package libplugin

import (
	"bufio"
	context "context"
	"fmt"
	"io"
	"net"
	"os"

	"github.com/tg123/sshpiper/libplugin/ioconn"
	"google.golang.org/grpc"
	codes "google.golang.org/grpc/codes"
	status "google.golang.org/grpc/status"
)

type ConnMetadata interface {
	User() string

	RemoteAddr() string

	UniqueID() string
}

func (c *ConnMeta) User() string {
	return c.UserName
}

func (c *ConnMeta) RemoteAddr() string {
	return c.FromAddr
}

func (c *ConnMeta) UniqueID() string {
	return c.UniqId
}

type KeyboardInteractiveChallenge func(instruction string, question string, echo bool) (answer string, err error)

type SshPiperPluginConfig struct {
	NewConnectionCallback func(conn ConnMetadata) error

	NextAuthMethodsCallback func(conn ConnMetadata) ([]string, error)

	NoneAuthCallback func(conn ConnMetadata) (*Upstream, error)

	PasswordCallback func(conn ConnMetadata, password []byte) (*Upstream, error)

	PublicKeyCallback func(conn ConnMetadata, key []byte) (*Upstream, error)

	KeyboardInteractiveCallback func(conn ConnMetadata, client KeyboardInteractiveChallenge) (*Upstream, error)

	UpstreamAuthFailureCallback func(conn ConnMetadata, method string, err error)

	BannerCallback func(conn ConnMetadata) string

	VerifyHostKeyCallback func(conn ConnMetadata, key []byte) (bool, error)
}

type SshPiperPlugin interface {
	GetLoggerOutput() io.Writer
	GetGrpcServer() *grpc.Server
	Serve() error
}

func NewFromStdio(config SshPiperPluginConfig) (SshPiperPlugin, error) {
	s := grpc.NewServer()
	l, err := ioconn.ListenFromSingleIO(os.Stdin, os.Stdout)
	if err != nil {
		return nil, err
	}

	return NewFromGrpc(config, s, l)
}

func NewFromGrpc(config SshPiperPluginConfig, grpc *grpc.Server, listener net.Listener) (SshPiperPlugin, error) {
	r, w := io.Pipe()

	s := &server{
		config:    config,
		grpc:      grpc,
		listener:  listener,
		logwriter: w,
		logs:      make(chan string, 1000),
	}

	go func() {
		scanner := bufio.NewScanner(r)

		for scanner.Scan() {
			s.logs <- scanner.Text()
		}
	}()

	RegisterSshPiperPluginServer(s.grpc, s)

	return s, nil
}

type server struct {
	UnimplementedSshPiperPluginServer

	config   SshPiperPluginConfig
	grpc     *grpc.Server
	listener net.Listener

	logs      chan string
	logwriter io.Writer
}

func (s *server) GetGrpcServer() *grpc.Server {
	return s.grpc
}

func (s *server) GetLoggerOutput() io.Writer {
	return s.logwriter
}

func (s *server) Serve() error {
	return s.grpc.Serve(s.listener)
}

func (s *server) Logs(req *StartLogRequest, stream SshPiperPlugin_LogsServer) error {
	for log := range s.logs {
		if err := stream.Send(&Log{
			Message: log,
		}); err != nil {
			return err
		}
	}

	return nil
}

func (s *server) ListCallbacks(ctx context.Context, req *ListCallbackRequest) (*ListCallbackResponse, error) {

	var cb []string

	if s.config.NewConnectionCallback != nil {
		cb = append(cb, "NewConnection")
	}

	if s.config.NextAuthMethodsCallback != nil {
		cb = append(cb, "NextAuthMethods")
	}

	if s.config.NoneAuthCallback != nil {
		cb = append(cb, "NoneAuth")
	}

	if s.config.PasswordCallback != nil {
		cb = append(cb, "PasswordAuth")
	}

	if s.config.PublicKeyCallback != nil {
		cb = append(cb, "PublicKeyAuth")
	}

	if s.config.KeyboardInteractiveCallback != nil {
		cb = append(cb, "KeyboardInteractiveAuth")
	}

	if s.config.UpstreamAuthFailureCallback != nil {
		cb = append(cb, "UpstreamAuthFailure")
	}

	if s.config.BannerCallback != nil {
		cb = append(cb, "Banner")
	}

	if s.config.VerifyHostKeyCallback != nil {
		cb = append(cb, "VerifyHostKey")
	}

	return &ListCallbackResponse{
		Callbacks: cb,
	}, nil
}

func (s *server) NewConnection(ctx context.Context, req *NewConnectionRequest) (*NewConnectionResponse, error) {
	if s.config.NewConnectionCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method NewConnection not implemented")
	}

	if err := s.config.NewConnectionCallback(req.Meta); err != nil {
		return nil, err
	}

	return &NewConnectionResponse{}, nil
}

func (s *server) NextAuthMethods(ctx context.Context, req *NextAuthMethodsRequest) (*NextAuthMethodsResponse, error) {
	if s.config.NextAuthMethodsCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method NextAuthMethods not implemented")
	}

	methods, err := s.config.NextAuthMethodsCallback(req.Meta)
	if err != nil {
		return nil, err
	}

