/*
Copyright 2016 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package clusterstate

import (
	"fmt"
	"reflect"
	"sync"
	"time"

	"k8s.io/autoscaler/cluster-autoscaler/cloudprovider"
	"k8s.io/autoscaler/cluster-autoscaler/clusterstate/api"
	"k8s.io/autoscaler/cluster-autoscaler/clusterstate/utils"
	"k8s.io/autoscaler/cluster-autoscaler/metrics"
	"k8s.io/autoscaler/cluster-autoscaler/utils/backoff"
	"k8s.io/autoscaler/cluster-autoscaler/utils/deletetaint"
	kube_util "k8s.io/autoscaler/cluster-autoscaler/utils/kubernetes"

	apiv1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/util/sets"
	schedulercache "k8s.io/kubernetes/pkg/scheduler/cache"

	"k8s.io/klog"
)

const (
	// MaxNodeStartupTime is the maximum time from the moment the node is registered to the time the node is ready.
	MaxNodeStartupTime = 15 * time.Minute

	// MaxStatusSettingDelayAfterCreation is the maximum time for node to set its initial status after the
	// node is registered.
	MaxStatusSettingDelayAfterCreation = 2 * time.Minute

	// MaxNodeGroupBackoffDuration is the maximum backoff duration for a NodeGroup after new nodes failed to start.
	MaxNodeGroupBackoffDuration = 30 * time.Minute

	// InitialNodeGroupBackoffDuration is the duration of first backoff after a new node failed to start.
	InitialNodeGroupBackoffDuration = 5 * time.Minute

	// NodeGroupBackoffResetTimeout is the time after last failed scale-up when the backoff duration is reset.
	NodeGroupBackoffResetTimeout = 3 * time.Hour
)

// ScaleUpRequest contains information about the requested node group scale up.
type ScaleUpRequest struct {
	// NodeGroup is the node group to be scaled up.
	NodeGroup cloudprovider.NodeGroup
	// Time is the time when the request was submitted.
	Time time.Time
	// ExpectedAddTime is the time at which the request should be fulfilled.
	ExpectedAddTime time.Time
	// How much the node group is increased.
	Increase int
}

// ScaleDownRequest contains information about the requested node deletion.
type ScaleDownRequest struct {
	// NodeName is the name of the node to be deleted.
	NodeName string
	// NodeGroup is the node group of the deleted node.
	NodeGroup cloudprovider.NodeGroup
	// Time is the time when the node deletion was requested.
	Time time.Time
	// ExpectedDeleteTime is the time when the node is expected to be deleted.
	ExpectedDeleteTime time.Time
}

// ClusterStateRegistryConfig contains configuration information for ClusterStateRegistry.
type ClusterStateRegistryConfig struct {
	// Maximum percentage of unready nodes in total, if the number of unready nodes is higher than OkTotalUnreadyCount.
	MaxTotalUnreadyPercentage float64
	// Minimum number of nodes that must be unready for MaxTotalUnreadyPercentage to apply.
	// This is to ensure that in very small clusters (e.g. 2 nodes) a single node's failure doesn't disable autoscaling.
	OkTotalUnreadyCount int
	//  Maximum time CA waits for node to be provisioned
	MaxNodeProvisionTime time.Duration
}

// IncorrectNodeGroupSize contains information about how much the current size of the node group
// differs from the expected size. Prolonged, stable mismatch is an indication of quota
// or startup issues.
type IncorrectNodeGroupSize struct {
	// ExpectedSize is the size of the node group measured on the cloud provider side.
	ExpectedSize int
	// CurrentSize is the size of the node group measured on the kubernetes side.
	CurrentSize int
	// FirstObserved is the time when the given difference occurred.
	FirstObserved time.Time
}

// UnregisteredNode contains information about nodes that are present on the cluster provider side
// but failed to register in Kubernetes.
type UnregisteredNode struct {
	// Node is a dummy node that contains only the name of the node.
	Node *apiv1.Node
	// UnregisteredSince is the time when the node was first spotted.
	UnregisteredSince time.Time
}

// ClusterStateRegistry is a structure to keep track the current state of the cluster.
type ClusterStateRegistry struct {
	sync.Mutex
	config                  ClusterStateRegistryConfig
	scaleUpRequests         map[string]*ScaleUpRequest // nodeGroupName -> ScaleUpRequest
	scaleDownRequests       []*ScaleDownRequest
	nodes                   []*apiv1.Node
	nodeInfosForGroups      map[string]*schedulercache.NodeInfo
	cloudProvider           cloudprovider.CloudProvider
	perNodeGroupReadiness   map[string]Readiness
	totalReadiness          Readiness
	acceptableRanges        map[string]AcceptableRange
	incorrectNodeGroupSizes map[string]IncorrectNodeGroupSize
	unregisteredNodes       map[string]UnregisteredNode
	candidatesForScaleDown  map[string][]string
	nodeGroupBackoffInfo    backoff.Backoff
	lastStatus              *api.ClusterAutoscalerStatus
	lastScaleDownUpdateTime time.Time
	logRecorder             *utils.LogEventRecorder
}

