drupal/core/modules/block/block.module

<?php

/**
 * @file
 * Controls the visual building blocks a page is constructed with.
 */

/**
 * Denotes that a block is not enabled in any region and should not be shown.
 */
const BLOCK_REGION_NONE = -1;

/**
 * Users cannot control whether or not they see this block.
 */
const BLOCK_CUSTOM_FIXED = 0;

/**
 *  Shows this block by default, but lets individual users hide it.
 */
const BLOCK_CUSTOM_ENABLED = 1;

/**
 * Hides this block by default but lets individual users show it.
 */
const BLOCK_CUSTOM_DISABLED = 2;

/**
 * Shows this block on every page except the listed pages.
 */
const BLOCK_VISIBILITY_NOTLISTED = 0;

/**
 * Shows this block on only the listed pages.
 */
const BLOCK_VISIBILITY_LISTED = 1;

/**
 * Shows this block if the associated PHP code returns TRUE.
 */
const BLOCK_VISIBILITY_PHP = 2;

/**
 * Implements hook_help().
 */
function block_help($path, $arg) {
  switch ($path) {
    case 'admin/help#block':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Block module allows you to create boxes of content, which are rendered into an area, or region, of one or more pages of a website. The core Seven administration theme, for example, implements the regions "Content", "Help", "Dashboard main", and "Dashboard sidebar", and a block may appear in any one of these regions. The <a href="@blocks">Blocks administration page</a> provides a drag-and-drop interface for assigning a block to a region, and for controlling the order of blocks within regions. For more information, see the online handbook entry for <a href="@block">Block module</a>.', array('@block' => 'http://drupal.org/documentation/modules/block', '@blocks' => url('admin/structure/block'))) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Positioning content') . '</dt>';
      $output .= '<dd>' . t('When working with blocks, remember that all themes do <em>not</em> implement the same regions, or display regions in the same way. Blocks are positioned on a per-theme basis. Users with the <em>Administer blocks</em> permission can disable blocks. Disabled blocks are listed on the <a href="@blocks">Blocks administration page</a>, but are not displayed in any region.', array('@block' => 'http://drupal.org/documentation/modules/block', '@blocks' => url('admin/structure/block'))) . '</dd>';
      $output .= '<dt>' . t('Controlling visibility') . '</dt>';
      $output .= '<dd>' . t('Blocks can be configured to be visible only on certain pages, only to users of certain roles, or only on pages displaying certain <a href="@content-type">content types</a>. Administrators can also allow specific blocks to be enabled or disabled by users when they edit their <a href="@user">My account</a> page. Some dynamic blocks, such as those generated by modules, will be displayed only on certain pages.', array('@content-type' => url('admin/structure/types'), '@user' => url('user'))) . '</dd>';
      $output .= '<dt>' . t('Creating custom blocks') . '</dt>';
      $output .= '<dd>' . t('Users with the <em>Administer blocks</em> permission can <a href="@block-add">add custom blocks</a>, which are then listed on the <a href="@blocks">Blocks administration page</a>. Once created, custom blocks behave just like default and module-generated blocks.', array('@blocks' => url('admin/structure/block'), '@block-add' => url('admin/structure/block/add'))) . '</dd>';
      $output .= '</dl>';
      return $output;
    case 'admin/structure/block/add':
      return '<p>' . t('Use this page to create a new custom block.') . '</p>';
  }
  if ($arg[0] == 'admin' && $arg[1] == 'structure' && $arg['2'] == 'block' && (empty($arg[3]) || $arg[3] == 'list')) {
    $demo_theme = !empty($arg[4]) ? $arg[4] : variable_get('theme_default', 'stark');
    $themes = list_themes();
    $output = '<p>' . t('This page provides a drag-and-drop interface for assigning a block to a region, and for controlling the order of blocks within regions. Since not all themes implement the same regions, or display regions in the same way, blocks are positioned on a per-theme basis. Remember that your changes will not be saved until you click the <em>Save blocks</em> button at the bottom of the page. Click the <em>configure</em> link next to each block to configure its specific title and visibility settings.') . '</p>';
    $output .= '<p>' . l(t('Demonstrate block regions (@theme)', array('@theme' => $themes[$demo_theme]->info['name'])), 'admin/structure/block/demo/' . $demo_theme) . '</p>';
    return $output;
  }
}

/**
 * Implements hook_theme().
 */
function block_theme() {
  return array(
    'block' => array(
      'render element' => 'elements',
      'template' => 'block',
    ),
    'block_admin_display_form' => array(
      'template' => 'block-admin-display-form',
      'file' => 'block.admin.inc',
      'render element' => 'form',
    ),
  );
}

