func (g *genericScheduler) Schedule(pod *api.Pod, nodeLister algorithm.NodeLister) (string, error) {
	nodes, err := nodeLister.List()
	if err != nil {
		return "", err
	}
	if len(nodes.Items) == 0 {
		return "", ErrNoNodesAvailable
	}

	filteredNodes, failedPredicateMap, err := findNodesThatFit(pod, g.pods, g.predicates, nodes)
	if err != nil {
		return "", err
	}

	priorityList, err := PrioritizeNodes(pod, g.pods, g.prioritizers, algorithm.FakeNodeLister(filteredNodes))
	if err != nil {
		return "", err
	}
	if len(priorityList) == 0 {
		return "", &FitError{
			Pod:              pod,
			FailedPredicates: failedPredicateMap,
		}
	}

	return g.selectHost(priorityList)
}

// CalculateNodeLabelPriority checks whether a particular label exists on a node or not, regardless of its value.
// If presence is true, prioritizes nodes that have the specified label, regardless of value.
// If presence is false, prioritizes nodes that do not have the specified label.
func (n *NodeLabelPrioritizer) CalculateNodeLabelPriority(pod *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	var score int
	nodes, err := nodeLister.List()
	if err != nil {
		return nil, err
	}

	labeledNodes := map[string]bool{}
	for _, node := range nodes.Items {
		exists := labels.Set(node.Labels).Has(n.label)
		labeledNodes[node.Name] = (exists && n.presence) || (!exists && !n.presence)
	}

	result := []algorithm.HostPriority{}
	//score int - scale of 0-10
	// 0 being the lowest priority and 10 being the highest
	for nodeName, success := range labeledNodes {
		if success {
			score = 10
		} else {
			score = 0
		}
		result = append(result, algorithm.HostPriority{Host: nodeName, Score: score})
	}
	return result, nil
}

// BalancedResourceAllocation favors nodes with balanced resource usage rate.
// BalancedResourceAllocation should **NOT** be used alone, and **MUST** be used together with LeastRequestedPriority.
// It calculates the difference between the cpu and memory fracion of capacity, and prioritizes the host based on how
// close the two metrics are to each other.
// Detail: score = 10 - abs(cpuFraction-memoryFraction)*10. The algorithm is partly inspired by:
// "Wei Huang et al. An Energy Efficient Virtual Machine Placement Algorithm with Balanced Resource Utilization"
func BalancedResourceAllocation(pod *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	nodes, err := nodeLister.List()
	if err != nil {
		return algorithm.HostPriorityList{}, err
	}
	podsToMachines, err := predicates.MapPodsToMachines(podLister)

	list := algorithm.HostPriorityList{}
	for _, node := range nodes.Items {
		list = append(list, calculateBalancedResourceAllocation(pod, node, podsToMachines[node.Name]))
	}
	return list, nil
}

// EqualPriority is a prioritizer function that gives an equal weight of one to all nodes
func EqualPriority(_ *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	nodes, err := nodeLister.List()
	if err != nil {
		glog.Errorf("failed to list nodes: %v", err)
		return []algorithm.HostPriority{}, err
	}

	result := []algorithm.HostPriority{}
	for _, node := range nodes.Items {
		result = append(result, algorithm.HostPriority{
			Host:  node.Name,
			Score: 1,
		})
	}
	return result, nil
}

func numericPriority(pod *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	nodes, err := nodeLister.List()
	result := []algorithm.HostPriority{}

	if err != nil {
		return nil, fmt.Errorf("failed to list nodes: %v", err)
	}
	for _, node := range nodes.Items {
		score, err := strconv.Atoi(node.Name)
		if err != nil {
			return nil, err
		}
		result = append(result, algorithm.HostPriority{
			Host:  node.Name,
			Score: score,
		})
	}
	return result, nil
}

