package server

import (
	"context"
	"errors"
	"fmt"
	"io"
	"reflect"
	"runtime/debug"
	"strings"
	"sync"
	"unicode"
	"unicode/utf8"

	"go-micro.dev/v6/codec"
	merrors "go-micro.dev/v6/errors"
	log "go-micro.dev/v6/logger"
)

var (
	errLastStreamResponse = errors.New("EOS")

	// Precompute the reflect type for error. Can't use error directly
	// because Typeof takes an empty interface value. This is annoying.
	typeOfError = reflect.TypeOf((*error)(nil)).Elem()
)

type methodType struct {
	ArgType     reflect.Type
	ReplyType   reflect.Type
	ContextType reflect.Type
	method      reflect.Method
	sync.Mutex  // protects counters
	stream      bool
}

type service struct {
	typ    reflect.Type           // type of the receiver
	method map[string]*methodType // registered methods
	rcvr   reflect.Value          // receiver of methods for the service
	name   string                 // name of service
}

type request struct {
	msg  *codec.Message
	next *request // for free list in Server
}

type response struct {
	msg  *codec.Message
	next *response // for free list in Server
}

// router represents an RPC router.
type router struct {
	ops RouterOptions

	serviceMap map[string]*service

	freeReq *request

	freeResp *response

	subscribers map[string][]*subscriber

	// handler wrappers
	hdlrWrappers []HandlerWrapper
	// subscriber wrappers
	subWrappers []SubscriberWrapper

	su sync.RWMutex

	mu sync.Mutex // protects the serviceMap

	reqLock sync.Mutex // protects freeReq

	respLock sync.Mutex // protects freeResp
}

// rpcRouter encapsulates functions that become a Router.
type rpcRouter struct {
	h func(context.Context, Request, interface{}) error
	m func(context.Context, string, Message) error
}

func (r rpcRouter) ProcessMessage(ctx context.Context, subscriber string, msg Message) error {
	return r.m(ctx, subscriber, msg)
}

func (r rpcRouter) ServeRequest(ctx context.Context, req Request, rsp Response) error {
	return r.h(ctx, req, rsp)
}

func newRpcRouter(opts ...RouterOption) *router {
	return &router{
		ops:         NewRouterOptions(opts...),
		serviceMap:  make(map[string]*service),
		subscribers: make(map[string][]*subscriber),
	}
}

// Is this an exported - upper case - name?
func isExported(name string) bool {
	rune, _ := utf8.DecodeRuneInString(name)
	return unicode.IsUpper(rune)
}

// Is this type exported or a builtin?
func isExportedOrBuiltinType(t reflect.Type) bool {
	for t.Kind() == reflect.Pointer {
		t = t.Elem()
	}
	// PkgPath will be non-empty even for an exported type,
	// so we need to check the type name as well.
	return isExported(t.Name()) || t.PkgPath() == ""
}

// prepareMethod returns a methodType for the provided method or nil
// in case if the method was unsuitable.
func prepareMethod(method reflect.Method, logger log.Logger) *methodType {
	mtype := method.Type
	mname := method.Name
	var replyType, argType, contextType reflect.Type
	var stream bool

	// Method must be exported.
	if method.PkgPath != "" {
		return nil
	}

	switch mtype.NumIn() {
	case 3:
		// assuming streaming
		argType = mtype.In(2)
		contextType = mtype.In(1)
		stream = true
	case 4:
		// method that takes a context
		argType = mtype.In(2)
		replyType = mtype.In(3)
		contextType = mtype.In(1)
	default:
		logger.Logf(log.ErrorLevel, "method %v of %v has wrong number of ins: %v", mname, mtype, mtype.NumIn())
		return nil
	}

	if stream {
		// check stream type
		streamType := reflect.TypeOf((*Stream)(nil)).Elem()
		if !argType.Implements(streamType) {
			logger.Logf(log.ErrorLevel, "%v argument does not implement Stream interface: %v", mname, argType)
			return nil
		}
	} else {
		// if not stream check the replyType

		// First arg need not be a pointer.
		if !isExportedOrBuiltinType(argType) {
			logger.Logf(log.ErrorLevel, "%v argument type not exported: %v", mname, argType)
			return nil
		}

		if replyType.Kind() != reflect.Pointer {
			logger.Logf(log.ErrorLevel, "method %v reply type not a pointer: %v", mname, replyType)
			return nil
		}