// NewClusterStateRegistry creates new ClusterStateRegistry.
func NewClusterStateRegistry(cloudProvider cloudprovider.CloudProvider, config ClusterStateRegistryConfig, logRecorder *utils.LogEventRecorder, backoff backoff.Backoff) *ClusterStateRegistry {
	emptyStatus := &api.ClusterAutoscalerStatus{
		ClusterwideConditions: make([]api.ClusterAutoscalerCondition, 0),
		NodeGroupStatuses:     make([]api.NodeGroupStatus, 0),
	}
	return &ClusterStateRegistry{
		scaleUpRequests:         make(map[string]*ScaleUpRequest),
		scaleDownRequests:       make([]*ScaleDownRequest, 0),
		nodes:                   make([]*apiv1.Node, 0),
		cloudProvider:           cloudProvider,
		config:                  config,
		perNodeGroupReadiness:   make(map[string]Readiness),
		acceptableRanges:        make(map[string]AcceptableRange),
		incorrectNodeGroupSizes: make(map[string]IncorrectNodeGroupSize),
		unregisteredNodes:       make(map[string]UnregisteredNode),
		candidatesForScaleDown:  make(map[string][]string),
		nodeGroupBackoffInfo:    backoff,
		lastStatus:              emptyStatus,
		logRecorder:             logRecorder,
	}
}

// RegisterScaleUp registers scale up.
func (csr *ClusterStateRegistry) RegisterScaleUp(request *ScaleUpRequest) {
	csr.Lock()
	defer csr.Unlock()

	oldScaleUpRequest, found := csr.scaleUpRequests[request.NodeGroup.Id()]
	if !found {
		csr.scaleUpRequests[request.NodeGroup.Id()] = request
		return
	}

	// update the old request
	oldScaleUpRequest.Time = request.Time
	oldScaleUpRequest.ExpectedAddTime = request.ExpectedAddTime
	oldScaleUpRequest.Increase += request.Increase
}

// RegisterScaleDown registers node scale down.
func (csr *ClusterStateRegistry) RegisterScaleDown(request *ScaleDownRequest) {
	csr.Lock()
	defer csr.Unlock()
	csr.scaleDownRequests = append(csr.scaleDownRequests, request)
}

// To be executed under a lock.
func (csr *ClusterStateRegistry) updateScaleRequests(currentTime time.Time) {
	// clean up stale backoff info
	csr.nodeGroupBackoffInfo.RemoveStaleBackoffData(currentTime)

	for nodeGroupName, scaleUpRequest := range csr.scaleUpRequests {
		if !csr.areThereUpcomingNodesInNodeGroup(nodeGroupName) {
			// scale-out finished successfully
			// remove it and reset node group backoff
			delete(csr.scaleUpRequests, nodeGroupName)
			csr.nodeGroupBackoffInfo.RemoveBackoff(scaleUpRequest.NodeGroup)
			klog.V(4).Infof("Scale up in group %v finished successfully in %v",
				nodeGroupName, currentTime.Sub(scaleUpRequest.Time))
			continue
		}

		if scaleUpRequest.ExpectedAddTime.Before(currentTime) {
			klog.Warningf("Scale-up timed out for node group %v after %v",
				nodeGroupName, currentTime.Sub(scaleUpRequest.Time))
			csr.logRecorder.Eventf(apiv1.EventTypeWarning, "ScaleUpTimedOut",
				"Nodes added to group %s failed to register within %v",
				scaleUpRequest.NodeGroup.Id(), currentTime.Sub(scaleUpRequest.Time))
			metrics.RegisterFailedScaleUp(metrics.Timeout)
			csr.backoffNodeGroup(scaleUpRequest.NodeGroup, currentTime)
			delete(csr.scaleUpRequests, nodeGroupName)
		}
	}

	newScaleDownRequests := make([]*ScaleDownRequest, 0)
	for _, scaleDownRequest := range csr.scaleDownRequests {
		if scaleDownRequest.ExpectedDeleteTime.After(currentTime) {
			newScaleDownRequests = append(newScaleDownRequests, scaleDownRequest)
		}
	}
	csr.scaleDownRequests = newScaleDownRequests
}

// To be executed under a lock.
func (csr *ClusterStateRegistry) backoffNodeGroup(nodeGroup cloudprovider.NodeGroup, currentTime time.Time) {
	backoffUntil := csr.nodeGroupBackoffInfo.Backoff(nodeGroup, currentTime)
	klog.Warningf("Disabling scale-up for node group %v until %v", nodeGroup.Id(), backoffUntil)
}

