func init() {
	kubeTestAPI := os.Getenv("KUBE_TEST_API")
	if kubeTestAPI != "" {
		testGroupVersions := strings.Split(kubeTestAPI, ",")
		for _, groupVersion := range testGroupVersions {
			// TODO: caesarxuchao: the apiutil package is hacky, it will be replaced
			// by a following PR.
			Groups[apiutil.GetGroup(groupVersion)] =
				TestGroup{apiutil.GetGroup(groupVersion), apiutil.GetVersion(groupVersion), groupVersion}
		}
	}

	// TODO: caesarxuchao: we need a central place to store all available API
	// groups and their metadata.
	if _, ok := Groups[""]; !ok {
		// TODO: The second latest.GroupOrDie("").Version will be latest.GroupVersion after we
		// have multiple group support
		Groups[""] = TestGroup{"", latest.GroupOrDie("").Version, latest.GroupOrDie("").GroupVersion}
	}
	if _, ok := Groups["extensions"]; !ok {
		Groups["extensions"] = TestGroup{"extensions", latest.GroupOrDie("extensions").Version, latest.GroupOrDie("extensions").GroupVersion}
	}

	Default = Groups[""]
	Extensions = Groups["extensions"]
}

func init() {
	groupMeta, err := latest.RegisterGroup("experimental")
	if err != nil {
		glog.V(4).Infof("%v", err)
		return
	}
	registeredGroupVersions := registered.GroupVersionsForGroup("experimental")
	groupVersion := registeredGroupVersions[0]
	*groupMeta = latest.GroupMeta{
		GroupVersion: groupVersion,
		Group:        apiutil.GetGroup(groupVersion),
		Version:      apiutil.GetVersion(groupVersion),
		Codec:        runtime.CodecFor(api.Scheme, groupVersion),
	}
	var versions []string
	var groupVersions []string
	for i := len(registeredGroupVersions) - 1; i >= 0; i-- {
		versions = append(versions, apiutil.GetVersion(registeredGroupVersions[i]))
		groupVersions = append(groupVersions, registeredGroupVersions[i])
	}
	groupMeta.Versions = versions
	groupMeta.GroupVersions = groupVersions

	groupMeta.SelfLinker = runtime.SelfLinker(accessor)

	// the list of kinds that are scoped at the root of the api hierarchy
	// if a kind is not enumerated here, it is assumed to have a namespace scope
	rootScoped := sets.NewString()

	ignoredKinds := sets.NewString()

	groupMeta.RESTMapper = api.NewDefaultRESTMapper("experimental", groupVersions, interfacesFor, importPrefix, ignoredKinds, rootScoped)
	api.RegisterRESTMapper(groupMeta.RESTMapper)
	groupMeta.InterfacesFor = interfacesFor
}

func init() {
	groupMeta, err := latest.RegisterGroup("")
	if err != nil {
		glog.V(4).Infof("%v", err)
		return
	}
	// Use the first API version in the list of registered versions as the latest.
	registeredGroupVersions := registered.GroupVersionsForGroup("")
	groupVersion := registeredGroupVersions[0]
	*groupMeta = latest.GroupMeta{
		GroupVersion: groupVersion,
		Group:        apiutil.GetGroup(groupVersion),
		Version:      apiutil.GetVersion(groupVersion),
		Codec:        runtime.CodecFor(api.Scheme, groupVersion),
	}
	var versions []string
	var groupVersions []string
	for i := len(registeredGroupVersions) - 1; i >= 0; i-- {
		versions = append(versions, apiutil.GetVersion(registeredGroupVersions[i]))
		groupVersions = append(groupVersions, registeredGroupVersions[i])
	}
	groupMeta.Versions = versions
	groupMeta.GroupVersions = groupVersions

	groupMeta.SelfLinker = runtime.SelfLinker(accessor)

	// the list of kinds that are scoped at the root of the api hierarchy
	// if a kind is not enumerated here, it is assumed to have a namespace scope
	// the list of kinds that are scoped at the root of the api hierarchy
	// if a kind is not enumerated here, it is assumed to have a namespace scope
	rootScoped := sets.NewString(
		"Node",
		"Minion",
		"Namespace",
		"PersistentVolume",
		"ComponentStatus",
	)

	// these kinds should be excluded from the list of resources
	ignoredKinds := sets.NewString(
		"ListOptions",
		"DeleteOptions",
		"Status",
		"PodLogOptions",
		"PodExecOptions",
		"PodAttachOptions",
		"PodProxyOptions",
		"ThirdPartyResource",
		"ThirdPartyResourceData",
		"ThirdPartyResourceList")

	mapper := api.NewDefaultRESTMapper("", versions, interfacesFor, importPrefix, ignoredKinds, rootScoped)
	// setup aliases for groups of resources
	mapper.AddResourceAlias("all", userResources...)
	groupMeta.RESTMapper = mapper
	api.RegisterRESTMapper(groupMeta.RESTMapper)
	groupMeta.InterfacesFor = interfacesFor
}

