<?php
// $Id$

/**
 * @file
 * Enables semantically enriched output for Drupal sites.
 *
 * This module introduces RDFa to Drupal, which provides a set of XHTML
 * attributes to augment visual data with machine-readable hints.
 * @see http://www.w3.org/TR/xhtml-rdfa-primer/
 *
 * Modules can provide mappings of their bundles' data and metadata to RDFa
 * properties using the appropriate vocabularies. This module takes care of
 * injecting that data into variables available to themers in the .tpl files.
 * Drupal core themes ship with RDFa output enabled.
 *
 * Example mapping from node.module:
 *   array(
 *    'type' => 'node',
 *    'bundle' => RDF_DEFAULT_BUNDLE,
 *    'mapping' => array(
 *      'rdftype' => array('sioc:Item', 'foaf:Document'),
 *      'title'   => array(
 *        'predicates' => array('dc:title'),
 *      ),
 *      'created' => array(
 *        'predicates' => array('dc:date', 'dc:created'),
 *        'datatype' => 'xsd:dateTime',
 *        'callback' => 'date_iso8601',
 *      ),
 *      'body'    => array(
 *        'predicates' => array('content:encoded'),
 *      ),
 *      'uid'     => array(
 *        'predicates' => array('sioc:has_creator'),
 *      ),
 *      'name'    => array(
 *        'predicates' => array('foaf:name'),
 *      ),
 *    ),
 *  );
 */

/**
 * Defines the empty string as the name of the bundle to store default
 * RDF mappings of a type's properties (fields, et. al.).
 */
define('RDF_DEFAULT_BUNDLE', '');

/**
 * Implements hook_theme().
 */
function rdf_theme() {
  return array(
    'rdf_template_variable_wrapper' => array(
      'arguments' => array('content' => NULL, 'attributes' => array(), 'context' => array(), 'inline' => TRUE),
    ),
    'rdf_metadata' => array(
      'arguments' => array('metadata' => array()),
    ),
  );
}

/**
 * Wraps a template variable in an HTML element with the desired attributes.
 *
 * This is called by rdf_process() shortly before the theme system renders
 * a template file. It is called once for each template variable for which
 * additional attributes are needed. While template files are responsible for
 * rendering the attributes for the template's primary object (via the
 * $attributes variable), title (via the $title_attributes variable), and
 * content (via the $content_attributes variable), additional template variables
 * that need containing attributes are routed through this function, allowing
 * the template file to receive properly wrapped variables.
 *
 * @param $variables
 *   An associative array containing:
 *   - content: A string of content to be wrapped with attributes.
 *   - attributes: An array of attributes desired on the wrapping element.
 *   - context: An array of context information about the content to be wrapped:
 *     - 'hook': The theme hook that will use the wrapped content. This
 *       corresponds to the key within the theme registry for this template.
 *       For example, if this content is about to be used in node.tpl.php or
 *       node-TYPE.tpl.php, then the 'hook' is 'node'.
 *     - 'variable_name': The name of the variable, by which the template will
 *       refer to this content. Each template file has documentation about
 *       the variables it uses. For example, if this function is called in
 *       preparing the $author variable for comment.tpl.php, then the
 *       'variable_name' is 'author'.
 *     - 'variables': The full array of variables about to be passed to the
 *       template.
 *   - inline: TRUE if the content contains only inline HTML elements and
 *     therefore can be validly wrapped by a 'span' tag. FALSE if the content
 *     might contain block level HTML elements and therefore cannot be validly
 *     wrapped by a 'span' tag. Modules implementing preprocess functions that
 *     set 'rdf_template_variable_attributes_array' for a particular template
 *     variable that might contain block level HTML must also implement
 *     hook_preprocess_rdf_template_variable_wrapper() and set 'inline' to FALSE
 *     for that context. Themes that render normally inline content with block
 *     level HTML must similarly implement
 *     hook_preprocess_rdf_template_variable_wrapper() and set 'inline'
 *     accordingly.
 *
 * @return
 *   A string containing the wrapped content. The template receives the for its
 *   variable instead of the original content.
 *
 * Tip for themers: if you're already outputting a wrapper element around a
 * particular template variable in your template file and if you don't want
 * an extra wrapper element, you can override this function to not wrap that
 * variable and instead print:
 * @code
 * drupal_attributes($rdf_template_variable_attributes_array[$variable_name])
 * @endcode
 * inside your template file.
 *
 * @see rdf_process()
 *
 * @ingroup themeable
 */
function theme_rdf_template_variable_wrapper($variables) {
  $output = $variables['content'];
  if (!empty($output) && !empty($variables['attributes'])) {
    $attributes = drupal_attributes($variables['attributes']);
    $output = $variables['inline'] ? "<span$attributes>$output</span>" : "<div$attributes>$output</div>";
  }
  return $output;
}

