// Copyright 2019 Yunion
//
// 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 pleg

import (
	"fmt"
	"sync/atomic"
	"time"

	runtimeapi "k8s.io/cri-api/pkg/apis/runtime/v1"

	"yunion.io/x/log"
	"yunion.io/x/pkg/util/clock"
	"yunion.io/x/pkg/util/sets"
	"yunion.io/x/pkg/util/wait"

	"yunion.io/x/onecloud/pkg/hostman/guestman/pod/runtime"
)

// plegContainerState has a one-to-one mapping to the
// kubecontainer.State except for the non-existent state. This state
// is introduced here to complete the state transition scenarios.
type plegContainerState string

const (
	plegContainerRunning     plegContainerState = "running"
	plegContainerExited      plegContainerState = "exited"
	plegContainerUnknown     plegContainerState = "unknown"
	plegContainerNonExistent plegContainerState = "non-existent"

	// The threshold needs to be greater than the relisting period + the
	// relisting time, which can vary significantly. Set a conservative
	// threshold to avoid flipping between healthy and unhealthy.
	relistThreshold = 3 * time.Minute
)

func convertState(state runtime.State) plegContainerState {
	switch state {
	case runtime.ContainerStateCreated:
		// kubelet doesn't use the "created" state yet, hence convert it to "unknown".
		return plegContainerUnknown
	case runtime.ContainerStateRunning:
		return plegContainerRunning
	case runtime.ContainerStateExited:
		return plegContainerExited
	case runtime.ContainerStateUnknown:
		return plegContainerUnknown
	default:
		panic(fmt.Sprintf("unrecognized container state: %v", state))
	}
}

type GenericPLEG struct {
	// The period for relisting.
	relistPeriod time.Duration
	// The container runtime.
	runtime runtime.Runtime
	// The channel from which the subscriber listens events.
	eventChannel chan *PodLifecycleEvent
	podRecords   podRecords
	// Time of the last relisting.
	relistTime atomic.Value
	// Cache for storing the runtime states required for syncing pods.
	cache runtime.Cache
	clock clock.Clock
	// Pods that failed to have their status retrieved during a relist. These pods will be
	// retried during the next relisting.
	podsToReinspect map[string]*runtime.Pod
}

const (
	// Capacity of the channel for receiving pod lifecycle events. This number
	// is a bit arbitrary and may be adjusted in the future.
	ChannelCapacity = 1000

	// Generic PLEG relies on relisting for discovering container events.
	// A longer period means that kubelet will take longer to detect container
	// changes and to update pod status. On the other hand, a shorter period
	// will cause more frequent relisting (e.g., container runtime operations),
	// leading to higher cpu usage.
	// Note that even though we set the period to 1s, the relisting itself can
	// take more than 1s to finish if the container runtime responds slowly
	// and/or when there are many container changes in one cycle.
	RelistPeriod = time.Second * 1
)

func NewGenericPLEG(runtimeManager runtime.Runtime, channelCapacity int,
	relistPeriod time.Duration, cache runtime.Cache, clock clock.Clock) PodLifecycleEventGenerator {
	return &GenericPLEG{
		relistPeriod: relistPeriod,
		runtime:      runtimeManager,
		eventChannel: make(chan *PodLifecycleEvent, channelCapacity),
		podRecords:   make(podRecords),
		cache:        cache,
		clock:        clock,
	}
}

func (g *GenericPLEG) Start() {
	go wait.Until(g.relist, g.relistPeriod, wait.NeverStop)
}

func (g *GenericPLEG) Watch() chan *PodLifecycleEvent {
	return g.eventChannel
}

func (g *GenericPLEG) getRelistTime() time.Time {
	val := g.relistTime.Load()
	if val == nil {
		return time.Time{}
	}
	return val.(time.Time)
}

func (g *GenericPLEG) updateRelistTime(timestamp time.Time) {
	g.relistTime.Store(timestamp)
}

// relist queries the container runtime for list of pods/containers, compare
// with the internal pods/containers, and generates events accordingly.
func (g *GenericPLEG) relist() {
	// log.Debugf("GenericPLEG: Relisting")

	timestamp := g.clock.Now()

	// Get all the pods.
	podList, err := g.runtime.GetPods(true)
	if err != nil {
		log.Errorf("Unable to retrieve pods: %v", err)
		return
	}

	g.updateRelistTime(timestamp)

	pods := runtime.Pods(podList)
	g.podRecords.setCurrent(pods)