	resp := &NextAuthMethodsResponse{}

	for _, method := range methods {
		m := AuthMethodFromName(method)
		if m == -1 {
			return nil, status.Errorf(codes.InvalidArgument, "unknown method %s", method)
		}
		resp.Methods = append(resp.Methods, m)
	}

	return resp, nil
}

func (s *server) NoneAuth(ctx context.Context, req *NoneAuthRequest) (*NoneAuthResponse, error) {
	if s.config.NoneAuthCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method NoneAuth not implemented")
	}

	upstream, err := s.config.NoneAuthCallback(req.Meta)
	if err != nil {
		return nil, err
	}

	return &NoneAuthResponse{
		Upstream: upstream,
	}, nil
}

func (s *server) PasswordAuth(ctx context.Context, req *PasswordAuthRequest) (*PasswordAuthResponse, error) {
	if s.config.PasswordCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method PasswordAuth not implemented")
	}

	upstream, err := s.config.PasswordCallback(req.Meta, req.Password)
	if err != nil {
		return nil, err
	}

	return &PasswordAuthResponse{
		Upstream: upstream,
	}, nil
}

func (s *server) PublicKeyAuth(ctx context.Context, req *PublicKeyAuthRequest) (*PublicKeyAuthResponse, error) {
	if s.config.PublicKeyCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method PublicKeyAuth not implemented")
	}

	upstream, err := s.config.PublicKeyCallback(req.Meta, req.PublicKey)
	if err != nil {
		return nil, err
	}

	return &PublicKeyAuthResponse{
		Upstream: upstream,
	}, nil
}

func (s *server) KeyboardInteractiveAuth(stream SshPiperPlugin_KeyboardInteractiveAuthServer) error {
	if s.config.KeyboardInteractiveCallback == nil {
		return status.Errorf(codes.Unimplemented, "method KeyboardInteractiveAuth not implemented")
	}

	if err := stream.Send(&KeyboardInteractiveAuthMessage{
		Message: &KeyboardInteractiveAuthMessage_MetaRequest{},
	}); err != nil {
		return err
	}

	metareply, err := stream.Recv()
	if err != nil {
		return err
	}

	meta := metareply.GetMetaResponse()
	if meta == nil {
		return status.Errorf(codes.InvalidArgument, "missing meta")
	}

	upstream, err := s.config.KeyboardInteractiveCallback(meta.Meta, func(instruction string, question string, echo bool) (answer string, err error) {
		var questions []*KeyboardInteractivePromptRequest_Question
		if question != "" {
			questions = append(questions, &KeyboardInteractivePromptRequest_Question{
				Text: question,
				Echo: echo,
			})
		}

		if err := stream.Send(&KeyboardInteractiveAuthMessage{
			Message: &KeyboardInteractiveAuthMessage_PromptRequest{
				PromptRequest: &KeyboardInteractivePromptRequest{
					Name:        "", // temporary unused
					Instruction: instruction,
					Questions:   questions,
				},
			},
		}); err != nil {
			return "", err
		}

		if question == "" {
			return "", nil
		}

		userInputReply, err := stream.Recv()
		if err != nil {
			return "", err
		}

		userInput := userInputReply.GetUserResponse()
		if userInput == nil {
			return "", status.Errorf(codes.InvalidArgument, "missing user input")
		}

		if len(userInput.Answers) != 1 {
			return "", status.Errorf(codes.InvalidArgument, "expected 1 answer, got %d", len(userInput.Answers))
		}

		return userInput.Answers[0], nil
	})

	if err != nil {
		return err
	}

	if err := stream.Send(&KeyboardInteractiveAuthMessage{
		Message: &KeyboardInteractiveAuthMessage_FinishRequest{
			FinishRequest: &KeyboardInteractiveFinishRequest{
				Upstream: upstream,
			},
		},
	}); err != nil {
		return err
	}

	return nil
}

func (s *server) UpstreamAuthFailureNotice(ctx context.Context, req *UpstreamAuthFailureNoticeRequest) (*UpstreamAuthFailureNoticeResponse, error) {
	if s.config.UpstreamAuthFailureCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method UpstreamAuthFailureNotice not implemented")
	}

	s.config.UpstreamAuthFailureCallback(req.Meta, req.Method, fmt.Errorf(req.Error))

	return &UpstreamAuthFailureNoticeResponse{}, nil
}

func (s *server) Banner(ctx context.Context, req *BannerRequest) (*BannerResponse, error) {
	if s.config.BannerCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method Banner not implemented")
	}

	msg := s.config.BannerCallback(req.Meta)

	return &BannerResponse{
		Message: msg,
	}, nil
}

func (s *server) VerifyHostKey(ctx context.Context, req *VerifyHostKeyRequest) (*VerifyHostKeyReply, error) {
	if s.config.VerifyHostKeyCallback == nil {
		return nil, status.Errorf(codes.Unimplemented, "method VerifyHostKey not implemented")
	}

	verifed, err := s.config.VerifyHostKeyCallback(req.Meta, req.Key)
	if err != nil {
		return nil, err
	}

	return &VerifyHostKeyReply{
		Verified: verifed,
	}, nil
}