// RegisterFailedScaleUp should be called after getting error from cloudprovider
// when trying to scale-up node group. It will mark this group as not safe to autoscale
// for some time.
func (csr *ClusterStateRegistry) RegisterFailedScaleUp(nodeGroup cloudprovider.NodeGroup, reason metrics.FailedScaleUpReason) {
	csr.Lock()
	defer csr.Unlock()

	metrics.RegisterFailedScaleUp(reason)
	csr.backoffNodeGroup(nodeGroup, time.Now())
}

// UpdateNodes updates the state of the nodes in the ClusterStateRegistry and recalculates the stats
func (csr *ClusterStateRegistry) UpdateNodes(nodes []*apiv1.Node, nodeInfosForGroups map[string]*schedulercache.NodeInfo, currentTime time.Time) error {
	csr.updateNodeGroupMetrics()
	targetSizes, err := getTargetSizes(csr.cloudProvider)
	if err != nil {
		return err
	}
	notRegistered, err := getNotRegisteredNodes(nodes, csr.cloudProvider, currentTime)
	if err != nil {
		return err
	}

	csr.Lock()
	defer csr.Unlock()

	csr.nodes = nodes
	csr.nodeInfosForGroups = nodeInfosForGroups

	csr.updateUnregisteredNodes(notRegistered)
	csr.updateReadinessStats(currentTime)

	// update acceptable ranges based on requests from last loop and targetSizes
	// updateScaleRequests relies on acceptableRanges being up to date
	csr.updateAcceptableRanges(targetSizes)
	csr.updateScaleRequests(currentTime)
	//  recalculate acceptable ranges after removing timed out requests
	csr.updateAcceptableRanges(targetSizes)
	csr.updateIncorrectNodeGroupSizes(currentTime)
	return nil
}

// Recalculate cluster state after scale-ups or scale-downs were registered.
func (csr *ClusterStateRegistry) Recalculate() {
	targetSizes, err := getTargetSizes(csr.cloudProvider)
	if err != nil {
		klog.Warningf("Failed to get target sizes, when trying to recalculate cluster state: %v", err)
	}

	csr.Lock()
	defer csr.Unlock()
	csr.updateAcceptableRanges(targetSizes)
}

// getTargetSizes gets target sizes of node groups.
func getTargetSizes(cp cloudprovider.CloudProvider) (map[string]int, error) {
	result := make(map[string]int)
	for _, ng := range cp.NodeGroups() {
		size, err := ng.TargetSize()
		if err != nil {
			return map[string]int{}, err
		}
		result[ng.Id()] = size
	}
	return result, nil
}

// IsClusterHealthy returns true if the cluster health is within the acceptable limits
func (csr *ClusterStateRegistry) IsClusterHealthy() bool {
	csr.Lock()
	defer csr.Unlock()

	totalUnready := csr.totalReadiness.Unready + csr.totalReadiness.LongNotStarted + csr.totalReadiness.LongUnregistered

	if totalUnready > csr.config.OkTotalUnreadyCount &&
		float64(totalUnready) > csr.config.MaxTotalUnreadyPercentage/100.0*float64(len(csr.nodes)) {
		return false
	}

	return true
}

// IsNodeGroupHealthy returns true if the node group health is within the acceptable limits
func (csr *ClusterStateRegistry) IsNodeGroupHealthy(nodeGroupName string) bool {
	acceptable, found := csr.acceptableRanges[nodeGroupName]
	if !found {
		klog.Warningf("Failed to find acceptable ranges for %v", nodeGroupName)
		return false
	}

	readiness, found := csr.perNodeGroupReadiness[nodeGroupName]
	if !found {
		// No nodes but target == 0 or just scaling up.
		if acceptable.CurrentTarget == 0 || (acceptable.MinNodes == 0 && acceptable.CurrentTarget > 0) {
			return true
		}
		klog.Warningf("Failed to find readiness information for %v", nodeGroupName)
		return false
	}

	unjustifiedUnready := 0
	// Too few nodes, something is missing. Below the expected node count.
	if readiness.Ready < acceptable.MinNodes {
		unjustifiedUnready += acceptable.MinNodes - readiness.Ready
	}
	// TODO: verify against max nodes as well.

	if unjustifiedUnready > csr.config.OkTotalUnreadyCount &&
		float64(unjustifiedUnready) > csr.config.MaxTotalUnreadyPercentage/100.0*
			float64(readiness.Ready+readiness.Unready+readiness.NotStarted+readiness.LongNotStarted) {
		return false
	}

	return true
}

// updateNodeGroupMetrics looks at NodeGroups provided by cloudprovider and updates corresponding metrics
func (csr *ClusterStateRegistry) updateNodeGroupMetrics() {
	autoscaled := 0
	autoprovisioned := 0
	for _, nodeGroup := range csr.cloudProvider.NodeGroups() {
		if !nodeGroup.Exist() {
			continue
		}
		if nodeGroup.Autoprovisioned() {
			autoprovisioned += 1
		} else {
			autoscaled += 1
		}
	}
	metrics.UpdateNodeGroupsCount(autoscaled, autoprovisioned)
}

