package station

import (
	"encoding/binary"

	"gitea.neitzel.de/konrad/funknetz/internal/gcm64"
)

func counterAAD(counter uint32) []byte {
	var b [4]byte
	binary.BigEndian.PutUint32(b[:], counter)
	return b[:]
}

func registrationAAD(clientID uint16) []byte {
	b := counterAAD(0)
	return appendU16(b, clientID)
}

func sealDatagram(key, prefix []byte, clientID uint16, counter uint32, aad, plain []byte) ([]byte, error) {
	tag, ct, err := gcm64.Seal(key, gcm64.IV(prefix, clientID, counter), plain, aad)
	if err != nil {
		return nil, err
	}
	wire := make([]byte, 0, len(aad)+len(tag)+len(ct))
	wire = append(wire, aad...)
	wire = append(wire, tag...)
	return append(wire, ct...), nil
}

func openDatagram(key, prefix []byte, clientID uint16, counter uint32, aad, tag, ct []byte) ([]byte, error) {
	return gcm64.Open(key, gcm64.IV(prefix, clientID, counter), tag, ct, aad)
}