// GroupVersionsForGroup returns the registered versions of a group in the form
// of "group/version".
func GroupVersionsForGroup(group string) []string {
	ret := []string{}
	for _, v := range RegisteredVersions {
		if apiutil.GetGroup(v) == group {
			ret = append(ret, v)
		}
	}
	return ret
}

// convert to a map between group and groupVersions.
func generateStorageVersionMap(legacyVersion string, storageVersions string) map[string]string {
	storageVersionMap := map[string]string{}
	if legacyVersion != "" {
		storageVersionMap[""] = legacyVersion
	}
	if storageVersions != "" {
		groupVersions := strings.Split(storageVersions, ",")
		for _, gv := range groupVersions {
			storageVersionMap[apiutil.GetGroup(gv)] = gv
		}
	}
	return storageVersionMap
}

// Check whether the kind in groupVersion is scoped at the root of the api hierarchy
func isNamespacedKind(kind, groupVersion string) (bool, error) {
	group := apiutil.GetGroup(groupVersion)
	g, err := latest.Group(group)
	if err != nil {
		return false, err
	}
	restMapping, err := g.RESTMapper.RESTMapping(unversioned.GroupKind{Group: group, Kind: kind}, apiutil.GetVersion(groupVersion))
	if err != nil {
		return false, err
	}
	scopeName := restMapping.Scope.Name()
	if scopeName == meta.RESTScopeNameNamespace {
		return true, nil
	}
	return false, nil
}

// StorageGroupsToEncodingVersion returns a map from group name to group version,
// computed from the s.DeprecatedStorageVersion and s.StorageVersions flags.
// TODO: can we move the whole storage version concept to the generic apiserver?
func (s *APIServer) StorageGroupsToEncodingVersion() (map[string]unversioned.GroupVersion, error) {
	storageVersionMap := map[string]unversioned.GroupVersion{}
	if s.DeprecatedStorageVersion != "" {
		storageVersionMap[""] = unversioned.GroupVersion{Group: apiutil.GetGroup(s.DeprecatedStorageVersion), Version: apiutil.GetVersion(s.DeprecatedStorageVersion)}
	}

	// First, get the defaults.
	if err := mergeGroupVersionIntoMap(s.DefaultStorageVersions, storageVersionMap); err != nil {
		return nil, err
	}
	// Override any defaults with the user settings.
	if err := mergeGroupVersionIntoMap(s.StorageVersions, storageVersionMap); err != nil {
		return nil, err
	}

	return storageVersionMap, nil
}

// dest must be a map of group to groupVersion.
func gvToMap(gvList string, dest map[string]string) {
	for _, gv := range strings.Split(gvList, ",") {
		if gv == "" {
			continue
		}
		// We accept two formats. "group/version" OR
		// "group=group/version". The latter is used when types
		// move between groups.
		if !strings.Contains(gv, "=") {
			dest[apiutil.GetGroup(gv)] = gv
		} else {
			parts := strings.SplitN(gv, "=", 2)
			// TODO: error checking.
			dest[parts[0]] = parts[1]
		}
	}
}

// ValidateEvent makes sure that the event makes sense.
func ValidateEvent(event *api.Event) field.ErrorList {
	allErrs := field.ErrorList{}
	// There is no namespace required for root-scoped kind, for example, node.
	// However, older client code accidentally sets event.Namespace
	// to api.NamespaceDefault, so we accept that too, but "" is preferred.
	// Todo: Events may reference 3rd party object, and we can't check whether the object is namespaced.
	// Suppose them are namespaced. Do check if we can get the piece of information.
	// This should apply to all groups served by this apiserver.
	group := apiutil.GetGroup(event.InvolvedObject.APIVersion)
	version := apiutil.GetVersion(event.InvolvedObject.APIVersion)
	if (group == "" || group == "extensions") && (version != "extensions" && version != "") {
		namespacedKindFlag, err := isNamespacedKind(event.InvolvedObject.Kind, event.InvolvedObject.APIVersion)
		if err != nil {
			allErrs = append(allErrs, field.Invalid(field.NewPath("involvedObject", "kind"), event.InvolvedObject.Kind, fmt.Sprintf("couldn't check whether namespace is allowed: %s", err)))
		} else {
			if !namespacedKindFlag &&
				event.Namespace != api.NamespaceDefault &&
				event.Namespace != "" {
				allErrs = append(allErrs, field.Invalid(field.NewPath("involvedObject", "namespace"), event.InvolvedObject.Namespace, fmt.Sprintf("not allowed for %s", event.InvolvedObject.Kind)))
			}
			if namespacedKindFlag &&
				event.Namespace != event.InvolvedObject.Namespace {
				allErrs = append(allErrs, field.Invalid(field.NewPath("involvedObject", "namespace"), event.InvolvedObject.Namespace, "does not match involvedObject"))
			}
		}
	} else {
		if event.Namespace != event.InvolvedObject.Namespace {
			allErrs = append(allErrs, field.Invalid(field.NewPath("involvedObject", "namespace"), event.InvolvedObject.Namespace, "does not match involvedObject"))
		}
	}

	if !validation.IsDNS1123Subdomain(event.Namespace) {
		allErrs = append(allErrs, field.Invalid(field.NewPath("namespace"), event.Namespace, ""))
	}
	return allErrs
}