// IsNodeGroupSafeToScaleUp returns true if node group can be scaled up now.
func (csr *ClusterStateRegistry) IsNodeGroupSafeToScaleUp(nodeGroup cloudprovider.NodeGroup, now time.Time) bool {
	if !csr.IsNodeGroupHealthy(nodeGroup.Id()) {
		return false
	}
	return !csr.nodeGroupBackoffInfo.IsBackedOff(nodeGroup, now)
}

func (csr *ClusterStateRegistry) getProvisionedAndTargetSizesForNodeGroup(nodeGroupName string) (provisioned, target int, ok bool) {
	acceptable, found := csr.acceptableRanges[nodeGroupName]
	if !found {
		klog.Warningf("Failed to find acceptable ranges for %v", nodeGroupName)
		return 0, 0, false
	}
	target = acceptable.CurrentTarget

	readiness, found := csr.perNodeGroupReadiness[nodeGroupName]
	if !found {
		// No need to warn if node group has size 0 (was scaled to 0 before).
		if acceptable.MinNodes != 0 {
			klog.Warningf("Failed to find readiness information for %v", nodeGroupName)
		}
		return 0, target, true
	}
	provisioned = readiness.Registered - readiness.NotStarted - readiness.LongNotStarted

	return provisioned, target, true
}

func (csr *ClusterStateRegistry) areThereUpcomingNodesInNodeGroup(nodeGroupName string) bool {
	provisioned, target, ok := csr.getProvisionedAndTargetSizesForNodeGroup(nodeGroupName)
	if !ok {
		return false
	}
	return target > provisioned
}

// IsNodeGroupAtTargetSize returns true if the number of nodes provisioned in the group is equal to the target number of nodes.
func (csr *ClusterStateRegistry) IsNodeGroupAtTargetSize(nodeGroupName string) bool {
	provisioned, target, ok := csr.getProvisionedAndTargetSizesForNodeGroup(nodeGroupName)
	if !ok {
		return false
	}
	return target == provisioned
}

// IsNodeGroupScalingUp returns true if the node group is currently scaling up.
func (csr *ClusterStateRegistry) IsNodeGroupScalingUp(nodeGroupName string) bool {
	if !csr.areThereUpcomingNodesInNodeGroup(nodeGroupName) {
		return false
	}
	_, found := csr.scaleUpRequests[nodeGroupName]
	return found
}

// AcceptableRange contains information about acceptable size of a node group.
type AcceptableRange struct {
	// MinNodes is the minimum number of nodes in the group.
	MinNodes int
	// MaxNodes is the maximum number of nodes in the group.
	MaxNodes int
	// CurrentTarget is the current target size of the group.
	CurrentTarget int
}

// updateAcceptableRanges updates cluster state registry with how many nodes can be in a cluster.
// The function assumes that the nodeGroup.TargetSize() is the desired number of nodes.
// So if there has been a recent scale up of size 5 then there should be between targetSize-5 and targetSize
// nodes in ready state. In the same way, if there have been 3 nodes removed recently then
// the expected number of ready nodes is between targetSize and targetSize + 3.
func (csr *ClusterStateRegistry) updateAcceptableRanges(targetSize map[string]int) {
	result := make(map[string]AcceptableRange)
	for _, nodeGroup := range csr.cloudProvider.NodeGroups() {
		size := targetSize[nodeGroup.Id()]
		readiness := csr.perNodeGroupReadiness[nodeGroup.Id()]
		result[nodeGroup.Id()] = AcceptableRange{
			MinNodes:      size - readiness.LongUnregistered,
			MaxNodes:      size,
			CurrentTarget: size,
		}
	}
	for nodeGroupName, scaleUpRequest := range csr.scaleUpRequests {
		acceptableRange := result[nodeGroupName]
		acceptableRange.MinNodes -= scaleUpRequest.Increase
		result[nodeGroupName] = acceptableRange
	}
	for _, scaleDownRequest := range csr.scaleDownRequests {
		acceptableRange := result[scaleDownRequest.NodeGroup.Id()]
		acceptableRange.MaxNodes += 1
		result[scaleDownRequest.NodeGroup.Id()] = acceptableRange
	}
	csr.acceptableRanges = result
}

