//运行
func (o TopNodeOptions) RunTopNode() error {
	var err error
	selector := labels.Everything()//设置selector
	if len(o.Selector) > 0 {//如果--selector有值
		selector, err = labels.Parse(o.Selector)//设置selector
		if err != nil {
			return err
		}
	}

	apiGroups, err := o.DiscoveryClient.ServerGroups()//获取apigroup
	if err != nil {
		return err
	}

	metricsAPIAvailable := SupportedMetricsAPIVersionAvailable(apiGroups)//判断Metrics是否支持这个apiGroup

	metrics := &metricsapi.NodeMetricsList{}
	if metricsAPIAvailable {//如果Metrics支持这个apiGroup
		metrics, err = getNodeMetricsFromMetricsAPI(o.MetricsClient, o.ResourceName, selector)//获取metrics
		if err != nil {
			return err
		}
	} else {//如果不支持
		metrics, err = o.Client.GetNodeMetrics(o.ResourceName, selector.String())//通过client获取metrics
		if err != nil {
			return err
		}
	}

	if len(metrics.Items) == 0 {//如果没有metrics
		return errors.New("metrics not available yet")
	}

	var nodes []v1.Node
	if len(o.ResourceName) > 0 {//如果资源有值
		node, err := o.NodeClient.Nodes().Get(o.ResourceName, metav1.GetOptions{})//获取资源名称对应节点
		if err != nil {
			return err
		}
		nodes = append(nodes, *node)//append节点
	} else {//如果selector有值
		nodeList, err := o.NodeClient.Nodes().List(metav1.ListOptions{//获取selector对应节点
			LabelSelector: selector.String(),
		})
		if err != nil {
			return err
		}
		nodes = append(nodes, nodeList.Items...)//append节点
	}

	allocatable := make(map[string]v1.ResourceList)//可分配资源map

	for _, n := range nodes {//遍历节点，设置可分配资源
		allocatable[n.Name] = n.Status.Allocatable
	}

	return o.Printer.PrintNodeMetrics(metrics.Items, allocatable, o.NoHeaders, o.SortBy)//打印结果
}

func getNodeMetricsFromMetricsAPI(metricsClient metricsclientset.Interface, resourceName string, selector labels.Selector) (*metricsapi.NodeMetricsList, error) {//获取metrics
	var err error
	versionedMetrics := &metricsV1beta1api.NodeMetricsList{}//构造metricsList对象
	mc := metricsClient.MetricsV1beta1()//获取client
	nm := mc.NodeMetricses()//获取node metrics client
	if resourceName != "" {//如果资源名称不为空
		m, err := nm.Get(resourceName, metav1.GetOptions{})//获取metrics
		if err != nil {
			return nil, err
		}
		versionedMetrics.Items = []metricsV1beta1api.NodeMetrics{*m}//包装metricsList
	} else {//如果selector有值
		versionedMetrics, err = nm.List(metav1.ListOptions{LabelSelector: selector.String()})//通过selector获取metrics
		if err != nil {
			return nil, err
		}
	}
	metrics := &metricsapi.NodeMetricsList{}
	err = metricsV1beta1api.Convert_v1beta1_NodeMetricsList_To_metrics_NodeMetricsList(versionedMetrics, metrics, nil)//把metrics转成NodeMetricsList
	if err != nil {
		return nil, err
	}
	return metrics, nil//返回NodeMetricsList
}

//打印node metrics
func (printer *TopCmdPrinter) PrintNodeMetrics(metrics []metricsapi.NodeMetrics, availableResources map[string]v1.ResourceList, noHeaders bool, sortBy string) error {
	if len(metrics) == 0 {//metrics为空返回
		return nil
	}
	w := printers.GetNewTabWriter(printer.out)//包装tab Writer
	defer w.Flush()//defer刷新

	n, err := NewNodeMetricsSorter(metrics, sortBy)//metrics排序
	if err != nil {
		return err
	}
	sort.Sort(n)//执行排序

	if !noHeaders {//如果不是noHeaders，打印headers
		printColumnNames(w, NodeColumns)
	}
	var usage v1.ResourceList
	for _, m := range metrics {//遍历metrics
		err := scheme.Scheme.Convert(&m.Usage, &usage, nil)//转换usage
		if err != nil {
			return err
		}
		printMetricsLine(w, &ResourceMetricsInfo{//打印一行metrics info
			Name:      m.Name,
			Metrics:   usage,
			Available: availableResources[m.Name],
		})
		delete(availableResources, m.Name)//删除availableResources 中已经打印的
	}

	// print lines for nodes of which the metrics is unreachable.
	for nodeName := range availableResources {//遍历availableResources，打印没有metrics的node
		printMissingMetricsNodeLine(w, nodeName)
	}
	return nil
}

//判断metrics是否支持apiGroup
func SupportedMetricsAPIVersionAvailable(discoveredAPIGroups *metav1.APIGroupList) bool {
	for _, discoveredAPIGroup := range discoveredAPIGroups.Groups {
		if discoveredAPIGroup.Name != metricsapi.GroupName {//如果groupname不同则跳过
			continue
		}
		for _, version := range discoveredAPIGroup.Versions {
			for _, supportedVersion := range supportedMetricsAPIVersions {
				if version.Version == supportedVersion {//如果version为supportedVersion 则返回true
					return true
				}
			}
		}
	}
	return false//返回false
}