		// Reply type must be exported.
		if !isExportedOrBuiltinType(replyType) {
			logger.Logf(log.ErrorLevel, "method %v reply type not exported: %v", mname, replyType)
			return nil
		}
	}

	// Method needs one out.
	if mtype.NumOut() != 1 {
		logger.Logf(log.ErrorLevel, "method %v has wrong number of outs: %v", mname, mtype.NumOut())
		return nil
	}

	// The return type of the method must be error.
	if returnType := mtype.Out(0); returnType != typeOfError {
		logger.Logf(log.ErrorLevel, "method %v returns %v not error", mname, returnType.String())
		return nil
	}

	return &methodType{method: method, ArgType: argType, ReplyType: replyType, ContextType: contextType, stream: stream}
}

func (router *router) sendResponse(sending sync.Locker,
	req *request,
	reply interface{},
	cc codec.Writer,
	last bool) error {
	msg := new(codec.Message)
	msg.Type = codec.Response
	resp := router.getResponse()
	resp.msg = msg

	resp.msg.Id = req.msg.Id

	sending.Lock()
	err := cc.Write(resp.msg, reply)
	sending.Unlock()

	router.freeResponse(resp)

	return err
}

func (s *service) call(ctx context.Context,
	router *router,
	sending *sync.Mutex,
	mtype *methodType,
	req *request,
	argv, replyv reflect.Value,
	cc codec.Writer) error {
	defer router.freeRequest(req)

	function := mtype.method.Func
	var returnValues []reflect.Value

	r := &rpcRequest{
		service:     req.msg.Target,
		contentType: req.msg.Header["Content-Type"],
		method:      req.msg.Method,
		endpoint:    req.msg.Endpoint,
		body:        req.msg.Body,
		header:      req.msg.Header,
	}

	// only set if not nil
	if argv.IsValid() {
		r.rawBody = argv.Interface()
	}

	if !mtype.stream {
		fn := func(ctx context.Context, req Request, rsp interface{}) error {
			returnValues = function.Call([]reflect.Value{s.rcvr, mtype.prepareContext(ctx),
				reflect.ValueOf(argv.Interface()), reflect.ValueOf(rsp)})

			// The return value for the method is an error.
			if err := returnValues[0].Interface(); err != nil {
				return err.(error)
			}

			return nil
		}

		// wrap the handler
		for i := len(router.hdlrWrappers); i > 0; i-- {
			fn = router.hdlrWrappers[i-1](fn)
		}

		// execute handler
		if err := fn(ctx, r, replyv.Interface()); err != nil {
			return err
		}

		// send response
		return router.sendResponse(sending, req, replyv.Interface(), cc, true)
	}

	// declare a local error to see if we errored out already
	// keep track of the type, to make sure we return
	// the same one consistently
	rawStream := &rpcStream{
		context: ctx,
		codec:   cc.(codec.Codec),
		request: r,
		id:      req.msg.Id,
	}

	// Invoke the method, providing a new value for the reply.
	fn := func(ctx context.Context, req Request, stream interface{}) error {
		returnValues = function.Call([]reflect.Value{s.rcvr, mtype.prepareContext(ctx), reflect.ValueOf(stream)})

		if err := returnValues[0].Interface(); err != nil {
			// the function returned an error, we use that
			return err.(error)
		} else if serr := rawStream.Error(); serr == io.EOF || serr == io.ErrUnexpectedEOF {
			return nil
		} else {
			// no error, we send the special EOS error
			return errLastStreamResponse
		}
	}

	// wrap the handler
	for i := len(router.hdlrWrappers); i > 0; i-- {
		fn = router.hdlrWrappers[i-1](fn)
	}

	// client.Stream request
	r.stream = true

	// execute handler
	return fn(ctx, r, rawStream)
}

func (m *methodType) prepareContext(ctx context.Context) reflect.Value {
	if contextv := reflect.ValueOf(ctx); contextv.IsValid() {
		return contextv
	}

	return reflect.Zero(m.ContextType)
}

func (router *router) getRequest() *request {
	router.reqLock.Lock()
	defer router.reqLock.Unlock()

	req := router.freeReq
	if req == nil {
		req = new(request)
	} else {
		router.freeReq = req.next
		*req = request{}
	}

	return req
}

func (router *router) freeRequest(req *request) {
	router.reqLock.Lock()
	defer router.reqLock.Unlock()