// Readiness contains readiness information about a group of nodes.
type Readiness struct {
	// Number of ready nodes.
	Ready int
	// Number of unready nodes that broke down after they started.
	Unready int
	// Number of nodes that are being currently deleted. They exist in K8S but
	// are not included in NodeGroup.TargetSize().
	Deleted int
	// Number of nodes that failed to start within a reasonable limit.
	LongNotStarted int
	// Number of nodes that are not yet fully started.
	NotStarted int
	// Number of all registered nodes in the group (ready/unready/deleted/etc).
	Registered int
	// Number of nodes that failed to register within a reasonable limit.
	LongUnregistered int
	// Number of nodes that haven't yet registered.
	Unregistered int
	// Time when the readiness was measured.
	Time time.Time
}

func (csr *ClusterStateRegistry) updateReadinessStats(currentTime time.Time) {

	perNodeGroup := make(map[string]Readiness)
	total := Readiness{Time: currentTime}

	update := func(current Readiness, node *apiv1.Node, ready bool) Readiness {
		current.Registered++
		if deletetaint.HasToBeDeletedTaint(node) {
			current.Deleted++
		} else if stillStarting := isNodeStillStarting(node); stillStarting && node.CreationTimestamp.Time.Add(MaxNodeStartupTime).Before(currentTime) {
			current.LongNotStarted++
		} else if stillStarting {
			current.NotStarted++
		} else if ready {
			current.Ready++
		} else {
			current.Unready++
		}
		return current
	}

	for _, node := range csr.nodes {
		nodeGroup, errNg := csr.cloudProvider.NodeGroupForNode(node)
		ready, _, errReady := kube_util.GetReadinessState(node)

		// Node is most likely not autoscaled, however check the errors.
		if nodeGroup == nil || reflect.ValueOf(nodeGroup).IsNil() {
			if errNg != nil {
				klog.Warningf("Failed to get nodegroup for %s: %v", node.Name, errNg)
			}
			if errReady != nil {
				klog.Warningf("Failed to get readiness info for %s: %v", node.Name, errReady)
			}
		} else {
			perNodeGroup[nodeGroup.Id()] = update(perNodeGroup[nodeGroup.Id()], node, ready)
		}
		total = update(total, node, ready)
	}

	for _, unregistered := range csr.unregisteredNodes {
		nodeGroup, errNg := csr.cloudProvider.NodeGroupForNode(unregistered.Node)
		if errNg != nil {
			klog.Warningf("Failed to get nodegroup for %s: %v", unregistered.Node.Name, errNg)
			continue
		}
		perNgCopy := perNodeGroup[nodeGroup.Id()]
		if unregistered.UnregisteredSince.Add(csr.config.MaxNodeProvisionTime).Before(currentTime) {
			perNgCopy.LongUnregistered += 1
			total.LongUnregistered += 1
		} else {
			perNgCopy.Unregistered += 1
			total.Unregistered += 1
		}
		perNodeGroup[nodeGroup.Id()] = perNgCopy
	}

	for ngId, ngReadiness := range perNodeGroup {
		ngReadiness.Time = currentTime
		perNodeGroup[ngId] = ngReadiness
	}
	csr.perNodeGroupReadiness = perNodeGroup
	csr.totalReadiness = total
}

// Calculates which node groups have incorrect size.
func (csr *ClusterStateRegistry) updateIncorrectNodeGroupSizes(currentTime time.Time) {
	result := make(map[string]IncorrectNodeGroupSize)
	for _, nodeGroup := range csr.cloudProvider.NodeGroups() {
		acceptableRange, found := csr.acceptableRanges[nodeGroup.Id()]
		if !found {
			klog.Warningf("Acceptable range for node group %s not found", nodeGroup.Id())
			continue
		}
		readiness, found := csr.perNodeGroupReadiness[nodeGroup.Id()]
		if !found {
			// if MinNodes == 0 node group has been scaled to 0 and everything's fine
			if acceptableRange.MinNodes != 0 {
				klog.Warningf("Readiness for node group %s not found", nodeGroup.Id())
			}
			continue
		}
		if readiness.Registered > acceptableRange.MaxNodes ||
			readiness.Registered < acceptableRange.MinNodes {
			incorrect := IncorrectNodeGroupSize{
				CurrentSize:   readiness.Registered,
				ExpectedSize:  acceptableRange.CurrentTarget,
				FirstObserved: currentTime,
			}
			existing, found := csr.incorrectNodeGroupSizes[nodeGroup.Id()]
			if found {
				if incorrect.CurrentSize == existing.CurrentSize &&
					incorrect.ExpectedSize == existing.ExpectedSize {
					incorrect = existing
				}
			}
			result[nodeGroup.Id()] = incorrect
		}
	}
	csr.incorrectNodeGroupSizes = result
}

func (csr *ClusterStateRegistry) updateUnregisteredNodes(unregisteredNodes []UnregisteredNode) {
	result := make(map[string]UnregisteredNode)
	for _, unregistered := range unregisteredNodes {
		if prev, found := csr.unregisteredNodes[unregistered.Node.Name]; found {
			result[unregistered.Node.Name] = prev
		} else {
			result[unregistered.Node.Name] = unregistered
		}
	}
	csr.unregisteredNodes = result
}

