
    if (isset($themes[$base_key]->base_themes)) {
      return $themes[$base_key]->base_themes + $current_base_theme;
    }
    // Prevent loops.
    if (!empty($used_keys[$base_key])) {
      return array($base_key => NULL);
    }
    $used_keys[$base_key] = TRUE;
    return backdrop_find_base_themes($themes, $base_key, $used_keys) + $current_base_theme;
  }
  // If we get here, then this is our parent theme.
  return $current_base_theme;
}

/**
 * Generates themed output.
 *
 * All requests for themed output must go through this function. It examines the
 * request and routes it to the appropriate @link themeable theme function or
 * template @endlink, by checking the theme registry.
 *
 * You can call this function directly, or you can make a call to
 * backdrop_render() by passing a render array with a #theme key, which in turn
 * calls theme(). Either is acceptable. In some situations a render array will
 * be preferable when the ability for other modules to alter the render array is
 * provided.
 *
 * @section sec_theme_hooks Theme Hooks
 * Most commonly, the first argument to this function is the name of the theme
 * hook. For instance, to theme a taxonomy term, the theme hook name is
 * 'taxonomy_term'. Modules register theme hooks within a hook_theme()
 * implementation and provide a default implementation via a function named
 * theme_HOOK() (e.g., theme_taxonomy_term()) or via a template file named
 * according to the value of the 'template' key registered with the theme hook
 * (see hook_theme() for details). Default templates are implemented with the
 * PHPTemplate rendering engine and are named the same as the theme hook, with
 * underscores changed to hyphens, so for the 'taxonomy_term' theme hook, the
 * default template is 'taxonomy-term.tpl.php'.
 *
 * @subsection sub_overriding_theme_hooks Overriding Theme Hooks
 * Themes may also register new theme hooks within a hook_theme()
 * implementation, but it is more common for themes to override default
 * implementations provided by modules than to register entirely new theme
 * hooks. Themes can override a default implementation by implementing a
 * function named THEME_HOOK() (for example, the 'bartik' theme overrides the
 * default implementation of the 'menu_tree' theme hook by implementing a
 * bartik_menu_tree() function), or by adding a template file within its folder
 * structure that follows the template naming structure used by the theme's
 * rendering engine (for example, since the Bartik theme uses the PHPTemplate
 * rendering engine, it overrides the default implementation of the 'page' theme
 * hook by containing a 'page.tpl.php' file within its folder structure).
 *
 * @subsection sub_preprocess_templates Preprocessing for Template Files
 * If the implementation is a template file, several functions are called
 * before the template file is invoked, to modify the $variables array. These
 * fall into the "preprocessing" phase, and are executed (if they exist) in the
 * following order (note that in the following list, HOOK indicates the theme
 * hook name, MODULE indicates a module name, THEME indicates a theme name, and
 * ENGINE indicates a theme engine name):
 * - template_preprocess(&$variables, $hook): Creates a default set of
 *   variables for all theme hooks with template implementations.
 * - template_preprocess_HOOK(&$variables): Should be implemented by the module
 *   that registers the theme hook, to set up default variables.
 * - MODULE_preprocess(&$variables, $hook): hook_preprocess() is invoked on all
 *   implementing modules.
 * - MODULE_preprocess_HOOK(&$variables): hook_preprocess_HOOK() is invoked on
 *   all implementing modules, so that modules that didn't define the theme
 *   hook can alter the variables.
 * - ENGINE_engine_preprocess(&$variables, $hook): Allows the theme engine to
 *   set necessary variables for all theme hooks with template implementations.
 * - ENGINE_engine_preprocess_HOOK(&$variables): Allows the theme engine to set
 *   necessary variables for the particular theme hook.
 * - THEME_preprocess(&$variables, $hook): Allows the theme to set necessary
 *   variables for all theme hooks with template implementations.
 * - THEME_preprocess_HOOK(&$variables): Allows the theme to set necessary
 *   variables specific to the particular theme hook.
 *
 * @subsection sub_preprocess_theme_funcs Preprocessing for Theme Functions
 * If the implementation is a function, only the theme-hook-specific preprocess
 * functions (the ones ending in _HOOK) are called from the list above. This is
 * because theme hooks with function implementations need to be fast, and
 * calling the non-theme-hook-specific preprocess functions for them would incur
 * a noticeable performance penalty.
 *
 * @subsection sub_alternate_suggestions Suggesting Alternate Hooks
 * There are two special variables that these preprocess functions can set:
 * 'theme_hook_suggestion' and 'theme_hook_suggestions'. These will be
 * merged together to form a list of 'suggested' alternate theme hooks to use,
 * in reverse order of priority. theme_hook_suggestion will always be a higher
 * priority than items in theme_hook_suggestions. theme() will use the
 * highest priority implementation that exists. If none exists, theme() will
 * use the implementation for the theme hook it was called with. These
 * suggestions are similar to and are used for similar reasons as calling
 * theme() with an array as the $hook parameter (see below). The difference
 * is whether the suggestions are determined by the code that calls theme() or
 * by a preprocess function.
 *
 * @param $hook
 *   The name of the theme hook to call. If the name contains a
 *   double-underscore ('__') and there isn't an implementation for the full
 *   name, the part before the '__' is checked. This allows a fallback to a
 *   more generic implementation. For example, if theme('links__node', ...) is
 *   called, but there is no implementation of that theme hook, then the
 *   'links' implementation is used. This process is iterative, so if
 *   theme('links__contextual__node', ...) is called, theme() checks for the
 *   following implementations, and uses the first one that exists:
 *   - links__contextual__node
 *   - links__contextual
 *   - links
 *   This allows themes to create specific theme implementations for named
 *   objects and contexts of otherwise generic theme hooks. The $hook parameter
 *   may also be an array, in which case the first theme hook that has an
 *   implementation is used. This allows for the code that calls theme() to
 *   explicitly specify the fallback order in a situation where using the '__'
 *   convention is not desired or is insufficient.
 * @param $variables
 *   An associative array of variables to merge with defaults from the theme
 *   registry, pass to preprocess functions for modification, and finally, pass
 *   to the function or template implementing the theme hook. Alternatively,
 *   this can be a renderable array, in which case, its properties are mapped
 *   to variables expected by the theme hook implementations.
 *
 * @return string
 *   An HTML string representing the themed output.
 *
 * @throws Exception
 *
 * @see backdrop_render()
 * @see themeable
 * @see hook_theme()
 * @see template_preprocess()
 *
 * @since 1.0.0 The template process layer and process functions (e.g.
 *   template_process_HOOK(), MODULE_process_HOOK(), THEME_process_HOOK()) have
 *   been removed.
 *   See https://docs.backdropcms.org/change-records/removed-the-theme-process-layer
 */
function theme($hook, $variables = array()) {
  // 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 _theme_load_registry().
  if (!module_load_all(NULL) && !defined('MAINTENANCE_MODE')) {
    throw new Exception(t('theme() may not be called until all modules are loaded.'));
  }

  $hooks = theme_get_registry(FALSE);

  // If an array of hook candidates were passed, use the first one that has an
  // implementation.
  if (is_array($hook)) {
    foreach ($hook as $candidate) {
      if (isset($hooks[$candidate])) {
        break;
      }
    }
    $hook = $candidate;
  }
  $theme_hook_original = $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 (!isset($hooks[$hook])) {
    // Iteratively strip everything after the last '__' delimiter, until an
    // implementation is found.
    while ($pos = strrpos($hook, '__')) {
      $hook = substr($hook, 0, $pos);
      if (isset($hooks[$hook])) {
        break;
      }
    }
    if (!isset($hooks[$hook])) {
      // Only log a message when not trying theme suggestions ($hook being an
      // array).
      if (!isset($candidate)) {
        watchdog('theme', 'Theme hook "@hook" not found.', array('@hook' => $hook), WATCHDOG_WARNING);
      }
      return '';
    }
  }

