package webhooks

import (
	"context"
	"crypto/tls"
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"net/http"
	"time"

	"github.com/golang/glog"
	kyvernoclient "github.com/nirmata/kyverno/pkg/client/clientset/versioned"
	kyvernoinformer "github.com/nirmata/kyverno/pkg/client/informers/externalversions/kyverno/v1alpha1"
	kyvernolister "github.com/nirmata/kyverno/pkg/client/listers/kyverno/v1alpha1"
	"github.com/nirmata/kyverno/pkg/config"
	client "github.com/nirmata/kyverno/pkg/dclient"
	"github.com/nirmata/kyverno/pkg/event"
	"github.com/nirmata/kyverno/pkg/policy"
	tlsutils "github.com/nirmata/kyverno/pkg/tls"
	userinfo "github.com/nirmata/kyverno/pkg/userinfo"
	"github.com/nirmata/kyverno/pkg/webhookconfig"
	v1beta1 "k8s.io/api/admission/v1beta1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/labels"
	rbacinformer "k8s.io/client-go/informers/rbac/v1"
	rbaclister "k8s.io/client-go/listers/rbac/v1"
	"k8s.io/client-go/tools/cache"
)

// WebhookServer contains configured TLS server with MutationWebhook.
// MutationWebhook gets policies from policyController and takes control of the cluster with kubeclient.
type WebhookServer struct {
	server                    http.Server
	client                    *client.Client
	kyvernoClient             *kyvernoclient.Clientset
	pLister                   kyvernolister.ClusterPolicyLister
	pvLister                  kyvernolister.ClusterPolicyViolationLister
	pListerSynced             cache.InformerSynced
	pvListerSynced            cache.InformerSynced
	rbLister                  rbaclister.RoleBindingLister
	crbLister                 rbaclister.ClusterRoleBindingLister
	eventGen                  event.Interface
	webhookRegistrationClient *webhookconfig.WebhookRegistrationClient
	// API to send policy stats for aggregation
	policyStatus policy.PolicyStatusInterface
	// helpers to validate against current loaded configuration
	configHandler config.Interface
	// channel for cleanup notification
	cleanUp chan<- struct{}
}

// NewWebhookServer creates new instance of WebhookServer accordingly to given configuration
// Policy Controller and Kubernetes Client should be initialized in configuration
func NewWebhookServer(
	kyvernoClient *kyvernoclient.Clientset,
	client *client.Client,
	tlsPair *tlsutils.TlsPemPair,
	pInformer kyvernoinformer.ClusterPolicyInformer,
	pvInformer kyvernoinformer.ClusterPolicyViolationInformer,
	rbInformer rbacinformer.RoleBindingInformer,
	crbInformer rbacinformer.ClusterRoleBindingInformer,
	eventGen event.Interface,
	webhookRegistrationClient *webhookconfig.WebhookRegistrationClient,
	policyStatus policy.PolicyStatusInterface,
	configHandler config.Interface,
	cleanUp chan<- struct{}) (*WebhookServer, error) {

	if tlsPair == nil {
		return nil, errors.New("NewWebhookServer is not initialized properly")
	}

	var tlsConfig tls.Config
	pair, err := tls.X509KeyPair(tlsPair.Certificate, tlsPair.PrivateKey)
	if err != nil {
		return nil, err
	}
	tlsConfig.Certificates = []tls.Certificate{pair}

	ws := &WebhookServer{

		client:                    client,
		kyvernoClient:             kyvernoClient,
		pLister:                   pInformer.Lister(),
		pvLister:                  pvInformer.Lister(),
		pListerSynced:             pvInformer.Informer().HasSynced,
		pvListerSynced:            pInformer.Informer().HasSynced,
		eventGen:                  eventGen,
		webhookRegistrationClient: webhookRegistrationClient,
		policyStatus:              policyStatus,
		configHandler:             configHandler,
		rbLister:                  rbInformer.Lister(),
		crbLister:                 crbInformer.Lister(),
		cleanUp:                   cleanUp,
	}
	mux := http.NewServeMux()
	mux.HandleFunc(config.MutatingWebhookServicePath, ws.serve)
	mux.HandleFunc(config.ValidatingWebhookServicePath, ws.serve)
	mux.HandleFunc(config.PolicyValidatingWebhookServicePath, ws.serve)
	mux.HandleFunc(config.PolicyMutatingWebhookServicePath, ws.serve)

	ws.server = http.Server{
		Addr:         ":443", // Listen on port for HTTPS requests
		TLSConfig:    &tlsConfig,
		Handler:      mux,
		ReadTimeout:  15 * time.Second,
		WriteTimeout: 15 * time.Second,
	}

	return ws, nil
}

// Main server endpoint for all requests
func (ws *WebhookServer) serve(w http.ResponseWriter, r *http.Request) {
	admissionReview := ws.bodyToAdmissionReview(r, w)
	if admissionReview == nil {
		return
	}

	admissionReview.Response = &v1beta1.AdmissionResponse{
		Allowed: true,
	}

	// Do not process the admission requests for kinds that are in filterKinds for filtering
	request := admissionReview.Request
	if !ws.configHandler.ToFilter(request.Kind.Kind, request.Namespace, request.Name) {
		// Resource CREATE
		// Resource UPDATE
		switch r.URL.Path {
		case config.MutatingWebhookServicePath:
			admissionReview.Response = ws.handleAdmissionRequest(request)
		case config.PolicyValidatingWebhookServicePath:
			admissionReview.Response = ws.handlePolicyValidation(request)
		case config.PolicyMutatingWebhookServicePath:
			admissionReview.Response = ws.handlePolicyMutation(request)
		}
	}

