/*
Copyright 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 flagz

import (
	"fmt"
	"net/http"
	"strings"
	"time"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/runtime/serializer"
	"k8s.io/apimachinery/pkg/runtime/serializer/cbor"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apiserver/pkg/endpoints/handlers/negotiation"
	"k8s.io/apiserver/pkg/endpoints/handlers/responsewriters"
	"k8s.io/apiserver/pkg/endpoints/metrics"
	"k8s.io/apiserver/pkg/endpoints/request"
	"k8s.io/apiserver/pkg/endpoints/responsewriter"
	"k8s.io/apiserver/pkg/features"
	"k8s.io/apiserver/pkg/server/flagz/api/v1alpha1"
	"k8s.io/apiserver/pkg/server/flagz/api/v1beta1"
	"k8s.io/apiserver/pkg/server/flagz/negotiate"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
)

var (
	v1alpha1FlagzKind         = v1alpha1.SchemeGroupVersion.WithKind("Flagz")
	v1beta1FlagzKind          = v1beta1.SchemeGroupVersion.WithKind("Flagz")
	recognizedStructuredKinds = map[schema.GroupVersionKind]bool{
		v1alpha1FlagzKind: true,
		v1beta1FlagzKind:  true,
	}
)

const DefaultFlagzPath = "/flagz"

// flagzCodecFactory wraps a CodecFactory to filter out unsupported media types (like protobuf)
// from the supported media types list, so error messages only show actually supported types.
type flagzCodecFactory struct {
	serializer.CodecFactory
	supportedMediaTypes []runtime.SerializerInfo
}

type mux interface {
	Handle(path string, handler http.Handler)
}

// Install installs the flagz endpoint to the given mux.
func Install(m mux, componentName string, flagReader Reader, opts ...Option) {
	reg := &registry{
		reader:                flagReader,
		deprecatedVersionsMap: map[string]bool{"v1alpha1": true},
	}
	for _, opt := range opts {
		opt(reg)
	}

	scheme := runtime.NewScheme()
	utilruntime.Must(v1alpha1.AddToScheme(scheme))
	utilruntime.Must(v1beta1.AddToScheme(scheme))
	filteredCodecFactory, err := newFlagzCodecFactory(scheme, componentName, reg.reader)
	if err != nil {
		utilruntime.HandleError(err)
	}
	restrictions := negotiate.FlagzEndpointRestrictions{
		RecognizedStructuredKinds: recognizedStructuredKinds,
	}
	m.Handle(DefaultFlagzPath, handleFlagz(componentName, reg, filteredCodecFactory, restrictions))
}

// newFlagzCodecFactory creates a codec factory with the standard serializers for flagz,
// filtering out unsupported media types (e.g., protobuf).
func newFlagzCodecFactory(scheme *runtime.Scheme, componentName string, flagReader Reader) (*flagzCodecFactory, error) {
	codecFactoryOpts := []serializer.CodecFactoryOptionsMutator{
		serializer.WithSerializer(func(_ runtime.ObjectCreater, _ runtime.ObjectTyper) runtime.SerializerInfo {
			textSerializer := flagzTextSerializer{componentName, flagReader}
			return runtime.SerializerInfo{
				MediaType:        "text/plain",
				MediaTypeType:    "text",
				MediaTypeSubType: "plain",
				EncodesAsText:    true,
				Serializer:       textSerializer,
				PrettySerializer: textSerializer,
			}
		}),
	}
	// TODO: remove this explicit check when https://github.com/kubernetes/enhancements/pull/5740 is implemented.
	if utilfeature.DefaultFeatureGate.Enabled(features.CBORServingAndStorage) {
		codecFactoryOpts = append(codecFactoryOpts, serializer.WithSerializer(cbor.NewSerializerInfo))
	}

