package reflection

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"io/ioutil"
	"reflect"

	"github.com/golang/protobuf/proto"
	dpb "github.com/golang/protobuf/protoc-gen-go/descriptor"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	rpb "google.golang.org/grpc/reflection/grpc_reflection_v1alpha"
)

type serverReflectionServer struct {
	s *grpc.Server
	// TODO add cache if necessary
}

// InstallOnServer installs server reflection service on the given grpc server.
func InstallOnServer(s *grpc.Server) {
	rpb.RegisterServerReflectionServer(s, &serverReflectionServer{
		s: s,
	})
}

type protoMessage interface {
	Descriptor() ([]byte, []int)
}

func (s *serverReflectionServer) fileDescForType(st reflect.Type) (*dpb.FileDescriptorProto, []int, error) {
	// Indexes list is not stored in cache.
	// So this step is needed to get idxs.
	m, ok := reflect.Zero(reflect.PtrTo(st)).Interface().(protoMessage)
	if !ok {
		return nil, nil, fmt.Errorf("failed to create message from type: %v", st)
	}
	enc, idxs := m.Descriptor()

	// Cache missed, try to decode.
	fd, err := s.decodeFileDesc(enc)
	if err != nil {
		return nil, nil, err
	}
	return fd, idxs, nil
}

func (s *serverReflectionServer) decodeFileDesc(enc []byte) (*dpb.FileDescriptorProto, error) {
	raw := decompress(enc)
	if raw == nil {
		return nil, fmt.Errorf("failed to decompress enc")
	}

	fd := new(dpb.FileDescriptorProto)
	if err := proto.Unmarshal(raw, fd); err != nil {
		return nil, fmt.Errorf("bad descriptor: %v", err)
	}
	return fd, nil
}

func decompress(b []byte) []byte {
	r, err := gzip.NewReader(bytes.NewReader(b))
	if err != nil {
		fmt.Printf("bad gzipped descriptor: %v\n", err)
		return nil
	}
	out, err := ioutil.ReadAll(r)
	if err != nil {
		fmt.Printf("bad gzipped descriptor: %v\n", err)
		return nil
	}
	return out
}

func (s *serverReflectionServer) typeForName(name string) (reflect.Type, error) {
	pt := proto.MessageType(name)
	if pt == nil {
		return nil, fmt.Errorf("unknown type: %q", name)
	}
	st := pt.Elem()

	return st, nil
}

func (s *serverReflectionServer) fileDescContainingExtension(st reflect.Type, ext int32) (*dpb.FileDescriptorProto, error) {
	m, ok := reflect.Zero(reflect.PtrTo(st)).Interface().(proto.Message)
	if !ok {
		return nil, fmt.Errorf("failed to create message from type: %v", st)
	}

	var extDesc *proto.ExtensionDesc
	for id, desc := range proto.RegisteredExtensions(m) {
		if id == ext {
			extDesc = desc
			break
		}
	}

	if extDesc == nil {
		return nil, fmt.Errorf("failed to find registered extension for extension number %v", ext)
	}

	extT := reflect.TypeOf(extDesc.ExtensionType).Elem()

	fd, _, err := s.fileDescForType(extT)
	if err != nil {
		return nil, err
	}
	return fd, nil
}

func (s *serverReflectionServer) allExtensionNumbersForType(st reflect.Type) ([]int32, error) {
	m, ok := reflect.Zero(reflect.PtrTo(st)).Interface().(proto.Message)
	if !ok {
		return nil, fmt.Errorf("failed to create message from type: %v", st)
	}

	var out []int32
	for id := range proto.RegisteredExtensions(m) {
		out = append(out, id)
	}
	return out, nil
}

func (s *serverReflectionServer) fileDescWireFormatByFilename(name string) ([]byte, error) {
	enc := proto.FileDescriptor(name)
	if enc == nil {
		return nil, fmt.Errorf("unknown file: %v", name)
	}
	fd, err := s.decodeFileDesc(enc)
	if err != nil {
		return nil, err
	}
	b, err := proto.Marshal(fd)
	if err != nil {
		return nil, err
	}
	return b, nil
}

func (s *serverReflectionServer) fileDescWireFormatContainingSymbol(name string) ([]byte, error) {
	var (
		fd *dpb.FileDescriptorProto
	)
	// Check if it's a type name.
	if st, err := s.typeForName(name); err == nil {
		fd, _, err = s.fileDescForType(st)
		if err != nil {
			return nil, err
		}
	} else {
		// Check if it's a service name or method name.
		meta := s.s.Metadata(name)
		if meta != nil {
			if enc, ok := meta.([]byte); ok {
				fd, err = s.decodeFileDesc(enc)
				if err != nil {
					return nil, err
				}
			}
		}
	}