	admissionReview.Response.UID = request.UID

	responseJSON, err := json.Marshal(admissionReview)
	if err != nil {
		http.Error(w, fmt.Sprintf("Could not encode response: %v", err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	if _, err := w.Write(responseJSON); err != nil {
		http.Error(w, fmt.Sprintf("could not write response: %v", err), http.StatusInternalServerError)
	}
}

func (ws *WebhookServer) handleAdmissionRequest(request *v1beta1.AdmissionRequest) *v1beta1.AdmissionResponse {
	// TODO: this will be replaced by policy store lookup
	policies, err := ws.pLister.List(labels.NewSelector())
	if err != nil {
		//TODO check if the CRD is created ?
		// Unable to connect to policy Lister to access policies
		glog.Errorf("Unable to connect to policy controller to access policies. Policies are NOT being applied: %v", err)
		return &v1beta1.AdmissionResponse{Allowed: true}
	}

	var roles, clusterRoles []string

	// TODO(shuting): replace containRBACinfo after policy cache lookup is introduced
	// getRoleRef only if policy has roles/clusterroles defined
	if containRBACinfo(policies) {
		roles, clusterRoles, err = userinfo.GetRoleRef(ws.rbLister, ws.crbLister, request)
		if err != nil {
			// TODO(shuting): continue apply policy if error getting roleRef?
			glog.Errorf("Unable to get rbac information for request Kind=%s, Namespace=%s Name=%s UID=%s patchOperation=%s: %v",
				request.Kind.Kind, request.Namespace, request.Name, request.UID, request.Operation, err)
		}
	}

	// MUTATION
	ok, patches, msg := ws.HandleMutation(request, policies, roles, clusterRoles)
	if !ok {
		glog.V(4).Infof("Deny admission request:  %v/%s/%s", request.Kind, request.Namespace, request.Name)
		return &v1beta1.AdmissionResponse{
			Allowed: false,
			Result: &metav1.Status{
				Status:  "Failure",
				Message: msg,
			},
		}
	}

	// patch the resource with patches before handling validation rules
	patchedResource := processResourceWithPatches(patches, request.Object.Raw)

	// VALIDATION
	ok, msg = ws.HandleValidation(request, policies, patchedResource, roles, clusterRoles)
	if !ok {
		glog.V(4).Infof("Deny admission request: %v/%s/%s", request.Kind, request.Namespace, request.Name)
		return &v1beta1.AdmissionResponse{
			Allowed: false,
			Result: &metav1.Status{
				Status:  "Failure",
				Message: msg,
			},
		}
	}

	// Succesfful processing of mutation & validation rules in policy
	patchType := v1beta1.PatchTypeJSONPatch
	return &v1beta1.AdmissionResponse{
		Allowed: true,
		Result: &metav1.Status{
			Status: "Success",
		},
		Patch:     patches,
		PatchType: &patchType,
	}
}

// RunAsync TLS server in separate thread and returns control immediately
func (ws *WebhookServer) RunAsync() {
	go func(ws *WebhookServer) {
		glog.V(3).Infof("serving on %s\n", ws.server.Addr)
		if err := ws.server.ListenAndServeTLS("", ""); err != http.ErrServerClosed {
			glog.Infof("HTTP server error: %v", err)
		}
	}(ws)
	glog.Info("Started Webhook Server")
}

// Stop TLS server and returns control after the server is shut down
func (ws *WebhookServer) Stop() {
	err := ws.server.Shutdown(context.Background())
	if err != nil {
		// Error from closing listeners, or context timeout:
		glog.Info("Server Shutdown error: ", err)
		ws.server.Close()
	}
	// cleanUp
	// remove the static webhookconfigurations for policy CRD
	ws.webhookRegistrationClient.RemovePolicyWebhookConfigurations(ws.cleanUp)

}

// bodyToAdmissionReview creates AdmissionReview object from request body
// Answers to the http.ResponseWriter if request is not valid
func (ws *WebhookServer) bodyToAdmissionReview(request *http.Request, writer http.ResponseWriter) *v1beta1.AdmissionReview {
	var body []byte
	if request.Body != nil {
		if data, err := ioutil.ReadAll(request.Body); err == nil {
			body = data
		}
	}
	if len(body) == 0 {
		glog.Error("Error: empty body")
		http.Error(writer, "empty body", http.StatusBadRequest)
		return nil
	}

	contentType := request.Header.Get("Content-Type")
	if contentType != "application/json" {
		glog.Error("Error: invalid Content-Type: ", contentType)
		http.Error(writer, "invalid Content-Type, expect `application/json`", http.StatusUnsupportedMediaType)
		return nil
	}

	admissionReview := &v1beta1.AdmissionReview{}
	if err := json.Unmarshal(body, &admissionReview); err != nil {
		glog.Errorf("Error: Can't decode body as AdmissionReview: %v", err)
		http.Error(writer, "Can't decode body as AdmissionReview", http.StatusExpectationFailed)
		return nil
	}

	return admissionReview
}