/**
 * Implements hook_permission().
 */
function block_permission() {
  return array(
    'administer blocks' => array(
      'title' => t('Administer blocks'),
    ),
  );
}

/**
 * Implements hook_menu().
 */
function block_menu() {
  $default_theme = variable_get('theme_default', 'stark');
  $items['admin/structure/block'] = array(
    'title' => 'Blocks',
    'description' => 'Configure what block content appears in your site\'s sidebars and other regions.',
    'page callback' => 'block_admin_display',
    'page arguments' => array($default_theme),
    'access arguments' => array('administer blocks'),
    'file' => 'block.admin.inc',
  );
  $items['admin/structure/block/manage/%/%'] = array(
    'title' => 'Configure block',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('block_admin_configure', 4, 5),
    'access arguments' => array('administer blocks'),
    'file' => 'block.admin.inc',
  );
  $items['admin/structure/block/manage/%/%/configure'] = array(
    'title' => 'Configure block',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'context' => MENU_CONTEXT_INLINE,
  );
  $items['admin/structure/block/manage/%/%/delete'] = array(
    'title' => 'Delete block',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('block_custom_block_delete', 4, 5),
    'access arguments' => array('administer blocks'),
    'type' => MENU_LOCAL_TASK,
    'context' => MENU_CONTEXT_NONE,
    'file' => 'block.admin.inc',
  );
  $items['admin/structure/block/add'] = array(
    'title' => 'Add block',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('block_add_block_form'),
    'access arguments' => array('administer blocks'),
    'type' => MENU_LOCAL_ACTION,
    'file' => 'block.admin.inc',
  );
  foreach (list_themes() as $key => $theme) {
    $items['admin/structure/block/list/' . $key] = array(
      'title' => check_plain($theme->info['name']),
      'page arguments' => array($key),
      'type' => $key == $default_theme ? MENU_DEFAULT_LOCAL_TASK : MENU_LOCAL_TASK,
      'weight' => $key == $default_theme ? -10 : 0,
      'access callback' => '_block_themes_access',
      'access arguments' => array($key),
      'file' => 'block.admin.inc',
    );
    if ($key != $default_theme) {
      $items['admin/structure/block/list/' . $key . '/add'] = array(
        'title' => 'Add block',
        'page callback' => 'drupal_get_form',
        'page arguments' => array('block_add_block_form'),
        'access arguments' => array('administer blocks'),
        'type' => MENU_LOCAL_ACTION,
        'file' => 'block.admin.inc',
      );
    }
    $items['admin/structure/block/demo/' . $key] = array(
      'title' => check_plain($theme->info['name']),
      'page callback' => 'block_admin_demo',
      'page arguments' => array($key),
      'type' => MENU_CALLBACK,
      'access callback' => '_block_themes_access',
      'access arguments' => array($key),
      'theme callback' => '_block_custom_theme',
      'theme arguments' => array($key),
      'file' => 'block.admin.inc',
    );
  }
  return $items;
}

/**
 * Access callback: Only admin or enabled themes can be accessed.
 *
 * Path:
 * - admin/structure/block/list/% (for each theme)
 * - admin/structure/block/demo/% (for each theme)
 *
 * @param $theme
 *   Either the name of a theme or a full theme object.
 *
 * @see block_menu()
 */
function _block_themes_access($theme) {
  return user_access('administer blocks') && drupal_theme_access($theme);
}

/**
 * Theme callback: Uses the theme specified in the parameter.
 *
 * @param $theme
 *   The theme whose blocks are being configured. If not set, the default theme
 *   is assumed.
 *
 * @return
 *   The theme that should be used for the block configuration page, or NULL
 *   to indicate that the default theme should be used.
 *
 * @see block_menu()
 */
function _block_custom_theme($theme = NULL) {
  // We return exactly what was passed in, to guarantee that the page will
  // always be displayed using the theme whose blocks are being configured.
  return $theme;
}

/**
 * Implements hook_block_info().
 */
function block_block_info() {
  $blocks = array();

  $result = db_query('SELECT bid, info FROM {block_custom} ORDER BY info');
  foreach ($result as $block) {
    $blocks[$block->bid]['info'] = $block->info;
    // Not worth caching.
    $blocks[$block->bid]['cache'] = DRUPAL_NO_CACHE;
  }
  return $blocks;
}

/**
 * Implements hook_block_configure().
 */
function block_block_configure($delta = 0) {
  if ($delta) {
    $custom_block = block_custom_block_get($delta);
  }
  else {
    $custom_block = array();
  }
  return block_custom_block_form($custom_block);
}