/**
 * Outputs a series of empty spans for exporting RDF metadata in RDFa.
 *
 * Sometimes it is useful to export data which is not semantically present in
 * the HTML output. For example, a hierarchy of comments is visible for a human
 * but not for machines because this hiearchy is not present in the DOM tree.
 * We can express it in RDFa via empty span tags. These won't be visible and
 * will give machines extra information about the content and its structure.
 *
 * @param $variables
 *   An associative array containing:
 *   - metadata: An array of attribute arrays. Each item in the array
 *     corresponds to its own set of attributes, and therefore, needs its own
 *     element.
 *
 * @return
 *   A string of HTML containing markup that can be understood by an RDF parser.
 *
 * Tip for themers: while this default implementation results in valid markup
 * for the XHTML+RDFa doctype, you may need to override this in your theme to be
 * valid for doctypes that don't support empty spans. Or, if empty spans create
 * visual problems in your theme, you may want to override this to set a
 * class on them, and apply a CSS rule of display:none for that class.
 *
 * @see rdf_process()
 *
 * @ingroup themeable
 */
function theme_rdf_metadata($variables) {
  $output = '';
  foreach ($variables['metadata'] as $attributes) {
    $output .= '<span' . drupal_attributes($attributes) . ' />';
  }
  return $output;
}

/**
 * Template process function for adding extra tags to hold RDFa attributes.
 *
 * Since template files already have built-in support for $attributes,
 * $title_attributes, and $content_attributes, and field templates have support
 * for $item_attributes, we try to leverage those as much as possible. However,
 * in some cases additional attributes are needed not covered by these. We deal
 * with those here.
 */
function rdf_process(&$variables, $hook) {
  // Handle attributes needed for content not covered by title, content,
  // and field items. Do this by adjusting the variable sent to the template
  // so that the template doesn't have to worry about it.
  // @see theme_rdf_template_variable_wrapper()
  if (!empty($variables['rdf_template_variable_attributes_array'])) {
    foreach ($variables['rdf_template_variable_attributes_array'] as $variable_name => $attributes) {
      $context = array('hook' => $hook, 'variable_name' => $variable_name, 'variables' => $variables);
      $variables[$variable_name] = theme('rdf_template_variable_wrapper', array('content' => $variables[$variable_name], 'attributes' => $attributes, 'context' => $context));
    }
  }
  // Handle additional attributes about a template entity that for RDF parsing
  // reasons, can't be placed into that template's $attributes variable. This
  // is "meta" information that is related to particular content, so render it
  // close to that content.
  if (!empty($variables['rdf_metadata_attributes_array'])) {
    if (!isset($variables['content']['#prefix'])) {
      $variables['content']['#prefix'] = '';
    }
    $variables['content']['#prefix'] = theme('rdf_metadata', array('metadata' => $variables['rdf_metadata_attributes_array'])) . $variables['content']['#prefix'];
  }
}

/**
 * Returns the mapping for the attributes of the given type, bundle pair.
 *
 * @param $type
 *   An entity type.
 * @param $bundle
 *   A bundle name.
 * @return array
 *   The mapping corresponding to the requested type, bundle pair or an empty
 *   array.
 */
function rdf_get_mapping($type, $bundle = RDF_DEFAULT_BUNDLE) {
  // Retrieve the mapping from the entity info.
  $entity_info = entity_get_info($type);
  if (!empty($entity_info['bundles'][$bundle]['rdf_mapping'])) {
    return $entity_info['bundles'][$bundle]['rdf_mapping'];
  }
  else {
    return _rdf_get_default_mapping($type);
  }
}

