package webhooks

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

	"github.com/golang/glog"
	"github.com/nirmata/kyverno/pkg/client/listers/policy/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/sharedinformer"
	tlsutils "github.com/nirmata/kyverno/pkg/tls"
	"github.com/nirmata/kyverno/pkg/violation"
	v1beta1 "k8s.io/api/admission/v1beta1"
)

// 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
	policyLister     v1alpha1.PolicyLister
	eventController  event.Generator
	violationBuilder violation.Generator
	filterKinds      []string
}

// NewWebhookServer creates new instance of WebhookServer accordingly to given configuration
// Policy Controller and Kubernetes Client should be initialized in configuration
func NewWebhookServer(
	client *client.Client,
	tlsPair *tlsutils.TlsPemPair,
	shareInformer sharedinformer.PolicyInformer,
	eventController event.Generator,
	violationBuilder violation.Generator,
	filterKinds []string) (*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,
		policyLister:     shareInformer.GetLister(),
		eventController:  eventController,
		violationBuilder: violationBuilder,
		filterKinds:      parseKinds(filterKinds),
	}
	mux := http.NewServeMux()
	mux.HandleFunc(config.MutatingWebhookServicePath, ws.serve)
	mux.HandleFunc(config.ValidatingWebhookServicePath, ws.serve)
	mux.HandleFunc(config.PolicyValidatingWebhookServicePath, 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
	if !StringInSlice(admissionReview.Request.Kind.Kind, ws.filterKinds) {

		switch r.URL.Path {
		case config.MutatingWebhookServicePath:
			admissionReview.Response = ws.HandleMutation(admissionReview.Request)
		case config.ValidatingWebhookServicePath:
			admissionReview.Response = ws.HandleValidation(admissionReview.Request)
		case config.PolicyValidatingWebhookServicePath:
			admissionReview.Response = ws.HandlePolicyValidation(admissionReview.Request)
		}
	}

	admissionReview.Response.UID = admissionReview.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)
	}
}

// RunAsync TLS server in separate thread and returns control immediately
func (ws *WebhookServer) RunAsync() {
	go func(ws *WebhookServer) {
		err := ws.server.ListenAndServeTLS("", "")
		if err != nil {
			glog.Fatal(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()
	}
}

// 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
}