/*
Copyright 2017 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 apiserver

import (
	"context"
	"fmt"
	"net/http"
	"net/url"
	"reflect"
	"sync"
	"time"

	v1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/api/equality"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/apimachinery/pkg/runtime"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/wait"
	v1informers "k8s.io/client-go/informers/core/v1"
	v1listers "k8s.io/client-go/listers/core/v1"
	"k8s.io/client-go/tools/cache"
	"k8s.io/client-go/transport"
	"k8s.io/client-go/util/workqueue"
	"k8s.io/component-base/metrics/legacyregistry"
	"k8s.io/klog/v2"
	apiregistrationv1 "k8s.io/kube-aggregator/pkg/apis/apiregistration/v1"
	apiregistrationv1apihelper "k8s.io/kube-aggregator/pkg/apis/apiregistration/v1/helper"
	apiregistrationclient "k8s.io/kube-aggregator/pkg/client/clientset_generated/clientset/typed/apiregistration/v1"
	informers "k8s.io/kube-aggregator/pkg/client/informers/externalversions/apiregistration/v1"
	listers "k8s.io/kube-aggregator/pkg/client/listers/apiregistration/v1"
	"k8s.io/kube-aggregator/pkg/controllers"
)

// making sure we only register metrics once into legacy registry
var registerIntoLegacyRegistryOnce sync.Once

type certKeyFunc func() ([]byte, []byte)

// ServiceResolver knows how to convert a service reference into an actual location.
type ServiceResolver interface {
	ResolveEndpoint(namespace, name string, port int32) (*url.URL, error)
}

// AvailableConditionController handles checking the availability of registered API services.
type AvailableConditionController struct {
	apiServiceClient apiregistrationclient.APIServicesGetter

	apiServiceLister listers.APIServiceLister
	apiServiceSynced cache.InformerSynced

	// serviceLister is used to get the IP to create the transport for
	serviceLister  v1listers.ServiceLister
	servicesSynced cache.InformerSynced

	endpointsLister v1listers.EndpointsLister
	endpointsSynced cache.InformerSynced

	// proxyTransportDial specifies the dial function for creating unencrypted TCP connections.
	proxyTransportDial         *transport.DialHolder
	proxyCurrentCertKeyContent certKeyFunc
	serviceResolver            ServiceResolver

	// To allow injection for testing.
	syncFn func(key string) error

	queue workqueue.RateLimitingInterface
	// map from service-namespace -> service-name -> apiservice names
	cache map[string]map[string][]string
	// this lock protects operations on the above cache
	cacheLock sync.RWMutex

	// metrics registered into legacy registry
	metrics *availabilityMetrics
}

// NewAvailableConditionController returns a new AvailableConditionController.
func NewAvailableConditionController(
	apiServiceInformer informers.APIServiceInformer,
	serviceInformer v1informers.ServiceInformer,
	endpointsInformer v1informers.EndpointsInformer,
	apiServiceClient apiregistrationclient.APIServicesGetter,
	proxyTransportDial *transport.DialHolder,
	proxyCurrentCertKeyContent certKeyFunc,
	serviceResolver ServiceResolver,
) (*AvailableConditionController, error) {
	c := &AvailableConditionController{
		apiServiceClient: apiServiceClient,
		apiServiceLister: apiServiceInformer.Lister(),
		serviceLister:    serviceInformer.Lister(),
		endpointsLister:  endpointsInformer.Lister(),
		serviceResolver:  serviceResolver,
		queue: workqueue.NewNamedRateLimitingQueue(
			// We want a fairly tight requeue time.  The controller listens to the API, but because it relies on the routability of the
			// service network, it is possible for an external, non-watchable factor to affect availability.  This keeps
			// the maximum disruption time to a minimum, but it does prevent hot loops.
			workqueue.NewItemExponentialFailureRateLimiter(5*time.Millisecond, 30*time.Second),
			"AvailableConditionController"),
		proxyTransportDial:         proxyTransportDial,
		proxyCurrentCertKeyContent: proxyCurrentCertKeyContent,
		metrics:                    newAvailabilityMetrics(),
	}