/**
 * Implements hook_block_save().
 */
function block_block_save($delta = 0, $edit = array()) {
  block_custom_block_save($edit, $delta);
}

/**
 * Implements hook_block_view().
 *
 * Generates the administrator-defined blocks for display.
 */
function block_block_view($delta = '') {
  $block = db_query('SELECT body, format FROM {block_custom} WHERE bid = :bid', array(':bid' => $delta))->fetchObject();
  $data['subject'] = NULL;
  $data['content'] = check_markup($block->body, $block->format, '', TRUE);
  return $data;
}

/**
 * Implements hook_page_build().
 *
 * Renders blocks into their regions.
 */
function block_page_build(&$page) {
  global $theme;

  // The theme system might not yet be initialized. We need $theme.
  drupal_theme_initialize();

  // Fetch a list of regions for the current theme.
  $all_regions = system_region_list($theme);

  $item = menu_get_item();
  if ($item['path'] != 'admin/structure/block/demo/' . $theme) {
    // Load all region content assigned via blocks.
    foreach (array_keys($all_regions) as $region) {
      // Assign blocks to region.
      if ($blocks = block_get_blocks_by_region($region)) {
        $page[$region] = $blocks;
      }
    }
    // Once we've finished attaching all blocks to the page, clear the static
    // cache to allow modules to alter the block list differently in different
    // contexts. For example, any code that triggers hook_page_build() more
    // than once in the same page request may need to alter the block list
    // differently each time, so that only certain parts of the page are
    // actually built. We do not clear the cache any earlier than this, though,
    // because it is used each time block_get_blocks_by_region() gets called
    // above.
    drupal_static_reset('block_list');
  }
  else {
    // Append region description if we are rendering the regions demo page.
    $item = menu_get_item();
    if ($item['path'] == 'admin/structure/block/demo/' . $theme) {
      $visible_regions = array_keys(system_region_list($theme, REGIONS_VISIBLE));
      foreach ($visible_regions as $region) {
        $description = '<div class="block-region">' . $all_regions[$region] . '</div>';
        $page[$region]['block_description'] = array(
          '#markup' => $description,
          '#weight' => 15,
        );
      }
      $page['page_top']['backlink'] = array(
        '#type' => 'link',
        '#title' => t('Exit block region demonstration'),
        '#href' => 'admin/structure/block' . (variable_get('theme_default', 'stark') == $theme ? '' : '/list/' . $theme),
        // Add the "overlay-restore" class to indicate this link should restore
        // the context in which the region demonstration page was opened.
        '#options' => array('attributes' => array('class' => array('block-demo-backlink', 'overlay-restore'))),
        '#weight' => -10,
      );
    }
  }
}

/**
 * Gets a renderable array of a region containing all enabled blocks.
 *
 * @param $region
 *   The requested region.
 *
 * @return
 *   A renderable array of a region containing all enabled blocks.
 */
function block_get_blocks_by_region($region) {
  $build = array();
  if ($list = block_list($region)) {
    $build = _block_get_renderable_region($list);
  }
  return $build;
}

/**
 * Gets an array of blocks suitable for drupal_render().
 *
 * @param $list
 *   A list of blocks such as that returned by block_list().
 *
 * @return
 *   A renderable array.
 */
function _block_get_renderable_region($list = array()) {
  $weight = 0;
  $build = array();
  // Block caching is not compatible with node_access modules. We also
  // preserve the submission of forms in blocks, by fetching from cache
  // only if the request method is 'GET' (or 'HEAD'). User 1 being out of
  // the regular 'roles define permissions' schema, it brings too many
  // chances of having unwanted output get in the cache and later be served
  // to other users. We therefore exclude user 1 from block caching.
  $not_cacheable = $GLOBALS['user']->uid == 1 ||
    count(module_implements('node_grants')) ||
    !in_array($_SERVER['REQUEST_METHOD'], array('GET', 'HEAD'));

  foreach ($list as $key => $block) {
    $build[$key] = array(
      '#block' => $block,
      '#weight' => ++$weight,
      '#theme_wrappers' => array('block'),
    );

    if ($not_cacheable || in_array($block->cache, array(DRUPAL_NO_CACHE, DRUPAL_CACHE_CUSTOM))) {
      // Non-cached blocks get built immediately. Provides more content
      // that can be easily manipulated during hook_page_alter().
      $build[$key] = _block_get_renderable_block($build[$key]);
    }
    else {
      $build[$key] += array(
        '#pre_render' => array('_block_get_renderable_block'),
        '#cache' => array(
          'keys' => array($block->module, $block->delta),
          'granularity' => $block->cache,
          'bin' => 'block',
          'tags' => array('content' => TRUE),
        ),
      );
    }