	codecFactory := serializer.NewCodecFactory(scheme, codecFactoryOpts...)
	allTypes := codecFactory.SupportedMediaTypes()
	filtered := make([]runtime.SerializerInfo, 0, len(allTypes))

	var unknownTypes []string
	for _, info := range allTypes {
		switch info.MediaType {
		// Supported media types
		case "text/plain", runtime.ContentTypeJSON, runtime.ContentTypeYAML, runtime.ContentTypeCBOR:
			filtered = append(filtered, info)
		// Unsupported media types
		case runtime.ContentTypeProtobuf:
			continue
		default:
			unknownTypes = append(unknownTypes, info.MediaType)
		}
	}

	var err error
	if len(unknownTypes) > 0 {
		err = fmt.Errorf("flagz: unknown media type(s) %v, excluding from supported types", unknownTypes)
	}

	return &flagzCodecFactory{
		CodecFactory:        codecFactory,
		supportedMediaTypes: filtered,
	}, err
}

func (f *flagzCodecFactory) SupportedMediaTypes() []runtime.SerializerInfo {
	return f.supportedMediaTypes
}

func handleFlagz(componentName string, reg *registry, serializer runtime.NegotiatedSerializer, restrictions negotiate.FlagzEndpointRestrictions) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		requestReceivedTimestamp, ok := request.ReceivedTimestampFrom(r.Context())
		if !ok {
			requestReceivedTimestamp = time.Now()
		}
		delegate := &metrics.ResponseWriterDelegator{ResponseWriter: w}
		w = responsewriter.WrapForHTTP1Or2(delegate)

		// Use MonitorRequest instead of InstrumentHandlerFunc because the group,
		// version, and deprecated status depend on per-request content negotiation.
		// For text/plain requests, group and version remain empty. For structured
		// responses (JSON/YAML/CBOR), they are set to the negotiated API group and
		// version (e.g., config.k8s.io/v1alpha1).
		var group, version string
		var deprecated bool
		defer func() {
			metrics.MonitorRequest(r, "GET", group, version,
				"flagz",       // resource
				"",            // subresource
				"",            // scope
				componentName, // component
				deprecated,
				"", // removedRelease
				delegate.Status(), delegate.ContentLength(), time.Since(requestReceivedTimestamp))
		}()

		acceptHeader := r.Header.Get("Accept")
		if strings.TrimSpace(acceptHeader) == "" {
			writePlainTextResponse(v1beta1Flagz(componentName, reg.reader), serializer, w, reg)
			return
		}

		mediaType, serializerInfo, err := negotiation.NegotiateOutputMediaType(r, serializer, restrictions)
		if err != nil {
			utilruntime.HandleError(err)
			responsewriters.ErrorNegotiated(
				err,
				serializer,
				schema.GroupVersion{},
				w,
				r,
			)
			return
		}

		switch serializerInfo.MediaType {
		case "application/json", "application/yaml", "application/cbor":
			if mediaType.Convert == nil {
				err := fmt.Errorf("content negotiation failed: mediaType.Convert is nil for %s", serializerInfo.MediaType)
				utilruntime.HandleError(err)
				responsewriters.ErrorNegotiated(
					err,
					serializer,
					schema.GroupVersion{},
					w,
					r,
				)
				return
			}
			group = mediaType.Convert.Group
			version = mediaType.Convert.Version
			deprecated = reg.deprecatedVersions()[version]
			if deprecated {
				w.Header().Set("Warning", `299 - "This version of the flagz endpoint is deprecated. Please use a newer version."`)
			}
			handleStructuredResponse(w, r, componentName, reg, serializer, restrictions, mediaType)
		case "text/plain":
			writePlainTextResponse(v1beta1Flagz(componentName, reg.reader), serializer, w, reg)
		default:
			err := fmt.Errorf("unsupported media type: %s/%s", serializerInfo.MediaType, serializerInfo.MediaTypeSubType)
			utilruntime.HandleError(err)
			responsewriters.ErrorNegotiated(
				err,
				serializer,
				schema.GroupVersion{},
				w,
				r,
			)
		}
	}
}

