/*
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 apiserver

import (
	"net/http"
	"os"
	"time"

	"k8s.io/apimachinery/pkg/util/sets"
	genericapifilters "k8s.io/apiserver/pkg/endpoints/filters"
	genericapirequest "k8s.io/apiserver/pkg/endpoints/request"
	"k8s.io/apiserver/pkg/registry/rest"
	genericapiserver "k8s.io/apiserver/pkg/server"
	genericfilters "k8s.io/apiserver/pkg/server/filters"
	kubeinformers "k8s.io/client-go/informers"
	kubeclientset "k8s.io/client-go/kubernetes"
	v1listers "k8s.io/client-go/listers/core/v1"
	"k8s.io/client-go/pkg/api"
	"k8s.io/client-go/pkg/version"

	"k8s.io/kube-aggregator/pkg/apis/apiregistration"
	"k8s.io/kube-aggregator/pkg/apis/apiregistration/v1alpha1"
	"k8s.io/kube-aggregator/pkg/client/clientset_generated/internalclientset"
	informers "k8s.io/kube-aggregator/pkg/client/informers/internalversion"
	listers "k8s.io/kube-aggregator/pkg/client/listers/apiregistration/internalversion"
	apiservicestorage "k8s.io/kube-aggregator/pkg/registry/apiservice/etcd"

	_ "k8s.io/client-go/pkg/api/install"
)

// legacyAPIServiceName is the fixed name of the only non-groupified API version
const legacyAPIServiceName = "v1."

type Config struct {
	GenericConfig       *genericapiserver.Config
	CoreAPIServerClient kubeclientset.Interface

	// ProxyClientCert/Key are the client cert used to identify this proxy. Backing APIServices use
	// this to confirm the proxy's identity
	ProxyClientCert []byte
	ProxyClientKey  []byte
}

// APIAggregator contains state for a Kubernetes cluster master/api server.
type APIAggregator struct {
	GenericAPIServer *genericapiserver.GenericAPIServer

	contextMapper genericapirequest.RequestContextMapper

	// proxyClientCert/Key are the client cert used to identify this proxy. Backing APIServices use
	// this to confirm the proxy's identity
	proxyClientCert []byte
	proxyClientKey  []byte

	// proxyHandlers are the proxy handlers that are currently registered, keyed by apiservice.name
	proxyHandlers map[string]*proxyHandler
	// handledGroups are the groups that already have routes
	handledGroups sets.String

	// lister is used to add group handling for /apis/<group> aggregator lookups based on
	// controller state
	lister listers.APIServiceLister

	// serviceLister is used by the aggregator handler to determine whether or not to try to expose the group
	serviceLister v1listers.ServiceLister
	// endpointsLister is used by the aggregator handler to determine whether or not to try to expose the group
	endpointsLister v1listers.EndpointsLister

	// proxyMux intercepts requests that need to be proxied to backing API servers
	proxyMux *http.ServeMux
}

type completedConfig struct {
	*Config
}

// Complete fills in any fields not set that are required to have valid data. It's mutating the receiver.
func (c *Config) Complete() completedConfig {
	c.GenericConfig.Complete()

	version := version.Get()
	c.GenericConfig.Version = &version

	return completedConfig{c}
}

// SkipComplete provides a way to construct a server instance without config completion.
func (c *Config) SkipComplete() completedConfig {
	return completedConfig{c}
}

// New returns a new instance of APIAggregator from the given config.
func (c completedConfig) New(stopCh <-chan struct{}) (*APIAggregator, error) {
	informerFactory := informers.NewSharedInformerFactory(
		internalclientset.NewForConfigOrDie(c.Config.GenericConfig.LoopbackClientConfig),
		5*time.Minute, // this is effectively used as a refresh interval right now.  Might want to do something nicer later on.
	)
	kubeInformers := kubeinformers.NewSharedInformerFactory(c.CoreAPIServerClient, 5*time.Minute)

	proxyMux := http.NewServeMux()