  $info = $hooks[$hook] + array(
    'includes' => array(),
    'preprocess functions' => array(),
  );

  global $theme_path;
  $temp = $theme_path;
  // point path_to_theme() to the currently used theme path:
  $theme_path = $info['theme path'];

  // Include a file if the theme function or variable preprocessor is held
  // elsewhere.
  foreach ($info['includes'] as $include_file) {
    include_once BACKDROP_ROOT . '/' . $include_file;
  }

  // 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;
    $variables = array();
    if (isset($info['variables'])) {
      foreach (array_keys($info['variables']) as $name) {
        if (isset($element["#$name"])) {
          $variables[$name] = $element["#$name"];
        }
      }
    }
    else {
      $variables[$info['render element']] = $element;
    }
  }

  // Merge in argument defaults.
  if (!empty($info['variables'])) {
    $variables += $info['variables'];
  }
  elseif (!empty($info['render element'])) {
    $variables += array($info['render element'] => array());
  }

  $variables['theme_hook_original'] = $theme_hook_original;

  // Invoke the variable preprocessors, if any. The preprocessors may specify
  // alternate suggestions for which hook's template/function to use. If the
  // hook is a suggestion of a base hook, invoke the variable preprocessors of
  // the base hook, but retain the suggestion as a high priority suggestion to
  // be used unless overridden by a variable preprocessor function.
  if (isset($info['base hook'])) {
    $base_hook = $info['base hook'];
    $base_hook_info = isset($hooks[$base_hook]) ? $hooks[$base_hook] : array();
    $base_hook_info += array(
      'includes' => array(),
      'preprocess functions' => array(),
    );
    // Include files required by the base hook, since its variable preprocessors
    // might reside there.
    foreach ($base_hook_info['includes'] as $include_file) {
      include_once BACKDROP_ROOT . '/' . $include_file;
    }
    $variables['theme_hook_suggestion'] = $hook;
    $hook = $base_hook;

    // Combine preprocess functions to call the base hook and child functions.
    $info['preprocess functions'] = array_unique(array_merge($base_hook_info['preprocess functions'], $info['preprocess functions']));
  }
  if (isset($info['preprocess functions'])) {
    $variables['theme_hook_suggestions'] = array();
    foreach ($info['preprocess functions'] as $processor_function) {
      if (function_exists($processor_function)) {
        // We don't want a poorly behaved preprocess function changing $hook.
        $hook_clone = $hook;
        $processor_function($variables, $hook_clone);
      }
    }
    // If the preprocess functions specified hook suggestions, and the
    // suggestion exists in the theme registry, use it instead of the hook that
    // theme() was called with. This allows the preprocess step to route to a
    // more specific theme hook. For example, a function may call
    // theme('node', ...), but a preprocess function can add 'node__post' as
    // a suggestion, enabling a theme to have an alternate template file for
    // post nodes. Suggestions are checked in the following order:
    // - The 'theme_hook_suggestion' variable is checked first. It overrides
    //   all others.
    // - The 'theme_hook_suggestions' variable is checked in FILO order, so the
    //   last suggestion added to the array takes precedence over suggestions
    //   added earlier.
    $suggestions = array();
    if (!empty($variables['theme_hook_suggestions'])) {
      $suggestions = $variables['theme_hook_suggestions'];
    }
    if (!empty($variables['theme_hook_suggestion'])) {
      $suggestions[] = $variables['theme_hook_suggestion'];
    }
    foreach (array_reverse($suggestions) as $suggestion) {
      if (isset($hooks[$suggestion])) {
        $info = $hooks[$suggestion];
        break;
      }
    }
  }

  // Generate the output using either a function or a template.
  $output = '';
  if (isset($info['function'])) {
    if (function_exists($info['function'])) {
      $output = $info['function']($variables);
    }
  }
  else {
    // Default render function and extension.
    $render_function = 'theme_render_template';
    $extension = '.tpl.php';

    // The theme engine may use a different extension and a different renderer.
    global $theme_engine;
    if (isset($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 to run template_preprocess()
    // twice (it would be inefficient and mess up zebra striping), 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'])) {
      $default_template_variables = array();
      template_preprocess($default_template_variables, $hook);
      $variables += $default_template_variables;
    }

    // Render the output using the template file.
    $template_file = $info['template'] . $extension;
    if (isset($info['path'])) {
      $template_file = $info['path'] . '/' . $template_file;
    }
    try {
      $theme_debug = config_get('system.core', 'theme_debug');
    }
    catch (ConfigException $e) {
      $theme_debug = FALSE;
    }
    if ($theme_debug) {
      $output = _theme_render_template_debug($render_function, $template_file, $variables, $extension);
    }
    else {
      $output = $render_function($template_file, $variables);
    }
  }

  // restore path_to_theme()
  $theme_path = $temp;
  return $output;
}

/**
 * Returns the path to the current themed element.
 *
 * It can point to the active theme or the module that handles the theme
 * implementation. For example:
 * - When invoked within the scope of a theme function it will depend on where
 *   where that theme function is being handled.
 * - If implemented from a module, it will point to the module.
 * - If implemented from the active theme, it will point to the active theme.
 * - When called outside the scope of a theme function call, it will always
 *   point to the active theme.
 */
function path_to_theme() {
  global $theme_path;

  if (!isset($theme_path)) {
    backdrop_theme_initialize();
  }

  return $theme_path;
}

/**
 * Allows themes and/or theme engines to discover overridden theme functions.
 *
 * @param $cache
 *   The existing cache of theme hooks to test against.
 * @param $prefixes
 *   An array of prefixes to test, in reverse order of importance.
 *
 * @return array
 *   An array of the functions found, suitable for returning from hook_theme.
 *   Keyed by the theme hook and includes the function that implements it.
 */
function backdrop_find_theme_functions($cache, $prefixes) {
  $implementations = array();
  $all_functions = get_defined_functions();
  $theme_functions = preg_grep('/^(' . implode(')|(', $prefixes) . ')_/', $all_functions['user']);

  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 . '/', $theme_functions);
        if ($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 discover overridden templates.
 *
 * @param $cache
 *   The existing cache of theme hooks to test against.
 * @param $extension
 *   The extension that these templates will have.
 * @param $path
 *   The path to search.
 *
 * @return array
 *   An array of all template locations. Keyed by the theme callback, each entry
 *   contains the following keys:
 *   - template: The template file name/
 *   - path: The path to the template file relative to the Backdrop root.
 *   - base hook: If this template is dynamically named (usually with two
 *     hyphens in the template name), a string indicating the base theme
 *     callback.
 */
function backdrop_find_theme_templates($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][$theme_info->name] = dirname($theme_info->filename);
    }
  }
  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]);
      }
    }
  }
  global $theme;
  $subtheme_paths = isset($theme_paths[$theme]) ? $theme_paths[$theme] : array();

  // Escape the periods in the extension.
  $regex = '/' . str_replace('.', '\.', $extension) . '$/';

  // Save effort by skipping directories that should not contain templates.
  $ignore_directories = array(
    'assets',
    'css',
    'scss',
    'less',
    'js',
    'images',
    'node_modules',
    'bower_components',
  );
  $no_mask = '/^((\..*)|' . implode('|', $ignore_directories) .  ')$/';

  // Get a listing of all template files in the path to search.
  $files = file_scan_directory($path, $regex, array('key' => 'name', 'nomask' => $no_mask));

  // 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;
    }
    // Chop off the remaining '.tpl' extension. $template already has the
    // rightmost extension removed, but there might still be more, such as with
    // .tpl.php, which still has .tpl in $template at this point.
    if (($pos = strpos($template, '.tpl')) !== FALSE) {
      $template = substr($template, 0, $pos);
    }
    // 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'] . '/', '', $info['template']));
        if (in_array($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
  // backdrop_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) {
          $file = substr($match, 0, strpos($match, '.'));
          // 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 default theme-specific settings defined in any base theme's .info file
 * - the default theme-specific settings defined in the theme's .info file
 * - the saved values from the theme's settings form
 *
 * @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) {
  $configs = &backdrop_static(__FUNCTION__, array());