    // Add contextual links for this block; skip the main content block, since
    // contextual links are basically output as tabs/local tasks already. Also
    // skip the help block, since we assume that most users do not need or want
    // to perform contextual actions on the help block, and the links needlessly
    // draw attention on it.
    if ($key != 'system_main' && $key != 'system_help') {
      $build[$key]['#contextual_links']['block'] = array('admin/structure/block/manage', array($block->module, $block->delta));
    }
  }
  $build['#sorted'] = TRUE;
  return $build;
}

/**
 * Updates the 'block' DB table with the blocks currently exported by modules.
 *
 * @param $theme
 *   The theme to rehash blocks for. If not provided, defaults to the currently
 *   used theme.
 *
 * @return
 *   Blocks currently exported by modules.
 */
function _block_rehash($theme = NULL) {
  global $theme_key;

  drupal_theme_initialize();
  if (!isset($theme)) {
    // If theme is not specifically set, rehash for the current theme.
    $theme = $theme_key;
  }
  $regions = system_region_list($theme);

  // These are the blocks the function will return.
  $blocks = array();
  // These are the blocks defined by code and modified by the database.
  $current_blocks = array();
  // These are {block}.bid values to be kept.
  $bids = array();
  $or = db_or();
  // Gather the blocks defined by modules.
  foreach (module_implements('block_info') as $module) {
    $module_blocks = module_invoke($module, 'block_info');
    foreach ($module_blocks as $delta => $block) {
      // Compile a condition to retrieve this block from the database.
      $condition = db_and()
        ->condition('module', $module)
        ->condition('delta', $delta);
      $or->condition($condition);
      // Add identifiers.
      $block['module'] = $module;
      $block['delta']  = $delta;
      $block['theme']  = $theme;
      $current_blocks[$module][$delta] = $block;
    }
  }
  // Save the blocks defined in code for alter context.
  $code_blocks = $current_blocks;
  $database_blocks = db_select('block', 'b')
    ->fields('b')
    ->condition($or)
    ->condition('theme', $theme)
    ->execute();
  foreach ($database_blocks as $block) {
    // Preserve info which is not in the database.
    $block->info = $current_blocks[$block->module][$block->delta]['info'];
    // The cache mode can only by set from hook_block_info(), so that has
    // precedence over the database's value.
    if (isset($current_blocks[$block->module][$block->delta]['cache'])) {
      $block->cache = $current_blocks[$block->module][$block->delta]['cache'];
    }
    // Blocks stored in the database override the blocks defined in code.
    $current_blocks[$block->module][$block->delta] = get_object_vars($block);
    // Preserve this block.
    $bids[$block->bid] = $block->bid;
  }
  drupal_alter('block_info', $current_blocks, $theme, $code_blocks);
  foreach ($current_blocks as $module => $module_blocks) {
    foreach ($module_blocks as $delta => $block) {
      if (!isset($block['pages'])) {
        // {block}.pages is type 'text', so it cannot have a
        // default value, and not null, so we need to provide
        // value if the module did not.
        $block['pages']  = '';
      }
      // Make sure weight is set.
      if (!isset($block['weight'])) {
        $block['weight'] = 0;
      }
      if (!empty($block['region']) && $block['region'] != BLOCK_REGION_NONE && !isset($regions[$block['region']]) && $block['status'] == 1) {
        drupal_set_message(t('The block %info was assigned to the invalid region %region and has been disabled.', array('%info' => $block['info'], '%region' => $block['region'])), 'warning');
        // Disabled modules are moved into the BLOCK_REGION_NONE later so no
        // need to move the block to another region.
        $block['status'] = 0;
      }
      // Set region to none if not enabled and make sure status is set.
      if (empty($block['status'])) {
        $block['status'] = 0;
        $block['region'] = BLOCK_REGION_NONE;
      }
      // There is no point saving disabled blocks. Still, we need to save them
      // because the 'title' attribute is saved to the {blocks} table.
      if (isset($block['bid'])) {
        // If the block has a bid property, it comes from the database and
        // the record needs to be updated, so set the primary key to 'bid'
        // before passing to drupal_write_record().
        $primary_keys = array('bid');
        // Remove a block from the list of blocks to keep if it became disabled.
        unset($bids[$block['bid']]);
      }
      else {
        $primary_keys = array();
      }
      drupal_write_record('block', $block, $primary_keys);
      // Add to the list of blocks we return.
      $blocks[] = $block;
    }
  }
  if ($bids) {
    // Remove disabled that are no longer defined by the code from the
    // database.
    db_delete('block')
      ->condition('bid', $bids, 'NOT IN')
      ->condition('theme', $theme)
      ->execute();
  }
  return $blocks;
}