//GetUnregisteredNodes returns a list of all unregistered nodes.
func (csr *ClusterStateRegistry) GetUnregisteredNodes() []UnregisteredNode {
	csr.Lock()
	defer csr.Unlock()

	result := make([]UnregisteredNode, 0, len(csr.unregisteredNodes))
	for _, unregistered := range csr.unregisteredNodes {
		result = append(result, unregistered)
	}
	return result
}

// UpdateScaleDownCandidates updates scale down candidates
func (csr *ClusterStateRegistry) UpdateScaleDownCandidates(nodes []*apiv1.Node, now time.Time) {
	result := make(map[string][]string)
	for _, node := range nodes {
		group, err := csr.cloudProvider.NodeGroupForNode(node)
		if err != nil {
			klog.Warningf("Failed to get node group for %s: %v", node.Name, err)
			continue
		}
		if group == nil || reflect.ValueOf(group).IsNil() {
			continue
		}
		result[group.Id()] = append(result[group.Id()], node.Name)
	}
	csr.candidatesForScaleDown = result
	csr.lastScaleDownUpdateTime = now
}

// GetStatus returns ClusterAutoscalerStatus with the current cluster autoscaler status.
func (csr *ClusterStateRegistry) GetStatus(now time.Time) *api.ClusterAutoscalerStatus {
	result := &api.ClusterAutoscalerStatus{
		ClusterwideConditions: make([]api.ClusterAutoscalerCondition, 0),
		NodeGroupStatuses:     make([]api.NodeGroupStatus, 0),
	}
	for _, nodeGroup := range csr.cloudProvider.NodeGroups() {
		nodeGroupStatus := api.NodeGroupStatus{
			ProviderID: nodeGroup.Id(),
			Conditions: make([]api.ClusterAutoscalerCondition, 0),
		}
		readiness := csr.perNodeGroupReadiness[nodeGroup.Id()]
		acceptable := csr.acceptableRanges[nodeGroup.Id()]

		// Health.
		nodeGroupStatus.Conditions = append(nodeGroupStatus.Conditions, buildHealthStatusNodeGroup(
			csr.IsNodeGroupHealthy(nodeGroup.Id()), readiness, acceptable, nodeGroup.MinSize(), nodeGroup.MaxSize()))

		// Scale up.
		nodeGroupStatus.Conditions = append(nodeGroupStatus.Conditions, buildScaleUpStatusNodeGroup(
			csr.IsNodeGroupScalingUp(nodeGroup.Id()),
			csr.IsNodeGroupSafeToScaleUp(nodeGroup, now),
			readiness,
			acceptable))

		// Scale down.
		nodeGroupStatus.Conditions = append(nodeGroupStatus.Conditions, buildScaleDownStatusNodeGroup(
			csr.candidatesForScaleDown[nodeGroup.Id()], csr.lastScaleDownUpdateTime))

		result.NodeGroupStatuses = append(result.NodeGroupStatuses, nodeGroupStatus)
	}
	result.ClusterwideConditions = append(result.ClusterwideConditions,
		buildHealthStatusClusterwide(csr.IsClusterHealthy(), csr.totalReadiness))
	result.ClusterwideConditions = append(result.ClusterwideConditions,
		buildScaleUpStatusClusterwide(result.NodeGroupStatuses, csr.totalReadiness))
	result.ClusterwideConditions = append(result.ClusterwideConditions,
		buildScaleDownStatusClusterwide(csr.candidatesForScaleDown, csr.lastScaleDownUpdateTime))

	updateLastTransition(csr.lastStatus, result)
	csr.lastStatus = result
	return result
}

// GetClusterReadiness returns current readiness stats of cluster
func (csr *ClusterStateRegistry) GetClusterReadiness() Readiness {
	return csr.totalReadiness
}

func buildHealthStatusNodeGroup(isReady bool, readiness Readiness, acceptable AcceptableRange, minSize, maxSize int) api.ClusterAutoscalerCondition {
	condition := api.ClusterAutoscalerCondition{
		Type: api.ClusterAutoscalerHealth,
		Message: fmt.Sprintf("ready=%d unready=%d notStarted=%d longNotStarted=%d registered=%d longUnregistered=%d cloudProviderTarget=%d (minSize=%d, maxSize=%d)",
			readiness.Ready,
			readiness.Unready,
			readiness.NotStarted,
			readiness.LongNotStarted,
			readiness.Registered,
			readiness.LongUnregistered,
			acceptable.CurrentTarget,
			minSize,
			maxSize),
		LastProbeTime: metav1.Time{Time: readiness.Time},
	}
	if isReady {
		condition.Status = api.ClusterAutoscalerHealthy
	} else {
		condition.Status = api.ClusterAutoscalerUnhealthy
	}
	return condition
}