// CalculateSpreadPriority spreads pods by minimizing the number of pods belonging to the same service or replication controller. It counts number of pods that run under
// Services or RCs as the pod being scheduled and tries to minimize the number of conflicts. I.e. pushes scheduler towards a Node where there's a smallest number of
// pods which match the same selectors of Services and RCs as current pod.
func (s *NetworkSpread) CalculateSpreadPriority(pod *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	var maxCount int
	var nsPods []*api.Pod

	selectors := make([]labels.Selector, 0)
	services, err := s.serviceLister.GetPodServices(pod)
	if err == nil {
		for _, service := range services {
			selectors = append(selectors, labels.SelectorFromSet(service.Spec.Selector))
		}
	}
	controllers, err := s.controllerLister.GetPodControllers(pod)
	if err == nil {
		for _, controller := range controllers {
			selectors = append(selectors, labels.SelectorFromSet(controller.Spec.Selector))
		}
	}

	if len(selectors) > 0 {
		pods, err := podLister.List(labels.Everything())
		if err != nil {
			return nil, err
		}
		// consider only the pods that belong to the same namespace
		for _, nsPod := range pods {
			if nsPod.Namespace == pod.Namespace {
				nsPods = append(nsPods, nsPod)
			}
		}
	}

	nodes, err := nodeLister.List()
	if err != nil {
		return nil, err
	}

	subnetMap := map[string]string{}

	for _, node := range nodes.Items {
		for _, addrs := range node.Status.Addresses {
			if addrs.Type == api.NodeLegacyHostIP {
				// for now wandoujia used 24 mask, a pit here.
				_, subnet, _ := net.ParseCIDR(fmt.Sprintf("%s/24", addrs.Address))
				subnetMap[node.Name] = subnet.String()
			}
		}
	}

	counts := map[string]int{}
	if len(nsPods) > 0 {
		for _, pod := range nsPods {
			matches := false
			for _, selector := range selectors {
				if selector.Matches(labels.Set(pod.ObjectMeta.Labels)) {
					matches = true
					break
				}
			}
			if matches {
				subnet := subnetMap[pod.Spec.NodeName]
				counts[subnet]++
				// Compute the maximum number of pods hosted on any node
				if counts[subnet] > maxCount {
					maxCount = counts[subnet]
				}
			}
		}
	}

	result := []algorithm.HostPriority{}
	//score int - scale of 0-10
	// 0 being the lowest priority and 10 being the highest
	for _, node := range nodes.Items {
		// initializing to the default/max node score of 10
		fScore := float32(10)
		subnet := subnetMap[node.Name]
		if maxCount > 0 {
			fScore = 10 * (float32(maxCount-counts[subnet]) / float32(maxCount))
		}
		glog.Infof("maxcount: %v, subNetCounts: %v, fscore: %v", maxCount, counts[subnet], fScore)
		result = append(result, algorithm.HostPriority{Host: node.Name, Score: int(fScore)})
		glog.V(10).Infof(
			"%v -> %v: SelectorSpreadPriority, Score: (%d)", pod.Name, node.Name, int(fScore),
		)
	}
	return result, nil
}

// CalculateSpreadPriority spreads pods by minimizing the number of pods belonging to the same service or replication controller. It counts number of pods that run under
// Services or RCs as the pod being scheduled and tries to minimize the number of conflicts. I.e. pushes scheduler towards a Node where there's a smallest number of
// pods which match the same selectors of Services and RCs as current pod.
func (s *SelectorSpread) CalculateSpreadPriority(pod *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	var maxCount int
	var nsPods []*api.Pod

	selectors := make([]labels.Selector, 0)
	services, err := s.serviceLister.GetPodServices(pod)
	if err == nil {
		for _, service := range services {
			selectors = append(selectors, labels.SelectorFromSet(service.Spec.Selector))
		}
	}
	controllers, err := s.controllerLister.GetPodControllers(pod)
	if err == nil {
		for _, controller := range controllers {
			selectors = append(selectors, labels.SelectorFromSet(controller.Spec.Selector))
		}
	}