/**
 * Returns information from database about a user-created (custom) block.
 *
 * @param $bid
 *   ID of the block to get information for.
 *
 * @return
 *   Associative array of information stored in the database for this block.
 *   Array keys:
 *   - bid: Block ID.
 *   - info: Block description.
 *   - body: Block contents.
 *   - format: Filter ID of the filter format for the body.
 */
function block_custom_block_get($bid) {
  return db_query("SELECT * FROM {block_custom} WHERE bid = :bid", array(':bid' => $bid))->fetchAssoc();
}

/**
 * Form constructor for the custom block form.
 *
 * @param $edit
 *   (optional) An associative array of information retrieved by
 *   block_custom_get_block() if an existing block is being edited, or an empty
 *   array otherwise. Defaults to array().
 *
 * @ingroup forms
 */
function block_custom_block_form($edit = array()) {
  $edit += array(
    'info' => '',
    'body' => '',
  );
  $form['info'] = array(
    '#type' => 'textfield',
    '#title' => t('Block description'),
    '#default_value' => $edit['info'],
    '#maxlength' => 64,
    '#description' => t('A brief description of your block. Used on the <a href="@overview">Blocks administration page</a>.', array('@overview' => url('admin/structure/block'))),
    '#required' => TRUE,
    '#weight' => -18,
  );
  $form['body_field']['#weight'] = -17;
  $form['body_field']['body'] = array(
    '#type' => 'text_format',
    '#title' => t('Block body'),
    '#default_value' => $edit['body'],
    '#format' => isset($edit['format']) ? $edit['format'] : NULL,
    '#rows' => 15,
    '#description' => t('The content of the block as shown to the user.'),
    '#required' => TRUE,
    '#weight' => -17,
  );

  return $form;
}

/**
 * Saves a user-created block in the database.
 *
 * @param $edit
 *   Associative array of fields to save. Array keys:
 *   - info: Block description.
 *   - body: Associative array of body value and format.  Array keys:
 *     - value: Block contents.
 *     - format: Filter ID of the filter format for the body.
 * @param $delta
 *   Block ID of the block to save.
 *
 * @return
 *   Always returns TRUE.
 */
function block_custom_block_save($edit, $delta) {
  db_update('block_custom')
    ->fields(array(
      'body' => $edit['body']['value'],
      'info' => $edit['info'],
      'format' => $edit['body']['format'],
    ))
    ->condition('bid', $delta)
    ->execute();
  return TRUE;
}

/**
 * Implements hook_form_FORM_ID_alter() for user_profile_form().
 */
function block_form_user_profile_form_alter(&$form, &$form_state) {
  $account = $form['#user'];
  $rids = array_keys($account->roles);
  $result = db_query("SELECT DISTINCT b.* FROM {block} b LEFT JOIN {block_role} r ON b.module = r.module AND b.delta = r.delta WHERE b.status = 1 AND b.custom <> 0 AND (r.rid IN (:rids) OR r.rid IS NULL) ORDER BY b.weight, b.module", array(':rids' => $rids));

  $blocks = array();
  foreach ($result as $block) {
    $data = module_invoke($block->module, 'block_info');
    if ($data[$block->delta]['info']) {
      $blocks[$block->module][$block->delta] = array(
        '#type' => 'checkbox',
        '#title' => check_plain($data[$block->delta]['info']),
        '#default_value' => isset($account->data['block'][$block->module][$block->delta]) ? $account->data['block'][$block->module][$block->delta] : ($block->custom == 1),
      );
    }
  }
  // Only display the fieldset if there are any personalizable blocks.
  if ($blocks) {
    $form['block'] = array(
      '#type' => 'fieldset',
      '#title' => t('Personalize blocks'),
      '#description' => t('Blocks consist of content or information that complements the main content of the page. Enable or disable optional blocks using the checkboxes below.'),
      '#weight' => 3,
      '#collapsible' => TRUE,
      '#tree' => TRUE,
    );
    $form['block'] += $blocks;
  }
}

/**
 * Implements hook_field_extra_fields().
 */
function block_field_extra_fields() {
  $extra['user']['user']['form']['block'] = array(
    'label' => t('Personalize blocks'),
    'description' => t('Block module form element.'),
    'weight' => 3,
  );

  return $extra;
}

/**
 * Implements hook_user_presave().
 */
function block_user_presave($account) {
  if (isset($account->block)) {
    $account->data['block'] = $account->block;
  }
}