	req.next = router.freeReq
	router.freeReq = req
}

func (router *router) getResponse() *response {
	router.respLock.Lock()
	defer router.respLock.Unlock()

	resp := router.freeResp
	if resp == nil {
		resp = new(response)
	} else {
		router.freeResp = resp.next
		*resp = response{}
	}

	return resp
}

func (router *router) freeResponse(resp *response) {
	router.respLock.Lock()
	defer router.respLock.Unlock()

	resp.next = router.freeResp
	router.freeResp = resp
}

func (router *router) readRequest(r Request) (service *service, mtype *methodType, req *request, argv, replyv reflect.Value, keepReading bool, err error) {
	cc := r.Codec()

	service, mtype, req, keepReading, err = router.readHeader(cc)
	if err != nil {
		if !keepReading {
			return
		}
		// discard body
		_ = cc.ReadBody(nil)

		return
	}

	// is it a streaming request? then we don't read the body
	if mtype.stream {
		if cc.(codec.Codec).String() != "grpc" {
			_ = cc.ReadBody(nil)
		}
		return
	}

	// Decode the argument value.
	argIsValue := false // if true, need to indirect before calling.
	if mtype.ArgType.Kind() == reflect.Pointer {
		argv = reflect.New(mtype.ArgType.Elem())
	} else {
		argv = reflect.New(mtype.ArgType)
		argIsValue = true
	}

	// argv guaranteed to be a pointer now.
	if err = cc.ReadBody(argv.Interface()); err != nil {
		return
	}

	if argIsValue {
		argv = argv.Elem()
	}

	if !mtype.stream {
		replyv = reflect.New(mtype.ReplyType.Elem())
	}

	return
}

func (router *router) readHeader(cc codec.Reader) (service *service, mtype *methodType, req *request, keepReading bool, err error) {
	// Grab the request header.
	msg := new(codec.Message)
	msg.Type = codec.Request
	req = router.getRequest()
	req.msg = msg

	err = cc.ReadHeader(msg, msg.Type)
	if err != nil {
		req = nil
		if err == io.EOF || err == io.ErrUnexpectedEOF {
			return
		}
		err = errors.New("rpc: router cannot decode request: " + err.Error())

		return
	}

	// We read the header successfully. If we see an error now,
	// we can still recover and move on to the next request.
	keepReading = true

	serviceMethod := strings.Split(req.msg.Endpoint, ".")
	if len(serviceMethod) != 2 {
		err = errors.New("rpc: service/endpoint request ill-formed: " + req.msg.Endpoint)
		return
	}

	// Look up the request.
	router.mu.Lock()
	service = router.serviceMap[serviceMethod[0]]
	router.mu.Unlock()

	if service == nil {
		err = errors.New("rpc: can't find service " + serviceMethod[0])
		return
	}

	mtype = service.method[serviceMethod[1]]
	if mtype == nil {
		err = errors.New("rpc: can't find method " + serviceMethod[1])
	}

	return
}

func (router *router) NewHandler(h interface{}, opts ...HandlerOption) Handler {
	return NewRpcHandler(h, opts...)
}

func (router *router) Handle(h Handler) error {
	router.mu.Lock()
	defer router.mu.Unlock()

	if router.serviceMap == nil {
		router.serviceMap = make(map[string]*service)
	}

	if len(h.Name()) == 0 {
		return errors.New("rpc.Handle: handler has no name")
	}

	if !isExported(h.Name()) {
		return errors.New("rpc.Handle: type " + h.Name() + " is not exported")
	}

	rcvr := h.Handler()
	s := new(service)
	s.typ = reflect.TypeOf(rcvr)
	s.rcvr = reflect.ValueOf(rcvr)

	// check name
	if _, present := router.serviceMap[h.Name()]; present {
		return errors.New("rpc.Handle: service already defined: " + h.Name())
	}

	s.name = h.Name()
	s.method = make(map[string]*methodType)

	// Install the methods
	for m := 0; m < s.typ.NumMethod(); m++ {
		method := s.typ.Method(m)
		if mt := prepareMethod(method, router.ops.Logger); mt != nil {
			s.method[method.Name] = mt
		}
	}

	// Check there are methods
	if len(s.method) == 0 {
		return errors.New("rpc Register: type " + s.name + " has no exported methods of suitable type")
	}

