/*
Copyright 2018 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 oom

import (
	"strings"
	"time"

	apiv1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/resource"
	"k8s.io/autoscaler/vertical-pod-autoscaler/pkg/recommender/model"
	"k8s.io/client-go/tools/cache"

	"k8s.io/klog/v2"
)

// OomInfo contains data of the OOM event occurrence
type OomInfo struct {
	Timestamp   time.Time
	Memory      model.ResourceAmount
	ContainerID model.ContainerID
}

// Observer can observe pod resource update and collect OOM events.
type Observer interface {
	GetObservedOomsChannel() chan OomInfo
	OnEvent(*apiv1.Event)
	cache.ResourceEventHandler
}

// observer can observe pod resource update and collect OOM events.
type observer struct {
	observedOomsChannel chan OomInfo
}

// NewObserver returns new instance of the observer.
func NewObserver() *observer {
	return &observer{
		observedOomsChannel: make(chan OomInfo, 5000),
	}
}

func (o *observer) GetObservedOomsChannel() chan OomInfo {
	return o.observedOomsChannel
}

func parseEvictionEvent(event *apiv1.Event) []OomInfo {
	if event.Reason != "Evicted" ||
		event.InvolvedObject.Kind != "Pod" {
		return []OomInfo{}
	}
	extractArray := func(annotationsKey string) []string {
		str, found := event.Annotations[annotationsKey]
		if !found {
			return []string{}
		}
		return strings.Split(str, ",")
	}
	offendingContainers := extractArray("offending_containers")
	offendingContainersUsage := extractArray("offending_containers_usage")
	starvedResource := extractArray("starved_resource")
	if len(offendingContainers) != len(offendingContainersUsage) ||
		len(offendingContainers) != len(starvedResource) {
		return []OomInfo{}
	}

	result := make([]OomInfo, 0, len(offendingContainers))

	for i, container := range offendingContainers {
		if starvedResource[i] != "memory" {
			continue
		}
		memory, err := resource.ParseQuantity(offendingContainersUsage[i])
		if err != nil {
			klog.ErrorS(err, "Cannot parse resource quantity in eviction", "event", offendingContainersUsage[i])
			continue
		}
		oomInfo := OomInfo{
			Timestamp: event.CreationTimestamp.Time.UTC(),
			Memory:    model.ResourceAmount(memory.Value()),
			ContainerID: model.ContainerID{
				PodID: model.PodID{
					Namespace: event.InvolvedObject.Namespace,
					PodName:   event.InvolvedObject.Name,
				},
				ContainerName: container,
			},
		}
		result = append(result, oomInfo)
	}
	return result
}

// OnEvent inspects k8s eviction events and translates them to OomInfo.
func (o *observer) OnEvent(event *apiv1.Event) {
	klog.V(1).InfoS("OOM Observer processing event", "event", event)
	for _, oomInfo := range parseEvictionEvent(event) {
		o.observedOomsChannel <- oomInfo
	}
}

func findStatus(name string, containerStatuses []apiv1.ContainerStatus) *apiv1.ContainerStatus {
	for _, containerStatus := range containerStatuses {
		if containerStatus.Name == name {
			return &containerStatus
		}
	}
	return nil
}

func findSpec(name string, containers []apiv1.Container) *apiv1.Container {
	for _, containerSpec := range containers {
		if containerSpec.Name == name {
			return &containerSpec
		}
	}
	return nil
}

// OnAdd is Noop
func (o *observer) OnAdd(obj interface{}, isInInitialList bool) {}

// OnUpdate inspects if the update contains oom information and
// passess it to the ObservedOomsChannel
func (o *observer) OnUpdate(oldObj, newObj interface{}) {
	oldPod, ok := oldObj.(*apiv1.Pod)
	if !ok {
		klog.ErrorS(nil, "OOM observer received invalid oldObj", "oldObj", oldObj)
	}
	newPod, ok := newObj.(*apiv1.Pod)
	if !ok {
		klog.ErrorS(nil, "OOM observer received invalid newObj", "newObj", newObj)
	}

	for _, containerStatus := range newPod.Status.ContainerStatuses {
		if containerStatus.RestartCount > 0 &&
			containerStatus.LastTerminationState.Terminated != nil &&
			containerStatus.LastTerminationState.Terminated.Reason == "OOMKilled" {

			oldStatus := findStatus(containerStatus.Name, oldPod.Status.ContainerStatuses)
			if oldStatus != nil && containerStatus.RestartCount > oldStatus.RestartCount {
				oldSpec := findSpec(containerStatus.Name, oldPod.Spec.Containers)
				if oldSpec != nil {
					memory := oldSpec.Resources.Requests[apiv1.ResourceMemory]
					oomInfo := OomInfo{
						Timestamp: containerStatus.LastTerminationState.Terminated.FinishedAt.Time.UTC(),
						Memory:    model.ResourceAmount(memory.Value()),
						ContainerID: model.ContainerID{
							PodID: model.PodID{
								Namespace: newPod.ObjectMeta.Namespace,
								PodName:   newPod.ObjectMeta.Name,
							},
							ContainerName: containerStatus.Name,
						},
					}
					o.observedOomsChannel <- oomInfo
				}
			}
		}
	}
}

// OnDelete is Noop
func (*observer) OnDelete(obj interface{}) {}