package vip

import (
	"errors"
	"net"
	"sync"

	"github.com/vishvananda/netlink"
)

var ErrNoDefaultInterface = errors.New("no default interface found")

func DefaultInterface() (iface string, err error) {
	routes, err := netlink.RouteGet(net.IPv4bcast)
	if err != nil {
		return
	}
	if len(routes) >= 1 {
		link, err := netlink.LinkByIndex(routes[0].LinkIndex)
		if err != nil {
			return "", err
		}
		return link.Attrs().Name, nil
	}
	err = ErrNoDefaultInterface
	return
}

type Network struct {
	sync.Mutex
	m     map[string]struct{}
	iface string
	label string
	link  netlink.Link
}

func NewNetwork(iface string) (n *Network, err error) {
	return NewNetworkWithLabel(iface, "")
}

func NewNetworkWithLabel(iface, label string) (n *Network, err error) {
	if iface == "" {
		iface, err = DefaultInterface()
		if err != nil {
			return
		}
	}
	link, err := netlink.LinkByName(iface)
	if err != nil {
		return
	}
	n = &Network{
		m:     make(map[string]struct{}),
		iface: iface,
		label: label,
		link:  link,
	}
	return
}

func (n *Network) Interface() string {
	return n.iface
}

func (n *Network) HasIP(a *netlink.Addr) bool {
	addrs, err := netlink.AddrList(n.link, 0)
	if err != nil {
		return false
	}
	for _, addr := range addrs {
		if addr.Equal(*a) {
			return true
		}
	}
	return false
}

func (n *Network) AddIP(cidr string) error {
	n.Lock()
	defer n.Unlock()
	addr, err := netlink.ParseAddr(cidr)
	if err != nil {
		return err
	}
	if n.HasIP(addr) {
		return nil
	}
	if n.label != "" {
		addr.Label = n.iface + ":" + n.label
	}
	err = netlink.AddrReplace(n.link, addr)
	if err != nil {
		return err
	}
	n.m[cidr] = struct{}{}
	return ARPSendGratuitous(cidr, n.iface)
}

func (n *Network) DeleteIP(cidr string) error {
	n.Lock()
	defer n.Unlock()
	addr, err := netlink.ParseAddr(cidr)
	if err != nil {
		return err
	}
	if !n.HasIP(addr) {
		return nil
	}
	err = netlink.AddrDel(n.link, addr)
	if err != nil {
		return err
	}
	delete(n.m, cidr)
	return nil
}

func (n *Network) GetIPs() (cidrs []string) {
	n.Lock()
	defer n.Unlock()
	cidrs = make([]string, len(n.m))
	c := 0
	for k := range n.m {
		cidrs[c] = k
		c++
	}
	return
}