<?php
// $Id: rdf.module,v 1.30 2009/03/25 04:20:41 arto Exp $

//////////////////////////////////////////////////////////////////////////////
// Module settings

define('RDF_SCHEMA_URI',        rdf_get_schema_uri());
define('RDF_SCHEMA_MODULE_URI', 'http://drupal.org/project/rdf#schema');
define('RDF_RSS_URI',           'http://purl.org/rss/1.0/');

//////////////////////////////////////////////////////////////////////////////
// Core API hooks

/**
 * Implementation of hook_init().
 */
function rdf_init() {
  module_load_include('inc', 'rdf', 'rdf.api');
  module_load_include('inc', 'rdf', 'rdf.db');
  module_load_include('inc', 'rdf', 'rdf.schema');

  rdf_define_vocabularies(); // TODO: replace with autoload-based solution

  if (user_access('access RDF data')) {
    rdf_add_autodiscovery_link(t('RDF'), url('rdf'));
  }

  // Attempt to load the ARC2 library, if available. This library must be
  // manually installed by the administrator due to license incompatibility.
  if (!class_exists('ARC2')) {
    @include_once RDF_ARC2_PATH . '/ARC2.php';
  }

  // Integrate some RDF operations into the Services API, if available:
  if (module_exists('services')) {
    module_load_include('inc', 'rdf', 'rdf.services');
  }

  // Integrate with FeedAPI and the Feed Element Mapper, if installed:
  if (module_exists('feedapi')) {
    module_load_include('inc', 'rdf', 'rdf.feedapi');
  }

  // Replace the theme's DOCTYPE with the RDFa DOCTYPE, if enabled:
  if (variable_get('rdf_rdfa_doctype', FALSE)) {
    // Implement hook_exit() to mark us as incompatible with aggressive caching:
    function rdf_exit($destination = NULL) {}
    ob_start('_rdf_ob_handler');
  }
}

/**
 * Implementation of hook_help().
 */
function rdf_help($path, $arg = NULL) {
  switch ($path) {
    case 'admin/content/rdf':
      return '<p>' . t('Any knowledge about anything can be decomposed into statements of <em>triples</em> (3-tuples) consisting of <em>subject</em>, <em>predicate</em>, and <em>object</em>.') . '</p>';
    case 'admin/settings/rdf':
      return '<p>' . t('<a href="http://drupal.org/handbook/modules/rdf" title="Resource Description Framework">RDF</a> is a <a href="http://www.w3.org/RDF/">W3C standard</a> for modeling and sharing distributed knowledge based on a decentralized open-world assumption.') . '</p>';
    case 'admin/settings/rdf#formats':
      return '<p>' . t('RDF data can be serialized into a number of textual formats (also known as representations). The two built-in, always available formats are <a href="http://drupal.org/node/219870">RDF/PHP</a> and <a href="http://drupal.org/node/219874">RDF/JSON</a>. For interoperability with more RDF formats, you can <a href="@status">install the ARC2 library</a> which adds parsing/serialization support for several widespread formats.', array('@status' => url('admin/reports/status'))) . '</p>';
    case 'admin/settings/rdf/mappings':
      return '<p>' . t('This is a summary of the currently defined mappings between Drupal data and RDF classes/properties.') . '</p>';
    case 'admin/settings/rdf/feeds':
      return '<p>' . t('This is a list of the <a href="http://web.resource.org/rss/1.0/">RSS 1.0</a>-compatible RDF feeds available on this Drupal site.') . '</p>';
    case 'admin/settings/rdf/feeds/edit/%':
      return '<p>' . t('') . '</p>'; // TODO
    case 'admin/settings/rdf/namespaces':
      return '<p>' . t('<a href="http://drupal.org/node/219858#namespaces">Namespaces</a> define URI abbreviations for use in <a href="http://drupal.org/node/219856#curie" title="Compact URIs">CURIEs</a> and for purposes of human-friendly display of RDF data.') . '</p>';
    case 'admin/settings/rdf/contexts':
      return '<p>' . t('<a href="http://drupal.org/node/219858#contexts">Contexts</a>, also known as <a href="http://www.w3.org/2004/03/trix/">named graphs</a>, provide a mechanism for grouping RDF statements (e.g. by their provenance), facilitating mass operations on a set of statements.') . '</p>';
    case 'admin/settings/rdf/repositories':
      return '<p>' . t('<a href="http://drupal.org/node/219858#repositories">Repositories</a> are storage containers for RDF data, and can be implemented, for instance, in terms of an in-memory triple store, a serialized file on disk, an RDBMS database, or an RPC connection to a remote service.') . '</p>';
    case 'admin/settings/rdf/repositories/rdf/add':
      return '<p>' . t('To create a new local RDF repository, enter the human-readable name, the machine-readable name, and all other relevant fields that are on this page.') . '</p>';
  }
}