/**
 * Saves an RDF mapping to the database.
 *
 * Takes a mapping structure returned by hook_rdf_mapping() implementations
 * and creates or updates a record mapping for each encountered
 * type, bundle pair. If available, adds default values for non-existent
 * mapping keys.
 *
 * @param $mapping
 *   The RDF mapping to save, as an array.
 * @return
 *   Status flag indicating the outcome of the operation.
 */
function rdf_save_mapping($mapping) {
  // Adds default values for non-existent keys.
  $new_mapping = $mapping['mapping'] + _rdf_get_default_mapping($mapping['type']);
  $exists = (bool)rdf_read_mapping($mapping['type'], $mapping['bundle']);

  if ($exists) {
    rdf_update_mapping($mapping['type'], $mapping['bundle'], $new_mapping);
    return SAVED_UPDATED;
  }
  else {
    rdf_create_mapping($mapping['type'], $mapping['bundle'], $new_mapping);
    return SAVED_NEW;
  }

  cache_clear_all('entity_info', 'cache');
  drupal_static_reset('entity_get_info');
}

/**
 * Implements hook_modules_installed().
 *
 * Checks if the installed modules have any RDF mapping definitions to declare
 * and stores them in the rdf_mapping table.
 *
 * While both default entity mappings and specific bundle mappings can be
 * defined in hook_rdf_mapping(), we do not want to save the default entity
 * mappings in the database because users are not expected to alter these.
 * Instead they should alter specific bundle mappings which are stored in the
 * database so that they can be altered via the RDF CRUD mapping API.
 */
function rdf_modules_installed($modules) {
  // We need to clear the caches of entity_info as this is not done right
  // during the tests. see http://drupal.org/node/594234
  cache_clear_all('entity_info', 'cache');
  drupal_static_reset('entity_get_info');

  foreach ($modules as $module) {
    if (function_exists($module . '_rdf_mapping')) {
      $mapping_array = call_user_func($module . '_rdf_mapping');
      foreach ($mapping_array as $mapping) {
        // Only the bundle mappings are saved in the database.
        if ($mapping['bundle'] != RDF_DEFAULT_BUNDLE) {
          rdf_save_mapping($mapping);
        }
      }
    }
  }
}

/**
 * Implements hook_modules_uninstalled().
 */
function rdf_modules_uninstalled($modules) {
// @todo remove the RDF mappings.
}

/**
 * Implements hook_entity_info_alter().
 *
 * Adds the proper RDF mapping to each entity type, bundle pair.
 */
function rdf_entity_info_alter(&$entity_info) {
  // Loop through each entity type and its bundles.
  foreach ($entity_info as $entity_type => $entity_type_info) {
    if (isset($entity_type_info['bundles'])) {
      foreach ($entity_type_info['bundles'] as $bundle => $bundle_info) {
        if ($mapping = rdf_read_mapping($entity_type, $bundle)) {
          $entity_info[$entity_type]['bundles'][$bundle]['rdf_mapping'] = $mapping;
        }
        else {
          // If no mapping was found in the database, assign the default RDF
          // mapping for this entity type.
          $entity_info[$entity_type]['bundles'][$bundle]['rdf_mapping'] = _rdf_get_default_mapping($entity_type);
        }
      }
    }
  }
}

/**
 * Returns ready to render RDFa attributes for the given mapping.
 *
 * @param $mapping
 *   An array containing a mandatory predicates key and optional datatype,
 *   callback and type keys.
 *   Example:
 *   array(
 *     'predicates' => array('dc:created'),
 *     'datatype' => 'xsd:dateTime',
 *     'callback' => 'date_iso8601',
 *   )
 * @param $data
 *   A value that needs to be converted by the provided callback function.
 * @return array
 *   An array containing RDFa attributes ready for rendering.
 */
function drupal_rdfa_attributes($mapping, $data = NULL) {
  // The type of mapping defaults to 'property'.
  $type = isset($mapping['type']) ? $mapping['type'] : 'property';

  switch ($type) {
  // The mapping expresses the relationship between two resources.
  case 'rel':
  case 'rev':
    $attributes[$type] = $mapping['predicates'];
    break;

