class BlockAccessController

class BlockAccessController extends EntityAccessController {

  /**
   * {@inheritdoc}
   */
  protected function checkAccess(EntityInterface $entity, $operation, $langcode, AccountInterface $account) {

    // Currently, only view access is implemented.
    if ($operation != 'view') {
      return FALSE;
    }

    // Deny access to disabled blocks.
    if (!$entity
      ->status()) {
      return FALSE;
    }

    // If the plugin denies access, then deny access.
    if (!$entity
      ->getPlugin()
      ->access()) {
      return FALSE;
    }

    // Otherwise, check for other access restrictions.
    global $user;

    // User role access handling.
    // 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, access is denied.
    $visibility = $entity
      ->get('visibility');
    if (!empty($visibility['role']['roles']) && !array_intersect(array_filter($visibility['role']['roles']), $user->roles)) {

      // No match.
      return FALSE;
    }

    // Page path handling.
    // Limited visibility blocks must list at least one page.
    if (!empty($visibility['path']['visibility']) && $visibility['path']['visibility'] == BLOCK_VISIBILITY_LISTED && empty($visibility['path']['pages'])) {
      return FALSE;
    }

    // Match path if necessary.
    if (!empty($visibility['path']['pages'])) {

      // Assume there are no matches until one is found.
      $page_match = FALSE;

      // Convert path to lowercase. This allows comparison of the same path
      // with different case. Ex: /Page, /page, /PAGE.
      $pages = drupal_strtolower($visibility['path']['pages']);
      if ($visibility['path']['visibility'] < BLOCK_VISIBILITY_PHP) {

        // Compare the lowercase path alias (if any) and internal path.
        $path = current_path();
        $path_alias = drupal_strtolower(drupal_container()
          ->get('path.alias_manager')
          ->getPathAlias($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.
        $page_match = !($visibility['path']['visibility'] xor $page_match);
      }
      elseif (module_exists('php')) {
        $page_match = php_eval($visibility['path']['pages']);
      }

      // If there are page visibility restrictions and this page does not
      // match, deny access.
      if (!$page_match) {
        return FALSE;
      }
    }

    // Language visibility settings.
    if (!empty($visibility['language']['langcodes']) && array_filter($visibility['language']['langcodes'])) {
      if (empty($visibility['language']['langcodes'][language($visibility['language']['language_type'])->langcode])) {
        return FALSE;
      }
    }
    return TRUE;
  }

}