// RunExplain executes the appropriate steps to print a model's documentation
func RunExplain(f *cmdutil.Factory, out, cmdErr io.Writer, cmd *cobra.Command, args []string) error {
	if len(args) == 0 {
		fmt.Fprint(cmdErr, "You must specify the type of resource to explain. ", valid_resources)
		return cmdutil.UsageError(cmd, "Required resource not specified.")
	}
	if len(args) > 1 {
		return cmdutil.UsageError(cmd, "We accept only this format: explain RESOURCE")
	}

	recursive := cmdutil.GetFlagBool(cmd, "recursive")
	apiVersionString := cmdutil.GetFlagString(cmd, "api-version")
	apiVersion := unversioned.GroupVersion{}

	mapper, _ := f.Object(cmdutil.GetIncludeThirdPartyAPIs(cmd))
	// TODO: After we figured out the new syntax to separate group and resource, allow
	// the users to use it in explain (kubectl explain <group><syntax><resource>).
	// Refer to issue #16039 for why we do this. Refer to PR #15808 that used "/" syntax.
	inModel, fieldsPath, err := kubectl.SplitAndParseResourceRequest(args[0], mapper)
	if err != nil {
		return err
	}

	// TODO: We should deduce the group for a resource by discovering the supported resources at server.
	fullySpecifiedGVR, groupResource := unversioned.ParseResourceArg(inModel)
	gvk := unversioned.GroupVersionKind{}
	if fullySpecifiedGVR != nil {
		gvk, _ = mapper.KindFor(*fullySpecifiedGVR)
	}
	if gvk.Empty() {
		gvk, err = mapper.KindFor(groupResource.WithVersion(""))
		if err != nil {
			return err
		}
	}

	if len(apiVersionString) == 0 {
		groupMeta, err := registered.Group(gvk.Group)
		if err != nil {
			return err
		}
		apiVersion = groupMeta.GroupVersion

	} else {
		apiVersion, err = unversioned.ParseGroupVersion(apiVersionString)
		if err != nil {
			return nil
		}
	}

	schema, err := f.SwaggerSchema(apiVersion.WithKind(gvk.Kind))
	if err != nil {
		return err
	}

	return kubectl.PrintModelDescription(inModel, fieldsPath, out, schema, recursive)
}

// mappingFor returns the RESTMapping for the Kind referenced by the resource.
// prefers a fully specified GroupVersionResource match.  If we don't have one match on GroupResource
func (b *Builder) mappingFor(resourceArg string) (*meta.RESTMapping, error) {
	fullySpecifiedGVR, groupResource := unversioned.ParseResourceArg(resourceArg)
	gvk := unversioned.GroupVersionKind{}
	if fullySpecifiedGVR != nil {
		gvk, _ = b.mapper.KindFor(*fullySpecifiedGVR)
	}
	if gvk.Empty() {
		var err error
		gvk, err = b.mapper.KindFor(groupResource.WithVersion(""))
		if err != nil {
			return nil, err
		}
	}

	return b.mapper.RESTMapping(gvk.GroupKind(), gvk.Version)
}

func resourceFor(mapper meta.RESTMapper, resourceArg string) unversioned.GroupVersionResource {
	fullySpecifiedGVR, groupResource := unversioned.ParseResourceArg(strings.ToLower(resourceArg))
	gvr := unversioned.GroupVersionResource{}
	if fullySpecifiedGVR != nil {
		gvr, _ = mapper.ResourceFor(*fullySpecifiedGVR)
	}
	if gvr.IsEmpty() {
		var err error
		gvr, err = mapper.ResourceFor(groupResource.WithVersion(""))
		if err != nil {
			return unversioned.GroupVersionResource{Resource: resourceArg}
		}
	}

	return gvr
}