	// resync on this one because it is low cardinality and rechecking the actual discovery
	// allows us to detect health in a more timely fashion when network connectivity to
	// nodes is snipped, but the network still attempts to route there.  See
	// https://github.com/openshift/origin/issues/17159#issuecomment-341798063
	apiServiceHandler, _ := apiServiceInformer.Informer().AddEventHandlerWithResyncPeriod(
		cache.ResourceEventHandlerFuncs{
			AddFunc:    c.addAPIService,
			UpdateFunc: c.updateAPIService,
			DeleteFunc: c.deleteAPIService,
		},
		30*time.Second)
	c.apiServiceSynced = apiServiceHandler.HasSynced

	serviceHandler, _ := serviceInformer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    c.addService,
		UpdateFunc: c.updateService,
		DeleteFunc: c.deleteService,
	})
	c.servicesSynced = serviceHandler.HasSynced

	endpointsHandler, _ := endpointsInformer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    c.addEndpoints,
		UpdateFunc: c.updateEndpoints,
		DeleteFunc: c.deleteEndpoints,
	})
	c.endpointsSynced = endpointsHandler.HasSynced

	c.syncFn = c.sync

	// TODO: decouple from legacyregistry
	var err error
	registerIntoLegacyRegistryOnce.Do(func() {
		err = c.metrics.Register(legacyregistry.Register, legacyregistry.CustomRegister)
	})
	if err != nil {
		return nil, err
	}

	return c, nil
}

func (c *AvailableConditionController) sync(key string) error {
	originalAPIService, err := c.apiServiceLister.Get(key)
	if apierrors.IsNotFound(err) {
		c.metrics.ForgetAPIService(key)
		return nil
	}
	if err != nil {
		return err
	}

	// if a particular transport was specified, use that otherwise build one
	// construct an http client that will ignore TLS verification (if someone owns the network and messes with your status
	// that's not so bad) and sets a very short timeout.  This is a best effort GET that provides no additional information
	transportConfig := &transport.Config{
		TLS: transport.TLSConfig{
			Insecure: true,
		},
		DialHolder: c.proxyTransportDial,
	}

	if c.proxyCurrentCertKeyContent != nil {
		proxyClientCert, proxyClientKey := c.proxyCurrentCertKeyContent()

		transportConfig.TLS.CertData = proxyClientCert
		transportConfig.TLS.KeyData = proxyClientKey
	}
	restTransport, err := transport.New(transportConfig)
	if err != nil {
		return err
	}
	discoveryClient := &http.Client{
		Transport: restTransport,
		// the request should happen quickly.
		Timeout: 5 * time.Second,
		CheckRedirect: func(req *http.Request, via []*http.Request) error {
			return http.ErrUseLastResponse
		},
	}

	apiService := originalAPIService.DeepCopy()

	availableCondition := apiregistrationv1.APIServiceCondition{
		Type:               apiregistrationv1.Available,
		Status:             apiregistrationv1.ConditionTrue,
		LastTransitionTime: metav1.Now(),
	}

	// local API services are always considered available
	if apiService.Spec.Service == nil {
		apiregistrationv1apihelper.SetAPIServiceCondition(apiService, apiregistrationv1apihelper.NewLocalAvailableAPIServiceCondition())
		_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
		return err
	}

