//
// Copyright (c) 2017 anygone contributors (see AUTHORS file)
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice, this
//   list of conditions and the following disclaimer.
//
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
//
// * Neither the name of anygone nor the names of its
//   contributors may be used to endorse or promote products derived from
//   this software without specific prior written permission.
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//

package tuntap

import (
	"context"
	"fmt"
	"net"
	"os/exec"
	"strings"
	"time"

	extlib "github.com/lab11/go-tuntap/tuntap"
	"github.com/vishvananda/netlink"
)

const (
	EtherTypeIPv4                      = 0x0800
	EtherTypeIPv6                      = 0x86DD
	EtherTypeTransparentEthernetBridge = 0x6558

	PostUpScriptTimeout = 10 * time.Second
)

type Device struct {
	iface  *extlib.Interface
	iftype extlib.DevKind
	nl     netlink.Link
}

func (dev *Device) Name() string {
	return dev.iface.Name()
}

func (dev *Device) AddAddress(addr net.IPNet) error {
	// TODO: this only works on linux...
	if err := netlink.AddrAdd(dev.nl, &netlink.Addr{IPNet: &addr}); err != nil {
		return fmt.Errorf("netlink(addr add) failed: %v", err)
	}
	return nil
}

func (dev *Device) SetMTU(mtu int) error {
	// TODO: this only works on linux...
	if err := netlink.LinkSetMTU(dev.nl, mtu); err != nil {
		return fmt.Errorf("netlink(link set mtu) failed: %v", err)
	}
	return nil
}

func (dev *Device) Up() error {
	// TODO: this only works on linux...
	if err := netlink.LinkSetUp(dev.nl); err != nil {
		return fmt.Errorf("netlink(link set up) failed: %v", err)
	}
	return nil
}

func (dev *Device) Down() error {
	// TODO: this only works on linux...
	if err := netlink.LinkSetDown(dev.nl); err != nil {
		return fmt.Errorf("netlink(link set down) failed: %v", err)
	}
	return nil
}

func (dev *Device) RunPostUp(script string) error {
	ctx, cancel := context.WithTimeout(context.Background(), PostUpScriptTimeout)
	defer cancel()

	if err := exec.CommandContext(ctx, script, dev.iface.Name()).Run(); err != nil {
		return err
	}
	return nil
}

func (dev *Device) ReadPacket() (pkt *extlib.Packet, err error) {
	pkt, err = dev.iface.ReadPacket()
	if dev.iftype == extlib.DevTap {
		pkt.Protocol = EtherTypeTransparentEthernetBridge
	}
	return
}

func (dev *Device) WritePacket(pkt *extlib.Packet) error {
	pkt.Protocol = 0
	return dev.iface.WritePacket(pkt)
}

func NewTunDevice(name string) (dev *Device, err error) {
	dev = &Device{iftype: extlib.DevTun}
	if dev.iface, err = extlib.Open(name, extlib.DevTun, true); err != nil {
		return
	}
	return
}

func NewTapDevice(name string) (dev *Device, err error) {
	dev = &Device{iftype: extlib.DevTap}
	if dev.iface, err = extlib.Open(name, extlib.DevTap, false); err != nil {
		return
	}
	return
}

func NewDevice(iftype, name string) (dev *Device, err error) {
	if iftype == "" {
		if strings.HasPrefix(name, "tun") {
			iftype = "tun"
		} else if strings.HasPrefix(name, "tap") {
			iftype = "tap"
		} else {
			return nil, fmt.Errorf("no device type is set and the given interface name(%s) doesn't start with 'tun' or 'tap'", name)
		}
	}

	switch strings.ToLower(iftype) {
	case "tun":
		dev, err = NewTunDevice(name)
	case "tap":
		dev, err = NewTapDevice(name)
	default:
		return nil, fmt.Errorf("invalid interface type: %s", iftype)
	}
	if err != nil {
		return nil, err
	}

	// TODO: this only works on linux...
	if dev.nl, err = netlink.LinkByName(dev.iface.Name()); err != nil {
		return nil, fmt.Errorf("netlink(open netlink by name) failed: %v", err)
	}
	return dev, nil
}