  // The mapping expressed the relationship between a resource and some
  // literal text.
  case 'property':
    $attributes['property'] = $mapping['predicates'];

    if (isset($mapping['callback']) && isset($data)) {
      $callback = $mapping['callback'];

      if (function_exists($callback)) {
        $attributes['content'] = call_user_func($callback, $data);
      }
      if (isset($mapping['datatype'])) {
        $attributes['datatype'] = $mapping['datatype'];
      }
    }
    break;
  }

  return $attributes;
}


/**
 * Implements hook_entity_load().
 */
function rdf_entity_load($entities, $type) {
  foreach ($entities as $entity) {
    // Extracts the bundle of the entity being loaded.
    list($id, $vid, $bundle) = field_extract_ids($type, $entity);
    $entity->rdf_mapping = rdf_get_mapping($type, $bundle);
  }
}

/**
 * Implements MODULE_preprocess_HOOK().
 */
function rdf_preprocess_node(&$variables) {
  // Add RDFa markup to the node container. The about attribute specifies the
  // URI of the resource described within the HTML element, while the typeof
  // attribute indicates its RDF type (foaf:Document, or sioc:User, etc.).
  $variables['attributes_array']['about'] = empty($variables['node_url']) ? NULL: $variables['node_url'];
  $variables['attributes_array']['typeof'] = empty($variables['node']->rdf_mapping['rdftype']) ? NULL : $variables['node']->rdf_mapping['rdftype'];

  // Add RDFa markup to the title of the node. Because the RDFa markup is added
  // to the h2 tag which might contain HTML code, we specify an empty datatype
  // to ensure the value of the title read by the RDFa parsers is a literal.
  $variables['title_attributes_array']['property'] = empty($variables['node']->rdf_mapping['title']['predicates']) ? NULL : $variables['node']->rdf_mapping['title']['predicates'];
  $variables['title_attributes_array']['datatype'] = '';

  // In full node mode, the title is not displayed by node.tpl.php so it is
  // added in the head tag of the HTML page.
  if ($variables['page']) {
    $title_attributes['property'] = empty($variables['node']->rdf_mapping['title']['predicates']) ? NULL : $variables['node']->rdf_mapping['title']['predicates'];
    $title_attributes['content'] = $variables['node_title'];
    $title_attributes['about'] = $variables['node_url'];
    drupal_add_html_head('<meta' . drupal_attributes($title_attributes) . ' />');
  }

  // Add RDFa markup for the date.
  if (!empty($variables['rdf_mapping']['created'])) {
    $date_attributes_array = drupal_rdfa_attributes($variables['rdf_mapping']['created'], $variables['created']);
    $variables['rdf_template_variable_attributes_array']['date'] = $date_attributes_array;
  }
}

/**
 * Implements MODULE_preprocess_HOOK().
 */
function rdf_preprocess_field(&$variables) {
  $entity_type = $variables['element']['#object_type'];
  $instance = $variables['instance'];
  $mapping = rdf_get_mapping($entity_type, $instance['bundle']);
  $field_name = $instance['field_name'];

  if (!empty($mapping) && !empty($mapping[$field_name])) {
    foreach ($variables['items'] as $delta => $item) {
      if (!empty($item['#item'])) {
        $variables['item_attributes_array'][$delta] = drupal_rdfa_attributes($mapping[$field_name], $item['#item']);
      }
    }
  }
}


/**
 * Implements MODULE_preprocess_HOOK().
 */
function rdf_preprocess_user_profile(&$variables) {
  // Adds RDFa markup to the user profile page. Fields displayed in this page
  // will automatically describe the user.
  // @todo move to user.module
  $account = user_load($variables['user']->uid);
  if (!empty($account->rdf_mapping['rdftype'])) {
    $variables['attributes_array']['typeof'] = $account->rdf_mapping['rdftype'];
    $variables['attributes_array']['about'] = url('user/' . $account->uid);
  }
}

/**
 * Implements MODULE_preprocess_HOOK().
 */
function rdf_preprocess_username(&$variables) {
  $account = $variables['account'];
  if (!empty($account->rdf_mapping['name'])) {
    if ($account->uid != 0) {
      // The following RDFa construct allows to fit all the needed information
      // into the a tag and avoids having to wrap it with an extra span.