func buildScaleUpStatusNodeGroup(isScaleUpInProgress bool, isSafeToScaleUp bool, readiness Readiness, acceptable AcceptableRange) api.ClusterAutoscalerCondition {
	condition := api.ClusterAutoscalerCondition{
		Type: api.ClusterAutoscalerScaleUp,
		Message: fmt.Sprintf("ready=%d cloudProviderTarget=%d",
			readiness.Ready,
			acceptable.CurrentTarget),
		LastProbeTime: metav1.Time{Time: readiness.Time},
	}
	if isScaleUpInProgress {
		condition.Status = api.ClusterAutoscalerInProgress
	} else if !isSafeToScaleUp {
		condition.Status = api.ClusterAutoscalerBackoff
	} else {
		condition.Status = api.ClusterAutoscalerNoActivity
	}
	return condition
}

func buildScaleDownStatusNodeGroup(candidates []string, lastProbed time.Time) api.ClusterAutoscalerCondition {
	condition := api.ClusterAutoscalerCondition{
		Type:          api.ClusterAutoscalerScaleDown,
		Message:       fmt.Sprintf("candidates=%d", len(candidates)),
		LastProbeTime: metav1.Time{Time: lastProbed},
	}
	if len(candidates) > 0 {
		condition.Status = api.ClusterAutoscalerCandidatesPresent
	} else {
		condition.Status = api.ClusterAutoscalerNoCandidates
	}
	return condition
}

func buildHealthStatusClusterwide(isReady bool, readiness Readiness) api.ClusterAutoscalerCondition {
	condition := api.ClusterAutoscalerCondition{
		Type: api.ClusterAutoscalerHealth,
		Message: fmt.Sprintf("ready=%d unready=%d notStarted=%d longNotStarted=%d registered=%d longUnregistered=%d",
			readiness.Ready,
			readiness.Unready,
			readiness.NotStarted,
			readiness.LongNotStarted,
			readiness.Registered,
			readiness.LongUnregistered,
		),
		LastProbeTime: metav1.Time{Time: readiness.Time},
	}
	if isReady {
		condition.Status = api.ClusterAutoscalerHealthy
	} else {
		condition.Status = api.ClusterAutoscalerUnhealthy
	}
	return condition
}

func buildScaleUpStatusClusterwide(nodeGroupStatuses []api.NodeGroupStatus, readiness Readiness) api.ClusterAutoscalerCondition {
	isScaleUpInProgress := false
	for _, nodeGroupStatuses := range nodeGroupStatuses {
		for _, condition := range nodeGroupStatuses.Conditions {
			if condition.Type == api.ClusterAutoscalerScaleUp &&
				condition.Status == api.ClusterAutoscalerInProgress {
				isScaleUpInProgress = true
			}
		}
	}

	condition := api.ClusterAutoscalerCondition{
		Type: api.ClusterAutoscalerScaleUp,
		Message: fmt.Sprintf("ready=%d registered=%d",
			readiness.Ready,
			readiness.Registered),
		LastProbeTime: metav1.Time{Time: readiness.Time},
	}
	if isScaleUpInProgress {
		condition.Status = api.ClusterAutoscalerInProgress
	} else {
		condition.Status = api.ClusterAutoscalerNoActivity
	}
	return condition
}

func buildScaleDownStatusClusterwide(candidates map[string][]string, lastProbed time.Time) api.ClusterAutoscalerCondition {
	totalCandidates := 0
	for _, val := range candidates {
		totalCandidates += len(val)
	}
	condition := api.ClusterAutoscalerCondition{
		Type:          api.ClusterAutoscalerScaleDown,
		Message:       fmt.Sprintf("candidates=%d", totalCandidates),
		LastProbeTime: metav1.Time{Time: lastProbed},
	}
	if totalCandidates > 0 {
		condition.Status = api.ClusterAutoscalerCandidatesPresent
	} else {
		condition.Status = api.ClusterAutoscalerNoCandidates
	}
	return condition
}

func isNodeStillStarting(node *apiv1.Node) bool {
	for _, condition := range node.Status.Conditions {
		if condition.Type == apiv1.NodeReady &&
			condition.Status != apiv1.ConditionTrue &&
			condition.LastTransitionTime.Time.Sub(node.CreationTimestamp.Time) < MaxStatusSettingDelayAfterCreation {
			return true
		}
		if condition.Type == apiv1.NodeOutOfDisk &&
			condition.Status == apiv1.ConditionTrue &&
			condition.LastTransitionTime.Time.Sub(node.CreationTimestamp.Time) < MaxStatusSettingDelayAfterCreation {
			return true
		}
		if condition.Type == apiv1.NodeNetworkUnavailable &&
			condition.Status == apiv1.ConditionTrue &&
			condition.LastTransitionTime.Time.Sub(node.CreationTimestamp.Time) < MaxStatusSettingDelayAfterCreation {
			return true
		}
	}
	return false
}