	// most API servers don't need to do this, but we need a custom handler chain to handle the special /apis handling here
	c.Config.GenericConfig.BuildHandlerChainsFunc = (&handlerChainConfig{
		informers:       informerFactory,
		proxyMux:        proxyMux,
		serviceLister:   kubeInformers.Core().V1().Services().Lister(),
		endpointsLister: kubeInformers.Core().V1().Endpoints().Lister(),
	}).handlerChain

	genericServer, err := c.Config.GenericConfig.SkipComplete().New() // completion is done in Complete, no need for a second time
	if err != nil {
		return nil, err
	}

	s := &APIAggregator{
		GenericAPIServer: genericServer,
		contextMapper:    c.GenericConfig.RequestContextMapper,
		proxyClientCert:  c.ProxyClientCert,
		proxyClientKey:   c.ProxyClientKey,
		proxyHandlers:    map[string]*proxyHandler{},
		handledGroups:    sets.String{},
		lister:           informerFactory.Apiregistration().InternalVersion().APIServices().Lister(),
		serviceLister:    kubeInformers.Core().V1().Services().Lister(),
		endpointsLister:  kubeInformers.Core().V1().Endpoints().Lister(),
		proxyMux:         proxyMux,
	}

	apiGroupInfo := genericapiserver.NewDefaultAPIGroupInfo(apiregistration.GroupName, api.Registry, api.Scheme, api.ParameterCodec, api.Codecs)
	apiGroupInfo.GroupMeta.GroupVersion = v1alpha1.SchemeGroupVersion
	v1alpha1storage := map[string]rest.Storage{}
	v1alpha1storage["apiservices"] = apiservicestorage.NewREST(c.GenericConfig.RESTOptionsGetter)
	apiGroupInfo.VersionedResourcesStorageMap["v1alpha1"] = v1alpha1storage

	if err := s.GenericAPIServer.InstallAPIGroup(&apiGroupInfo); err != nil {
		return nil, err
	}

	apiserviceRegistrationController := NewAPIServiceRegistrationController(informerFactory.Apiregistration().InternalVersion().APIServices(), s)

	s.GenericAPIServer.AddPostStartHook("start-informers", func(context genericapiserver.PostStartHookContext) error {
		informerFactory.Start(stopCh)
		kubeInformers.Start(stopCh)
		return nil
	})
	s.GenericAPIServer.AddPostStartHook("apiservice-registration-controller", func(context genericapiserver.PostStartHookContext) error {
		apiserviceRegistrationController.Run(stopCh)
		return nil
	})

	return s, nil
}

// handlerChainConfig is the config used to build the custom handler chain for this api server
type handlerChainConfig struct {
	informers       informers.SharedInformerFactory
	proxyMux        *http.ServeMux
	serviceLister   v1listers.ServiceLister
	endpointsLister v1listers.EndpointsLister
}

// handlerChain is a method to build the handler chain for this API server.  We need a custom handler chain so that we
// can have custom handling for `/apis`, since we're hosting aggregation differently from anyone else and we're hosting
// the endpoints differently, since we're proxying all groups except for apiregistration.k8s.io.
func (h *handlerChainConfig) handlerChain(apiHandler http.Handler, c *genericapiserver.Config) (secure, insecure http.Handler) {
	// add this as a filter so that we never collide with "already registered" failures on `/apis`
	handler := WithAPIs(apiHandler, h.informers.Apiregistration().InternalVersion().APIServices(), h.serviceLister, h.endpointsLister)

	handler = genericapifilters.WithAuthorization(handler, c.RequestContextMapper, c.Authorizer)

