/*
Copyright 2022 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 legacytokentracking

import (
	"context"
	"fmt"
	"time"

	"golang.org/x/time/rate"

	corev1 "k8s.io/api/core/v1"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/fields"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/wait"
	corev1informers "k8s.io/client-go/informers/core/v1"
	"k8s.io/client-go/kubernetes"
	corev1client "k8s.io/client-go/kubernetes/typed/core/v1"
	"k8s.io/client-go/tools/cache"
	"k8s.io/client-go/util/workqueue"
	"k8s.io/klog/v2"
	"k8s.io/utils/clock"
)

const (
	ConfigMapName    = "kube-apiserver-legacy-service-account-token-tracking"
	ConfigMapDataKey = "since"
	dateFormat       = "2006-01-02"
)

var (
	queueKey = metav1.NamespaceSystem + "/" + ConfigMapName
)

// Controller maintains a timestamp value configmap `kube-apiserver-legacy-service-account-token-tracking`
// in `kube-system` to indicates if the tracking for legacy tokens is enabled in
// the cluster. For HA clusters, the configmap will be eventually created after
// all controller instances have enabled the feature. When disabling this
// feature, existing configmap will be deleted.
type Controller struct {
	configMapClient   corev1client.ConfigMapsGetter
	configMapInformer cache.SharedIndexInformer
	configMapCache    cache.Indexer
	configMapSynced   cache.InformerSynced
	queue             workqueue.RateLimitingInterface

	// rate limiter controls the rate limit of the creation of the configmap.
	// this is useful in multi-apiserver cluster to prevent config existing in a
	// cluster with mixed enabled/disabled controllers. otherwise, those
	// apiservers will fight to create/delete until all apiservers are enabled
	// or disabled.
	creationRatelimiter *rate.Limiter
	clock               clock.Clock
}

// NewController returns a Controller struct.
func NewController(cs kubernetes.Interface) *Controller {
	return newController(cs, clock.RealClock{}, rate.NewLimiter(rate.Every(30*time.Minute), 1))
}

func newController(cs kubernetes.Interface, cl clock.Clock, limiter *rate.Limiter) *Controller {
	informer := corev1informers.NewFilteredConfigMapInformer(cs, metav1.NamespaceSystem, 12*time.Hour, cache.Indexers{cache.NamespaceIndex: cache.MetaNamespaceIndexFunc}, func(options *metav1.ListOptions) {
		options.FieldSelector = fields.OneTermEqualSelector("metadata.name", ConfigMapName).String()
	})

	c := &Controller{
		configMapClient:     cs.CoreV1(),
		queue:               workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), "legacy_token_tracking_controller"),
		configMapInformer:   informer,
		configMapCache:      informer.GetIndexer(),
		configMapSynced:     informer.HasSynced,
		creationRatelimiter: limiter,
		clock:               cl,
	}

	informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc: func(obj interface{}) {
			c.enqueue()
		},
		UpdateFunc: func(oldObj, newObj interface{}) {
			c.enqueue()
		},
		DeleteFunc: func(obj interface{}) {
			c.enqueue()
		},
	})

	return c
}

func (c *Controller) enqueue() {
	c.queue.Add(queueKey)
}

// Run starts the controller sync loop.
func (c *Controller) Run(stopCh <-chan struct{}) {
	defer utilruntime.HandleCrash()
	defer c.queue.ShutDown()

	klog.Info("Starting legacy_token_tracking_controller")
	defer klog.Infof("Shutting down legacy_token_tracking_controller")

	go c.configMapInformer.Run(stopCh)
	if !cache.WaitForNamedCacheSync("configmaps", stopCh, c.configMapSynced) {
		return
	}

	go wait.Until(c.runWorker, time.Second, stopCh)

	c.queue.Add(queueKey)

	<-stopCh
	klog.Info("Ending legacy_token_tracking_controller")
}

func (c *Controller) runWorker() {
	for c.processNext() {
	}
}

func (c *Controller) processNext() bool {
	key, quit := c.queue.Get()
	if quit {
		return false
	}
	defer c.queue.Done(key)

	if err := c.syncConfigMap(); err != nil {
		utilruntime.HandleError(fmt.Errorf("while syncing ConfigMap %q, err: %w", key, err))
		c.queue.AddRateLimited(key)
		return true
	}
	c.queue.Forget(key)
	return true
}

func (c *Controller) syncConfigMap() error {
	obj, exists, err := c.configMapCache.GetByKey(queueKey)
	if err != nil {
		return err
	}

	now := c.clock.Now()
	if !exists {
		r := c.creationRatelimiter.ReserveN(now, 1)
		if delay := r.DelayFrom(now); delay > 0 {
			c.queue.AddAfter(queueKey, delay)
			r.CancelAt(now)
			return nil
		}

		if _, err = c.configMapClient.ConfigMaps(metav1.NamespaceSystem).Create(context.TODO(), &corev1.ConfigMap{
			ObjectMeta: metav1.ObjectMeta{Namespace: metav1.NamespaceSystem, Name: ConfigMapName},
			Data:       map[string]string{ConfigMapDataKey: now.UTC().Format(dateFormat)},
		}, metav1.CreateOptions{}); err != nil {
			if apierrors.IsAlreadyExists(err) {
				return nil
			}
			// don't consume the creationRatelimiter for an unsuccessful attempt
			r.CancelAt(now)
			return err
		}
	} else {
		configMap := obj.(*corev1.ConfigMap)
		if _, err = time.Parse(dateFormat, configMap.Data[ConfigMapDataKey]); err != nil {
			configMap := configMap.DeepCopy()
			if configMap.Data == nil {
				configMap.Data = map[string]string{}
			}
			configMap.Data[ConfigMapDataKey] = now.UTC().Format(dateFormat)
			if _, err = c.configMapClient.ConfigMaps(metav1.NamespaceSystem).Update(context.TODO(), configMap, metav1.UpdateOptions{}); err != nil {
				if apierrors.IsNotFound(err) || apierrors.IsConflict(err) {
					return nil
				}
				return err
			}
		}
	}

	return nil
}