// Performs handshake and returns a new authenticated SecretConnection.
// Returns nil if error in handshake.
// Caller should call conn.Close()
// See docs/sts-final.pdf for more information.
func MakeSecretConnection(conn io.ReadWriteCloser, locPrivKey acm.PrivKeyEd25519) (*SecretConnection, error) {

	locPubKey := locPrivKey.PubKey().(acm.PubKeyEd25519)

	// Generate ephemeral keys for perfect forward secrecy.
	locEphPub, locEphPriv := genEphKeys()

	// Write local ephemeral pubkey and receive one too.
	// NOTE: every 32-byte string is accepted as a Curve25519 public key
	// (see DJB's Curve25519 paper: http://cr.yp.to/ecdh/curve25519-20060209.pdf)
	remEphPub, err := shareEphPubKey(conn, locEphPub)
	if err != nil {
		return nil, err
	}

	// Compute common shared secret.
	shrSecret := computeSharedSecret(remEphPub, locEphPriv)

	// Sort by lexical order.
	loEphPub, hiEphPub := sort32(locEphPub, remEphPub)

	// Generate nonces to use for secretbox.
	recvNonce, sendNonce := genNonces(loEphPub, hiEphPub, locEphPub == loEphPub)

	// Generate common challenge to sign.
	challenge := genChallenge(loEphPub, hiEphPub)

	// Construct SecretConnection.
	sc := &SecretConnection{
		conn:       conn,
		recvBuffer: nil,
		recvNonce:  recvNonce,
		sendNonce:  sendNonce,
		shrSecret:  shrSecret,
	}

	// Sign the challenge bytes for authentication.
	locSignature := signChallenge(challenge, locPrivKey)

	// Share (in secret) each other's pubkey & challenge signature
	authSigMsg, err := shareAuthSignature(sc, locPubKey, locSignature)
	if err != nil {
		return nil, err
	}
	remPubKey, remSignature := authSigMsg.Key, authSigMsg.Sig
	if !remPubKey.VerifyBytes(challenge[:], remSignature) {
		return nil, errors.New("Challenge verification failed")
	}

	// We've authorized.
	sc.remPubKey = remPubKey
	return sc, nil
}

func makeNodeInfo(sw *p2p.Switch, privKey acm.PrivKeyEd25519, genesisRoot []byte) *types.NodeInfo {

	nodeInfo := &types.NodeInfo{
		PubKey:  privKey.PubKey().(acm.PubKeyEd25519),
		Moniker: config.GetString("moniker"),
		ChainID: config.GetString("chain_id"),
		Genesis: genesisRoot,
		Version: types.Versions{
			Tendermint: Version,
			P2P:        p2p.Version,
			RPC:        rpc.Version,
			Wire:       wire.Version,
		},
	}

	// include git hash in the nodeInfo if available
	if rev, err := ReadFile(config.GetString("revision_file")); err == nil {
		nodeInfo.Version.Revision = string(rev)
	}

	if !sw.IsListening() {
		return nodeInfo
	}

	p2pListener := sw.Listeners()[0]
	p2pHost := p2pListener.ExternalAddress().IP.String()
	p2pPort := p2pListener.ExternalAddress().Port
	rpcListenAddr := config.GetString("rpc_laddr")
	_, rpcPortStr, _ := net.SplitHostPort(rpcListenAddr)
	rpcPort, err := strconv.Atoi(rpcPortStr)
	if err != nil {
		PanicSanity(Fmt("Expected numeric RPC.ListenAddr port but got %v", rpcPortStr))
	}

	// We assume that the rpcListener has the same ExternalAddress.
	// This is probably true because both P2P and RPC listeners use UPnP,
	// except of course if the rpc is only bound to localhost
	nodeInfo.Host = p2pHost
	nodeInfo.P2PPort = p2pPort
	nodeInfo.RPCPort = uint16(rpcPort)
	return nodeInfo
}

// Not goroutine safe.
// NOTE: Overwrites sw.nodeInfo.PubKey
func (sw *Switch) SetNodePrivKey(nodePrivKey acm.PrivKeyEd25519) {
	sw.nodePrivKey = nodePrivKey
	if sw.nodeInfo != nil {
		sw.nodeInfo.PubKey = nodePrivKey.PubKey().(acm.PubKeyEd25519)
	}
}

func signChallenge(challenge *[32]byte, locPrivKey acm.PrivKeyEd25519) (signature acm.SignatureEd25519) {
	signature = locPrivKey.Sign(challenge[:]).(acm.SignatureEd25519)
	return
}