	// this mux is NOT protected by authorization, but DOES have authentication information
	// this is so that everyone can hit the proxy and we can properly identify the user.  The backing
	// API server will deal with authorization
	handler = WithProxyMux(handler, h.proxyMux)

	handler = genericapifilters.WithImpersonation(handler, c.RequestContextMapper, c.Authorizer)
	// audit to stdout to help with debugging as we get this started
	handler = genericapifilters.WithAudit(handler, c.RequestContextMapper, os.Stdout)
	handler = genericapifilters.WithAuthentication(handler, c.RequestContextMapper, c.Authenticator, genericapifilters.Unauthorized(c.SupportsBasicAuth))

	handler = genericfilters.WithCORS(handler, c.CorsAllowedOriginList, nil, nil, nil, "true")
	handler = genericfilters.WithPanicRecovery(handler, c.RequestContextMapper)
	handler = genericfilters.WithTimeoutForNonLongRunningRequests(handler, c.RequestContextMapper, c.LongRunningFunc)
	handler = genericfilters.WithMaxInFlightLimit(handler, c.MaxRequestsInFlight, c.MaxMutatingRequestsInFlight, c.RequestContextMapper, c.LongRunningFunc)
	handler = genericapifilters.WithRequestInfo(handler, genericapiserver.NewRequestInfoResolver(c), c.RequestContextMapper)
	handler = genericapirequest.WithRequestContext(handler, c.RequestContextMapper)

	return handler, nil
}

// AddAPIService adds an API service.  It is not thread-safe, so only call it on one thread at a time please.
// It's a slow moving API, so its ok to run the controller on a single thread
func (s *APIAggregator) AddAPIService(apiService *apiregistration.APIService) {
	// if the proxyHandler already exists, it needs to be updated. The aggregation bits do not
	// since they are wired against listers because they require multiple resources to respond
	if proxyHandler, exists := s.proxyHandlers[apiService.Name]; exists {
		proxyHandler.updateAPIService(apiService)
		return
	}

	proxyPath := "/apis/" + apiService.Spec.Group + "/" + apiService.Spec.Version
	// v1. is a special case for the legacy API.  It proxies to a wider set of endpoints.
	if apiService.Name == "v1." {
		proxyPath = "/api"
	}

	// register the proxy handler
	proxyHandler := &proxyHandler{
		contextMapper:          s.contextMapper,
		proxyClientCert:        s.proxyClientCert,
		proxyClientKey:         s.proxyClientKey,
		transportBuildingError: nil,
		proxyRoundTripper:      nil,
	}
	proxyHandler.updateAPIService(apiService)
	s.proxyHandlers[apiService.Name] = proxyHandler
	s.proxyMux.Handle(proxyPath, proxyHandler)
	s.proxyMux.Handle(proxyPath+"/", proxyHandler)

	// if we're dealing with the legacy group, we're done here
	if apiService.Name == legacyAPIServiceName {
		return
	}

	// if we've already registered the path with the handler, we don't want to do it again.
	if s.handledGroups.Has(apiService.Spec.Group) {
		return
	}

	// it's time to register the group aggregation endpoint
	groupPath := "/apis/" + apiService.Spec.Group
	groupDiscoveryHandler := &apiGroupHandler{
		groupName:       apiService.Spec.Group,
		lister:          s.lister,
		serviceLister:   s.serviceLister,
		endpointsLister: s.endpointsLister,
	}
	// aggregation is protected
	s.GenericAPIServer.HandlerContainer.UnlistedRoutes.Handle(groupPath, groupDiscoveryHandler)
	s.GenericAPIServer.HandlerContainer.UnlistedRoutes.Handle(groupPath+"/", groupDiscoveryHandler)
	s.handledGroups.Insert(apiService.Spec.Group)
}

// RemoveAPIService removes the APIService from being handled.  Later on it will disable the proxy endpoint.
// Right now it does nothing because our handler has to properly 404 itself since muxes don't unregister
func (s *APIAggregator) RemoveAPIService(apiServiceName string) {
	proxyHandler, exists := s.proxyHandlers[apiServiceName]
	if !exists {
		return
	}
	proxyHandler.removeAPIService()
}

func WithProxyMux(handler http.Handler, mux *http.ServeMux) http.Handler {
	if mux == nil {
		return handler
	}

	// register the handler at this stage against everything under slash.  More specific paths that get registered will take precedence
	// this effectively delegates by default unless something specific gets registered.
	mux.Handle("/", handler)

	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		mux.ServeHTTP(w, req)
	})
}