/**
 * Implementation of hook_perm().
 */
function rdf_perm() {
  return array(
    'access RDF data',
    'administer RDF data',
    'administer RDF repositories',
    'import RDF data',
    'export RDF data',
    'export site settings',
    'import site settings',
    'export enabled modules',
    'import enabled modules',
  );
}

/**
 * Implementation of hook_menu().
 */
function rdf_menu() {
  module_load_include('inc', 'rdf', 'rdf.menu');
  return rdf_menu_build();
}

/**
 * Implementation of hook_menu_alter().
 */
function rdf_menu_alter(&$items) {
  // Override the RSS feeds output by Drupal's core modules:
  foreach (rdf_rdf_feeds() as $feed_id => $feed) {
    if (($feed = (object)$feed) && !empty($feed->enabled) && module_exists($feed->module)) {
      $path = isset($feed->menu) ? $feed->menu : $feed->path;

      if (isset($items[$path])) {
        $arguments = empty($items[$path]['page arguments']) ? array($feed_id) : array_merge(array($feed_id), $items[$path]['page arguments']);
        $items[$path]['page callback']  = 'rdf_feed_callback';
        $items[$path]['page arguments'] = $arguments;
        $items[$path]['module']         = 'rdf';
        $items[$path]['file']           = 'rdf.pages.inc';
      }
    }
  }
}

/**
 * Implementation of hook_hook_info()
 */
function rdf_hook_info() {
  return array(
    'rdf' => array(
      'rdf' => array(
        'insert' => array(
          'runs when' => t('After inserting a new RDF statement'),
        ),
        'update' => array(
          'runs when' => t('After deleting an existing RDF statement'),
        ),
      ),
    ),
  );
}

/**
 * Implementation of hook_theme()
 */
function rdf_theme() {
  return array(
    'rdf_property_table' => array(
      'arguments' => array('data' => NULL),
      'file' => 'rdf.theme.inc',
    ),
    'rdf_triple_table' => array(
      'arguments' => array('data' => NULL),
      'file' => 'rdf.theme.inc',
    ),
    'rdf_triple_row' => array(
      'arguments' => array('subject' => NULL, 'predicate' => NULL, 'object' => NULL),
      'file' => 'rdf.theme.inc',
    ),
    'rdf_triple_cell' => array(
      'arguments' => array('value' => NULL),
      'file' => 'rdf.theme.inc',
    ),
    'rdf_value' => array(
      'arguments' => array('value' => NULL),
      'file' => 'rdf.theme.inc',
    ),
    'rdf_admin_settings' => array(
      'arguments' => array('form' => NULL),
      'file' => 'rdf.admin.inc',
    ),
    'rdf_admin_data' => array(
      'arguments' => array('form' => NULL),
      'file' => 'rdf.admin.inc',
    ),
  );
}

/**
 * Implementation of hook_cron().
 */
function rdf_cron() {
  // TODO: Run CHECK TABLE on {rdf_data_*}

  // Merge duplicate statements in the {rdf_data_*} tables:
  if (variable_get('rdf_db_merge_duplicates', FALSE)) {
    foreach (rdf_db_get_repository_tables() as $table) {
      rdf_db_merge_duplicate_statements($table);
    }
  }

  // Purge unused URLs from the {rdf_resources} table:
  if (variable_get('rdf_db_purge_resources', FALSE)) {
    // TODO
  }
}

/**
 * Implementation of hook_user().
 */
function rdf_user($op, &$edit, &$account, $category = NULL) {
  switch ($op) {
    case 'view':
      if (user_access('access RDF data')) {
        rdf_add_autodiscovery_link(t('RDF'), url('user/' . $account->uid . '/rdf'));
      }
      break;
  }
}

