// Sends a direct message to a known node.
func (o *Overlay) Direct(dest *big.Int, msg *proto.Message) error {
	if err := msg.Encrypt(); err != nil {
		return err
	}
	o.sendDirect(dest, msg)
	return nil
}

// Balances a message to one of the subscribed nodes.
func (o *Overlay) Balance(topic string, msg *proto.Message) error {
	if err := msg.Encrypt(); err != nil {
		return err
	}
	o.sendBalance(pastry.Resolve(topic), msg)
	return nil
}

// The actual message receiving logic. Reads a message from the stream, verifies
// its mac, decodes the headers and send it upwards. Direct receive is public for
// handshake simplifications, after which the link should switch to channel mode.
func (l *Link) RecvDirect() (*proto.Message, error) {
	var msg proto.Message
	var err error

	// Retrieve a new package
	if err = l.socket.Recv(&l.inHeadBuf); err != nil {
		return nil, err
	}
	if err = l.socket.Recv(&msg.Data); err != nil {
		return nil, err
	}
	if err = l.socket.Recv(&l.inMacBuf); err != nil {
		return nil, err
	}
	// Verify the message contents (payload + header)
	l.inMacer.Write(l.inHeadBuf)
	l.inMacer.Write(msg.Data)
	if !bytes.Equal(l.inMacBuf, l.inMacer.Sum(nil)) {
		err = errors.New(fmt.Sprintf("mac mismatch: have %v, want %v.", l.inMacer.Sum(nil), l.inMacBuf))
		return nil, err
	}
	// Extract the package contents
	l.inCipher.XORKeyStream(l.inHeadBuf, l.inHeadBuf)
	l.inBuffer.Write(l.inHeadBuf)
	if err = l.inCoder.Decode(&msg.Head); err != nil {
		return nil, err
	}
	// Set the message security knowingly to true
	msg.KnownSecure()
	return &msg, nil
}

// The actual message sending logic. Calculates the payload MAC, encrypts the
// headers and sends it down to the stream. Direct send is public for handshake
// simplifications. After that is done, the link should switch to channel mode.
func (l *Link) SendDirect(msg *proto.Message) error {
	var err error

	// Sanity check for message data security
	if !msg.Secure() && len(msg.Data) > 0 {
		log.Printf("link: unsecured data, send denied.")
		return errors.New("unsecured data, send denied")
	}
	// Flatten and encrypt the headers
	if err = l.outCoder.Encode(msg.Head); err != nil {
		return err
	}
	l.outCipher.XORKeyStream(l.outBuffer.Bytes(), l.outBuffer.Bytes())
	defer l.outBuffer.Reset()

	// Generate the MAC of the encrypted payload and headers
	l.outMacer.Write(l.outBuffer.Bytes())
	l.outMacer.Write(msg.Data)

	// Send the multi-part message (headers + payload + MAC)
	if err = l.socket.Send(l.outBuffer.Bytes()); err != nil {
		return err
	}
	if err = l.socket.Send(msg.Data); err != nil {
		return err
	}
	if err = l.socket.Send(l.outMacer.Sum(nil)); err != nil {
		return err
	}
	return l.socket.Flush()
}

// Handles the load balancing event of a topio.
func (o *Overlay) handleBalance(msg *proto.Message, topicId *big.Int, prevHop *big.Int) (bool, error) {
	sid := topicId.String()

	// Fetch the topic or report not found
	o.lock.RLock()
	top, ok := o.topics[sid]
	topName := o.names[sid]
	o.lock.RUnlock()
	if !ok {
		// No error, but not handled either
		return false, nil
	}
	// Fetch the recipient and either forward or deliver
	node, err := top.Balance(prevHop)
	if err != nil {
		return true, err
	}
	// If it's a remote node, forward
	if node.Cmp(o.pastry.Self()) != 0 {
		o.fwdBalance(node, msg)
		return true, nil
	}
	// Remove all carrier headers and decrypt
	head := msg.Head.Meta.(*header)
	msg.Head.Meta = head.Meta
	if err := msg.Decrypt(); err != nil {
		return true, err
	}
	// Deliver to the application on the specific topic
	o.app.HandleBalance(head.Sender, topName, msg)
	return true, nil
}

// Handles the receiving of a direct message and delivers the contents upstream.
func (o *Overlay) handleDirect(msg *proto.Message) error {
	// Remove all scribe headers and decrypt contents
	head := msg.Head.Meta.(*header)
	msg.Head.Meta = head.Meta
	if err := msg.Decrypt(); err != nil {
		return err
	}
	// Deliver the message upstream
	o.app.HandleDirect(head.Sender, msg)
	return nil
}