package socket

import (
	"errors"
	"fmt"
	"golang.org/x/sys/unix"
	"log"
	"os"
	"strings"
	"sync"
	"unsafe"

	"tunnel/pkg/pack"
	"tunnel/pkg/server/env"
	"tunnel/pkg/server/queue"
)

const maxTunBufSize = 65535

var errPartialWrite = errors.New("partial write")

type ifReq struct {
	name  [unix.IFNAMSIZ]uint8
	flags uint16
}

type tunSocket struct {
	Name string `opts:"required"`
}

type tunConn struct {
	name string
	s    *tunSocket
	fp   *os.File
	once sync.Once
}

func (s *tunSocket) String() string {
	return fmt.Sprintf("tun/%s", s.Name)
}

func (s *tunSocket) Single() {}

func (s *tunSocket) New(env.Env) (Conn, error) {
	fd, err := unix.Open("/dev/net/tun", unix.O_RDWR, 0)
	if err != nil {
		return nil, err
	}

	ifr := &ifReq{}
	copy(ifr.name[:], s.Name)
	ifr.flags = unix.IFF_TUN | unix.IFF_NO_PI

	if err := ioctl(fd, unix.TUNSETIFF, unsafe.Pointer(ifr)); err != nil {
		unix.Close(fd)
		return nil, fmt.Errorf("ioctl TUNSETIFF %s: %w", s.Name, err)
	}

	if err := unix.SetNonblock(fd, true); err != nil {
		unix.Close(fd)
		return nil, fmt.Errorf("set nonblock %s: %w", s.Name, err)
	}

	c := &tunConn{
		name: strings.Trim(string(ifr.name[:]), "\x00"),
		fp:   os.NewFile(uintptr(fd), "tun"),
	}

	return c, nil
}

func (s *tunSocket) Close() {
}

func (c *tunConn) Send(wq queue.Q) error {
	buf := make([]byte, maxTunBufSize)
	enc := pack.NewEncoder(wq.Writer())

	for {
		n, err := c.fp.Read(buf)
		if err != nil {
			return err
		}

		enc.Lps(buf[0:n])
	}
}

func (c *tunConn) Recv(rq queue.Q) error {
	dec := pack.NewDecoder(rq.Reader())

	for {
		b, err := dec.Lps()
		if err != nil {
			return err
		}

		n, err := c.fp.Write(b)
		if err != nil {
			return err
		}

		if n != len(b) {
			return errPartialWrite
		}
	}
}

func (c *tunConn) String() string {
	return "tun/" + c.name
}

func (c *tunConn) Close() error {
	err := ErrAlreadyClosed

	c.once.Do(func() {
		log.Println("close", c)
		err = c.fp.Close()
	})

	return err
}

func init() {
	register("tun", tunSocket{})
}