/**
 * Implementation of hook_nodeapi().
 */
function rdf_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  switch ($op) {
    case 'load':
    case 'prepare':
      $node->rdf = isset($node->rdf) ? $node->rdf : array(); // used e.g. by rdf_feedapi_mapper()
      break;

    case 'insert':
    case 'update':
      // This is a mechanism for overcoming the limitation that when working
      // with a new $node object that hasn't yet been stored in the
      // database, and hence doesn't have a $node->nid, it isn't possible to
      // stores triples relating to the node; a lack of $node->nid implies a
      // lack of an URI for the node. However, by populating $node->rdf with
      // properties and values, we'll here take care of inserting triples,
      // using the node's URI as subject, once the node has been created and
      // $node->nid is available. For convenience and consistency, we
      // provide the same facility for node updates, too.
      //
      // For example:
      //   $node->rdf['dc:origin'] = rdf_uri("http://...");
      // ...will result in the insertion of a triple of:
      //   array('node/' . $node->nid, 'dc:origin', rdf_uri("http://..."));
      //
      if (isset($node->nid) && !empty($node->rdf)) {
        $uri = url('node/' . $node->nid, array('absolute' => TRUE, 'alias' => TRUE));
        rdf_insert_all(rdf_denormalize(array($uri => $node->rdf)), !empty($node->rdf_options) ? $node->rdf_options : array());
        $node->rdf = array();
      }
      break;

    case 'view':
      // Add an RDF autodiscovery link when the node is displayed by itself as a page:
      if (user_access('access RDF data') && !empty($a4)) {
        rdf_add_autodiscovery_link(t('RDF'), url('node/' . $node->nid . '/rdf'));
      }
      break;
  }
}

/**
 * Implementation of hook_taxonomy().
 */
function rdf_taxonomy($op, $type, $array = NULL) {
  if ($type == 'vocabulary') {
    switch ($op) {
      case 'insert':
      case 'update':
        if (!empty($array['rdf_property'])) {
          variable_set('rdf_schema_property_vocabulary_'. $array['vid'], rdf_qname_to_uri($array['rdf_property']));
        }
        else {
          variable_del('rdf_schema_property_vocabulary_'. $array['vid']);
        }
        break;
      case 'delete':
        variable_del('rdf_schema_property_vocabulary_'. $array['vid']);
        break;
    }
  }
}

/**
 * Implementation of hook_form_alter().
 */
function rdf_form_alter(&$form, $form_state, $form_id) {
  switch ($form_id) {
    // Administer >> User management >> Profiles >> Edit
    case 'profile_field_form':
      // The submitted value is stored using the callback function defined below.
      $rdf_mapping = isset($form['fid']['#value']) ? variable_get('rdf_schema_property_profile_'. $form['fid']['#value'], '') : '';
      $form['rdf_mapping'] = array('#type' => 'fieldset', '#title' => t('RDF mapping'), '#collapsible' => TRUE, '#collapsed' => FALSE, '#weight' => 1);
      $form['rdf_mapping']['rdf_property'] = array(
        '#type'          => 'textfield',
        '#title'         => t('RDF property'),
        '#default_value' => rdf_uri_to_qname($rdf_mapping, FALSE, $rdf_mapping),
        '#maxlength'     => 255,
        '#description'   => t(''), // TODO
        '#autocomplete_path' => 'rdf/autocomplete/property',
      );
      $form['submit']['#weight'] = 40;
      $form['#validate'][] = 'rdf_schema_property_form_validate';
      $form['#submit'][] = 'rdf_schema_profile_field_form_submit';
      break;

    // Administer >> Content management >> Taxonomy >> Edit vocabulary
    case 'taxonomy_form_vocabulary':
      // The submitted value is stored in our implementation of hook_taxonomy()
      $rdf_mapping = isset($form['vid']['#value']) ? variable_get('rdf_schema_property_vocabulary_'. $form['vid']['#value'], '') : '';
      $form['rdf_mapping'] = array('#type' => 'fieldset', '#title' => t('RDF mapping'), '#collapsible' => TRUE, '#collapsed' => FALSE, '#weight' => 1);
      $form['rdf_mapping']['rdf_property'] = array(
        '#type'          => 'textfield',
        '#title'         => t('RDF property'),
        '#default_value' => rdf_uri_to_qname($rdf_mapping, FALSE, $rdf_mapping),
        '#maxlength'     => 255,
        '#description'   => t(''), // TODO
        '#autocomplete_path' => 'rdf/autocomplete/property',
      );
      $form['submit']['#weight'] = 40;
      $form['delete']['#weight'] = 45;
      $form['#validate'][] = 'rdf_schema_property_form_validate';
      break;

    // Administer >> Content management >> Content types >> Edit
    case 'node_type_form':
      // The submitted value is auto-saved by node.module as a configuration variable with a name in the form 'rdf_schema_class_TYPE'
      $rdf_mapping = variable_get('rdf_schema_class_'. $form['#node_type']->type, '');
      $form['rdf_mapping'] = array('#type' => 'fieldset', '#title' => t('RDF mapping'), '#collapsible' => TRUE, '#collapsed' => TRUE, '#weight' => 1);
      $form['rdf_mapping']['rdf_schema_class'] = array(
        '#type'          => 'textfield',
        '#title'         => t('RDF class'),
        '#default_value' => rdf_uri_to_qname($rdf_mapping, FALSE, $rdf_mapping),
        '#maxlength'     => 255,
        '#description'   => t(''), // TODO
        '#autocomplete_path' => 'rdf/autocomplete/class',
      );
      $form['#validate'][] = 'rdf_schema_class_form_validate';
      break;