      // An RDF resource for the user is created with the 'about' attribute and
      // the profile URI is used to identify this resource. Even if the user
      // profile is not accessible, we generate its URI regardless in order to
      // be able to identify the user in RDF.
      $variables['attributes_array']['about'] = url('user/' . $account->uid);
      // The 'typeof' attribute specifies the RDF type(s) of this resource. They
      // are defined in the 'rdftype' property of the user object RDF mapping.
      // Since the full user object is not available in $variables, it needs to
      // be loaded. This is due to the collision between the node and user
      // when they are merged into $account and some properties are overridden.
      $variables['attributes_array']['typeof'] = user_load($account->uid)->rdf_mapping['rdftype'];

      // This first thing we are describing is the relation between the user and
      // the parent resource (e.g. a node). Because the set of predicate link
      // the parent to the user, we must use the 'rev' RDFa attribute to specify
      // that the relationship is reverse.
      if (!empty($account->rdf_mapping['uid']['predicates'])) {
        $variables['attributes_array']['rev'] = $account->rdf_mapping['uid']['predicates'];
        // We indicate the parent identifier in the 'resource' attribute,
        // typically this is the entity URI. This is the object in RDF.
        $parent_uri = '';
        if (!empty($account->path['source'])) {
          $parent_uri = url($account->path['source']);
        }
        elseif (!empty($account->cid)) {
          $parent_uri = url('comment/' . $account->cid, array('fragment' => 'comment-' . $account->cid));
        }
        $variables['attributes_array']['resource'] = $parent_uri;
      }

      // The second information we annotate is the name of the user with the
      // 'property' attribute. We do not need to specify the RDF object here
      // because it's the value inside the a tag which will be used
      // automatically according to the RDFa parsing rules.
      $variables['attributes_array']['property'] = $account->rdf_mapping['name']['predicates'];
    }
  }
}

/**
 * Implements MODULE_preprocess_HOOK().
 */
function rdf_preprocess_comment(&$variables) {
  $comment = $variables['comment'];
  if (!empty($comment->rdf_mapping['rdftype'])) {
    // Add RDFa markup to the comment container. The about attribute specifies
    // the URI of the resource described within the HTML element, while the
    // typeof attribute indicates its RDF type (e.g. sioc:Post, etc.).
    $variables['attributes_array']['about'] = url('comment/' . $comment->cid, array('fragment' => 'comment-' . $comment->cid));
    $variables['attributes_array']['typeof'] = $comment->rdf_mapping['rdftype'];
  }

  // RDFa markup for the date of the comment.
  if (!empty($comment->rdf_mapping['created'])) {
    $date_attributes_array = drupal_rdfa_attributes($comment->rdf_mapping['created'], $comment->created);
    $variables['rdf_template_variable_attributes_array']['created'] = $date_attributes_array;
  }
  if (!empty($comment->rdf_mapping['title'])) {
    // Add RDFa markup to the subject of the comment. Because the RDFa markup is
    // added to an h3 tag which might contain HTML code, we specify an empty
    // datatype to ensure the value of the title read by the RDFa parsers is a
    // literal.
    $variables['title_attributes_array']['property'] = $comment->rdf_mapping['title']['predicates'];
    $variables['title_attributes_array']['datatype'] = '';
  }
  if (!empty($comment->rdf_mapping['body'])) {
    // We need a special case here since the comment body is not a field. Note
    // that for that reason, fields attached to comment will be ignored by RDFa
    // parsers since we set the property attribute here.
    // @todo use fields instead, see http://drupal.org/node/538164
    $variables['content_attributes_array']['property'] = $comment->rdf_mapping['body']['predicates'];
  }

  // Annotates the parent relationship between the current comment and the node
  // it belongs to. If available, the parent comment is also annotated.
  if (!empty($comment->rdf_mapping['pid'])) {
    // Relation to parent node.
    $parent_node_attributes['rel'] = $comment->rdf_mapping['pid']['predicates'];
    $parent_node_attributes['resource'] = url('node/' . $comment->nid);
    $variables['rdf_metadata_attributes_array'][] = $parent_node_attributes;

    // Relation to parent comment if it exists.
    if ($comment->pid != 0) {
      $parent_comment_attributes['rel'] = $comment->rdf_mapping['pid']['predicates'];
      $parent_comment_attributes['resource'] = url('comment/' . $comment->pid, array('fragment' => 'comment-' . $comment->pid));
      $variables['rdf_metadata_attributes_array'][] = $parent_comment_attributes;
    }
  }
}

