package node

import "golang.org/x/crypto/nacl/box"

// Encrypting the packet will also set the header's DataSize field.
func encryptPacket(h *header, sharedKey, data, out []byte) []byte {
	h.DataSize = uint16(len(data) + box.Overhead)
	out = out[:h.DataSize+headerSize]
	h.Marshal(out)
	box.SealAfterPrecomputation(out[headerSize:headerSize], data, (*[24]byte)(out[:headerSize]), (*[32]byte)(sharedKey))
	return out
}

func decryptPacket(sharedKey, packetAndHeader, out []byte) (decrypted []byte, ok bool) {
	return box.OpenAfterPrecomputation(
		out[:0],
		packetAndHeader[headerSize:],
		(*[24]byte)(packetAndHeader[:headerSize]),
		(*[32]byte)(sharedKey))
}

func computeSharedKey(peerPubKey, privKey []byte) []byte {
	shared := [32]byte{}
	box.Precompute(&shared, (*[32]byte)(peerPubKey), (*[32]byte)(privKey))
	return shared[:]
}