    // Administer >> Content management >> Content types >> (content type) >> Manage fields >> Configure
    case 'content_field_edit_form':
      // The submitted value is stored using the callback function defined below.
      $rdf_mapping = variable_get('rdf_schema_property_content_' . $form['field_name']['#value'], '');
      $form['rdf_mapping'] = array('#type' => 'fieldset', '#title' => t('RDF mapping'), '#collapsible' => FALSE, '#collapsed' => FALSE, '#weight' => 1);

      // Ordinary CCK fields
      if (empty($form['#field']['todate'])) {
        $form['rdf_mapping']['rdf_property'] = array(
          '#type'          => 'textfield',
          '#title'         => t('RDF property'),
          '#default_value' => rdf_uri_to_qname($rdf_mapping, FALSE, $rdf_mapping),
          '#maxlength'     => 255,
          '#description'   => t(''), // TODO
          '#autocomplete_path' => 'rdf/autocomplete/property',
        );
      }
      // HACK: support CCK Date fields that have both a start and an end date:
      else { // $form['#field']['todate'] == 'optional' | 'required'
        // From date
        $rdf_mapping = variable_get('rdf_schema_property_content_' . $form['field_name']['#value'] . '[from]', $rdf_mapping);
        $form['rdf_mapping']['rdf_property_from'] = array(
          '#type'          => 'textfield',
          '#title'         => t('RDF property (from date)'),
          '#default_value' => rdf_uri_to_qname($rdf_mapping, FALSE, $rdf_mapping),
          '#maxlength'     => 255,
          '#description'   => t(''), // TODO
          '#autocomplete_path' => 'rdf/autocomplete/property',
        );
        // To date
        $rdf_mapping = variable_get('rdf_schema_property_content_' . $form['field_name']['#value'] . '[to]', '');
        $form['rdf_mapping']['rdf_property_to'] = array(
          '#type'          => 'textfield',
          '#title'         => t('RDF property (to date)'),
          '#default_value' => rdf_uri_to_qname($rdf_mapping, FALSE, $rdf_mapping),
          '#maxlength'     => 255,
          '#description'   => t(''), // TODO
          '#autocomplete_path' => 'rdf/autocomplete/property',
        );
      }

      $form['submit']['#weight'] = 90;
      $form['#validate'][] = 'rdf_schema_property_form_validate';
      $form['#submit'][]   = 'rdf_schema_content_field_form_submit';
      break;
  }
}

//////////////////////////////////////////////////////////////////////////////
// Forms API callbacks

/**
 * @see rdf_form_alter()
 */
function rdf_schema_class_form_validate($form, &$form_state) {
  extract($form_state['values'], EXTR_SKIP | EXTR_REFS);
  $rdf_schema_class = trim($rdf_schema_class);

  if ($rdf_schema_class != '' && !rdf_is_valid_uri($rdf_schema_class) && !rdf_is_valid_curie($rdf_schema_class)) {
    form_set_error('rdf_schema_class', t('RDF class is not a valid URI or CURIE.'));
  }
  else {
    $rdf_schema_class = rdf_qname_to_uri($rdf_schema_class);
  }
}

/**
 * @see rdf_form_alter()
 */
function rdf_schema_property_form_validate($form, &$form_state) {
  extract($form_state['values'], EXTR_SKIP | EXTR_REFS);

  if (isset($rdf_property)) {
    if (($rdf_property = trim($rdf_property)) != '' && !rdf_is_valid_uri($rdf_property) &&
        !(rdf_is_valid_curie($rdf_property) && rdf_is_valid_prefix($rdf_property))) {
      form_set_error('rdf_property', t('RDF property is not a valid URI or CURIE.'));
    }
  }
  // HACK: support CCK Date fields that have both a start and an end date:
  else if (isset($rdf_property_from, $rdf_property_to)) {
    foreach (array('rdf_property_from', 'rdf_property_to') as $rdf_property) {
      if (($$rdf_property = trim($$rdf_property)) != '' && !rdf_is_valid_uri($$rdf_property) &&
          !(rdf_is_valid_curie($$rdf_property) && rdf_is_valid_prefix($$rdf_property))) {
        form_set_error($rdf_property, t('RDF property is not a valid URI or CURIE.'));
      }
    }
  }
}