/**
 * Initializes blocks for enabled themes.
 *
 * @param $theme_list
 *   An array of theme names.
 */
function block_themes_enabled($theme_list) {
  foreach ($theme_list as $theme) {
    block_theme_initialize($theme);
  }
}

/**
 * Assigns an initial, default set of blocks for a theme.
 *
 * This function is called the first time a new theme is enabled. The new theme
 * gets a copy of the default theme's blocks, with the difference that if a
 * particular region isn't available in the new theme, the block is assigned
 * to the new theme's default region.
 *
 * @param $theme
 *   The name of a theme.
 */
function block_theme_initialize($theme) {
  // Initialize theme's blocks if none already registered.
  $has_blocks = (bool) db_query_range('SELECT 1 FROM {block} WHERE theme = :theme', 0, 1, array(':theme' => $theme))->fetchField();
  if (!$has_blocks) {
    $default_theme = variable_get('theme_default', 'stark');
    // Apply only to new theme's visible regions.
    $regions = system_region_list($theme, REGIONS_VISIBLE);
    $result = db_query("SELECT * FROM {block} WHERE theme = :theme", array(':theme' => $default_theme), array('fetch' => PDO::FETCH_ASSOC));
    foreach ($result as $block) {
      // If the region isn't supported by the theme, assign the block to the theme's default region.
      if ($block['status'] && !isset($regions[$block['region']])) {
        $block['region'] = system_default_region($theme);
      }
      $block['theme'] = $theme;
      unset($block['bid']);
      drupal_write_record('block', $block);
    }
  }
}

/**
 * Returns all blocks in the specified region for the current user.
 *
 * @param $region
 *   The name of a region.
 *
 * @return
 *   An array of block objects, indexed with the module name and block delta
 *   concatenated with an underscore, thus: MODULE_DELTA. If you are displaying
 *   your blocks in one or two sidebars, you may check whether this array is
 *   empty to see how many columns are going to be displayed.
 *
 * @todo
 *   Now that the block table has a primary key, we should use that as the
 *   array key instead of MODULE_DELTA.
 */
function block_list($region) {
  $blocks = &drupal_static(__FUNCTION__);

  if (!isset($blocks)) {
    $blocks = _block_load_blocks();
  }

  // Create an empty array if there are no entries.
  if (!isset($blocks[$region])) {
    $blocks[$region] = array();
  }

  return $blocks[$region];
}

/**
 * Loads a block object from the database.
 *
 * @param $module
 *   Name of the module that implements the block to load.
 * @param $delta
 *   Unique ID of the block within the context of $module. Pass NULL to return
 *   an empty block object for $module.
 *
 * @return
 *   A block object.
 */
function block_load($module, $delta) {
  if (isset($delta)) {
    $block = db_query('SELECT * FROM {block} WHERE module = :module AND delta = :delta', array(':module' => $module, ':delta' => $delta))->fetchObject();
  }

  // If the block does not exist in the database yet return a stub block
  // object.
  if (empty($block)) {
    $block = new stdClass();
    $block->module = $module;
    $block->delta = $delta;
  }

  return $block;
}

/**
 * Loads blocks' information from the database.
 *
 * @return
 *   An array of blocks grouped by region.
 */
function _block_load_blocks() {
  global $theme_key;

  $query = db_select('block', 'b');
  $query->addField('b', 'title', 'subject');
  $result = $query
    ->fields('b')
    ->condition('b.theme', $theme_key)
    ->condition('b.status', 1)
    ->orderBy('b.region')
    ->orderBy('b.weight')
    ->orderBy('b.module')
    ->addTag('block_load')
    ->addTag('translatable')
    ->execute();

  $block_info = $result->fetchAllAssoc('bid');
  // Allow modules to modify the block list.
  drupal_alter('block_list', $block_info);

  $blocks = array();
  foreach ($block_info as $block) {
    $blocks[$block->region]["{$block->module}_{$block->delta}"] = $block;
  }
  return $blocks;
}

/**
 * Implements hook_block_list_alter().
 *
 * Checks the page, user role, and user-specific visibilty settings.
 * Removes the block if the visibility conditions are not met.
 */
function block_block_list_alter(&$blocks) {
  global $user, $theme_key;

  // Build an array of roles for each block.
  $block_roles = array();
  $result = db_query('SELECT module, delta, rid FROM {block_role}');
  foreach ($result as $record) {
    $block_roles[$record->module][$record->delta][] = $record->rid;
  }