  // If no key is given, use the current theme if we can determine it.
  if (!isset($theme)) {
    $theme = !empty($GLOBALS['theme_key']) ? $GLOBALS['theme_key'] : '';
  }

  if (empty($theme)) {
    return;
  }

  if (empty($configs[$theme])) {
    $configs[$theme] = config($theme . '.settings');
    $configs[$theme]->load();
  }

  // If the setting is not found in config, load the default from the theme's
  // info file.
  $value = $configs[$theme]->get($setting_name);
  if (is_null($value)) {
    $themes = list_themes();
    $theme_info = $themes[$theme];
    $value = isset($theme_info->info['settings'][$setting_name]) ? $theme_info->info['settings'][$setting_name] : NULL;
  }

  // Loop up through any base themes.
  if (is_null($value) && isset($theme_info->info['base theme'])) {
    $value = theme_get_setting($setting_name, $theme_info->info['base theme']);
  }

  return $value;
}

/**
 * Detect if a theme has any theme settings.
 *
 * This utility function checks a theme's .info file for any settings. If the
 * theme has a base theme, it loops through the .info files of the parent themes
 * as well.
 *
 * @param string $theme
 *   The theme name to be checked for settings.
 *
 * @return bool
 *   TRUE if the theme has settings, FALSE otherwise.
 */
function theme_has_settings($theme) {
  if (config_get_names_with_prefix($theme . '.settings')) {
    return TRUE;
  }
  $themes = list_themes();
  $theme_info = $themes[$theme];
  if (!empty($theme_info->info['settings'])) {
    return TRUE;
  }
  if (isset($theme_info->info['base theme'])) {
    return theme_has_settings($theme_info->info['base theme']);
  }
  return FALSE;
}

/**
 * Detect if a theme has support for the Color module.
 *
 * This utility function checks a theme's .info file for whether support for the
 * Color module has been enabled. If the theme has a base theme, it loops
 * through the .info files of the parent themes as well.
 *
 * @param string $theme
 *   The theme name to be checked for Color module support.
 *
 * @return bool
 *   TRUE if the theme supports Color module, FALSE otherwise.
 *
 * @since 1.16.0
 */
function theme_has_color_support($theme) {
  $themes = list_themes();
  $theme_info = $themes[$theme];
  if (!empty($theme_info->info['settings']['color']) && file_exists(backdrop_get_path('theme', $theme_info->name) . '/color/color.inc')) {
    return TRUE;
  }
  if (isset($theme_info->info['base theme'])) {
    return theme_has_color_support($theme_info->info['base theme']);
  }
  return FALSE;
}

/**
 * Renders a system default template, which is essentially a PHP template.
 *
 * @param $template_file
 *   The filename of the template to render.
 * @param $variables
 *   A keyed array of variables that will appear in the output.
 *
 * @return string
 *   The output generated by the template.
 */
function theme_render_template($template_file, $variables) {
  // Extract the variables to a local namespace
  extract($variables, EXTR_SKIP);

  // Start output buffering
  ob_start();

  // Include the template file
  include BACKDROP_ROOT . '/' . $template_file;

  // End buffering and return its contents
  return ob_get_clean();
}

/**
 * Renders a template for any engine.
 *
 * Includes the possibility to get debug output by setting the
 * theme_debug value to TRUE.
 *
 * @param string $template_function
 *   The function to call for rendering the template.
 * @param string $template_file
 *   The filename of the template to render.
 * @param array $variables
 *   A keyed array of variables that will appear in the output.
 * @param string $extension
 *   The extension used by the theme engine for template files.
 *
 * @return string
 *   The output generated by the template including debug information.
 */
function _theme_render_template_debug($template_function, $template_file, $variables, $extension) {
  $output = array(
    'debug_prefix' => '',
    'debug_info' => '',
    'rendered_markup' => call_user_func($template_function, $template_file, $variables),
    'debug_suffix' => '',
  );
  $output['debug_prefix'] .= "\n\n<!-- THEME DEBUG -->";
  $output['debug_prefix'] .= "\n<!-- CALL: theme('" . check_plain($variables['theme_hook_original']) . "') -->";
  // If there are theme suggestions, reverse the array so more specific
  // suggestions are shown first.
  if (!empty($variables['theme_hook_suggestions'])) {
    $variables['theme_hook_suggestions'] = array_reverse($variables['theme_hook_suggestions']);
  }
  // Add debug output for directly called suggestions like
  // '#theme' => 'comment__node__post'.
  if (strpos($variables['theme_hook_original'], '__') !== FALSE) {
    $derived_suggestions[] = $hook = $variables['theme_hook_original'];
    while ($pos = strrpos($hook, '__')) {
      $hook = substr($hook, 0, $pos);
      $derived_suggestions[] = $hook;
    }
    // Get the value of the base hook (last derived suggestion) and append it
    // to the end of all theme suggestions.
    $base_hook = array_pop($derived_suggestions);
    $variables['theme_hook_suggestions'] = array_merge($derived_suggestions, $variables['theme_hook_suggestions']);
    $variables['theme_hook_suggestions'][] = $base_hook;
  }
  if (!empty($variables['theme_hook_suggestions'])) {
    $current_template = basename($template_file);
    $suggestions = $variables['theme_hook_suggestions'];
    // Only add the original theme hook if it wasn't a directly called
    // suggestion.
    if (strpos($variables['theme_hook_original'], '__') === FALSE) {
      $suggestions[] = $variables['theme_hook_original'];
    }
    foreach ($suggestions as &$suggestion) {
      $template = strtr($suggestion, '_', '-') . $extension;
      $prefix = ($template == $current_template) ? 'x' : '*';
      $suggestion = $prefix . ' ' . $template;
    }
    $output['debug_info'] .= "\n<!-- FILE NAME SUGGESTIONS:\n   " . check_plain(implode("\n   ", $suggestions)) . "\n-->";
  }
  $output['debug_info'] .= "\n<!-- BEGIN OUTPUT from '" . check_plain($template_file) . "' -->\n";
  $output['debug_suffix'] .= "\n<!-- END OUTPUT from '" . check_plain($template_file) . "' -->\n\n";
  return implode('', $output);
}

/**
 * Enables a given list of themes.
 *
 * @param $theme_list
 *   An array of theme names.
 */
function theme_enable($theme_list) {
  backdrop_clear_css_cache();

  foreach ($theme_list as $key) {
    db_update('system')
      ->fields(array('status' => 1))
      ->condition('type', 'theme')
      ->condition('name', $key)
      ->execute();

    // Copy any default configuration data to the system config directory.
    config_install_default_config($key);
  }

  list_themes(TRUE);
  menu_rebuild();
  backdrop_theme_rebuild();

  // Invoke hook_themes_enabled() after the themes have been enabled.
  module_invoke_all('themes_enabled', $theme_list);
}

/**
 * Disables a given list of themes.
 *
 * @param $theme_list
 *   An array of theme names.
 */
function theme_disable($theme_list) {
  // Don't disable the default theme.
  if ($pos = array_search(config_get('system.core', 'theme_default'), $theme_list) !== FALSE) {
    unset($theme_list[$pos]);
    if (empty($theme_list)) {
      return;
    }
  }

  backdrop_clear_css_cache();

  foreach ($theme_list as $key) {
    db_update('system')
      ->fields(array('status' => 0))
      ->condition('type', 'theme')
      ->condition('name', $key)
      ->execute();

    config_uninstall_config($key);
  }

  list_themes(TRUE);
  menu_rebuild();
  backdrop_theme_rebuild();

  // Invoke hook_themes_disabled after the themes have been disabled.
  module_invoke_all('themes_disabled', $theme_list);
}