	// Compare the old and the current pods, and generate events.
	eventsByPodID := map[string][]*PodLifecycleEvent{}
	for pid := range g.podRecords {
		oldPod := g.podRecords.getOld(pid)
		pod := g.podRecords.getCurrent(pid)
		// Get all containers in the old and the new pod.
		allContainers := getContainersFromPods(oldPod, pod)
		for _, container := range allContainers {
			events := computeEvents(oldPod, pod, &container.ID)
			for _, e := range events {
				updateEvents(eventsByPodID, e)
			}
		}
	}

	var needsReinspection map[string]*runtime.Pod
	if g.cacheEnabled() {
		needsReinspection = make(map[string]*runtime.Pod)
	}

	// If there are events associated with a pod, we should update the
	// podCache.
	for pid, events := range eventsByPodID {
		pod := g.podRecords.getCurrent(pid)
		if g.cacheEnabled() {
			// updateCache() will inspect the pod and update the cache. If an
			// error occurs during the inspection, we want PLEG to retry again
			// in the next relist. To achieve this, we do not update the
			// associated podRecord of the pod, so that the change will be
			// detect again in the next relist.
			// TODO: If many pods changed during the same relist period,
			// inspecting the pod and getting the PodStatus to update the cache
			// serially may take a while. We should be aware of this and
			// parallelize if needed.
			if err := g.updateCache(pod, pid); err != nil {
				// Rely on updateCache calling GetPodStatus to log the actual error.
				log.Infof("PLEG: Ignoring events for pod %s/%s: %v", pod.Name, pod.Namespace, err)

				// make sure we try to reinspect the pod during the next relisting
				needsReinspection[pid] = pod

				continue
			} else {
				// this pod was in the list to reinspect and we did so because it had events, so remove it
				// from the list (we don't want the reinspection code below to inspect it a second time in
				// this relist execution)
				delete(g.podsToReinspect, pid)
			}
		}
		// Update the internal storage and send out the events.
		g.podRecords.update(pid)
		for i := range events {
			// Filter out events that are not reliable and no other components use yet.
			if events[i].Type == ContainerChanged {
				continue
			}
			select {
			case g.eventChannel <- events[i]:
			default:
				log.Errorf("event channel is full, discard this relist() cycle event")
			}
		}
	}

	if g.cacheEnabled() {
		// reinspect any pods that failed inspection during the previous relist
		if len(g.podsToReinspect) > 0 {
			log.Infof("GenericPLEG: Reinspecting pods that previously failed inspection")
			for pid, pod := range g.podsToReinspect {
				if err := g.updateCache(pod, pid); err != nil {
					// Rely on updateCache calling GetPodStatus to log the actual error.
					log.Infof("PLEG: pod %s/%s failed reinspection: %v", pod.Name, pod.Namespace, err)
					needsReinspection[pid] = pod
				}
			}
		}

		// Update the cache timestamp.  This needs to happen *after*
		// all pods have been properly updated in the cache.
		g.cache.UpdateTime(timestamp)
	}

	// make sure we retain the list of pods that need reinspecting the next time relist is called
	g.podsToReinspect = needsReinspection
}

func (g *GenericPLEG) cacheEnabled() bool {
	return g.cache != nil
}

func (g *GenericPLEG) updateCache(pod *runtime.Pod, pid string) error {
	if pod == nil {
		// The pod is missing in the current relist. This means that
		// the pod has no visible (active or inactive) containers.
		log.Infof("PLEG: Delete status for pod %q", string(pid))
		g.cache.Delete(pid)
		return nil
	}
	timestamp := g.clock.Now()
	// TODO: Consider adding a new runtime method
	// GetPodStatus(pod *kubecontainer.Pod) so that Docker can avoid listing
	// all containers again.
	status, err := g.runtime.GetPodStatus(pod.Id, pod.Name, pod.Namespace)
	log.Debugf("PLEG: Write status for %s/%s: %#v (err: %v)", pod.Name, pod.Namespace, status, err)
	if err == nil {
		// Preserve the pod IP across cache updates if the new IP is empty.
		// When a pod is torn down, kubelet may race with PLEG and retrieve
		// a pod status after network teardown, but the kubernetes API expects
		// the completed pod's IP to be available after the pod is dead.
		status.IPs = g.getPodIPs(pid, status)
	}

	g.cache.Set(pod.Id, status, err, timestamp)
	return err
}

// getPodIP preserves an older cached status' pod IP if the new status has no pod IPs
// and its sandboxes have exited
func (g *GenericPLEG) getPodIPs(pid string, status *runtime.PodStatus) []string {
	if len(status.IPs) != 0 {
		return status.IPs
	}

	oldStatus, err := g.cache.Get(pid)
	if err != nil || len(oldStatus.IPs) == 0 {
		return nil
	}

	for _, sandboxStatus := range status.SandboxStatuses {
		// If at least one sandbox is ready, then use this status update's pod IP
		if sandboxStatus.State == runtimeapi.PodSandboxState_SANDBOX_READY {
			return status.IPs
		}
	}

