package tlv

import (
	"bytes"
	"encoding/binary"
	"net"
)

type PacketUpdateHeader struct {
	AE       uint8
	Flags    uint8
	Plen     uint8
	Omitted  uint8
	Interval uint16
	Seqno    uint16
	Metric   uint16
}

type PacketUpdate struct {
	PacketUpdateHeader
	Prefix net.IPNet
}

type PacketDecoder struct {
	routerID [8]byte
	v4       [4]byte
	v6       [16]byte
}

func (s *PacketDecoder) UpdateFromBytes(b []byte) (PacketUpdate, error) {
	var u PacketUpdate

	r := bytes.NewReader(b[:10])
	err := binary.Read(r, binary.BigEndian, &u.PacketUpdateHeader)

	b = b[10:]

	psize := (u.Plen+7)/8 - u.Omitted
	switch u.AE {
	case 0:
	case 1:
		u.Prefix.Mask = net.CIDRMask(int(u.Plen), 4*8)
		u.Prefix.IP = append([]byte{}, s.v4[:]...)
		copy(u.Prefix.IP[u.Omitted:], b[:psize])
		if u.Flags&0x80 > 0 {
			copy(s.v4[:], u.Prefix.IP)
		}
	case 2:
		u.Prefix.Mask = net.CIDRMask(int(u.Plen), 16*8)
		u.Prefix.IP = append([]byte{}, s.v6[:]...)
		copy(u.Prefix.IP[u.Omitted:], b[:psize])
		if u.Flags&0x80 > 0 {
			copy(s.v6[:], u.Prefix.IP)
		}
	case 3:
		u.Prefix.Mask = net.CIDRMask(8, 16*8)
		u.Prefix.IP = make([]byte, 16)
		u.Prefix.IP[0] = 0xfe
		u.Prefix.IP[1] = 0x80
		copy(u.Prefix.IP[8:], b[:8])
	}

	return u, err
}