//go:generate stringer -type=TLV
package tlv

import "fmt"

type TLV uint8

const (
	Pad1 TLV = iota
	PadN
	AckReq
	Ack
	Hello
	IHU
	RouterID
	NextHop
	Update
	RouteRequest
	RouteUpdate
	TSPC
	HMAC
)

type Scanner struct {
	buf []byte
	err error
	t   TLV
	l   uint8
}

func NewTLVScanner(buf []byte) *Scanner {
	return &Scanner{
		buf: buf,
	}
}

func (ts *Scanner) Scan() bool {
	if ts.err != nil {
		return false
	}

	if len(ts.buf) <= int(ts.l) {
		return false
	}

	// move beginning of the buffer to the next TLV
	ts.buf = ts.buf[ts.l:]
	ts.t, ts.l = TLV(ts.buf[0]), 0

	switch ts.t {
	case Pad1:
		ts.buf = ts.buf[1:]
	default:
		ts.l = ts.buf[1]
		if 2+int(ts.l) > len(ts.buf) {
			ts.err = fmt.Errorf("Invalid length: type %d, length %d, size %d", ts.t, ts.l, len(ts.buf))
			return false
		}
		// move beginning of the buffer behind the header
		ts.buf = ts.buf[2:]
	}
	return true
}

func (ts *Scanner) Err() error {
	return ts.err
}

func (ts *Scanner) TLV() (TLV, []byte) {
	if ts.err != nil {
		return 0, nil
	}
	return ts.t, ts.buf[:ts.l]
}