/**
 * @see rdf_form_alter()
 */
function rdf_schema_profile_field_form_submit($form, &$form_state) {
  extract($form_state['values'], EXTR_SKIP | EXTR_REFS);

  if (!empty($rdf_property)) {
    variable_set('rdf_schema_property_profile_' . $fid, rdf_qname_to_uri($rdf_property));
  }
  else {
    variable_del('rdf_schema_property_profile_' . $fid);
  }
}

/**
 * @see rdf_form_alter()
 */
function rdf_schema_content_field_form_submit($form, &$form_state) {
  extract($form_state['values'], EXTR_SKIP | EXTR_REFS);

  // HACK: support CCK Date fields that have both a start and an end date:
  $rdf_properties = isset($rdf_property) ?
    array('rdf_property' => '') :
    array('rdf_property_from' => '[from]', 'rdf_property_to' => '[to]');

  foreach ($rdf_properties as $rdf_property_var => $field_suffix) {
    if (!empty($$rdf_property_var)) {
      variable_set('rdf_schema_property_content_' . $field_name . $field_suffix, rdf_qname_to_uri($$rdf_property_var));
    }
    else {
      variable_del('rdf_schema_property_content_' . $field_name . $field_suffix);
    }
  }
}

//////////////////////////////////////////////////////////////////////////////
// Views API hooks

/**
 * Implementation of hook_views_api().
 */
function rdf_views_api() {
  return array(
    'api'  => 2,
    'path' => drupal_get_path('module', 'rdf'),
  );
}

//////////////////////////////////////////////////////////////////////////////
// RDF API hooks

/**
 * Implementation of hook_rdf_feeds().
 */
function rdf_rdf_feeds() {
  $enabled = variable_get('rdf_feed_override', array());

  // Declare all RSS feeds provided by Drupal's core modules:
  $feeds = array(
    // node.module (front page feed)
    'node_feed' => array(
      'type'        => RDF_RSS_URI,
      'path'        => 'rss.xml',
      'title'       => t('Front page feed'),
      'module'      => 'node',
      'callback'    => 'rdf_feed_node_frontpage',
      'enabled'     => !empty($enabled['node_feed']),
    ),
    // taxonomy.module
    'taxonomy_term_feed' => array(
      'type'        => RDF_RSS_URI,
      'path'        => 'taxonomy/term/%/0/feed',
      'menu'        => 'taxonomy/term/%',
      'title'       => t('Taxonomy term feed'),
      'module'      => 'taxonomy',
      'callback'    => 'rdf_feed_taxonomy_term',
      'enabled'     => !empty($enabled['taxonomy_term_feed']),
    ),
    // blog.module
    'blog_feed_user' => array(
      'type'        => RDF_RSS_URI,
      'path'        => 'blog/%user/feed',
      'title'       => 'Users\' recent blog entries feed',
      'module'      => 'blog',
      'callback'    => 'rdf_feed_blog_user',
      'enabled'     => !empty($enabled['blog_feed_user']),
    ),
    'blog_feed_last' => array(
      'type'        => RDF_RSS_URI,
      'path'        => 'blog/feed',
      'title'       => 'All recent blog entries feed',
      'module'      => 'blog',
      'callback'    => 'rdf_feed_blog_last',
      'enabled'     => !empty($enabled['blog_feed_last']),
    ),
    // aggregator.module
    'aggregator_page_rss' => array(
      'type'        => RDF_RSS_URI,
      'path'        => 'aggregator/rss',
      'title'       => t('Aggregator feed'),
      'module'      => 'aggregator',
      'callback'    => 'rdf_feed_aggregator_rss',
      'enabled'     => !empty($enabled['aggregator_page_rss']),
    ),
  );

  // Declare all Views module feeds, if the module is installed:
  if (module_exists('views')) {
    module_load_include('inc', 'rdf', 'rdf.views');
    $feeds = array_merge($feeds, rdf_views_get_feeds());
  }