	service, err := c.serviceLister.Services(apiService.Spec.Service.Namespace).Get(apiService.Spec.Service.Name)
	if apierrors.IsNotFound(err) {
		availableCondition.Status = apiregistrationv1.ConditionFalse
		availableCondition.Reason = "ServiceNotFound"
		availableCondition.Message = fmt.Sprintf("service/%s in %q is not present", apiService.Spec.Service.Name, apiService.Spec.Service.Namespace)
		apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
		_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
		return err
	} else if err != nil {
		availableCondition.Status = apiregistrationv1.ConditionUnknown
		availableCondition.Reason = "ServiceAccessError"
		availableCondition.Message = fmt.Sprintf("service/%s in %q cannot be checked due to: %v", apiService.Spec.Service.Name, apiService.Spec.Service.Namespace, err)
		apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
		_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
		return err
	}

	if service.Spec.Type == v1.ServiceTypeClusterIP {
		// if we have a cluster IP service, it must be listening on configured port and we can check that
		servicePort := apiService.Spec.Service.Port
		portName := ""
		foundPort := false
		for _, port := range service.Spec.Ports {
			if port.Port == *servicePort {
				foundPort = true
				portName = port.Name
				break
			}
		}
		if !foundPort {
			availableCondition.Status = apiregistrationv1.ConditionFalse
			availableCondition.Reason = "ServicePortError"
			availableCondition.Message = fmt.Sprintf("service/%s in %q is not listening on port %d", apiService.Spec.Service.Name, apiService.Spec.Service.Namespace, *apiService.Spec.Service.Port)
			apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
			_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
			return err
		}

		endpoints, err := c.endpointsLister.Endpoints(apiService.Spec.Service.Namespace).Get(apiService.Spec.Service.Name)
		if apierrors.IsNotFound(err) {
			availableCondition.Status = apiregistrationv1.ConditionFalse
			availableCondition.Reason = "EndpointsNotFound"
			availableCondition.Message = fmt.Sprintf("cannot find endpoints for service/%s in %q", apiService.Spec.Service.Name, apiService.Spec.Service.Namespace)
			apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
			_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
			return err
		} else if err != nil {
			availableCondition.Status = apiregistrationv1.ConditionUnknown
			availableCondition.Reason = "EndpointsAccessError"
			availableCondition.Message = fmt.Sprintf("service/%s in %q cannot be checked due to: %v", apiService.Spec.Service.Name, apiService.Spec.Service.Namespace, err)
			apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
			_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
			return err
		}
		hasActiveEndpoints := false
	outer:
		for _, subset := range endpoints.Subsets {
			if len(subset.Addresses) == 0 {
				continue
			}
			for _, endpointPort := range subset.Ports {
				if endpointPort.Name == portName {
					hasActiveEndpoints = true
					break outer
				}
			}
		}
		if !hasActiveEndpoints {
			availableCondition.Status = apiregistrationv1.ConditionFalse
			availableCondition.Reason = "MissingEndpoints"
			availableCondition.Message = fmt.Sprintf("endpoints for service/%s in %q have no addresses with port name %q", apiService.Spec.Service.Name, apiService.Spec.Service.Namespace, portName)
			apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
			_, err := c.updateAPIServiceStatus(originalAPIService, apiService)
			return err
		}
	}
	// actually try to hit the discovery endpoint when it isn't local and when we're routing as a service.
	if apiService.Spec.Service != nil && c.serviceResolver != nil {
		attempts := 5
		results := make(chan error, attempts)
		for i := 0; i < attempts; i++ {
			go func() {
				discoveryURL, err := c.serviceResolver.ResolveEndpoint(apiService.Spec.Service.Namespace, apiService.Spec.Service.Name, *apiService.Spec.Service.Port)
				if err != nil {
					results <- err
					return
				}
				// render legacyAPIService health check path when it is delegated to a service
				if apiService.Name == "v1." {
					discoveryURL.Path = "/api/" + apiService.Spec.Version
				} else {
					discoveryURL.Path = "/apis/" + apiService.Spec.Group + "/" + apiService.Spec.Version
				}

				errCh := make(chan error, 1)
				go func() {
					// be sure to check a URL that the aggregated API server is required to serve
					newReq, err := http.NewRequest("GET", discoveryURL.String(), nil)
					if err != nil {
						errCh <- err
						return
					}

