package tun

import (
	"context"
	"time"

	"gvisor.dev/gvisor/pkg/tcpip"
	"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
	"gvisor.dev/gvisor/pkg/tcpip/header"
	"gvisor.dev/gvisor/pkg/tcpip/stack"
	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
	"gvisor.dev/gvisor/pkg/waiter"

	tun_net "github.com/v2fly/v2ray-core/v5/app/tun/net"
	"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/session"
	"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"
	internet "github.com/v2fly/v2ray-core/v5/transport/internet"
)

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

type tcpConn struct {
	*gonet.TCPConn
	id stack.TransportEndpointID
}

func (c *tcpConn) ID() *stack.TransportEndpointID {
	return &c.id
}

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

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)

			if config.SocketSettings != nil {
				if err := applySocketOptions(s, linkedEndpoint, config.SocketSettings); err != nil {
					newError("failed to apply socket options: ", err).WriteToLog(session.ExportIDToError(ctx))
				}
			}

			conn := &tcpConn{
				TCPConn: gonet.NewTCPConn(wg, linkedEndpoint),
				id:      r.ID(),
			}

			handler := &TCPHandler{
				ctx:           ctx,
				dispatcher:    dispatcher,
				policyManager: policyManager,
				config:        config,
			}

			go handler.Handle(conn)
		})

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

		return nil
	}
}

func (h *TCPHandler) Handle(conn tun_net.TCPConn) error {
	defer conn.Close()
	id := conn.ID()
	ctx := session.ContextWithInbound(h.ctx, &session.Inbound{Tag: h.config.Tag})
	sessionPolicy := h.policyManager.ForLevel(h.config.UserLevel)

	dest := net.TCPDestination(tun_net.AddressFromTCPIPAddr(id.LocalAddress), net.Port(id.LocalPort))
	src := net.TCPDestination(tun_net.AddressFromTCPIPAddr(id.RemoteAddress), net.Port(id.RemotePort))
	ctx = log.ContextWithAccessMessage(ctx, &log.AccessMessage{
		From:   src,
		To:     dest,
		Status: log.AccessAccepted,
		Reason: "",
	})
	content := new(session.Content)
	if h.config.SniffingSettings != nil {
		content.SniffingRequest.Enabled = h.config.SniffingSettings.Enabled
		content.SniffingRequest.OverrideDestinationForProtocol = h.config.SniffingSettings.DestinationOverride
		content.SniffingRequest.MetadataOnly = h.config.SniffingSettings.MetadataOnly
	}
	ctx = session.ContextWithContent(ctx, content)
	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
}

func applySocketOptions(s *stack.Stack, endpoint tcpip.Endpoint, config *internet.SocketConfig) tcpip.Error {
	if config.TcpKeepAliveInterval > 0 {
		interval := tcpip.KeepaliveIntervalOption(time.Duration(config.TcpKeepAliveInterval) * time.Second)
		if err := endpoint.SetSockOpt(&interval); err != nil {
			return err
		}
	}

	if config.TcpKeepAliveIdle > 0 {
		idle := tcpip.KeepaliveIdleOption(time.Duration(config.TcpKeepAliveIdle) * time.Second)
		if err := endpoint.SetSockOpt(&idle); err != nil {
			return err
		}
	}

	if config.TcpKeepAliveInterval > 0 || config.TcpKeepAliveIdle > 0 {
		endpoint.SocketOptions().SetKeepAlive(true)
	}
	{
		var sendBufferSizeRangeOption tcpip.TCPSendBufferSizeRangeOption
		if err := s.TransportProtocolOption(header.TCPProtocolNumber, &sendBufferSizeRangeOption); err == nil {
			endpoint.SocketOptions().SetReceiveBufferSize(int64(sendBufferSizeRangeOption.Default), false)
		}

		var receiveBufferSizeRangeOption tcpip.TCPReceiveBufferSizeRangeOption
		if err := s.TransportProtocolOption(header.TCPProtocolNumber, &receiveBufferSizeRangeOption); err == nil {
			endpoint.SocketOptions().SetSendBufferSize(int64(receiveBufferSizeRangeOption.Default), false)
		}
	}

	return nil
}