package netlink

import (
	"antoine-roux.tk/projects/go/firecracker-netns/internal/netns"
	"crypto/rand"
	"fmt"
	"github.com/vishvananda/netlink"
)

// inspired by https://github.com/containernetworking/plugins/blob/main/pkg/ip/link_linux.go#L57

type Peer struct {
	link  netlink.Link
	netNs netns.NsHandle
}

type PairLink struct {
	host  Peer
	guest Peer
}

func NewVethPair(ns netns.NsHandle) (pair *PairLink, error error) {

	origins, err := netns.Get()
	if err != nil {
		return nil, err
	}

	err = netns.Set(ns)
	if err != nil {
		return nil, err
	}

	name, err := randomVethName()
	if err != nil {
		return nil, err
	}

	peerName, err := randomVethName()
	if err != nil {
		return nil, err
	}

	attrs := netlink.NewLinkAttrs()
	attrs.Name = name
	veth := &netlink.Veth{
		LinkAttrs:     attrs,
		PeerName:      peerName,
		PeerNamespace: netlink.NsFd(origins.Fd),
	}

	if err := netlink.LinkAdd(veth); err != nil {
		return nil, err
	}

	// Re-fetch the container link to get its creation-time parameters, e.g. index and mac
	fmt.Println(name)
	veth2, err := netlink.LinkByName(name)
	if err != nil {
		netlink.LinkDel(veth)
		return nil, err
	}

	err = netns.Set(origins)
	if err != nil {
		return nil, err
	}

	fmt.Println(peerName)
	veth1, err := netlink.LinkByName(peerName)
	if err != nil {
		netlink.LinkDel(veth)
		return nil, err
	}

	return &PairLink{host: Peer{veth1, origins}, guest: Peer{veth2, ns}}, nil
}

// DeleteLink removes an interface link.
func (p *PairLink) DeleteLink() error {
	err := netns.Set(p.host.netNs)
	if err != nil {
		return fmt.Errorf("set original Ns for deleting veth %q: %v", p.host.link.Attrs().Name, err)
	}

	if err := netlink.LinkDel(p.host.link); err != nil {
		return fmt.Errorf("failed to delete %q: %v", p.host.link.Attrs().Name, err)
	}

	return nil
}

// randomVethName returns string "veth" with random prefix (hashed from entropy)
func randomVethName() (string, error) {
	entropy := make([]byte, 4)
	_, err := rand.Read(entropy)
	if err != nil {
		return "", fmt.Errorf("failed to generate random veth name: %v", err)
	}

	// NetworkManager (recent versions) will ignore veth devices that start with "veth"
	return fmt.Sprintf("veth%x", entropy), nil
}