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

/**
 * Preprocess variables for theme_datetime().
 */
function template_preprocess_datetime(&$variables) {
  // Format the 'datetime' attribute based on the timestamp.
  // @see http://www.w3.org/TR/html5-author/the-time-element.html#attr-time-datetime
  if (!isset($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;
    }
  }
}

/**
 * Returns HTML for a date / time.
 *
 * @param $variables
 *   An associative array containing:
 *   - timestamp: (optional) A UNIX timestamp for the datetime attribute. If the
 *     datetime cannot be represented as a UNIX timestamp, use a valid datetime
 *     attribute value in $variables['attributes']['datetime'].
 *   - text: (optional) The content to display within the <time> element. Set
 *     'html' to TRUE if this value is already sanitized for output in HTML.
 *     Defaults to a human-readable representation of the timestamp value or the
 *     datetime attribute value using format_date().
 *     When invoked as #theme or #theme_wrappers of a render element, the
 *     rendered #children are automatically taken over as 'text', unless #text
 *     is explicitly set.
 *   - attributes: (optional) An associative array of HTML attributes to apply
 *     to the <time> element. A datetime attribute in 'attributes' overrides the
 *     'timestamp'. To create a valid datetime attribute value from a UNIX
 *     timestamp, use format_date() with one of the predefined 'html_*' formats.
 *   - html: (optional) Whether 'text' is HTML markup (TRUE) or plain-text
 *     (FALSE). Defaults to FALSE. For example, to use a SPAN tag within the
 *     TIME element, this must be set to TRUE, or the SPAN tag will be escaped.
 *     It is the responsibility of the caller to properly sanitize the value
 *     contained in 'text' (or within the SPAN tag in aforementioned example).
 *
 * @see template_preprocess_datetime()
 * @see http://www.w3.org/TR/html5-author/the-time-element.html#attr-time-datetime
 */
function theme_datetime($variables) {
  $output = '<time' . backdrop_attributes($variables['attributes']) . '>';
  $output .= !empty($variables['html']) ? $variables['text'] : check_plain($variables['text']);
  $output .= '</time>';
  return $output;
}

/**
 * Returns HTML for status and/or error messages, grouped by type.
 *
 * An invisible heading identifies the messages for assistive technology.
 * Sighted users see a colored box. See http://www.w3.org/TR/WCAG-TECHS/H69.html
 * for info.
 *
 * @param $variables
 *   An associative array containing:
 *   - display: (optional) Set to 'status' or 'error' to display only messages
 *     of that type.
 */
function theme_status_messages($variables) {
  $display = $variables['display'];
  $message_types = (empty($variables['messages']))? backdrop_get_messages($display) : $variables['messages'];
  $output = '';

  $status_heading = array(
    'status' => t('Status message'),
    'error' => t('Error message'),
    'warning' => t('Warning message'),
    'info' => t('Info message'),
  );

  foreach ($message_types as $type => $messages) {
    $output .= "<div class=\"messages $type\">\n";
    if (!empty($status_heading[$type])) {
      $output .= '  <h2 class="element-invisible">' . $status_heading[$type] . "</h2>\n";
    }
    if (count($messages) > 1) {
      $output .= "  <ul>\n";
      foreach ($messages as $message) {
        $output .= '    <li>' . $message . "</li>\n";
      }
      $output .= "  </ul>\n";
    }
    else {
      $output .= reset($messages) . "\n";
    }
    if (config_get('system.core', 'messages_dismissible')) {
      // Add the 'Dismiss' library and place a 'Dismiss' link on messages.
      backdrop_add_library('system', 'backdrop.dismiss');
      $output .= '<a href="#" class="dismiss" title="' . t('Dismiss') . '"><span class="element-invisible">' . t('Dismiss') . '</span></a>' . "\n";
    }
    $output .= "</div>\n";
  }

  return $output;
}

/**
 * Returns HTML for a link.
 *
 * This is a wrapper around l() to allow for more flexible link theming.
 *
 * Where performance is more important than theme flexibility, Backdrop code that
 * outputs a link should call the l() function directly, as #theme 'link'
 * implementations have a measurable performance impact.
 *
 * @param array $variables
 *   An associative array containing the keys:
 *   - text: The text of the link.
 *   - path: The internal path or external URL being linked to. It is used as
 *     the $path parameter of the url() function.
 *   - options: (optional) An array that defaults to empty, but can contain:
 *     - attributes: Can contain optional attributes:
 *       - class: must be declared in an array. Example: 'class' =>
 *         array('class_name1','class_name2').
 *       - title: must be a string. Example: 'title' => 'Example title'
 *       - Others are more flexible as long as they work with
 *         backdrop_attributes($variables['options']['attributes]).
 *     - html: Boolean flag that tells whether text contains
 *       html or plain text.  If not set to TRUE the text value will be
 *       sanitized.
 *   The elements $variables['options']['attributes'] and
 *   $variables['options']['html'] are used in this function similarly to the
 *   way that $options['attributes'] and $options['html'] are used in l().
 *   The link itself is built by the url() function, which takes
 *   $variables['path'] and $variables['options'] as arguments.
 *
 * @see l()
 * @see url()
 */
function theme_link($variables) {
  $rendered_text = is_array($variables['text']) ? backdrop_render($variables['text']) : $variables['text'];
  return l($rendered_text, $variables['path'], $variables['options']);
}

/**
 * Returns HTML for a set of links.
 *
 * @param $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.
 *     - href: The link URL. If omitted, the 'title' is shown as a plain text
 *       item in the links list.
 *     - html: (optional) Whether or not 'title' is HTML. If set, the title
 *       will not be passed through check_plain().
 *     - 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 $options parameter.
 *   - attributes: A keyed array of attributes for the UL containing the
 *     list of links.
 *   - heading: (optional) A heading to precede the links. May be an
 *     associative array or a string. If it's an array, it can have the
 *     following elements:
 *     - text: The heading text.
 *     - level: The heading level (e.g. 'h2', 'h3').
 *     - class: (optional) An array of the CSS classes for the heading.
 *     When using a string it will be used as the text of the heading and the
 *     level will default to 'h2'. Headings should be used on navigation menus
 *     and any list of links that consistently appears on multiple pages. To
 *     make the heading invisible use the 'element-invisible' CSS class. Do not
 *     use 'display:none', which removes it from screen-readers and assistive
 *     technology. Headings allow screen-reader and keyboard only users to
 *     navigate to or skip the links. See
 *     http://juicystudio.com/article/screen-readers-display-none.php and
 *     http://www.w3.org/TR/WCAG-TECHS/H42.html for more information.
 */
function theme_links($variables) {
  global $language_url;

  $links = (array) $variables['links'];
  $attributes = (array) $variables['attributes'];
  $heading = $variables['heading'];
  $output = '';

  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(),
      );
      // @todo Remove backwards compatibility for $heading['class'].
      if (isset($heading['class'])) {
        $heading['attributes']['class'] = $heading['class'];
      }

      $output .= '<' . $heading['level'] . backdrop_attributes($heading['attributes']) . '>';
      $output .= check_plain($heading['text']);
      $output .= '</' . $heading['level'] . '>';
    }

    $output .= '<ul' . backdrop_attributes($attributes) . '>';

    $num_links = count($links);
    $i = 0;
    foreach ($links as $key => $link) {
      $i++;

      $class = array();
      // Use the array key as class name.
      $class[] = backdrop_html_class($key);
      // Add odd/even, first, and last classes.
      $class[] = ($i % 2 ? 'odd' : 'even');
      if ($i == 1) {
        $class[] = 'first';
      }
      if ($i == $num_links) {
        $class[] = 'last';
      }