func writePlainTextResponse(obj runtime.Object, serializer runtime.NegotiatedSerializer, w http.ResponseWriter, reg *registry) {
	reg.cachedPlainTextResponseLock.Lock()
	defer reg.cachedPlainTextResponseLock.Unlock()
	if reg.cachedPlainTextResponse != nil {
		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
		if _, err := w.Write(reg.cachedPlainTextResponse); err != nil {
			utilruntime.HandleError(fmt.Errorf("error writing cached flagz as text/plain: %w", err))
		}
		return
	}

	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	var textSerializer runtime.Serializer
	for _, info := range serializer.SupportedMediaTypes() {
		if info.MediaType == "text/plain" {
			textSerializer = info.Serializer
			break
		}
	}
	if textSerializer == nil {
		utilruntime.HandleError(fmt.Errorf("text/plain serializer not available"))
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	var buf strings.Builder
	if err := textSerializer.Encode(obj, &buf); err != nil {
		utilruntime.HandleError(fmt.Errorf("error encoding flagz as text/plain: %w", err))
		w.WriteHeader(http.StatusInternalServerError)
		return
	}
	reg.cachedPlainTextResponse = []byte(buf.String())
	if _, err := w.Write(reg.cachedPlainTextResponse); err != nil {
		utilruntime.HandleError(fmt.Errorf("error writing flagz as text/plain: %w", err))
	}
}

func writeStructuredResponse(obj runtime.Object, serializer runtime.NegotiatedSerializer, targetGV schema.GroupVersion, restrictions negotiate.FlagzEndpointRestrictions, w http.ResponseWriter, r *http.Request) {
	responsewriters.WriteObjectNegotiated(
		serializer,
		restrictions,
		targetGV,
		w,
		r,
		http.StatusOK,
		obj,
		true,
	)
}

func handleStructuredResponse(w http.ResponseWriter, r *http.Request, componentName string, reg *registry, serializer runtime.NegotiatedSerializer, restrictions negotiate.FlagzEndpointRestrictions, mediaType negotiation.MediaTypeOptions) {
	switch *mediaType.Convert {
	case v1alpha1FlagzKind:
		writeStructuredResponse(v1alpha1Flagz(componentName, reg.reader), serializer, v1alpha1FlagzKind.GroupVersion(), restrictions, w, r)
	case v1beta1FlagzKind:
		writeStructuredResponse(v1beta1Flagz(componentName, reg.reader), serializer, v1beta1FlagzKind.GroupVersion(), restrictions, w, r)
	default:
		err := fmt.Errorf("unsupported media type: %s", mediaType.Convert.String())
		utilruntime.HandleError(err)
		responsewriters.ErrorNegotiated(
			err,
			serializer,
			schema.GroupVersion{},
			w,
			r,
		)
	}
}

func v1alpha1Flagz(componentName string, flagReader Reader) *v1alpha1.Flagz {
	flags := flagReader.GetFlagz()
	return &v1alpha1.Flagz{
		TypeMeta: metav1.TypeMeta{
			Kind:       v1alpha1FlagzKind.Kind,
			APIVersion: v1alpha1FlagzKind.GroupVersion().String(),
		},
		ObjectMeta: metav1.ObjectMeta{
			Name: componentName,
		},
		Flags: flags,
	}
}

func v1beta1Flagz(componentName string, flagReader Reader) *v1beta1.Flagz {
	flags := flagReader.GetFlagz()
	return &v1beta1.Flagz{
		TypeMeta: metav1.TypeMeta{
			Kind:       v1beta1FlagzKind.Kind,
			APIVersion: v1beta1FlagzKind.GroupVersion().String(),
		},
		ObjectMeta: metav1.ObjectMeta{
			Name: componentName,
		},
		Flags: flags,
	}
}