					// setting the system-masters identity ensures that we will always have access rights
					transport.SetAuthProxyHeaders(newReq, "system:kube-aggregator", []string{"system:masters"}, nil)
					resp, err := discoveryClient.Do(newReq)
					if resp != nil {
						resp.Body.Close()
						// we should always been in the 200s or 300s
						if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
							errCh <- fmt.Errorf("bad status from %v: %v", discoveryURL, resp.StatusCode)
							return
						}
					}

					errCh <- err
				}()

				select {
				case err = <-errCh:
					if err != nil {
						results <- fmt.Errorf("failing or missing response from %v: %v", discoveryURL, err)
						return
					}

					// we had trouble with slow dial and DNS responses causing us to wait too long.
					// we added this as insurance
				case <-time.After(6 * time.Second):
					results <- fmt.Errorf("timed out waiting for %v", discoveryURL)
					return
				}

				results <- nil
			}()
		}

		var lastError error
		for i := 0; i < attempts; i++ {
			lastError = <-results
			// if we had at least one success, we are successful overall and we can return now
			if lastError == nil {
				break
			}
		}

		if lastError != nil {
			availableCondition.Status = apiregistrationv1.ConditionFalse
			availableCondition.Reason = "FailedDiscoveryCheck"
			availableCondition.Message = lastError.Error()
			apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
			_, updateErr := c.updateAPIServiceStatus(originalAPIService, apiService)
			if updateErr != nil {
				return updateErr
			}
			// force a requeue to make it very obvious that this will be retried at some point in the future
			// along with other requeues done via service change, endpoint change, and resync
			return lastError
		}
	}

	availableCondition.Reason = "Passed"
	availableCondition.Message = "all checks passed"
	apiregistrationv1apihelper.SetAPIServiceCondition(apiService, availableCondition)
	_, err = c.updateAPIServiceStatus(originalAPIService, apiService)
	return err
}

// updateAPIServiceStatus only issues an update if a change is detected.  We have a tight resync loop to quickly detect dead
// apiservices. Doing that means we don't want to quickly issue no-op updates.
func (c *AvailableConditionController) updateAPIServiceStatus(originalAPIService, newAPIService *apiregistrationv1.APIService) (*apiregistrationv1.APIService, error) {
	// update this metric on every sync operation to reflect the actual state
	c.setUnavailableGauge(newAPIService)

	if equality.Semantic.DeepEqual(originalAPIService.Status, newAPIService.Status) {
		return newAPIService, nil
	}

	orig := apiregistrationv1apihelper.GetAPIServiceConditionByType(originalAPIService, apiregistrationv1.Available)
	now := apiregistrationv1apihelper.GetAPIServiceConditionByType(newAPIService, apiregistrationv1.Available)
	unknown := apiregistrationv1.APIServiceCondition{
		Type:   apiregistrationv1.Available,
		Status: apiregistrationv1.ConditionUnknown,
	}
	if orig == nil {
		orig = &unknown
	}
	if now == nil {
		now = &unknown
	}
	if *orig != *now {
		klog.V(2).InfoS("changing APIService availability", "name", newAPIService.Name, "oldStatus", orig.Status, "newStatus", now.Status, "message", now.Message, "reason", now.Reason)
	}

	newAPIService, err := c.apiServiceClient.APIServices().UpdateStatus(context.TODO(), newAPIService, metav1.UpdateOptions{})
	if err != nil {
		return nil, err
	}

	c.setUnavailableCounter(originalAPIService, newAPIService)
	return newAPIService, nil
}

// Run starts the AvailableConditionController loop which manages the availability condition of API services.
func (c *AvailableConditionController) Run(workers int, stopCh <-chan struct{}) {
	defer utilruntime.HandleCrash()
	defer c.queue.ShutDown()

	klog.Info("Starting AvailableConditionController")
	defer klog.Info("Shutting down AvailableConditionController")