	// save handler
	router.serviceMap[s.name] = s

	return nil
}

func (router *router) ServeRequest(ctx context.Context, r Request, rsp Response) error {
	sending := new(sync.Mutex)
	service, mtype, req, argv, replyv, keepReading, err := router.readRequest(r)
	if err != nil {
		if !keepReading {
			return err
		}
		// send a response if we actually managed to read a header.
		if req != nil {
			router.freeRequest(req)
		}

		return err
	}

	return service.call(ctx, router, sending, mtype, req, argv, replyv, rsp.Codec())
}

func (router *router) NewSubscriber(topic string, handler interface{}, opts ...SubscriberOption) Subscriber {
	return newSubscriber(topic, handler, opts...)
}

func (router *router) Subscribe(s Subscriber) error {
	sub, ok := s.(*subscriber)
	if !ok {
		return fmt.Errorf("invalid subscriber: expected *subscriber")
	}

	if len(sub.handlers) == 0 {
		return fmt.Errorf("invalid subscriber: no handler functions")
	}

	if err := validateSubscriber(sub); err != nil {
		return err
	}

	router.su.Lock()
	defer router.su.Unlock()

	// append to subscribers
	subs := router.subscribers[sub.Topic()]
	subs = append(subs, sub)
	router.subscribers[sub.Topic()] = subs

	return nil
}

func (router *router) ProcessMessage(ctx context.Context, subscriber string, msg Message) (err error) {
	defer func() {
		// recover any panics
		if r := recover(); r != nil {
			router.ops.Logger.Logf(log.ErrorLevel, "panic recovered: %v", r)
			router.ops.Logger.Log(log.ErrorLevel, string(debug.Stack()))
			err = merrors.InternalServerError("go.micro.server", "panic recovered: %v", r)
		}
	}()

	// get the subscribers by topic
	router.su.RLock()
	subs, ok := router.subscribers[subscriber]
	router.su.RUnlock()
	if !ok {
		log.Warnf("Subscriber not found for topic %s", msg.Topic())
		return nil
	}

	var errResults []string

	// we may have multiple subscribers for the topic
	for _, sub := range subs {
		// we may have multiple handlers per subscriber
		for i := 0; i < len(sub.handlers); i++ {
			// get the handler
			handler := sub.handlers[i]

			var isVal bool
			var req reflect.Value

			// check whether the handler is a pointer
			if handler.reqType.Kind() == reflect.Pointer {
				req = reflect.New(handler.reqType.Elem())
			} else {
				req = reflect.New(handler.reqType)
				isVal = true
			}

			// if its a value get the element
			if isVal {
				req = req.Elem()
			}

			cc := msg.Codec()

			// read the header. mostly a noop
			if err = cc.ReadHeader(&codec.Message{}, codec.Event); err != nil {
				return err
			}

			// make request value a pointer, if it's not already
			reqVal := req.Interface()
			if req.CanAddr() {
				reqVal = req.Addr().Interface()
			}

			// read the body into the handler request value
			if err = cc.ReadBody(reqVal); err != nil {
				return err
			}

			// create the handler which will honor the SubscriberFunc type
			fn := func(ctx context.Context, msg Message) error {
				var vals []reflect.Value
				if sub.typ.Kind() != reflect.Func {
					vals = append(vals, sub.rcvr)
				}
				if handler.ctxType != nil {
					vals = append(vals, reflect.ValueOf(ctx))
				}

				// values to pass the handler
				vals = append(vals, reflect.ValueOf(msg.Payload()))

				// execute the actuall call of the handler
				returnValues := handler.method.Call(vals)
				if rerr := returnValues[0].Interface(); rerr != nil {
					err = rerr.(error)
				}
				return err
			}

			// wrap with subscriber wrappers
			for i := len(router.subWrappers); i > 0; i-- {
				fn = router.subWrappers[i-1](fn)
			}

			// create new rpc message
			rpcMsg := &rpcMessage{
				topic:       msg.Topic(),
				contentType: msg.ContentType(),
				payload:     req.Interface(),
				codec:       msg.(*rpcMessage).codec,
				header:      msg.Header(),
				body:        msg.Body(),
			}

			// execute the message handler
			if err = fn(ctx, rpcMsg); err != nil {
				errResults = append(errResults, err.Error())
			}
		}
	}

	// if no errors just return
	if len(errResults) > 0 {
		err = merrors.InternalServerError("go.micro.server", "subscriber error: %v", strings.Join(errResults, "\n"))
	}

	return err
}
