package wireguard

import (
	"context"
	"net"
	"net/netip"
	"os"

	"github.com/sagernet/sing-box/adapter"
	"github.com/sagernet/sing-box/common/dialer"
	"github.com/sagernet/sing-box/option"
	"github.com/sagernet/sing-tun"
	M "github.com/sagernet/sing/common/metadata"
	N "github.com/sagernet/sing/common/network"

	wgTun "golang.zx2c4.com/wireguard/tun"
)

var _ Device = (*SystemDevice)(nil)

type SystemDevice struct {
	dialer N.Dialer
	device tun.Tun
	name   string
	mtu    int
	events chan wgTun.Event
}

/*func (w *SystemDevice) NewEndpoint() (stack.LinkEndpoint, error) {
	gTun, isGTun := w.device.(tun.GVisorTun)
	if !isGTun {
		return nil, tun.ErrGVisorUnsupported
	}
	return gTun.NewEndpoint()
}*/

func NewSystemDevice(router adapter.Router, interfaceName string, localPrefixes []netip.Prefix, mtu uint32) (*SystemDevice, error) {
	var inet4Addresses []netip.Prefix
	var inet6Addresses []netip.Prefix
	for _, prefixes := range localPrefixes {
		if prefixes.Addr().Is4() {
			inet4Addresses = append(inet4Addresses, prefixes)
		} else {
			inet6Addresses = append(inet6Addresses, prefixes)
		}
	}
	if interfaceName == "" {
		interfaceName = tun.CalculateInterfaceName("wg")
	}
	tunInterface, err := tun.Open(tun.Options{
		Name:         interfaceName,
		Inet4Address: inet4Addresses,
		Inet6Address: inet6Addresses,
		MTU:          mtu,
	})
	if err != nil {
		return nil, err
	}
	return &SystemDevice{
		dialer.NewDefault(router, option.DialerOptions{
			BindInterface: interfaceName,
		}),
		tunInterface, interfaceName, int(mtu), make(chan wgTun.Event),
	}, nil
}

func (w *SystemDevice) DialContext(ctx context.Context, network string, destination M.Socksaddr) (net.Conn, error) {
	return w.dialer.DialContext(ctx, network, destination)
}

func (w *SystemDevice) ListenPacket(ctx context.Context, destination M.Socksaddr) (net.PacketConn, error) {
	return w.dialer.ListenPacket(ctx, destination)
}

func (w *SystemDevice) Start() error {
	w.events <- wgTun.EventUp
	return nil
}

func (w *SystemDevice) File() *os.File {
	return nil
}

func (w *SystemDevice) Read(bytes []byte, index int) (int, error) {
	return w.device.Read(bytes[index-tunPacketOffset:])
}

func (w *SystemDevice) Write(bytes []byte, index int) (int, error) {
	return w.device.Write(bytes[index:])
}

func (w *SystemDevice) Flush() error {
	return nil
}

func (w *SystemDevice) MTU() (int, error) {
	return w.mtu, nil
}

func (w *SystemDevice) Name() (string, error) {
	return w.name, nil
}

func (w *SystemDevice) Events() chan wgTun.Event {
	return w.events
}

func (w *SystemDevice) Close() error {
	select {
	case <-w.events:
		return os.ErrClosed
	default:
		close(w.events)
	}
	return w.device.Close()
}