/*
Copyright 2020 The KubeSphere 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 filters

import (
	"k8s.io/apimachinery/pkg/util/net"
	"k8s.io/apimachinery/pkg/util/proxy"
	"k8s.io/apiserver/pkg/endpoints/handlers/responsewriters"
	"k8s.io/client-go/rest"
	"k8s.io/klog"
	"kubesphere.io/kubesphere/pkg/apiserver/request"
	"kubesphere.io/kubesphere/pkg/server/errors"
	"net/http"
	"net/url"
)

// WithKubeAPIServer proxy request to kubernetes service if requests path starts with /api
func WithKubeAPIServer(handler http.Handler, config *rest.Config, failed proxy.ErrorResponder) http.Handler {
	kubernetes, _ := url.Parse(config.Host)
	defaultTransport, err := rest.TransportFor(config)
	if err != nil {
		klog.Errorf("Unable to create transport from rest.Config: %v", err)
		return handler
	}

	tlsConfig, err := net.TLSClientConfig(defaultTransport)
	if err != nil {
		klog.V(5).Infof("Unable to unwrap transport %T to get at TLS config: %v", defaultTransport, err)
	}

	// since http2 doesn't support websocket, we need to disable http2 when using websocket
	if supportsHTTP11(tlsConfig.NextProtos) {
		tlsConfig.NextProtos = []string{"http/1.1"}
	}

	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		info, ok := request.RequestInfoFrom(req.Context())
		if !ok {
			err := errors.New("Unable to retrieve request info from request")
			klog.Error(err)
			responsewriters.InternalError(w, req, err)
		}

		if info.IsKubernetesRequest {
			s := *req.URL
			s.Host = kubernetes.Host
			s.Scheme = kubernetes.Scheme

			// make sure we don't override kubernetes's authorization
			req.Header.Del("Authorization")
			httpProxy := proxy.NewUpgradeAwareHandler(&s, defaultTransport, true, false, failed)
			httpProxy.UpgradeTransport = proxy.NewUpgradeRequestRoundTripper(defaultTransport, defaultTransport)
			httpProxy.ServeHTTP(w, req)
			return
		}

		handler.ServeHTTP(w, req)
	})
}

// copy from https://github.com/kubernetes/apimachinery/blob/master/pkg/util/proxy/dial.go
func supportsHTTP11(nextProtos []string) bool {
	if len(nextProtos) == 0 {
		return true
	}

	for _, proto := range nextProtos {
		if proto == "http/1.1" {
			return true
		}
	}

	return false
}