  return $feeds;
}

/**
 * Implementation of hook_rdf_formats().
 */
function rdf_rdf_formats() {
  return array(
    'rdf+php' => array(
      'title'       => t('RDF/PHP'),
      'link'        => 'http://drupal.org/node/219870',
      'mime_type'   => 'application/vnd.php.serialized',
      'encoding'    => 'ascii',
      'file_ext'    => 'txt',
      'serialize'   => 'rdf_serialize_php',
      'unserialize' => 'rdf_unserialize_php',
    ),
    'rdf+json' => array(
      'title'       => t('RDF/JSON'),
      'link'        => 'http://drupal.org/node/219874',
      'mime_type'   => 'application/json',
      'encoding'    => 'utf-8',
      'file_ext'    => 'js',
      'serialize'   => 'rdf_serialize_json',
      'unserialize' => 'rdf_unserialize_json',
    ),
    'rdf+xml' => array(
      'title'       => t('RDF/XML'),
      'link'        => 'http://www.w3.org/TR/rdf-syntax-grammar/',
      'mime_type'   => 'application/rdf+xml',
      'encoding'    => 'utf-8',
      'file_ext'    => 'rdf',
      'serialize'   => 'rdf_serialize_xml',
      'unserialize' => class_exists('ARC2') ? 'rdf_unserialize_xml' : NULL,
    ),
    'trix' => array(
      'title'       => t('TriX'),
      'link'        => 'http://www.w3.org/2004/03/trix/',
      'mime_type'   => 'application/trix',
      'encoding'    => 'utf-8',
      'file_ext'    => 'xml',
      'serialize'   => 'rdf_serialize_trix',
      'unserialize' => NULL,
    ),
    'turtle' => array(
      'title'       => t('Turtle'),
      'link'        => 'http://www.dajobe.org/2004/01/turtle/',
      'mime_type'   => 'application/x-turtle',
      'encoding'    => 'utf-8',
      'file_ext'    => 'ttl',
      'serialize'   => 'rdf_serialize_turtle',
      'unserialize' => class_exists('ARC2') ? 'rdf_unserialize_turtle' : NULL,
    ),
    'ntriples' => array(
      'title'       => t('N-Triples'),
      'link'        => 'http://www.w3.org/TR/rdf-testcases/#ntriples',
      'mime_type'   => 'text/plain', // TODO: any semi-standardized alternative?
      'encoding'    => 'ascii',
      'file_ext'    => 'nt',
      'serialize'   => 'rdf_serialize_ntriples',
      'unserialize' => class_exists('ARC2') ? 'rdf_unserialize_ntriples' : NULL,
    ),
  );
}

/**
 * Implementation of hook_rdf_namespaces().
 */
function rdf_rdf_namespaces() {
  $namespaces = array(
    '_'        => 'http://bnode.net/',
    'rdf'      => 'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
    'rdfs'     => 'http://www.w3.org/2000/01/rdf-schema#',
    'xsi'      => 'http://www.w3.org/2001/XMLSchema-instance#',
    'xsd'      => 'http://www.w3.org/2001/XMLSchema#',
    'owl'      => 'http://www.w3.org/2002/07/owl#',
    'dc'       => 'http://purl.org/dc/elements/1.1/',
    'dcterms'  => 'http://purl.org/dc/terms/',
    'dcmitype' => 'http://purl.org/dc/dcmitype/',
    'foaf'     => 'http://xmlns.com/foaf/0.1/',
    'rss'      => RDF_RSS_URI,
    'drupal'   => RDF_SCHEMA_URI,
  );
  foreach (rdf_schema_get_entities() as $entity) {
    $namespaces[$entity] = RDF_SCHEMA_URI . $entity .'#';
  }
  return array_merge($namespaces, rdf_db_rdf_namespaces());
}

/**
 * Implementation of hook_rdf_contexts().
 */
function rdf_rdf_contexts() {
  return array_merge(array(RDF_SITE_URI, RDF_SCHEMA_URI), rdf_db_rdf_contexts());
}

/**
 * Implementation of hook_rdf_repositories().
 */
function rdf_rdf_repositories() {
  return array_merge(array(
    'system' => array(
      'title'      => t('System'),
      'type'       => 'system',
      'persistent' => TRUE,
      'mutable'    => FALSE,
      'enabled'    => TRUE,
      'statements' => NULL,
      'module'     => 'rdf',
      'callbacks'  => array(
        'query'    => array('function' => 'rdf_rdf_query', 'arguments' => array()),
      ),
      'filters'    => array(
        'subject'  => RDF_SITE_URI,
      ),
    ),
  ), rdf_db_rdf_repositories());
}