	// This waits not just for the informers to sync, but for our handlers
	// to be called; since the handlers are three different ways of
	// enqueueing the same thing, waiting for this permits the queue to
	// maximally de-duplicate the entries.
	if !controllers.WaitForCacheSync("AvailableConditionController", stopCh, c.apiServiceSynced, c.servicesSynced, c.endpointsSynced) {
		return
	}

	for i := 0; i < workers; i++ {
		go wait.Until(c.runWorker, time.Second, stopCh)
	}

	<-stopCh
}

func (c *AvailableConditionController) runWorker() {
	for c.processNextWorkItem() {
	}
}

// processNextWorkItem deals with one key off the queue.  It returns false when it's time to quit.
func (c *AvailableConditionController) processNextWorkItem() bool {
	key, quit := c.queue.Get()
	if quit {
		return false
	}
	defer c.queue.Done(key)

	err := c.syncFn(key.(string))
	if err == nil {
		c.queue.Forget(key)
		return true
	}

	utilruntime.HandleError(fmt.Errorf("%v failed with: %v", key, err))
	c.queue.AddRateLimited(key)

	return true
}

func (c *AvailableConditionController) addAPIService(obj interface{}) {
	castObj := obj.(*apiregistrationv1.APIService)
	klog.V(4).Infof("Adding %s", castObj.Name)
	if castObj.Spec.Service != nil {
		c.rebuildAPIServiceCache()
	}
	c.queue.Add(castObj.Name)
}

func (c *AvailableConditionController) updateAPIService(oldObj, newObj interface{}) {
	castObj := newObj.(*apiregistrationv1.APIService)
	oldCastObj := oldObj.(*apiregistrationv1.APIService)
	klog.V(4).Infof("Updating %s", oldCastObj.Name)
	if !reflect.DeepEqual(castObj.Spec.Service, oldCastObj.Spec.Service) {
		c.rebuildAPIServiceCache()
	}
	c.queue.Add(oldCastObj.Name)
}

func (c *AvailableConditionController) deleteAPIService(obj interface{}) {
	castObj, ok := obj.(*apiregistrationv1.APIService)
	if !ok {
		tombstone, ok := obj.(cache.DeletedFinalStateUnknown)
		if !ok {
			klog.Errorf("Couldn't get object from tombstone %#v", obj)
			return
		}
		castObj, ok = tombstone.Obj.(*apiregistrationv1.APIService)
		if !ok {
			klog.Errorf("Tombstone contained object that is not expected %#v", obj)
			return
		}
	}
	klog.V(4).Infof("Deleting %q", castObj.Name)
	if castObj.Spec.Service != nil {
		c.rebuildAPIServiceCache()
	}
	c.queue.Add(castObj.Name)
}

func (c *AvailableConditionController) getAPIServicesFor(obj runtime.Object) []string {
	metadata, err := meta.Accessor(obj)
	if err != nil {
		utilruntime.HandleError(err)
		return nil
	}
	c.cacheLock.RLock()
	defer c.cacheLock.RUnlock()
	return c.cache[metadata.GetNamespace()][metadata.GetName()]
}

// if the service/endpoint handler wins the race against the cache rebuilding, it may queue a no-longer-relevant apiservice
// (which will get processed an extra time - this doesn't matter),
// and miss a newly relevant apiservice (which will get queued by the apiservice handler)
func (c *AvailableConditionController) rebuildAPIServiceCache() {
	apiServiceList, _ := c.apiServiceLister.List(labels.Everything())
	newCache := map[string]map[string][]string{}
	for _, apiService := range apiServiceList {
		if apiService.Spec.Service == nil {
			continue
		}
		if newCache[apiService.Spec.Service.Namespace] == nil {
			newCache[apiService.Spec.Service.Namespace] = map[string][]string{}
		}
		newCache[apiService.Spec.Service.Namespace][apiService.Spec.Service.Name] = append(newCache[apiService.Spec.Service.Namespace][apiService.Spec.Service.Name], apiService.Name)
	}

