gistfile1.php

function og_context($group_type = 'node', $group = NULL, $account = NULL, $check_access = TRUE) {
  global $user;
  // User account is sent.
  $account = $account ? $account : user_load($user->uid);

  $id = FALSE;
  if ($group) {
    list($id) = entity_extract_ids($group_type, $group);
  }

  $cache_keys = array(
    $group_type,
    $id,
    $account->uid,
    $check_access,
  );
  $cache_key = implode(':', $cache_keys);
  $context = &drupal_static(__FUNCTION__, array());

  if (is_null($context[$cache_key])) {
    // Mark that this context hasn't been checked yet.
    $context[$cache_key] = FALSE;
  }

  if (empty($group) && $context[$cache_key] !== FALSE) {
    // Determine if we can return cached values.
    if (empty($context[$cache_key])) {
      // We already tried to find a context, but couldn't.
      return FALSE;
    }

    if ($context[$cache_key]['group_type'] == $group_type) {
      // Return the cached values.
      return $context[$cache_key];
    }
  }

  // Set the context to array, so we can know this function has been already
  // executed.
  $context[$cache_key] = array();

  if (!empty($group)) {
    if (!og_is_group($group_type, $group)) {
      // The passed entity isn't a valid group.
      return FALSE;
    }

    if ($check_access && !entity_access('view', $group_type, $group, $account)) {
      // User doesn't have access to the group.
      return FALSE;
    }

    list($id) = entity_extract_ids($group_type, $group);
    $context = array('group_type' => $group_type, 'gid' => $id);
  }
  // Get context from context handlers.
  elseif ($gid = og_context_determine_context($group_type, NULL, $check_access)) {
    $context = array('group_type' => $group_type, 'gid' => $gid);
    if ($user->uid) {
      // Save the group ID in the authenticated user's session.
      $_SESSION['og_context'] = array('group_type' => $group_type, 'gid' => $gid);
    }
  }

  return $context[$cache_key];
}