package tun

import (
	"context"

	"github.com/v2fly/v2ray-core/v5/common"
	"github.com/v2fly/v2ray-core/v5/common/buf"
	"github.com/v2fly/v2ray-core/v5/common/log"
	"github.com/v2fly/v2ray-core/v5/common/net"
	"github.com/v2fly/v2ray-core/v5/common/signal"
	"github.com/v2fly/v2ray-core/v5/common/task"
	"github.com/v2fly/v2ray-core/v5/features/policy"
	"github.com/v2fly/v2ray-core/v5/features/routing"
	"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
	"gvisor.dev/gvisor/pkg/tcpip/stack"
	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
	"gvisor.dev/gvisor/pkg/waiter"
)

const (
	rcvWnd      = 0 // default settings
	maxInFlight = 2 << 10
)

type TCPHandler struct {
	ctx           context.Context
	dispatcher    routing.Dispatcher
	policyManager policy.Manager
	config        *Config

	stack *stack.Stack
}

func SetTCPHandler(ctx context.Context, dispatcher routing.Dispatcher, policyManager policy.Manager, config *Config) StackOption {
	return func(s *stack.Stack) error {
		tcpForwarder := tcp.NewForwarder(s, rcvWnd, maxInFlight, func(r *tcp.ForwarderRequest) {
			wg := new(waiter.Queue)
			linkedEndpoint, err := r.CreateEndpoint(wg)
			if err != nil {
				r.Complete(true)
				return
			}
			defer r.Complete(false)

			// TODO: set sockopt

			tcpHandler := &TCPHandler{
				ctx:           ctx,
				dispatcher:    dispatcher,
				policyManager: policyManager,
				config:        config,
				stack:         s,
			}

			if err := tcpHandler.Handle(gonet.NewTCPConn(wg, linkedEndpoint)); err != nil {
				// TODO: log
				// return newError("failed to handle tcp connection").Base(err)
			}

		})
		s.SetTransportProtocolHandler(tcp.ProtocolNumber, tcpForwarder.HandlePacket)

		return nil
	}
}

func (h *TCPHandler) Handle(conn net.Conn) error {
	sessionPolicy := h.policyManager.ForLevel(h.config.UserLevel)

	addr := conn.RemoteAddr()

	dest := net.DestinationFromAddr(addr)
	ctx := log.ContextWithAccessMessage(h.ctx, &log.AccessMessage{
		From:   addr,
		To:     dest,
		Status: log.AccessAccepted,
		Reason: "",
	})
	ctx, cancel := context.WithCancel(ctx)
	timer := signal.CancelAfterInactivity(ctx, cancel, sessionPolicy.Timeouts.ConnectionIdle)
	link, err := h.dispatcher.Dispatch(ctx, dest)
	if err != nil {
		return newError("failed to dispatch").Base(err)
	}

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

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

		return nil
	}

	requestDoneAndCloseWriter := task.OnSuccess(requestDone, task.Close(link.Writer))
	if err := task.Run(h.ctx, requestDoneAndCloseWriter, responseDone); err != nil {
		common.Interrupt(link.Reader)
		common.Interrupt(link.Writer)
		return newError("connection ends").Base(err)
	}

	return nil
}