func (mon *SlaveMonitor) slaveDidBeginRegistration(fd int) {
	// Having just started the process, we expect an IO, which we convert to a UNIX domain socket
	fileName := strconv.Itoa(rand.Int())
	slaveFile := os.NewFile(uintptr(fd), fileName)
	slaveUsock, err := unixsocket.NewFromFile(slaveFile)
	if err != nil {
		slog.Error(err)
	}

	// We now expect the slave to use this fd they send us to send a Pid&Identifier Message
	msg, err := slaveUsock.ReadMessage()
	if err != nil {
		slog.Error(err)
	}
	pid, identifier, err := messages.ParsePidMessage(msg)

	// And the last step before executing its action, the slave sends us a pipe it will later use to
	// send us all the features it's loaded.
	featurePipeFd, err := slaveUsock.ReadFD()
	if err != nil {
		slog.Error(err)
	}

	slaveNode := mon.tree.FindSlaveByName(identifier)
	if slaveNode == nil {
		Error("slavemonitor.go:slaveDidBeginRegistration:Unknown identifier:" + identifier)
	}

	slaveNode.SlaveWasInitialized(pid, slaveUsock, featurePipeFd)
}

func (mon *SlaveMonitor) slaveDidBeginRegistration(fd int) {
	// Having just started the process, we expect an IO, which we convert to a UNIX domain socket
	fileName := strconv.Itoa(rand.Int())
	slaveFile := unixsocket.FdToFile(fd, fileName)
	slaveUsock, err := unixsocket.NewUsockFromFile(slaveFile)
	if err != nil {
		slog.Error(err)
	}
	if err = slaveUsock.Conn.SetReadBuffer(1024); err != nil {
		slog.Error(err)
	}
	if err = slaveUsock.Conn.SetWriteBuffer(1024); err != nil {
		slog.Error(err)
	}

	// We now expect the slave to use this fd they send us to send a Pid&Identifier Message
	msg, err := slaveUsock.ReadMessage()
	if err != nil {
		slog.Error(err)
	}
	pid, identifier, err := ParsePidMessage(msg)

	slaveNode := mon.tree.FindSlaveByName(identifier)
	if slaveNode == nil {
		Error("slavemonitor.go:slaveDidBeginRegistration:Unknown identifier:" + identifier)
	}

	slaveNode.SlaveWasInitialized(pid, slaveUsock)
}

// In "SBooting", we have a pid and socket to the process we will use,
// but it has not yet finished initializing (generally, running the code
// specific to this slave. When we receive a message about the success or
// failure of this operation, we transition to either crashed or ready.
func (s *SlaveNode) doBootingState() string { // -> {SCrashed, SReady}
	// The slave will execute its action and respond with a status...
	// Note we don't hold the mutex while waiting for the action to execute.
	msg, err := s.socket.ReadMessage()
	if err != nil {
		slog.Error(err)
	}
	s.trace("in booting state")
	s.L.Lock()
	defer s.L.Unlock()

	msg, err = messages.ParseActionResponseMessage(msg)
	if err != nil {
		slog.ErrorString("[" + s.Name + "] " + err.Error())
	}
	if msg == "OK" {
		return SReady
	}

	// Drain the process's feature messages, if we have any, so
	// that reloads happen when any load-time problems get fixed:
	s.L.Unlock()
	s.handleMessages()
	s.L.Lock()

	// Clean up:
	if s.Pid > 0 {
		syscall.Kill(s.Pid, syscall.SIGKILL)
	}
	s.wipe()
	s.Error = msg
	return SCrashed
}

// In "SBooting", we have a pid and socket to the process we will use,
// but it has not yet finished initializing (generally, running the code
// specific to this slave. When we receive a message about the success or
// failure of this operation, we transition to either crashed or ready.
func (s *SlaveNode) doBootingState() string { // -> {SCrashed, SReady}
	// The slave will execute its action and respond with a status...
	// Note we don't hold the mutex while waiting for the action to execute.
	msg, err := s.socket.ReadMessage()
	if err != nil {
		slog.Error(err)
	}

	s.L.Lock()
	defer s.L.Unlock()

	msg, err = messages.ParseActionResponseMessage(msg)
	if err != nil {
		slog.ErrorString("[" + s.Name + "] " + err.Error())
	}
	if msg == "OK" {
		return SReady
	}

	if s.Pid > 0 {
		syscall.Kill(s.Pid, syscall.SIGKILL)
	}
	s.wipe()
	s.Error = msg
	return SCrashed
}

func (s *SlaveNode) handleFeatureMessage(msg string) {
	if file, err := ParseFeatureMessage(msg); err != nil {
		slog.Error(err)
	} else {
		s.Features[file] = true
		AddFile(file)
	}
}