	if len(selectors) > 0 {
		pods, err := podLister.List(labels.Everything())
		if err != nil {
			return nil, err
		}
		// consider only the pods that belong to the same namespace
		for _, nsPod := range pods {
			if nsPod.Namespace == pod.Namespace {
				nsPods = append(nsPods, nsPod)
			}
		}
	}

	nodes, err := nodeLister.List()
	if err != nil {
		return nil, err
	}

	counts := map[string]int{}
	if len(nsPods) > 0 {
		for _, pod := range nsPods {
			matches := false
			for _, selector := range selectors {
				if selector.Matches(labels.Set(pod.ObjectMeta.Labels)) {
					matches = true
					break
				}
			}
			if matches {

				counts[pod.Spec.NodeName]++
				// Compute the maximum number of pods hosted on any node
				if counts[pod.Spec.NodeName] > maxCount {
					maxCount = counts[pod.Spec.NodeName]
				}

			}
		}
	}

	result := []algorithm.HostPriority{}
	//score int - scale of 0-10
	// 0 being the lowest priority and 10 being the highest
	for _, node := range nodes.Items {
		// initializing to the default/max node score of 10
		fScore := float32(10)
		if maxCount > 0 {
			fScore = 10 * (float32(maxCount-counts[node.Name]) / float32(maxCount))
		}
		result = append(result, algorithm.HostPriority{Host: node.Name, Score: int(fScore)})
		glog.V(10).Infof(
			"%v -> %v: SelectorSpreadPriority, Score: (%d)", pod.Name, node.Name, int(fScore),
		)
	}
	return result, nil
}

// CalculateAntiAffinityPriority spreads pods by minimizing the number of pods belonging to the same service
// on machines with the same value for a particular label.
// The label to be considered is provided to the struct (ServiceAntiAffinity).
func (s *ServiceAntiAffinity) CalculateAntiAffinityPriority(pod *api.Pod, podLister algorithm.PodLister, nodeLister algorithm.NodeLister) (algorithm.HostPriorityList, error) {
	var nsServicePods []*api.Pod

	services, err := s.serviceLister.GetPodServices(pod)
	if err == nil {
		// just use the first service and get the other pods within the service
		// TODO: a separate predicate can be created that tries to handle all services for the pod
		selector := labels.SelectorFromSet(services[0].Spec.Selector)
		pods, err := podLister.List(selector)
		if err != nil {
			return nil, err
		}
		// consider only the pods that belong to the same namespace
		for _, nsPod := range pods {
			if nsPod.Namespace == pod.Namespace {
				nsServicePods = append(nsServicePods, nsPod)
			}
		}
	}

	nodes, err := nodeLister.List()
	if err != nil {
		return nil, err
	}

	// separate out the nodes that have the label from the ones that don't
	otherNodes := []string{}
	labeledNodes := map[string]string{}
	for _, node := range nodes.Items {
		if labels.Set(node.Labels).Has(s.label) {
			label := labels.Set(node.Labels).Get(s.label)
			labeledNodes[node.Name] = label
		} else {
			otherNodes = append(otherNodes, node.Name)
		}
	}

	podCounts := map[string]int{}
	for _, pod := range nsServicePods {
		label, exists := labeledNodes[pod.Spec.NodeName]
		if !exists {
			continue
		}
		podCounts[label]++
	}

	numServicePods := len(nsServicePods)
	result := []algorithm.HostPriority{}
	//score int - scale of 0-10
	// 0 being the lowest priority and 10 being the highest
	for node := range labeledNodes {
		// initializing to the default/max node score of 10
		fScore := float32(10)
		if numServicePods > 0 {
			fScore = 10 * (float32(numServicePods-podCounts[labeledNodes[node]]) / float32(numServicePods))
		}
		result = append(result, algorithm.HostPriority{Host: node, Score: int(fScore)})
	}
	// add the open nodes with a score of 0
	for _, node := range otherNodes {
		result = append(result, algorithm.HostPriority{Host: node, Score: 0})
	}

	return result, nil
}