/*
Copyright 2017 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 server

import (
	"bytes"
	"fmt"
	"net/http"
	rt "runtime"
	"sort"
	"strings"

	"github.com/emicklei/go-restful/v3"
	"k8s.io/klog/v2"

	apierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apiserver/pkg/endpoints/handlers/responsewriters"
	"k8s.io/apiserver/pkg/server/mux"
)

// APIServerHandlers holds the different http.Handlers used by the API server.
// This includes the full handler chain, the director (which chooses between gorestful and nonGoRestful,
// the gorestful handler (used for the API) which falls through to the nonGoRestful handler on unregistered paths,
// and the nonGoRestful handler (which can contain a fallthrough of its own)
// FullHandlerChain -> Director -> {GoRestfulContainer,NonGoRestfulMux} based on inspection of registered web services
type APIServerHandler struct {
	// FullHandlerChain is the one that is eventually served with.  It should include the full filter
	// chain and then call the Director.
	FullHandlerChain http.Handler
	// The registered APIs.  InstallAPIs uses this.  Other servers probably shouldn't access this directly.
	GoRestfulContainer *restful.Container
	// NonGoRestfulMux is the final HTTP handler in the chain.
	// It comes after all filters and the API handling
	// This is where other servers can attach handler to various parts of the chain.
	NonGoRestfulMux *mux.PathRecorderMux

	// Director is here so that we can properly handle fall through and proxy cases.
	// This looks a bit bonkers, but here's what's happening.  We need to have /apis handling registered in gorestful in order to have
	// swagger generated for compatibility.  Doing that with `/apis` as a webservice, means that it forcibly 404s (no defaulting allowed)
	// all requests which are not /apis or /apis/.  We need those calls to fall through behind gorestful for proper delegation.  Trying to
	// register for a pattern which includes everything behind it doesn't work because gorestful negotiates for verbs and content encoding
	// and all those things go crazy when gorestful really just needs to pass through.  In addition, openapi enforces unique verb constraints
	// which we don't fit into and it still muddies up swagger.  Trying to switch the webservices into a route doesn't work because the
	//  containing webservice faces all the same problems listed above.
	// This leads to the crazy thing done here.  Our mux does what we need, so we'll place it in front of gorestful.  It will introspect to
	// decide if the route is likely to be handled by gorestful and route there if needed.  Otherwise, it goes to NonGoRestfulMux mux in
	// order to handle "normal" paths and delegation. Hopefully no API consumers will ever have to deal with this level of detail.  I think
	// we should consider completely removing gorestful.
	// Other servers should only use this opaquely to delegate to an API server.
	Director http.Handler
}

// HandlerChainBuilderFn is used to wrap the GoRestfulContainer handler using the provided handler chain.
// It is normally used to apply filtering like authentication and authorization
type HandlerChainBuilderFn func(apiHandler http.Handler) http.Handler

func NewAPIServerHandler(name string, s runtime.NegotiatedSerializer, handlerChainBuilder HandlerChainBuilderFn, notFoundHandler http.Handler) *APIServerHandler {
	nonGoRestfulMux := mux.NewPathRecorderMux(name)
	if notFoundHandler != nil {
		nonGoRestfulMux.NotFoundHandler(notFoundHandler)
	}

	gorestfulContainer := restful.NewContainer()
	gorestfulContainer.ServeMux = http.NewServeMux()
	gorestfulContainer.Router(restful.CurlyRouter{}) // e.g. for proxy/{kind}/{name}/{*}
	gorestfulContainer.RecoverHandler(func(panicReason interface{}, httpWriter http.ResponseWriter) {
		logStackOnRecover(s, panicReason, httpWriter)
	})
	gorestfulContainer.ServiceErrorHandler(func(serviceErr restful.ServiceError, request *restful.Request, response *restful.Response) {
		serviceErrorHandler(s, serviceErr, request, response)
	})

	director := director{
		name:               name,
		goRestfulContainer: gorestfulContainer,
		nonGoRestfulMux:    nonGoRestfulMux,
	}

	return &APIServerHandler{
		FullHandlerChain:   handlerChainBuilder(director),
		GoRestfulContainer: gorestfulContainer,
		NonGoRestfulMux:    nonGoRestfulMux,
		Director:           director,
	}
}