      // Handle links.
      if (isset($link['href'])) {
        $is_current_path = ($link['href'] == $_GET['q'] || ($link['href'] == '<front>' && backdrop_is_front_page()));
        $is_current_language = (empty($link['language']) || $link['language']->langcode == $language_url->langcode);
        if ($is_current_path && $is_current_language) {
          $class[] = 'active';
        }
        // Pass in $link as $options, they share the same keys.
        $item = l($link['title'], $link['href'], $link);
      }
      // Handle title-only text items.
      else {
        // Merge in default array properties into $link.
        $link += array(
          'html' => FALSE,
          'attributes' => array(),
        );
        $item = '<span' . backdrop_attributes($link['attributes']) . '>';
        $item .= ($link['html'] ? $link['title'] : check_plain($link['title']));
        $item .= '</span>';
      }

      $output .= '<li' . backdrop_attributes(array('class' => $class)) . '>';
      $output .= $item;
      $output .= '</li>';
    }

    $output .= '</ul>';
  }

  return $output;
}

/**
 * Provide wrapper HTML around dropbutton lists.
 *
 * @param $variables
 *   An associative array containing:
 *     - children: Contains the rendered children of the dropbutton menu.
 */
function theme_dropbutton_wrapper($variables) {
  $output = '';
  $output .= '<div class="dropbutton-wrapper">';
  $output .= '<div class="dropbutton-widget">';
  $output .= $variables['children'];
  $output .= '</div>';
  $output .= '</div>';
  return $output;
}

/**
 * Preprocess variables for theme_image().
 *
 * @since 1.8.0 Function added. Populates $variables['attributes'] before
 *   theme_image() is called.
 */
function template_preprocess_image(&$variables) {
  // Accept either URI or path key. But both are handled by file_create_url().
  $path_or_uri = $variables['uri'] ? $variables['uri'] : $variables['path'];
  $variables['attributes']['src'] = file_create_url($path_or_uri);

  // Convert all other variables into the attributes array.
  foreach (array('width', 'height', 'alt', 'title') as $key) {
    if (isset($variables[$key])) {
      $variables['attributes'][$key] = $variables[$key];
    }
  }
}

/**
 * Returns HTML for an image.
 *
 * Either a "uri" or "path" should be provided to the image. URIs should be used
 * for files that are stored in the public or private file directories. Paths
 * should be used for images relative to the Backdrop installation.
 *
 * @param $variables
 *   An associative array containing:
 *   - uri: A file URI, prefixed with a file scheme such as public://
 *   - path: A file path relative to the root of the Backdrop installation.
 *   - 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.
 *     All attributes should be populated with the correct values that match
 *     the other input variables.
 *
 * @since 1.8.0 Added support for $variables['path']. All variables are now
 *   populated into $variables['attributes'] in template_preprocess_image().
 */
function theme_image($variables) {
  return '<img' . backdrop_attributes($variables['attributes']) . ' />';
}

/**
 * Returns HTML for a breadcrumb trail.
 *
 * @param $variables
 *   An associative array containing:
 *   - breadcrumb: An array containing the breadcrumb links.
 */
function theme_breadcrumb($variables) {
  $breadcrumb = $variables['breadcrumb'];
  $output = '';
  if (!empty($breadcrumb)) {
    $output .= '<nav class="breadcrumb" aria-label="' . t('Website Orientation') . '">';
    $output .= '<ol><li>' . implode('<span class="breadcrumb-separator" aria-hidden="true"> » </span></li><li>', $breadcrumb) . '</li></ol>';
    $output .= '</nav>';
  }
  return $output;
}

/**
 * Returns HTML for a table.
 *
 * @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").
 *     - "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. Only
 *       one column should be given a default sort order because table sorting
 *       only applies to one column at a time.
 *     - Any HTML attributes, such as "colspan", to apply to the column header
 *       cell.
 *   - footer: An array of table rows which will be printed within a <tfoot>
 *     tag, in the same format as the rows element (see above).
 *     The structure is the same the one defined for the "rows" key except
 *     that the no_striping boolean has no effect, there is no rows striping
 *     for the table footer.
 *   - 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
 *   - 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 group three columns and apply the
 *     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.
 *
 * @return string
 *   The HTML output.
 *
 * @since 1.18.4 "footer" key added to $variables parameter.
 */
function theme_table(array $variables) {
  $header = (array) $variables['header'];
  $rows = (array) $variables['rows'];
  $attributes = $variables['attributes'];
  $caption = $variables['caption'];
  $colgroups = $variables['colgroups'];
  $sticky = $variables['sticky'];
  $empty = $variables['empty'];

  // The output string contains the inner content of the table. The table tag
  // itself is added at the end.
  $output = '';
  if (isset($caption)) {
    $output .= '<caption>' . $caption . "</caption>\n";
  }

  // Format the table columns:
  if (!empty($colgroups)) {
    foreach ($colgroups as $colgroup) {
      $colgroup_attributes = array();

      // Check if we're dealing with a simple or complex column.
      if (isset($colgroup['data'])) {
        foreach ($colgroup as $key => $value) {
          if ($key == 'data') {
            $cols = $value;
          }
          else {
            $colgroup_attributes[$key] = $value;
          }
        }
      }
      else {
        $cols = $colgroup;
      }

      // Build colgroup.
      if (is_array($cols) && count($cols)) {
        $output .= ' <colgroup' . backdrop_attributes($colgroup_attributes) . '>';
        foreach ($cols as $col) {
          $output .= ' <col' . backdrop_attributes($col) . ' />';
        }
        $output .= " </colgroup>\n";
      }
      else {
        $output .= ' <colgroup' . backdrop_attributes($colgroup_attributes) . " />\n";
      }
    }
  }

  // Add the 'empty' row message if available.
  if (empty($rows) && $empty) {
    $header_count = 0;
    if (!empty($header)) {
      foreach ($header as $header_cell) {
        if (is_array($header_cell)) {
          $header_count += isset($header_cell['colspan']) ? $header_cell['colspan'] : 1;
        }
        else {
          $header_count++;
        }
      }
    }
    $rows[] = array(array('data' => $empty, 'colspan' => $header_count, 'class' => array('empty', 'message')));
  }

  $responsive_columns = array();
  // Format the table header.
  if (!empty($header)) {
    $ts = tablesort_init($header);
    // HTML requires that the thead tag has tr tags in it followed by tbody
    // tags. Using ternary operator to check and see if we have any rows.
    $output .= (!empty($rows) ? ' <thead><tr>' : ' <tr>');
    $i = 0;
    foreach ($header as $cell) {
      $i++;
      // Track responsive classes for each column as needed. Only the header
      // cells for a column are marked up with the responsive classes by a
      // module developer or themer. The responsive classes on the header cells
      // must be transferred to the content cells.
      if (!empty($cell['class']) && is_array($cell['class'])) {
        if (in_array(RESPONSIVE_PRIORITY_MEDIUM, $cell['class'])) {
          $responsive_columns[$i] =  RESPONSIVE_PRIORITY_MEDIUM;
        }
        elseif (in_array(RESPONSIVE_PRIORITY_LOW, $cell['class'])) {
          $responsive_columns[$i] =  RESPONSIVE_PRIORITY_LOW;
        }
      }
      $cell = tablesort_header($cell, $header, $ts);
      $output .= _theme_table_cell($cell, TRUE);
    }
    // Using ternary operator to close the tags, based on whether or not there
    // are rows.
    $output .= (!empty($rows) ? " </tr></thead>\n" : "</tr>\n");
  }
  else {
    $ts = array();
  }

  // Format the table and footer rows.
  $sections = array();

  if (!empty($rows)) {
    $sections['tbody'] = $rows;
  }

  if (!empty($variables['footer'])) {
    $sections['tfoot'] = $variables['footer'];
  }

  // The tbody and tfoot HTML tags have the same structure, and are built
  // using the same procedure.
  foreach ($sections as $tag => $content) {
    $output .= "<$tag>\n";
    $flip = array('even' => 'odd', 'odd' => 'even');
    $class = 'even';
    $default_no_striping = ($tag === 'tfoot');

    foreach ($content as $number => $row) {
      // Check if we're dealing with a simple or complex row.