  // Build an array of langcodes allowed per block.
  $result = db_query('SELECT module, delta, type, langcode FROM {block_language}');
  $block_langcodes = array();
  foreach ($result as $record) {
    $block_langcodes[$record->module][$record->delta][$record->type][$record->langcode] = TRUE;
  }

  foreach ($blocks as $key => $block) {
    if (!isset($block->theme) || !isset($block->status) || $block->theme != $theme_key || $block->status != 1) {
      // This block was added by a contrib module, leave it in the list.
      continue;
    }

    // If a block has no roles associated, it is displayed for every role.
    // For blocks with roles associated, if none of the user's roles matches
    // the settings from this block, remove it from the block list.
    if (isset($block_roles[$block->module][$block->delta]) && !array_intersect($block_roles[$block->module][$block->delta], array_keys($user->roles))) {
      // No match.
      unset($blocks[$key]);
      continue;
    }

    // Use the user's block visibility setting, if necessary.
    if ($block->custom != BLOCK_CUSTOM_FIXED) {
      if ($user->uid && isset($user->data['block'][$block->module][$block->delta])) {
        $enabled = $user->data['block'][$block->module][$block->delta];
      }
      else {
        $enabled = ($block->custom == BLOCK_CUSTOM_ENABLED);
      }
    }
    else {
      $enabled = TRUE;
    }

    // Limited visibility blocks must list at least one page.
    if ($block->visibility == BLOCK_VISIBILITY_LISTED && empty($block->pages)) {
      $enabled = FALSE;
    }

    if (!$enabled) {
      unset($blocks[$key]);
      continue;
    }

    // Match path if necessary.
    if ($block->pages) {
      // Convert path to lowercase. This allows comparison of the same path
      // with different case. Ex: /Page, /page, /PAGE.
      $pages = drupal_strtolower($block->pages);
      if ($block->visibility < BLOCK_VISIBILITY_PHP) {
        // Compare the lowercase path alias (if any) and internal path.
        $path = current_path();
        $path_alias = drupal_strtolower(drupal_get_path_alias($path));
        $page_match = drupal_match_path($path_alias, $pages) || (($path != $path_alias) && drupal_match_path($path, $pages));
        // When $block->visibility has a value of 0 (BLOCK_VISIBILITY_NOTLISTED),
        // the block is displayed on all pages except those listed in $block->pages.
        // When set to 1 (BLOCK_VISIBILITY_LISTED), it is displayed only on those
        // pages listed in $block->pages.
        $page_match = !($block->visibility xor $page_match);
      }
      elseif (module_exists('php')) {
        $page_match = php_eval($block->pages);
      }
      else {
        $page_match = FALSE;
      }
    }
    else {
      $page_match = TRUE;
    }
    if (!$page_match) {
      unset($blocks[$key]);
      continue;
    }

    // Language visibility settings.
    // No language setting for this block, leave it in the list.
    if (!isset($block_langcodes[$block->module][$block->delta])) {
      continue;
    }
    foreach ($block_langcodes[$block->module][$block->delta] as $language_type => $langcodes) {
      if (isset($langcodes[drupal_container()->get($language_type)->langcode])) {
        // Found a language type - langcode combination in the configuration
        // that is applicable to the current request.
        continue 2;
      }
    }
    // Had language configuration but none matched.
    unset($blocks[$key]);
  }
}

/**
 * Builds the content and subject for a block.
 *
 * For cacheable blocks, this is called during #pre_render.
 *
 * @param $element
 *   A renderable array.
 *
 * @return
 *   A renderable array.
 */
function _block_get_renderable_block($element) {
  $block = $element['#block'];

  // Render the block content if it has not been created already.
  if (!isset($block->content)) {
    $array = module_invoke($block->module, 'block_view', $block->delta);

    // Allow modules to modify the block before it is viewed, via either
    // hook_block_view_alter() or hook_block_view_MODULE_DELTA_alter().
    drupal_alter(array('block_view', "block_view_{$block->module}_{$block->delta}"), $array, $block);

    if (empty($array['content'])) {
      // Blocks without content should emit no markup at all.
      $element += array(
        '#access' => FALSE,
        '#printed' => TRUE,
      );
    }
    elseif (isset($array) && is_array($array)) {
      foreach ($array as $k => $v) {
        $block->$k = $v;
      }
    }
  }

  if (isset($block->content) && $block->content) {
    // Normalize to the drupal_render() structure.
    if (is_string($block->content)) {
      $block->content = array('#markup' => $block->content);
    }
    // Override default block title if a custom display title is present.
    if ($block->title) {
      // Check plain here to allow module generated titles to keep any
      // markup.
      $block->subject = $block->title == '<none>' ? '' : check_plain($block->title);
    }