	// Marshal to wire format.
	if fd != nil {
		b, err := proto.Marshal(fd)
		if err != nil {
			return nil, err
		}
		return b, nil
	}
	return nil, fmt.Errorf("unknown symbol: %v", name)
}

func (s *serverReflectionServer) fileDescWireFormatContainingExtension(typeName string, extNum int32) ([]byte, error) {
	st, err := s.typeForName(typeName)
	if err != nil {
		return nil, err
	}
	fd, err := s.fileDescContainingExtension(st, extNum)
	if err != nil {
		return nil, err
	}
	b, err := proto.Marshal(fd)
	if err != nil {
		return nil, err
	}
	return b, nil
}

func (s *serverReflectionServer) allExtensionNumbersForTypeName(name string) ([]int32, error) {
	st, err := s.typeForName(name)
	if err != nil {
		return nil, err
	}
	extNums, err := s.allExtensionNumbersForType(st)
	if err != nil {
		return nil, err
	}
	return extNums, nil
}

func (s *serverReflectionServer) ServerReflectionInfo(stream rpb.ServerReflection_ServerReflectionInfoServer) error {
	for {
		in, err := stream.Recv()
		if err == io.EOF {
			return nil
		}
		if err != nil {
			return err
		}

		out := &rpb.ServerReflectionResponse{
			ValidHost:       in.Host,
			OriginalRequest: in,
		}
		switch req := in.MessageRequest.(type) {
		case *rpb.ServerReflectionRequest_FileByFilename:
			b, err := s.fileDescWireFormatByFilename(req.FileByFilename)
			if err != nil {
				out.MessageResponse = &rpb.ServerReflectionResponse_ErrorResponse{
					ErrorResponse: &rpb.ErrorResponse{
						ErrorCode:    int32(codes.NotFound),
						ErrorMessage: err.Error(),
					},
				}
			} else {
				out.MessageResponse = &rpb.ServerReflectionResponse_FileDescriptorResponse{
					FileDescriptorResponse: &rpb.FileDescriptorResponse{FileDescriptorProto: [][]byte{b}},
				}
			}
		case *rpb.ServerReflectionRequest_FileContainingSymbol:
			b, err := s.fileDescWireFormatContainingSymbol(req.FileContainingSymbol)
			if err != nil {
				out.MessageResponse = &rpb.ServerReflectionResponse_ErrorResponse{
					ErrorResponse: &rpb.ErrorResponse{
						ErrorCode:    int32(codes.NotFound),
						ErrorMessage: err.Error(),
					},
				}
			} else {
				out.MessageResponse = &rpb.ServerReflectionResponse_FileDescriptorResponse{
					FileDescriptorResponse: &rpb.FileDescriptorResponse{FileDescriptorProto: [][]byte{b}},
				}
			}
		case *rpb.ServerReflectionRequest_FileContainingExtension:
			typeName := req.FileContainingExtension.ContainingType
			extNum := req.FileContainingExtension.ExtensionNumber
			b, err := s.fileDescWireFormatContainingExtension(typeName, extNum)
			if err != nil {
				out.MessageResponse = &rpb.ServerReflectionResponse_ErrorResponse{
					ErrorResponse: &rpb.ErrorResponse{
						ErrorCode:    int32(codes.NotFound),
						ErrorMessage: err.Error(),
					},
				}
			} else {
				out.MessageResponse = &rpb.ServerReflectionResponse_FileDescriptorResponse{
					FileDescriptorResponse: &rpb.FileDescriptorResponse{FileDescriptorProto: [][]byte{b}},
				}
			}
		case *rpb.ServerReflectionRequest_AllExtensionNumbersOfType:
			extNums, err := s.allExtensionNumbersForTypeName(req.AllExtensionNumbersOfType)
			if err != nil {
				out.MessageResponse = &rpb.ServerReflectionResponse_ErrorResponse{
					ErrorResponse: &rpb.ErrorResponse{
						ErrorCode:    int32(codes.NotFound),
						ErrorMessage: err.Error(),
					},
				}
			} else {
				out.MessageResponse = &rpb.ServerReflectionResponse_AllExtensionNumbersResponse{
					AllExtensionNumbersResponse: &rpb.ExtensionNumberResponse{
						BaseTypeName:    req.AllExtensionNumbersOfType,
						ExtensionNumber: extNums,
					},
				}
			}
		case *rpb.ServerReflectionRequest_ListServices:
			services := s.s.AllServiceNames()
			serviceResponses := make([]*rpb.ServiceResponse, len(services))
			for i, s := range services {
				serviceResponses[i] = &rpb.ServiceResponse{
					Name: s,
				}
			}
			out.MessageResponse = &rpb.ServerReflectionResponse_ListServicesResponse{
				ListServicesResponse: &rpb.ListServiceResponse{
					Service: serviceResponses,
				},
			}
		default:
			return grpc.Errorf(codes.InvalidArgument, "invalid MessageRequest: %v", in.MessageRequest)
		}

		if err := stream.Send(out); err != nil {
			return err
		}
	}
}