      if (isset($row['data'])) {
        $cells = $row['data'];
        $no_striping = isset($row['no_striping']) ? $row['no_striping'] : $default_no_striping;

        // Set the attributes array and exclude 'data' and 'no_striping'.
        $tr_attributes = $row;
        unset($tr_attributes['data']);
        unset($tr_attributes['no_striping']);
      }
      else {
        $cells = $row;
        $tr_attributes = array();
        $no_striping = $default_no_striping;
      }

      if (!empty($cells)) {
        // Add odd/even class.
        if (!$no_striping) {
          $class = $flip[$class];
          $tr_attributes['class'][] = $class;
        }

        // Build row.
        $output .= ' <tr' . backdrop_attributes($tr_attributes) . '>';
        $i = 0;
        foreach ($cells as $cell) {
          // Add active class if needed for sortable tables.
          $cell = tablesort_cell($cell, $header, $ts, $i);
          $i++;
          // Copy RESPONSIVE_PRIORITY_LOW/RESPONSIVE_PRIORITY_MEDIUM
          // class from header to cell as needed.
          if (isset($responsive_columns[$i])) {
            if (is_array($cell)) {
              $cell['class'][] = $responsive_columns[$i];
            }
            else {
              $cell = array('data' => $cell, 'class' => array($responsive_columns[$i]));
            }
          }
          $output .= _theme_table_cell($cell);
        }
        $output .= " </tr>\n";
      }
    }

    $output .= "</$tag>\n";
  }

  // Add sticky headers if enabled.
  if (!empty($header) && $sticky) {
    backdrop_add_js('core/misc/tableheader.js');
    // Add 'sticky-enabled' class to the table to identify it for JS.
    // This is needed to target tables constructed by this function.
    $attributes['class'][] = 'sticky-enabled';
  }
  // If the responsive classes were used, add the matching library.
  if (count($responsive_columns)) {
    backdrop_add_library('system', 'backdrop.tableresponsive');
    // Add 'responsive-enabled' class to the table to identify it for JS.
    // This is needed to target tables constructed by this function.
    $attributes['class'][] = 'responsive-enabled';
  }

  // Wrap the result in the table tag. This is done last so that the
  // responsive-enabled class is added only when needed.
  $output = '<table' . backdrop_attributes($attributes) . ">\n$output</table>\n";

  return $output;
}

/**
 * Returns HTML for a sort icon.
 *
 * @param $variables
 *   An associative array containing:
 *   - style: Set to either 'asc' or 'desc', this determines which icon to
 *     show.
 */
function theme_tablesort_indicator($variables) {
  if ($variables['style'] == "asc") {
    return theme('image', array('path' => 'core/misc/arrow-asc.png', 'width' => 13, 'height' => 13, 'alt' => t('sort ascending'), 'title' => t('sort ascending')));
  }
  else {
    return theme('image', array('path' => 'core/misc/arrow-desc.png', 'width' => 13, 'height' => 13, 'alt' => t('sort descending'), 'title' => t('sort descending')));
  }
}

/**
 * Returns HTML for a marker for new or updated content.
 *
 * @param $variables
 *   An associative array containing:
 *   - type: Number representing the marker type to display. See MARK_NEW,
 *     MARK_UPDATED, MARK_READ.
 */
function theme_mark($variables) {
  $type = $variables['type'];
  global $user;
  if ($user->uid) {
    if ($type == MARK_NEW) {
      return ' <span class="marker">' . t('new') . '</span>';
    }
    elseif ($type == MARK_UPDATED) {
      return ' <span class="marker">' . t('updated') . '</span>';
    }
  }
}

/**
 * Returns HTML for a list or nested list of items.
 *
 * @param $variables
 *   An associative array containing:
 *   - items: A list of items to render. String values are rendered as is. Each
 *     item can also be an associative array containing:
 *     - data: The string content of the list item.
 *     - children: A list of nested child items to render that behave
 *       identically to 'items', but any non-numeric string keys are treated as
 *       HTML attributes for the child list that wraps 'children'.
 *     Any other key/value pairs are used as HTML attributes for the list item
 *     in 'data'.
 *   - title: The title of the list.
 *   - type: The type of list to return (e.g. "ul", "ol").
 *   - attributes: The attributes applied to the list element.
 *   - wrapper_attributes: Any additional attributes that should be applied to
 *       the wrapper DIV around the list element (the "item-list" CSS class is
 *       added by default).
 *   - empty: A message to display when there are no items. Allowed value is a
 *     string or render array.
 *
 * @since 1.21.0: added the "empty" variable.
 * @since 1.27.0: added the "wrapper_attributes" variable.
 */
function theme_item_list($variables) {
  $items = $variables['items'];
  $title = $variables['title'];
  $type = $variables['type'];
  $list_attributes = $variables['attributes'];
  $wrapper_attributes = $variables['wrapper_attributes'];

  $output = '';
  if ($items) {
    $output .= '<' . $type . backdrop_attributes($list_attributes) . '>';

    $num_items = count($items);
    $i = 0;
    foreach ($items as $key => $item) {
      $i++;
      $attributes = array();

      if (is_array($item)) {
        $value = '';
        if (isset($item['data'])) {
          $value .= $item['data'];
        }
        $attributes = array_diff_key($item, array('data' => 0, 'children' => 0));

        // Append nested child list, if any.
        if (isset($item['children'])) {
          // HTML attributes for the outer list are defined in the 'attributes'
          // theme variable, but not inherited by children. For nested lists,
          // all non-numeric keys in 'children' are used as list attributes.
          $child_list_attributes = array();
          foreach ($item['children'] as $child_key => $child_item) {
            if (is_string($child_key)) {
              $child_list_attributes[$child_key] = $child_item;
              unset($item['children'][$child_key]);
            }
          }
          $value .= theme('item_list', array(
            'items' => $item['children'],
            'type' => $type,
            'attributes' => $child_list_attributes,
          ));
        }
      }
      else {
        $value = $item;
      }

      $attributes['class'][] = ($i % 2 ? 'odd' : 'even');
      if ($i == 1) {
        $attributes['class'][] = 'first';
      }
      if ($i == $num_items) {
        $attributes['class'][] = 'last';
      }

      $output .= '<li' . backdrop_attributes($attributes) . '>' . $value . '</li>';
    }
    $output .= "</$type>";
  }
  elseif (!empty($variables['empty'])) {
    $output .= render($variables['empty']);
  }

  // Only output the list container and title if there are any list items.
  if ($output !== '') {
    // Check to see whether the list title exists before adding a header. Empty
    // headers are not semantic and present accessibility challenges.
    if (isset($title) && $title !== '') {
      $title = '<h3>' . $title . '</h3>';
    }

    // Add any attributes specified for the wrapper div tag.
    if (!isset($wrapper_attributes['class'])) {
      // Make sure that the 'class' key exists in the array.
      $wrapper_attributes['class'] = array();
    }
    elseif (is_string($wrapper_attributes['class'])) {
      // Do not choke if 'class' was provided as a string which may include
      // commas, spaces, or semicolons. Convert sub-strings into array items.
      $wrapper_class_items = array_map('trim', preg_split("/[;,]/", $wrapper_attributes['class']));
      $wrapper_attributes['class'] = $wrapper_class_items;
    }
    // Finally, include a default CSS class "item-list".
    $wrapper_attributes['class'][] = 'item-list';

    $output = '<div' . backdrop_attributes($wrapper_attributes) . '>' . $title . $output . '</div>';
  }

  return $output;
}

/**
 * Returns HTML for a help element.
 */
function theme_help($variables) {
  // Wrap in a paragraph tag if one is not present.
  if (strpos($variables['markup'], '<p') === FALSE) {
    $variables['markup'] = '<p>' . $variables['markup'] . '</p>';
  }
  return '<div class="help">' . $variables['markup'] . '</div>';
}