/**
 * Implementation of hook_rdf_classes().
 */
function rdf_rdf_classes() {
  return array(
    'user' => array(
      'title'   => t('User'),
      'module'  => 'user',
      'table'   => 'users',
      'query'   => 'SELECT uid FROM {users} WHERE uid > 0',
      'uri'     => 'user/%uid',
      'enabled' => TRUE,
    ),
    'vocabulary' => array(
      'title'   => t('Taxonomy vocabulary'),
      'module'  => 'taxonomy',
      'table'   => 'vocabulary',
      'query'   => 'SELECT vid FROM {vocabulary}',
      // NOTE: Drupal vocabularies don't actually have dereferenceable URIs
      'uri'     => 'taxonomy/vocabulary/%vid',
      'enabled' => FALSE, // TODO
    ),
    'term' => array(
      'title'   => t('Taxonomy term'),
      'module'  => 'taxonomy',
      'table'   => 'term_data',
      'query'   => 'SELECT tid FROM {term_data}',
      'uri'     => 'taxonomy/term/%tid',
      'enabled' => FALSE, // TODO
    ),
    'node' => array(
      'title'   => t('Node'),
      'module'  => 'node',
      'table'   => 'node',
      'query'   => 'SELECT nid FROM {node}',
      'uri'     => 'node/%nid',
      'load'    => 'node_load',
      'enabled' => TRUE,
    ),
    'comment' => array(
      'title'   => t('Comment'),
      'module'  => 'comment',
      'table'   => 'comments',
      'query'   => 'SELECT nid, cid FROM {comments}',
      'uri'     => 'node/%nid#comment-%cid',
      'enabled' => FALSE, // TODO
    ),
    'path' => array(
      'title'   => t('URL alias'),
      'module'  => 'path',
      'table'   => 'url_alias',
      'query'   => 'SELECT dst FROM {url_alias}',
      'uri'     => '%dst',
      'enabled' => FALSE, // TODO
    ),
    'variable' => array(
      'title'   => t('Setting'),
      'module ' => 'system',
      'table'   => 'variable',
      'query'   => 'SELECT name FROM {variable}',
      'uri'     => 'rdf/variable/%name',
      'enabled' => FALSE, // TODO
    ),
  );
}

/**
 * Implementation of hook_rdf_properties().
 */
function rdf_rdf_properties() {
  return array(
    'rdf'      => array('first', 'object', 'predicate', 'rest', 'subject', 'type', 'value'),
    'rdfs'     => array('comment', 'domain', 'isDefinedBy', 'label', 'member', 'range', 'seeAlso', 'subClassOf', 'subPropertyOf'),
    'xsd'      => array('base64Binary', 'boolean', 'byte', 'date', 'dateTime', 'decimal', 'double', 'duration', 'float', 'hexBinary', 'int', 'integer', 'language', 'long', 'short', 'string', 'time', 'token'),
    'owl'      => array('allValuesFrom', 'backwardCompatibleWith', 'cardinality', 'complementOf', 'differentFrom', 'disjointWith', 'distinctMembers', 'equivalentClass', 'equivalentProperty', 'hasValue', 'imports', 'incompatibleWith', 'intersectionOf', 'inverseOf', 'maxCardinality', 'minCardinality', 'oneOf', 'onProperty', 'priorVersion', 'sameAs', 'someValuesFrom', 'unionOf', 'versionInfo'),
    'dc'       => array('contributor', 'coverage', 'creator', 'date', 'description', 'format', 'identifier', 'language', 'publisher', 'relation', 'rights', 'source', 'subject', 'title', 'type'),
    'dcterms'  => array('abstract_', 'accessRights', 'accrualMethod', 'accrualPeriodicity', 'accrualPolicy', 'alternative', 'audience', 'available', 'bibliographicCitation', 'conformsTo', 'contributor', 'coverage', 'created', 'creator', 'date', 'dateAccepted', 'dateCopyrighted', 'dateSubmitted', 'description', 'educationLevel', 'extent', 'format', 'hasFormat', 'hasPart', 'hasVersion', 'identifier', 'instructionalMethod', 'isFormatOf', 'isPartOf', 'isReferencedBy', 'isReplacedBy', 'isRequiredBy', 'issued', 'isVersionOf', 'language', 'license', 'mediator', 'medium', 'modified', 'provenance', 'publisher', 'references', 'relation', 'replaces', 'requires', 'rights', 'rightsHolder', 'source', 'spatial', 'subject', 'tableOfContents', 'temporal', 'title', 'type', 'valid'),
    'dcmitype' => array(),
    'foaf'     => array(/*stable:*/'homepage', 'made', 'maker', 'mbox', 'member', /*testing:*/'depiction', 'depicts', 'family_name', 'firstName', 'gender', 'givenname', 'img', 'interest', 'isPrimaryTopicOf', 'knows', 'logo', 'mbox_sha1sum', 'name', 'nick', 'page', 'phone', 'primaryTopic', 'surname', 'thumbnail', 'title', 'topic', 'weblog'),
  );
}