	c.cacheLock.Lock()
	defer c.cacheLock.Unlock()
	c.cache = newCache
}

// TODO, think of a way to avoid checking on every service manipulation

func (c *AvailableConditionController) addService(obj interface{}) {
	for _, apiService := range c.getAPIServicesFor(obj.(*v1.Service)) {
		c.queue.Add(apiService)
	}
}

func (c *AvailableConditionController) updateService(obj, _ interface{}) {
	for _, apiService := range c.getAPIServicesFor(obj.(*v1.Service)) {
		c.queue.Add(apiService)
	}
}

func (c *AvailableConditionController) deleteService(obj interface{}) {
	castObj, ok := obj.(*v1.Service)
	if !ok {
		tombstone, ok := obj.(cache.DeletedFinalStateUnknown)
		if !ok {
			klog.Errorf("Couldn't get object from tombstone %#v", obj)
			return
		}
		castObj, ok = tombstone.Obj.(*v1.Service)
		if !ok {
			klog.Errorf("Tombstone contained object that is not expected %#v", obj)
			return
		}
	}
	for _, apiService := range c.getAPIServicesFor(castObj) {
		c.queue.Add(apiService)
	}
}

func (c *AvailableConditionController) addEndpoints(obj interface{}) {
	for _, apiService := range c.getAPIServicesFor(obj.(*v1.Endpoints)) {
		c.queue.Add(apiService)
	}
}

func (c *AvailableConditionController) updateEndpoints(obj, _ interface{}) {
	for _, apiService := range c.getAPIServicesFor(obj.(*v1.Endpoints)) {
		c.queue.Add(apiService)
	}
}

func (c *AvailableConditionController) deleteEndpoints(obj interface{}) {
	castObj, ok := obj.(*v1.Endpoints)
	if !ok {
		tombstone, ok := obj.(cache.DeletedFinalStateUnknown)
		if !ok {
			klog.Errorf("Couldn't get object from tombstone %#v", obj)
			return
		}
		castObj, ok = tombstone.Obj.(*v1.Endpoints)
		if !ok {
			klog.Errorf("Tombstone contained object that is not expected %#v", obj)
			return
		}
	}
	for _, apiService := range c.getAPIServicesFor(castObj) {
		c.queue.Add(apiService)
	}
}

// setUnavailableGauge set the metrics so that it reflect the current state base on availability of the given service
func (c *AvailableConditionController) setUnavailableGauge(newAPIService *apiregistrationv1.APIService) {
	if apiregistrationv1apihelper.IsAPIServiceConditionTrue(newAPIService, apiregistrationv1.Available) {
		c.metrics.SetAPIServiceAvailable(newAPIService.Name)
		return
	}

	c.metrics.SetAPIServiceUnavailable(newAPIService.Name)
}

// setUnavailableCounter increases the metrics only if the given service is unavailable and its APIServiceCondition has changed
func (c *AvailableConditionController) setUnavailableCounter(originalAPIService, newAPIService *apiregistrationv1.APIService) {
	wasAvailable := apiregistrationv1apihelper.IsAPIServiceConditionTrue(originalAPIService, apiregistrationv1.Available)
	isAvailable := apiregistrationv1apihelper.IsAPIServiceConditionTrue(newAPIService, apiregistrationv1.Available)
	statusChanged := isAvailable != wasAvailable

	if statusChanged && !isAvailable {
		reason := "UnknownReason"
		if newCondition := apiregistrationv1apihelper.GetAPIServiceConditionByType(newAPIService, apiregistrationv1.Available); newCondition != nil {
			reason = newCondition.Reason
		}
		c.metrics.UnavailableCounter(newAPIService.Name, reason).Inc()
	}
}