/**
 * Returns HTML for a "more help" link.
 *
 * @param $variables
 *   An associative array containing:
 *   - url: The URL for the link.
 */
function theme_more_help_link($variables) {
  return '<div class="more-help-link">' . l(t('More help'), $variables['url']) . '</div>';
}

/**
 * Returns HTML for a feed icon.
 *
 * @param $variables
 *   An associative array containing:
 *   - url: An internal system path or a fully qualified external URL of the
 *     feed.
 *   - title: A descriptive title of the feed.
 */
function theme_feed_icon($variables) {
  $text = t('Subscribe to !feed-title', array('!feed-title' => $variables['title']));
  if ($image = theme('image', array('path' => 'core/misc/feed.png', 'width' => 16, 'height' => 16, 'alt' => $text))) {
    return l($image, $variables['url'], array('html' => TRUE, 'attributes' => array('class' => array('feed-icon'), 'title' => $text)));
  }
}

/**
 * Returns HTML for a generic HTML tag with attributes.
 *
 * This function should only be used for adding HTML tags within the HEAD tag
 * on the page.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: An associative array describing the tag:
 *     - #tag: The HTML tag to output. Typical tags added within the HEAD tag
 *       of the page:
 *       - meta: To provide meta information, such as a page refresh.
 *       - link: To refer to stylesheets and other contextual information.
 *       - script: To load JavaScript.
 *     - #attributes: (optional) An array of HTML attributes to apply to the
 *       tag.
 *     - #value: (optional) A string containing tag content, such as inline
 *       CSS.
 *     - #value_prefix: (optional) A string to prepend to #value, e.g. a CDATA
 *       wrapper prefix.
 *     - #value_suffix: (optional) A string to append to #value, e.g. a CDATA
 *       wrapper suffix.
 *
 * @since 1.0.0
 */
function theme_head_tag($variables) {
  $element = $variables['element'];
  $attributes = isset($element['#attributes']) ? backdrop_attributes($element['#attributes']) : '';
  if (!isset($element['#value'])) {
    return '<' . $element['#tag'] . $attributes . " />\n";
  }
  else {
    $output = '<' . $element['#tag'] . $attributes . '>';
    if (isset($element['#value_prefix'])) {
      $output .= $element['#value_prefix'];
    }
    $output .= $element['#value'];
    if (isset($element['#value_suffix'])) {
      $output .= $element['#value_suffix'];
    }
    $output .= '</' . $element['#tag'] . ">\n";
    return $output;
  }
}

/**
 * Returns HTML for a "more" link, like those used in blocks.
 *
 * @param $variables
 *   An associative array containing:
 *   - url: The URL of the main page.
 *   - title: A descriptive verb for the link, like 'Read more'.
 */
function theme_more_link($variables) {
  return '<div class="more-link">' . l(t('More'), $variables['url'], array('attributes' => array('title' => $variables['title']))) . '</div>';
}

/**
 * Returns HTML for a progress bar.
 *
 * Note that the core Batch API uses this only for non-JavaScript batch jobs.
 *
 * @param $variables
 *   An associative array containing:
 *   - percent: The percentage of the progress.
 *   - message: A string containing information to be displayed.
 */
function theme_progress_bar($variables) {
  $output = '<div id="progress" class="progress">';
  $output .= '<div class="bar"><div class="filled" style="width: ' . $variables['percent'] . '%"></div></div>';
  $output .= '<div class="percentage">' . $variables['percent'] . '%</div>';
  $output .= '<div class="message">' . $variables['message'] . '</div>';
  $output .= '</div>';

  return $output;
}

/**
 * Returns HTML for an indentation div. Used for drag and drop tables.
 *
 * @param $variables
 *   An associative array containing:
 *   - size: Optional. The number of indentations to create.
 */
function theme_indentation($variables) {
  $output = '';
  for ($n = 0; $n < $variables['size']; $n++) {
    $output .= '<div class="indentation">&nbsp;</div>';
  }
  return $output;
}

/**
 * @} End of "addtogroup themeable".
 */

/**
 * Returns HTML output for a single table cell for theme_table().
 *
 * @param $cell
 *   Array of cell information, or string to display in cell.
 * @param bool $header
 *   TRUE if this cell is a table header cell, FALSE if it is an ordinary
 *   table cell. If $cell is an array with element 'header' set to TRUE, that
 *   will override the $header parameter.
 *
 * @return
 *   HTML for the cell.
 */
function _theme_table_cell($cell, $header = FALSE) {
  $attributes = '';

  if (is_array($cell)) {
    $data = isset($cell['data']) ? $cell['data'] : '';
    // Cell's data property can be a string or a renderable array.
    if (is_array($data)) {
      $data = backdrop_render($data);
    }
    $header |= isset($cell['header']);
    unset($cell['data']);
    unset($cell['header']);
    $attributes = backdrop_attributes($cell);
  }
  else {
    $data = $cell;
  }

  if ($header) {
    $output = "<th$attributes>$data</th>";
  }
  else {
    $output = "<td$attributes>$data</td>";
  }

  return $output;
}

/**
 * Adds a default set of variables for variable preprocessors and templates.
 *
 * This function is called for theme hooks implemented as templates only, not
 * for theme hooks implemented as functions. This preprocess function is the
 * first in the sequence of preprocessing functions that is called when
 * preparing variables for a template. See theme() for more details about the
 * full sequence.
 *
 * @see theme()
 */
function template_preprocess(&$variables, $hook) {
  global $user;
  static $count = array();

  // Track run count for each hook to provide zebra striping. See
  // "template_preprocess_block()" which provides the same feature specific to
  // blocks.
  $count[$hook] = isset($count[$hook]) && is_int($count[$hook]) ? $count[$hook] : 1;
  $variables['zebra'] = ($count[$hook] % 2) ? 'odd' : 'even';
  $variables['id'] = $count[$hook]++;

  // Tell all templates where they are located.
  $variables['directory'] = path_to_theme();

  // Initialize html class attribute for the current hook.
  $variables['classes'] = array(backdrop_html_class($hook));

  // Initialize additional attribute placeholder for the current hook.
  $variables['attributes'] = array();

  // Merge in variables that don't depend on hook and don't change during a
  // single page request.
  // Use the advanced backdrop_static() pattern, since this is called very often.
  static $backdrop_static_fast;
  if (!isset($backdrop_static_fast)) {
    $backdrop_static_fast['default_variables'] = &backdrop_static(__FUNCTION__);
  }
  $default_variables = &$backdrop_static_fast['default_variables'];
  // Global $user object shouldn't change during a page request once rendering
  // has started, but if there's an edge case where it does, re-fetch the
  // variables appropriate for the new user.
  if (!isset($default_variables) || ($user !== $default_variables['user'])) {
    $default_variables = _template_preprocess_default_variables();
  }
  $variables += $default_variables;
}

/**
 * Returns hook-independent variables to template_preprocess().
 */
function _template_preprocess_default_variables() {
  global $user;

  // Variables that don't depend on a database connection.
  $variables = array(
    'attributes' => array(),
    'content_attributes' => array(),
    'title_prefix' => array(),
    'title_suffix' => array(),
    'user' => $user,
    'db_is_active' => !defined('MAINTENANCE_MODE'),
    'is_admin' => FALSE,
    'logged_in' => FALSE,
  );

  // The user object has no uid property when the database does not exist during
  // install. The user_access() check deals with issues when in maintenance mode
  // as uid is set but the user.module has not been included.
  if (isset($user->uid) && function_exists('user_access')) {
    $variables['is_admin'] = user_access('access administration pages');
    $variables['logged_in'] = ($user->uid > 0);
  }

  // backdrop_is_front_page() might throw an exception.
  try {
    $variables['is_front'] = backdrop_is_front_page();
  }
  catch (Exception $e) {
    // If the database is not yet available, set default values for these
    // variables.
    $variables['is_front'] = FALSE;
    $variables['db_is_active'] = FALSE;
  }

  return $variables;
}

/**
 * Preprocess variables for header.tpl.php
 */
function template_preprocess_header(&$variables) {
  $variables['front_page'] = url();
  $variables['base_path'] = base_path();
}

/**
 * Preprocess variables for page.tpl.php
 *
 * @see system_element_info()
 * @see page.tpl.php
 */
function template_preprocess_page(&$variables) {
  // Compile a list of classes that are going to be applied to the body element.
  // This allows for easy CSS overrides based on context (home page, node of
  // certain type, etc.).