/**
 * Implementation of hook_rdf_resources().
 */
function rdf_rdf_resources($context) {
  switch ($context) {
    case NULL:
      return array(); // FIXME
      //return array_merge(rdf_schema_get_resources(), rdf_schema_get_classes());
    case RDF_SITE_URI:
      return array(RDF_SITE_URI => new RDF_QueryCallback('rdf_load_site'));
      //return rdf_schema_get_resources(); // rdf_schema.module
    case RDF_SCHEMA_URI:
      return rdf_schema_get_classes();
  }
}

/**
 * Implementation of hook_rdf_query().
 */
function rdf_rdf_query($subject, $predicate, $object, $options = array()) {
  $context = isset($options['context']) ? $options['context'] : NULL;

  $data = array();
  foreach (module_implements('rdf_resources') as $module) {
    $function = $module . '_rdf_resources';
    if ($resources = $function($context)) {
      foreach ($resources as $uri => $callback) {
        if (!$subject || (string)$subject == $uri) {
          $data = array_merge_recursive($data, _rdf_filter(array($uri => rdf_expand_qnames($callback->call())), $subject, $predicate, $object, $options));
        }
      }
    }
  }
  return rdf_denormalize($data);
}

//////////////////////////////////////////////////////////////////////////////
// Miscellaneous helpers

function rdf_get_schema_uri() {
  $uri = 'rdf/schema';
  $uri = (function_exists('url') ? url($uri, array('absolute' => TRUE)) : $uri) . '/';
  return variable_get('rdf_schema_uri', $uri);
}

function rdf_menu_access_user($account) {
  return user_access('access RDF data') && user_view_access($account);
}

function rdf_menu_access_node($op, $node, $account = NULL) {
  return user_access('access RDF data') && node_access($op, $node, $account);
}

function rdf_menu_access_http($perm_get, $perm_post) {
  return user_access($_SERVER['REQUEST_METHOD'] == 'POST' ? $perm_post : $perm_get);
}

//////////////////////////////////////////////////////////////////////////////
// Output buffering callback

function _rdf_ob_handler($buffer) {
  static $mimetypes = array('text/html');
  static $doctype   = "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML+RDFa 1.0//EN\"\n  \"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd\">\n";

  // Only attempt RDFa modifications for HTML output:
  if (in_array($mimetype = _rdf_ob_handler_get_content_type(), $mimetypes)) {
    $buffer = _rdf_ob_handler_remove_doctype($buffer, $doctype);
    $buffer = _rdf_ob_handler_insert_namespaces($buffer);
    $buffer = $doctype . $buffer;
  }
  return $buffer;
}

function _rdf_ob_handler_get_content_type($default = NULL) {
  static $regex = '!^Content-Type:\s*([\w\d\/\-]+)!i';
  return _rdf_ob_handler_get_http_header($regex, $default);
}

function _rdf_ob_handler_get_http_header($regex, $default = NULL) {
  // The last header is the one that counts:
  //$headers = preg_grep($regex, explode("\n", drupal_get_headers()));
  $headers = preg_grep($regex, headers_list());
  if (!empty($headers) && preg_match($regex, array_pop($headers), $matches)) {
    return $matches[1]; // found it
  }
  return $default; // no such luck
}

function _rdf_ob_handler_remove_doctype($buffer, &$doctype) {
  $lines = $cutoff = 0;
  $line  = strtok($buffer, "\n");

  // Attempt to find the opening <html> tag in the first 15 lines:
  while ($line !== FALSE && $lines++ < 15) {
    if (($pos = strpos($line, '<html')) !== FALSE) {
      // If we managed to find <html>, substitute the DOCTYPE; otherwise, the
      // page output will be returned unmodified.
      return substr($buffer, $cutoff += $pos);
    }

    $cutoff += strlen($line) + 1; // line length and "\n"
    $line = strtok("\n");
  }

  $doctype = ''; // Don't prepend the new doctype
  return $buffer;
}

function _rdf_ob_handler_insert_namespaces($buffer) {
  $namespaces = rdf_get_namespaces('rdfa');

  // Attempt to find the last character of the opening <html> tag:
  if (!empty($namespaces) && ($html = strtok($buffer, '>'))) {
    $buffer = substr($buffer, strlen($html) + 1);

    // Insert the xmlns:prefix="uri" definitions at the end of the opening <html> tag:
    $xmlns  = array();
    foreach ($namespaces as $prefix => $uri) {
      $xmlns[] = '      xmlns:' . $prefix . '="' . $uri . '"';
    }
    $html  .= "\n" . implode("\n", $xmlns) . '>';
    return $html . $buffer;
  }
  return $buffer;
}