package outbound

//go:generate go run github.com/v2fly/v2ray-core/v4/common/errors/errorgen

import (
	"context"
	"time"

	core "github.com/v2fly/v2ray-core/v4"
	"github.com/v2fly/v2ray-core/v4/common"
	"github.com/v2fly/v2ray-core/v4/common/buf"
	"github.com/v2fly/v2ray-core/v4/common/net"
	"github.com/v2fly/v2ray-core/v4/common/protocol"
	"github.com/v2fly/v2ray-core/v4/common/retry"
	"github.com/v2fly/v2ray-core/v4/common/session"
	"github.com/v2fly/v2ray-core/v4/common/signal"
	"github.com/v2fly/v2ray-core/v4/common/task"
	"github.com/v2fly/v2ray-core/v4/features/policy"
	"github.com/v2fly/v2ray-core/v4/proxy/vless"
	"github.com/v2fly/v2ray-core/v4/proxy/vless/encoding"
	"github.com/v2fly/v2ray-core/v4/transport"
	"github.com/v2fly/v2ray-core/v4/transport/internet"
)

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

// Handler is an outbound connection handler for VLess protocol.
type Handler struct {
	serverList    *protocol.ServerList
	serverPicker  protocol.ServerPicker
	policyManager policy.Manager
}

// New creates a new VLess outbound handler.
func New(ctx context.Context, config *Config) (*Handler, error) {
	serverList := protocol.NewServerList()
	for _, rec := range config.Vnext {
		s, err := protocol.NewServerSpecFromPB(rec)
		if err != nil {
			return nil, newError("failed to parse server spec").Base(err).AtError()
		}
		serverList.AddServer(s)
	}

	v := core.MustFromContext(ctx)
	handler := &Handler{
		serverList:    serverList,
		serverPicker:  protocol.NewRoundRobinServerPicker(serverList),
		policyManager: v.GetFeature(policy.ManagerType()).(policy.Manager),
	}

	return handler, nil
}

// Process implements proxy.Outbound.Process().
func (h *Handler) Process(ctx context.Context, link *transport.Link, dialer internet.Dialer) error {
	var rec *protocol.ServerSpec
	var conn internet.Connection

	if err := retry.ExponentialBackoff(5, 200).On(func() error {
		rec = h.serverPicker.PickServer()
		var err error
		conn, err = dialer.Dial(ctx, rec.Destination())
		if err != nil {
			return err
		}
		return nil
	}); err != nil {
		return newError("failed to find an available destination").Base(err).AtWarning()
	}
	defer conn.Close()

	outbound := session.OutboundFromContext(ctx)
	if outbound == nil || !outbound.Target.IsValid() {
		return newError("target not specified").AtError()
	}

	target := outbound.Target
	newError("tunneling request to ", target, " via ", rec.Destination()).AtInfo().WriteToLog(session.ExportIDToError(ctx))

	command := protocol.RequestCommandTCP
	if target.Network == net.Network_UDP {
		command = protocol.RequestCommandUDP
	}
	if target.Address.Family().IsDomain() && target.Address.Domain() == "v1.mux.cool" {
		command = protocol.RequestCommandMux
	}

	request := &protocol.RequestHeader{
		Version: encoding.Version,
		User:    rec.PickUser(),
		Command: command,
		Address: target.Address,
		Port:    target.Port,
	}

	account := request.User.Account.(*vless.MemoryAccount)

	requestAddons := &encoding.Addons{
		Flow: account.Flow,
	}

	sessionPolicy := h.policyManager.ForLevel(request.User.Level)
	ctx, cancel := context.WithCancel(ctx)
	timer := signal.CancelAfterInactivity(ctx, cancel, sessionPolicy.Timeouts.ConnectionIdle)

	clientReader := link.Reader // .(*pipe.Reader)
	clientWriter := link.Writer // .(*pipe.Writer)

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

		bufferWriter := buf.NewBufferedWriter(buf.NewWriter(conn))
		if err := encoding.EncodeRequestHeader(bufferWriter, request, requestAddons); err != nil {
			return newError("failed to encode request header").Base(err).AtWarning()
		}

		// default: serverWriter := bufferWriter
		serverWriter := encoding.EncodeBodyAddons(bufferWriter, request, requestAddons)
		if err := buf.CopyOnceTimeout(clientReader, serverWriter, time.Millisecond*100); err != nil && err != buf.ErrNotTimeoutReader && err != buf.ErrReadTimeout {
			return err // ...
		}

		// Flush; bufferWriter.WriteMultiBufer now is bufferWriter.writer.WriteMultiBuffer
		if err := bufferWriter.SetBuffered(false); err != nil {
			return newError("failed to write A request payload").Base(err).AtWarning()
		}

		// from clientReader.ReadMultiBuffer to serverWriter.WriteMultiBufer
		if err := buf.Copy(clientReader, serverWriter, buf.UpdateActivity(timer)); err != nil {
			return newError("failed to transfer request payload").Base(err).AtInfo()
		}

		return nil
	}

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

		responseAddons, err := encoding.DecodeResponseHeader(conn, request)
		if err != nil {
			return newError("failed to decode response header").Base(err).AtInfo()
		}

		// default: serverReader := buf.NewReader(conn)
		serverReader := encoding.DecodeBodyAddons(conn, request, responseAddons)

		// from serverReader.ReadMultiBuffer to clientWriter.WriteMultiBufer
		if err := buf.Copy(serverReader, clientWriter, buf.UpdateActivity(timer)); err != nil {
			return newError("failed to transfer response payload").Base(err).AtInfo()
		}

		return nil
	}

	if err := task.Run(ctx, postRequest, task.OnSuccess(getResponse, task.Close(clientWriter))); err != nil {
		return newError("connection ends").Base(err).AtInfo()
	}

	return nil
}