	// For pods with no ready containers or sandboxes (like exited pods)
	// use the old status' pod IP
	return oldStatus.IPs
}

func updateEvents(eventsByPodID map[string][]*PodLifecycleEvent, e *PodLifecycleEvent) {
	if e == nil {
		return
	}
	eventsByPodID[e.Id] = append(eventsByPodID[e.Id], e)
}

func getContainersFromPods(pods ...*runtime.Pod) []*runtime.Container {
	cidSet := sets.NewString()
	var containers []*runtime.Container
	for _, p := range pods {
		if p == nil {
			continue
		}
		for _, c := range p.Containers {
			cid := string(c.ID.ID)
			if cidSet.Has(cid) {
				continue
			}
			cidSet.Insert(cid)
			containers = append(containers, c)
		}
		// Update sandboxes as containers
		// TODO: keep track of sandboxes explicitly.
		for _, c := range p.Sandboxes {
			cid := string(c.ID.ID)
			if cidSet.Has(cid) {
				continue
			}
			cidSet.Insert(cid)
			containers = append(containers, c)
		}

	}
	return containers
}

func computeEvents(oldPod, newPod *runtime.Pod, cid *runtime.ContainerID) []*PodLifecycleEvent {
	var pid string
	if oldPod != nil {
		pid = oldPod.Id
	} else if newPod != nil {
		pid = newPod.Id
	}
	oldState := getContainerState(oldPod, cid)
	newState := getContainerState(newPod, cid)
	return generateEvents(pid, cid.ID, oldState, newState)
}

func generateEvents(podID string, cid string, oldState, newState plegContainerState) []*PodLifecycleEvent {
	if newState == oldState {
		return nil
	}

	log.Infof("GenericPLEG: %v/%v: %v -> %v", podID, cid, oldState, newState)
	switch newState {
	case plegContainerRunning:
		return []*PodLifecycleEvent{{Id: podID, Type: ContainerStarted, Data: cid}}
	case plegContainerExited:
		return []*PodLifecycleEvent{{Id: podID, Type: ContainerDied, Data: cid}}
	case plegContainerUnknown:
		return []*PodLifecycleEvent{{Id: podID, Type: ContainerChanged, Data: cid}}
	case plegContainerNonExistent:
		switch oldState {
		case plegContainerExited:
			// We already reported that the container died before.
			return []*PodLifecycleEvent{{Id: podID, Type: ContainerRemoved, Data: cid}}
		default:
			return []*PodLifecycleEvent{{Id: podID, Type: ContainerDied, Data: cid}, {Id: podID, Type: ContainerRemoved, Data: cid}}
		}
	default:
		panic(fmt.Sprintf("unrecognized container state: %v", newState))
	}
}

func getContainerState(pod *runtime.Pod, cid *runtime.ContainerID) plegContainerState {
	// Default to the non-existent state.
	state := plegContainerNonExistent
	if pod == nil {
		return state
	}
	c := pod.FindContainerByID(*cid)
	if c != nil {
		return convertState(c.State)
	}
	// Search through sandboxes too.
	c = pod.FindSandboxByID(*cid)
	if c != nil {
		return convertState(c.State)
	}

	return state
}

type podRecord struct {
	old     *runtime.Pod
	current *runtime.Pod
}

type podRecords map[string]*podRecord

func (pr podRecords) getOld(id string) *runtime.Pod {
	r, ok := pr[id]
	if !ok {
		return nil
	}
	return r.old
}

func (pr podRecords) getCurrent(id string) *runtime.Pod {
	r, ok := pr[id]
	if !ok {
		return nil
	}
	return r.current
}

func (pr podRecords) setCurrent(pods []*runtime.Pod) {
	for i := range pr {
		pr[i].current = nil
	}
	for _, pod := range pods {
		if r, ok := pr[pod.Id]; ok {
			r.current = pod
		} else {
			pr[pod.Id] = &podRecord{current: pod}
		}
	}
}

func (pr podRecords) update(id string) {
	r, ok := pr[id]
	if !ok {
		return
	}
	pr.updateInternal(id, r)
}

func (pr podRecords) updateInternal(id string, r *podRecord) {
	if r.current == nil {
		// Pod no longer exists; delete the entry.
		delete(pr, id)
		return
	}
	r.old = r.current
	r.current = nil
}