/**
 * Implements MODULE_preprocess_HOOK().
 */
function rdf_preprocess_field_formatter_taxonomy_term_link(&$variables) {
  $term = $variables['element']['#item']['taxonomy_term'];
  if (!empty($term->rdf_mapping['rdftype'])) {
    $variables['link_options']['attributes']['typeof'] = $term->rdf_mapping['rdftype'];
  }
  if (!empty($term->rdf_mapping['name']['predicates'])) {
    $variables['link_options']['attributes']['property'] = $term->rdf_mapping['name']['predicates'];
  }
}

/**
 * Returns the default RDF mapping for the given entity type.
 *
 * @param $type
 *   An entity type.
 * @return array
 *   The RDF mapping or an empty array.
 */
function _rdf_get_default_mapping($type) {
  $default_mappings = &drupal_static(__FUNCTION__, array());

  if (empty($default_mappings)) {
    // Get all modules implementing hook_rdf_mapping().
    $modules = module_implements('rdf_mapping');

    // Only consider the default entity mapping definitions.
    foreach ($modules as $module) {
      $mappings = module_invoke($module, 'rdf_mapping');
      foreach ($mappings as $mapping) {
        if ($mapping['bundle'] == RDF_DEFAULT_BUNDLE) {
          $default_mappings[$mapping['type']] = $mapping['mapping'];
        }
      }
    }
  }

  return empty($default_mappings[$type]) ? array() : $default_mappings[$type];
}

/**
 * Create an RDF mapping binded to a bundle and an entity type.
 *
 * RDF CRUD API, handling RDF mapping creation and deletion.
 *
 * @param $type
 *   The entity type the mapping refers to (node, user, comment, term, etc.).
 * @param $bundle
 *   The bundle the mapping refers to.
 * @param $mapping
 *   An associative array represeting an RDF mapping structure.
 * @return array
 *   The stored mapping.
 */
function rdf_create_mapping($type, $bundle, $mapping) {
  $fields = array(
    'type' => $type,
    'bundle' => $bundle,
    'mapping' => serialize($mapping)
  );

  db_insert('rdf_mapping')->fields($fields)->execute();

  return $mapping;
}

/**
 * Read an RDF mapping record directly from the database.
 *
 * RDF CRUD API, handling RDF mapping creation and deletion.
 *
 * @param $type
 *   The entity type the mapping refers to.
 * @param $bundle
 *   The bundle the mapping refers to.
 * @return array
 *   An RDF mapping structure or FALSE if the mapping could not be found.
 */
function rdf_read_mapping($type, $bundle) {
  $query = db_select('rdf_mapping')->fields(NULL, array('mapping'))
    ->condition('type', $type)->condition('bundle', $bundle)->execute();

  $mapping = unserialize($query->fetchField());

  if (!is_array($mapping)) {
    $mapping = array();
  }

  return $mapping;
}

/**
 * Update an RDF mapping binded to a bundle and an entity type.
 *
 * RDF CRUD API, handling RDF mapping creation and deletion.
 *
 * @param $type
 *   The entity type the mapping refers to.
 * @param $bundle
 *   The bundle the mapping refers to.
 * @param $mapping
 *   An associative array representing an RDF mapping structure.
 * @return bool
 *   Return boolean TRUE if mapping updated, FALSE if not.
 */
function rdf_update_mapping($type, $bundle, $mapping) {
  $fields = array('mapping' => serialize($mapping));
  $num_rows = db_update('rdf_mapping')->fields($fields)
    ->condition('type', $type)->condition('bundle', $bundle)->execute();

  return (bool) ($num_rows > 0);
}

/**
 * Delete the mapping for the given pair of type and bundle from the database.
 *
 * RDF CRUD API, handling RDF mapping creation and deletion.
 *
 * @param $type
 *   The entity type the mapping refers to.
 * @param $bundle
 *   The bundle the mapping refers to.
 * @return bool
 *   Return boolean TRUE if mapping deleted, FALSE if not.
 */
function rdf_delete_mapping($type, $bundle) {
  $num_rows = db_delete('rdf_mapping')->condition('type', $type)
    ->condition('bundle', $bundle)->execute();

  return (bool) ($num_rows > 0);
}