// ListedPaths returns the paths that should be shown under /
func (a *APIServerHandler) ListedPaths() []string {
	var handledPaths []string
	// Extract the paths handled using restful.WebService
	for _, ws := range a.GoRestfulContainer.RegisteredWebServices() {
		handledPaths = append(handledPaths, ws.RootPath())
	}
	handledPaths = append(handledPaths, a.NonGoRestfulMux.ListedPaths()...)
	sort.Strings(handledPaths)

	return handledPaths
}

type director struct {
	name               string
	goRestfulContainer *restful.Container
	nonGoRestfulMux    *mux.PathRecorderMux
}

func (d director) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	path := req.URL.Path

	// check to see if our webservices want to claim this path
	for _, ws := range d.goRestfulContainer.RegisteredWebServices() {
		switch {
		case ws.RootPath() == "/apis":
			// if we are exactly /apis or /apis/, then we need special handling in loop.
			// normally these are passed to the nonGoRestfulMux, but if discovery is enabled, it will go directly.
			// We can't rely on a prefix match since /apis matches everything (see the big comment on Director above)
			if path == "/apis" || path == "/apis/" {
				klog.V(5).Infof("%v: %v %q satisfied by gorestful with webservice %v", d.name, req.Method, path, ws.RootPath())
				// don't use servemux here because gorestful servemuxes get messed up when removing webservices
				// TODO fix gorestful, remove TPRs, or stop using gorestful
				d.goRestfulContainer.Dispatch(w, req)
				return
			}

		case strings.HasPrefix(path, ws.RootPath()):
			// ensure an exact match or a path boundary match
			if len(path) == len(ws.RootPath()) || path[len(ws.RootPath())] == '/' {
				klog.V(5).Infof("%v: %v %q satisfied by gorestful with webservice %v", d.name, req.Method, path, ws.RootPath())
				// don't use servemux here because gorestful servemuxes get messed up when removing webservices
				// TODO fix gorestful, remove TPRs, or stop using gorestful
				d.goRestfulContainer.Dispatch(w, req)
				return
			}
		}
	}

	// if we didn't find a match, then we just skip gorestful altogether
	klog.V(5).Infof("%v: %v %q satisfied by nonGoRestful", d.name, req.Method, path)
	d.nonGoRestfulMux.ServeHTTP(w, req)
}

// TODO: Unify with RecoverPanics?
func logStackOnRecover(s runtime.NegotiatedSerializer, panicReason interface{}, w http.ResponseWriter) {
	var buffer bytes.Buffer
	buffer.WriteString(fmt.Sprintf("recover from panic situation: - %v\r\n", panicReason))
	for i := 2; ; i++ {
		_, file, line, ok := rt.Caller(i)
		if !ok {
			break
		}
		buffer.WriteString(fmt.Sprintf("    %s:%d\r\n", file, line))
	}
	klog.Errorln(buffer.String())

	headers := http.Header{}
	if ct := w.Header().Get("Content-Type"); len(ct) > 0 {
		headers.Set("Accept", ct)
	}
	responsewriters.ErrorNegotiated(apierrors.NewGenericServerResponse(http.StatusInternalServerError, "", schema.GroupResource{}, "", "", 0, false), s, schema.GroupVersion{}, w, &http.Request{Header: headers})
}

func serviceErrorHandler(s runtime.NegotiatedSerializer, serviceErr restful.ServiceError, request *restful.Request, resp *restful.Response) {
	responsewriters.ErrorNegotiated(
		apierrors.NewGenericServerResponse(serviceErr.Code, "", schema.GroupResource{}, "", serviceErr.Message, 0, false),
		s,
		schema.GroupVersion{},
		resp,
		request.Request,
	)
}

// ServeHTTP makes it an http.Handler
func (a *APIServerHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	a.FullHandlerChain.ServeHTTP(w, r)
}