func updateLastTransition(oldStatus, newStatus *api.ClusterAutoscalerStatus) {
	newStatus.ClusterwideConditions = updateLastTransitionSingleList(
		oldStatus.ClusterwideConditions, newStatus.ClusterwideConditions)
	updatedNgStatuses := make([]api.NodeGroupStatus, 0)
	for _, ngStatus := range newStatus.NodeGroupStatuses {
		oldConds := make([]api.ClusterAutoscalerCondition, 0)
		for _, oldNgStatus := range oldStatus.NodeGroupStatuses {
			if ngStatus.ProviderID == oldNgStatus.ProviderID {
				oldConds = oldNgStatus.Conditions
				break
			}
		}
		newConds := updateLastTransitionSingleList(oldConds, ngStatus.Conditions)
		updatedNgStatuses = append(
			updatedNgStatuses,
			api.NodeGroupStatus{
				ProviderID: ngStatus.ProviderID,
				Conditions: newConds,
			})
	}
	newStatus.NodeGroupStatuses = updatedNgStatuses
}

func updateLastTransitionSingleList(oldConds, newConds []api.ClusterAutoscalerCondition) []api.ClusterAutoscalerCondition {
	result := make([]api.ClusterAutoscalerCondition, 0)
	// We have ~3 conditions, so O(n**2) is good enough
	for _, condition := range newConds {
		condition.LastTransitionTime = condition.LastProbeTime
		for _, oldCondition := range oldConds {
			if condition.Type == oldCondition.Type {
				if condition.Status == oldCondition.Status {
					condition.LastTransitionTime = oldCondition.LastTransitionTime
				}
				break
			}
		}
		result = append(result, condition)
	}
	return result
}

// GetIncorrectNodeGroupSize gets IncorrectNodeGroupSizeInformation for the given node group.
func (csr *ClusterStateRegistry) GetIncorrectNodeGroupSize(nodeGroupName string) *IncorrectNodeGroupSize {
	result, found := csr.incorrectNodeGroupSizes[nodeGroupName]
	if !found {
		return nil
	}
	return &result
}

// GetUpcomingNodes returns how many new nodes will be added shortly to the node groups or should become ready soon.
// The function may overestimate the number of nodes.
func (csr *ClusterStateRegistry) GetUpcomingNodes() map[string]int {
	csr.Lock()
	defer csr.Unlock()

	result := make(map[string]int)
	for _, nodeGroup := range csr.cloudProvider.NodeGroups() {
		id := nodeGroup.Id()
		readiness := csr.perNodeGroupReadiness[id]
		ar := csr.acceptableRanges[id]
		// newNodes is the number of nodes that
		newNodes := ar.CurrentTarget - (readiness.Ready + readiness.Unready + readiness.LongNotStarted + readiness.LongUnregistered)
		if newNodes <= 0 {
			// Negative value is unlikely but theoretically possible.
			continue
		}
		result[id] = newNodes
	}
	return result
}

// Calculates which of the existing cloud provider nodes are not registered in Kubernetes.
func getNotRegisteredNodes(allNodes []*apiv1.Node, cloudProvider cloudprovider.CloudProvider, time time.Time) ([]UnregisteredNode, error) {
	registered := sets.NewString()
	for _, node := range allNodes {
		registered.Insert(cloudProvider.GetInstanceID(node))
	}
	notRegistered := make([]UnregisteredNode, 0)
	for _, nodeGroup := range cloudProvider.NodeGroups() {
		nodes, err := nodeGroup.Nodes()
		if err != nil {
			return []UnregisteredNode{}, err
		}
		for _, node := range nodes {
			if !registered.Has(node.Id) {
				notRegistered = append(notRegistered, UnregisteredNode{
					Node: &apiv1.Node{
						ObjectMeta: metav1.ObjectMeta{
							Name: node.Id,
						},
						Spec: apiv1.NodeSpec{
							ProviderID: node.Id,
						},
					},
					UnregisteredSince: time,
				})
			}
		}
	}
	return notRegistered, nil
}

// GetClusterSize calculates and returns cluster's current size and target size. The current size is the
// actual number of nodes provisioned in Kubernetes, the target size is the number of nodes the CA wants.
func (csr *ClusterStateRegistry) GetClusterSize() (currentSize, targetSize int) {
	csr.Lock()
	defer csr.Unlock()

	for _, accRange := range csr.acceptableRanges {
		targetSize += accRange.CurrentTarget
	}
	currentSize = csr.totalReadiness.Registered - csr.totalReadiness.NotStarted - csr.totalReadiness.LongNotStarted
	return currentSize, targetSize
}