  // Add a class that tells us whether we're on the home page or not.
  if ($variables['is_front']) {
    $variables['classes'][] = 'front';
  }

  // Add a class that tells us whether the page is viewed by an authenticated user or not.
  if ($variables['logged_in']) {
    $variables['classes'][] = 'logged-in';
  }

  // If on an individual node page, add the node type to body classes.
  if ($node = menu_get_object()) {
    $variables['classes'][] = backdrop_html_class('node-type-' . $node->type);
  }

  // Initialize attributes which are specific to the html and body elements.
  $variables['html_attributes'] = array();
  $variables['html_attributes']['lang'] = $GLOBALS['language']->langcode;
  $variables['html_attributes']['dir'] = $GLOBALS['language']->direction ? 'rtl' : 'ltr';
  $variables['body_attributes'] = array();

  // Add favicon.
  $favicon = backdrop_get_favicon();
  backdrop_add_html_head_link(array('rel' => 'shortcut icon', 'href' => $favicon['path'], 'type' => $favicon['type']));

  $site_config = config('system.core');
  // Construct head <title>.
  if (backdrop_get_title()) {
    $head_title = array(
      'title' => strip_tags(backdrop_get_title()),
      'name' => check_plain($site_config->getTranslated('site_name')),
    );
  }
  else {
    $head_title = array('name' => check_plain($site_config->getTranslated('site_name')));
    if ($slogan = $site_config->getTranslated('site_slogan')) {
      $head_title['slogan'] = check_plain($slogan);
    }
  }
  $variables['head_title_array'] = $head_title;
  $variables['head_title'] = implode(' | ', $head_title);
}

/**
 * Generate an array of suggestions from path arguments.
 *
 * This is typically called for adding to the 'theme_hook_suggestions' or
 * 'classes' variables from within preprocess functions, when wanting to
 * base the additional suggestions on the path of the current page.
 *
 * @param $args
 *   An array of path arguments, such as from function arg().
 * @param $base
 *   A string identifying the base 'thing' from which more specific suggestions
 *   are derived. For example, 'page' or 'html'.
 * @param $delimiter
 *   The string used to delimit increasingly specific information. The default
 *   of '__' is appropriate for theme hook suggestions. '-' is appropriate for
 *   extra classes.
 *
 * @return
 *   An array of suggestions, suitable for adding to
 *   $variables['theme_hook_suggestions'] within a preprocess function or to
 *   $variables['classes'] if the suggestions represent extra CSS classes.
 */
function theme_get_suggestions($args, $base, $delimiter = '__') {

  // Build a list of suggested theme hooks or body classes in order of
  // specificity. One suggestion is made for every element of the current path,
  // though numeric elements are not carried to subsequent suggestions. For
  // example, for $base='page', http://www.example.com/node/1/edit would result
  // in the following suggestions and body classes:
  //
  // page__node              page-node
  // page__node__%           page-node-%
  // page__node__1           page-node-1
  // page__node__edit        page-node-edit

  $suggestions = array();
  $prefix = $base;
  foreach ($args as $arg) {
    // Remove slashes or null per SA-CORE-2009-003 and change - (hyphen) to _
    // (underscore).
    //
    // When we discover templates in @see backdrop_find_theme_templates,
    // hyphens (-) are converted to underscores (_) before the theme hook
    // is registered. We do this because the hyphens used for delimiters
    // in hook suggestions cannot be used in the function names of the
    // associated preprocess functions. Any page templates designed to be used
    // on paths that contain a hyphen are also registered with these hyphens
    // converted to underscores so here we must convert any hyphens in path
    // arguments to underscores here before fetching theme hook suggestions
    // to ensure the templates are appropriately recognized.
    $arg = str_replace(array("/", "\\", "\0", '-'), array('', '', '', '_'), $arg);
    // The percent acts as a wildcard for numeric arguments since
    // asterisks are not valid filename characters on many filesystems.
    if (is_numeric($arg)) {
      $suggestions[] = $prefix . $delimiter . '%';
    }
    $suggestions[] = $prefix . $delimiter . $arg;
    if (!is_numeric($arg)) {
      $prefix .= $delimiter . $arg;
    }
  }
  if (backdrop_is_front_page()) {
    // Front templates should be based on root only, not prefixed arguments.
    $suggestions[] = $base . $delimiter . 'front';
  }

  return $suggestions;
}

/**
 * Prepares variables for maintenance-page templates.
 *
 * The variables array generated here is a mirror of
 * template_preprocess_page(). This preprocessor will run its course when
 * theme_maintenance_page() is invoked. An alternate template file of
 * maintenance-page--offline.tpl.php can be used when the database is offline to
 * hide errors and completely replace the content.
 *
 * The $variables array contains the following arguments:
 * - $content
 *
 * @see maintenance-page.tpl.php
 */
function template_preprocess_maintenance_page(&$variables) {
  // Load site config if available, fallback to the default.
  try {
    $site_config = config('system.core');
    $site_name = filter_xss_admin($site_config->getTranslated('site_name'));
    $site_slogan = filter_xss_admin($site_config->getTranslated('site_slogan'));
  }
  catch (ConfigException $e) {
    $site_name = 'Backdrop CMS';
    $site_slogan = '';
  }

  // Add favicon to the page.
  $favicon = backdrop_get_favicon();
  backdrop_add_html_head_link(array('rel' => 'shortcut icon', 'href' => $favicon['path'], 'type' => $favicon['type']));

  // Construct head <title>.
  $head_title = array();
  if (backdrop_get_title()) {
    $head_title['title'] = strip_tags(backdrop_get_title());
  }
  $head_title['name'] = $site_name ? $site_name : 'Backdrop CMS';
  if ($site_slogan) {
    $head_title['slogan'] = $site_slogan;
  }

  // Set the default language if necessary.
  $language = isset($GLOBALS['language']) ? $GLOBALS['language'] : language_default();

  // Initialize attributes which are specific to the html element.
  $variables['html_attributes'] = array();
  $variables['html_attributes']['lang'] = $language->langcode;
  $variables['html_attributes']['dir'] = $language->direction ? 'rtl' : 'ltr';

  $variables['head_title_array']  = $head_title;
  $variables['head_title']        = implode(' | ', $head_title);
  $variables['base_path']         = base_path();
  $variables['front_page']        = url();
  $variables['breadcrumb']        = '';
  $variables['feed_icons']        = '';
  $variables['messages']          = $variables['show_messages'] ? theme('status_messages') : '';
  $variables['main_menu']         = array();
  $variables['secondary_menu']    = array();
  $variables['logo']              = backdrop_get_logo();
  $variables['site_name']         = $site_name;
  $variables['site_slogan']       = $site_slogan;
  $variables['tabs']              = '';
  $variables['title']             = backdrop_get_title();

  // Compile a list of classes that are going to be applied to the body element.
  $variables['classes'][] = 'in-maintenance';
  if (isset($variables['db_is_active']) && !$variables['db_is_active']) {
    $variables['classes'][] = 'db-offline';
  }

  // Dead databases will show error messages so supplying this template will
  // allow themers to override the page and the content completely.
  if (isset($variables['db_is_active']) && !$variables['db_is_active']) {
    $variables['theme_hook_suggestion'] = 'maintenance_page__offline';
  }
}