    // Add the content renderable array to the main element.
    $element['content'] = $block->content;
    unset($block->content);
    $element['#block'] = $block;
  }
  return $element;
}

/**
 * Implements hook_cache_flush().
 */
function block_cache_flush() {
  return array('block');
}

/**
 * Implements hook_rebuild().
 */
function block_rebuild() {
  // Rehash blocks for active themes. We don't use list_themes() here,
  // because if MAINTENANCE_MODE is defined it skips reading the database,
  // and we can't tell which themes are active.
  $themes = db_query("SELECT name FROM {system} WHERE type = 'theme' AND status = 1");
  foreach ($themes as $theme) {
    _block_rehash($theme->name);
  }
}

/**
 * Processes variables for block.tpl.php.
 *
 * Prepares the values passed to the theme_block function to be passed
 * into a pluggable template engine. Uses block properties to generate a
 * series of template file suggestions. If none are found, the default
 * block.tpl.php is used.
 *
 * Most themes utilize their own copy of block.tpl.php. The default is located
 * inside "modules/block/block.tpl.php". Look in there for the full list of
 * variables.
 *
 * The $variables array contains the following arguments:
 * - $block
 *
 * @see block.tpl.php
 */
function template_preprocess_block(&$variables) {
  $block_counter = &drupal_static(__FUNCTION__, array());
  $variables['block'] = $variables['elements']['#block'];
  // All blocks get an independent counter for each region.
  if (!isset($block_counter[$variables['block']->region])) {
    $block_counter[$variables['block']->region] = 1;
  }
  // Same with zebra striping.
  $variables['block_zebra'] = ($block_counter[$variables['block']->region] % 2) ? 'odd' : 'even';
  $variables['block_id'] = $block_counter[$variables['block']->region]++;

  // Create the $content variable that templates expect.
  $variables['content'] = $variables['elements']['#children'];

  $variables['classes_array'][] = drupal_html_class('block-' . $variables['block']->module);

  // Add default class for block content.
  $variables['content_attributes_array']['class'][] = 'content';

  $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->region;
  $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->module;
  // Hyphens (-) and underscores (_) play a special role in theme suggestions.
  // Theme suggestions should only contain underscores, because within
  // drupal_find_theme_templates(), underscores are converted to hyphens to
  // match template file names, and then converted back to underscores to match
  // pre-processing and other function names. So if your theme suggestion
  // contains a hyphen, it will end up as an underscore after this conversion,
  // and your function names won't be recognized. So, we need to convert
  // hyphens to underscores in block deltas for the theme suggestions.
  $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->module . '__' . strtr($variables['block']->delta, '-', '_');

  // Create a valid HTML ID and make sure it is unique.
  $variables['block_html_id'] = drupal_html_id('block-' . $variables['block']->module . '-' . $variables['block']->delta);
}

/**
 * Implements hook_user_role_delete().
 *
 * Removes deleted role from blocks that use it.
 */
function block_user_role_delete($role) {
  db_delete('block_role')
    ->condition('rid', $role->rid)
    ->execute();
}

/**
 * Implements hook_menu_delete().
 */
function block_menu_delete($menu) {
  db_delete('block')
    ->condition('module', 'menu')
    ->condition('delta', $menu['menu_name'])
    ->execute();
  db_delete('block_role')
    ->condition('module', 'menu')
    ->condition('delta', $menu['menu_name'])
    ->execute();
}

/**
 * Implements hook_admin_paths().
 */
function block_admin_paths() {
  $paths = array(
    // Exclude the block demonstration page from admin (overlay) treatment.
    // This allows us to present this page in its true form, full page.
    'admin/structure/block/demo/*' => FALSE,
  );
  return $paths;
}

/**
 * Implements hook_modules_uninstalled().
 *
 * Cleans up {block}, {block_role} and {block_language} tables
 * from modules' blocks.
 */
function block_modules_uninstalled($modules) {
  db_delete('block')
    ->condition('module', $modules, 'IN')
    ->execute();
  db_delete('block_role')
    ->condition('module', $modules, 'IN')
    ->execute();
  db_delete('block_language')
    ->condition('module', $modules, 'IN')
    ->execute();
}

/**
 * Implements hook_language_delete().
 *
 * Delete the potential block visibility settings of the deleted language.
 */
function block_language_delete($language) {
  // Remove the block visibility settings for the deleted language.
  db_delete('block_language')
    ->condition('langcode', $language->langcode)
    ->execute();
}