package shadowsocks

import (
	"context"
	"time"

	"v2ray.com/core"
	"v2ray.com/core/common"
	"v2ray.com/core/common/buf"
	"v2ray.com/core/common/log"
	"v2ray.com/core/common/net"
	"v2ray.com/core/common/protocol"
	"v2ray.com/core/common/session"
	"v2ray.com/core/common/signal"
	"v2ray.com/core/common/task"
	"v2ray.com/core/proxy"
	"v2ray.com/core/transport/internet"
	"v2ray.com/core/transport/internet/udp"
	"v2ray.com/core/transport/pipe"
)

type Server struct {
	config ServerConfig
	user   *protocol.MemoryUser
	v      *core.Instance
}

// NewServer create a new Shadowsocks server.
func NewServer(ctx context.Context, config *ServerConfig) (*Server, error) {
	if config.GetUser() == nil {
		return nil, newError("user is not specified")
	}

	mUser, err := config.User.ToMemoryUser()
	if err != nil {
		return nil, newError("failed to parse user account").Base(err)
	}

	s := &Server{
		config: *config,
		user:   mUser,
		v:      core.MustFromContext(ctx),
	}

	return s, nil
}

func (s *Server) Network() net.NetworkList {
	list := net.NetworkList{
		Network: s.config.Network,
	}
	if len(list.Network) == 0 {
		list.Network = append(list.Network, net.Network_TCP)
	}
	if s.config.UdpEnabled {
		list.Network = append(list.Network, net.Network_UDP)
	}
	return list
}

func (s *Server) Process(ctx context.Context, network net.Network, conn internet.Connection, dispatcher core.Dispatcher) error {
	switch network {
	case net.Network_TCP:
		return s.handleConnection(ctx, conn, dispatcher)
	case net.Network_UDP:
		return s.handlerUDPPayload(ctx, conn, dispatcher)
	default:
		return newError("unknown network: ", network)
	}
}

func (s *Server) handlerUDPPayload(ctx context.Context, conn internet.Connection, dispatcher core.Dispatcher) error {
	udpServer := udp.NewDispatcher(dispatcher, func(ctx context.Context, payload *buf.Buffer) {
		request := protocol.RequestHeaderFromContext(ctx)
		if request == nil {
			return
		}

		data, err := EncodeUDPPacket(request, payload.Bytes())
		payload.Release()
		if err != nil {
			newError("failed to encode UDP packet").Base(err).AtWarning().WriteToLog(session.ExportIDToError(ctx))
			return
		}
		defer data.Release()

		conn.Write(data.Bytes())
	})

	account := s.user.Account.(*MemoryAccount)

	reader := buf.NewReader(conn)
	for {
		mpayload, err := reader.ReadMultiBuffer()
		if err != nil {
			break
		}

		for _, payload := range mpayload {
			request, data, err := DecodeUDPPacket(s.user, payload)
			if err != nil {
				if source, ok := proxy.SourceFromContext(ctx); ok {
					newError("dropping invalid UDP packet from: ", source).Base(err).WriteToLog(session.ExportIDToError(ctx))
					log.Record(&log.AccessMessage{
						From:   source,
						To:     "",
						Status: log.AccessRejected,
						Reason: err,
					})
				}
				payload.Release()
				continue
			}

			if request.Option.Has(RequestOptionOneTimeAuth) && account.OneTimeAuth == Account_Disabled {
				newError("client payload enables OTA but server doesn't allow it").WriteToLog(session.ExportIDToError(ctx))
				payload.Release()
				continue
			}

			if !request.Option.Has(RequestOptionOneTimeAuth) && account.OneTimeAuth == Account_Enabled {
				newError("client payload disables OTA but server forces it").WriteToLog(session.ExportIDToError(ctx))
				payload.Release()
				continue
			}

			dest := request.Destination()
			if source, ok := proxy.SourceFromContext(ctx); ok {
				log.Record(&log.AccessMessage{
					From:   source,
					To:     dest,
					Status: log.AccessAccepted,
					Reason: "",
				})
			}
			newError("tunnelling request to ", dest).WriteToLog(session.ExportIDToError(ctx))

			ctx = protocol.ContextWithUser(ctx, request.User)
			ctx = protocol.ContextWithRequestHeader(ctx, request)
			udpServer.Dispatch(ctx, dest, data)
		}
	}

	return nil
}

func (s *Server) handleConnection(ctx context.Context, conn internet.Connection, dispatcher core.Dispatcher) error {
	sessionPolicy := s.v.PolicyManager().ForLevel(s.user.Level)
	conn.SetReadDeadline(time.Now().Add(sessionPolicy.Timeouts.Handshake))

	bufferedReader := buf.BufferedReader{Reader: buf.NewReader(conn)}
	request, bodyReader, err := ReadTCPSession(s.user, &bufferedReader)
	if err != nil {
		log.Record(&log.AccessMessage{
			From:   conn.RemoteAddr(),
			To:     "",
			Status: log.AccessRejected,
			Reason: err,
		})
		return newError("failed to create request from: ", conn.RemoteAddr()).Base(err)
	}
	conn.SetReadDeadline(time.Time{})

	dest := request.Destination()
	log.Record(&log.AccessMessage{
		From:   conn.RemoteAddr(),
		To:     dest,
		Status: log.AccessAccepted,
		Reason: "",
	})
	newError("tunnelling request to ", dest).WriteToLog(session.ExportIDToError(ctx))

	ctx = protocol.ContextWithUser(ctx, request.User)

	ctx, cancel := context.WithCancel(ctx)
	timer := signal.CancelAfterInactivity(ctx, cancel, sessionPolicy.Timeouts.ConnectionIdle)

	ctx = core.ContextWithBufferPolicy(ctx, sessionPolicy.Buffer)
	link, err := dispatcher.Dispatch(ctx, dest)
	if err != nil {
		return err
	}

	responseDone := func() error {
		defer timer.SetTimeout(sessionPolicy.Timeouts.UplinkOnly)

		bufferedWriter := buf.NewBufferedWriter(buf.NewWriter(conn))
		responseWriter, err := WriteTCPResponse(request, bufferedWriter)
		if err != nil {
			return newError("failed to write response").Base(err)
		}

		{
			payload, err := link.Reader.ReadMultiBuffer()
			if err != nil {
				return err
			}
			if err := responseWriter.WriteMultiBuffer(payload); err != nil {
				return err
			}
		}

		if err := bufferedWriter.SetBuffered(false); err != nil {
			return err
		}

		if err := buf.Copy(link.Reader, responseWriter, buf.UpdateActivity(timer)); err != nil {
			return newError("failed to transport all TCP response").Base(err)
		}

		return nil
	}

	requestDone := func() error {
		defer timer.SetTimeout(sessionPolicy.Timeouts.DownlinkOnly)

		if err := buf.Copy(bodyReader, link.Writer, buf.UpdateActivity(timer)); err != nil {
			return newError("failed to transport all TCP request").Base(err)
		}

		return nil
	}

	var requestDoneAndCloseWriter = task.Single(requestDone, task.OnSuccess(task.Close(link.Writer)))
	if err := task.Run(task.WithContext(ctx), task.Parallel(requestDoneAndCloseWriter, responseDone))(); err != nil {
		pipe.CloseError(link.Reader)
		pipe.CloseError(link.Writer)
		return newError("connection ends").Base(err)
	}

	return nil
}

func init() {
	common.Must(common.RegisterConfig((*ServerConfig)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
		return NewServer(ctx, config.(*ServerConfig))
	}))
}