// This should only be called while holding a lock on s.L.
// This unfortunately holds the mutex for a little while, and if the
// command dies super early, the entire slave pretty well deadlocks.
// TODO: review this.
func (s *SlaveNode) bootCommand(request *CommandRequest) {
	identifier := request.Name
	// TODO: If crashed, do something different...
	msg := messages.CreateSpawnCommandMessage(identifier)
	_, err := s.socket.WriteMessage(msg)
	if err != nil {
		slog.Error(err)
		return
	}
	commandFD, err := s.socket.ReadFD()
	if err != nil {
		fmt.Println(s.socket)
		slog.Error(err)
		return
	}
	fileName := strconv.Itoa(rand.Int())
	commandFile := unixsocket.FdToFile(commandFD, fileName)
	request.Retchan <- commandFile
}

func (s *SlaveNode) bootSlave(slave *SlaveNode) {
	s.L.Lock()
	defer s.L.Unlock()

	s.trace("now sending slave boot request for %s", slave.Name)

	msg := messages.CreateSpawnSlaveMessage(slave.Name)
	_, err := s.socket.WriteMessage(msg)
	if err != nil {
		slog.Error(err)
	}
}

// This should only be called while holding a lock on s.L.
// This unfortunately holds the mutex for a little while, and if the
// command dies super early, the entire slave pretty well deadlocks.
// TODO: review this.
func (s *SlaveNode) bootCommand(request *CommandRequest) {
	if s.State == SCrashed {
		request.Retchan <- &CommandReply{SCrashed, nil}
		return
	}
	identifier := request.Name
	msg := messages.CreateSpawnCommandMessage(identifier)
	_, err := s.socket.WriteMessage(msg)
	if err != nil {
		slog.Error(err)
		return
	}
	commandFD, err := s.socket.ReadFD()
	if err != nil {
		fmt.Println(s.socket)
		slog.Error(err)
		return
	}
	fileName := strconv.Itoa(rand.Int())
	commandFile := unixsocket.FdToFile(commandFD, fileName)
	request.Retchan <- &CommandReply{s.State, commandFile}
}

// This should only be called while holding a lock on s.L.
func (s *SlaveNode) bootSlave(slave *SlaveNode) {
	if s.Error != "" {
		slave.L.Lock()
		slave.Error = s.Error
		slave.event <- true
		slave.L.Unlock()
		return
	}
	msg := messages.CreateSpawnSlaveMessage(slave.Name)
	_, err := s.socket.WriteMessage(msg)
	if err != nil {
		slog.Error(err)
	}
}

// This unfortunately holds the mutex for a little while, and if the
// command dies super early, the entire slave pretty well deadlocks.
// TODO: review this.
func (s *SlaveNode) bootCommand(request *CommandRequest) {
	s.L.Lock()
	defer s.L.Unlock()

	s.trace("now sending command boot request %v", request)

	identifier := request.Name
	msg := messages.CreateSpawnCommandMessage(identifier)
	_, err := s.socket.WriteMessage(msg)
	if err != nil {
		slog.Error(err)
		return
	}
	commandFD, err := s.socket.ReadFD()
	if err != nil {
		fmt.Println(s.socket)
		slog.Error(err)
		return
	}
	fileName := strconv.Itoa(rand.Int())
	commandFile := os.NewFile(uintptr(commandFD), fileName)
	request.Retchan <- &CommandReply{s.state, commandFile}
}

func StartSlaveMonitor(tree *ProcessTree, fileChanges <-chan []string, done chan bool) chan bool {
	quit := make(chan bool)
	go func() {
		localMasterFile, remoteMasterFile, err := unixsocket.Socketpair(syscall.SOCK_DGRAM)
		if err != nil {
			Error("Couldn't create socketpair")
		}

		monitor := &SlaveMonitor{tree, remoteMasterFile}
		defer monitor.cleanupChildren()

		localMasterSocket, err := unixsocket.NewFromFile(localMasterFile)
		if err != nil {
			Error("Couldn't Open UNIXSocket")
		}

		// We just want this unix socket to be a channel so we can select on it...
		registeringFds := make(chan int, 3)
		go func() {
			for {
				if fd, err := localMasterSocket.ReadFD(); err != nil {
					slog.Error(err)
				} else {
					registeringFds <- fd
				}
			}
		}()

		for _, slave := range monitor.tree.SlavesByName {
			go slave.Run(monitor)
		}

		for {
			select {
			case <-quit:
				done <- true
				return
			case fd := <-registeringFds:
				go monitor.slaveDidBeginRegistration(fd)
			case files := <-fileChanges:
				if len(files) > 0 {
					tree.RestartNodesWithFeatures(files)
				}
			}
		}
	}()
	return quit
}

// see docs/client_master_handshake.md
func handleClientConnection(tree *processtree.ProcessTree, usock *unixsocket.Usock) {
	defer usock.Close()
	// we have established first contact to the client.

	command, clientPid, argCount, argFD, err := receiveCommandArgumentsAndPid(usock, nil)
	commandNode, slaveNode, err := findCommandAndSlaveNodes(tree, command, err)
	if err != nil {
		// connection was established, no data was sent. Ignore.
		return
	}
	command = commandNode.Name // resolve aliases

	clientFile, err := receiveTTY(usock, err)
	defer clientFile.Close()

	if err == nil && slaveNode.Error != "" {
		writeStacktrace(usock, slaveNode, clientFile)
		return
	}

	commandUsock, err := bootNewCommand(slaveNode, command, err)
	if err != nil {
		// If a client connects while the command is just
		// booting up, it actually makes it here - still
		// expects a backtrace, of course.
		writeStacktrace(usock, slaveNode, clientFile)
		return
	}
	defer commandUsock.Close()

	err = sendClientPidAndArgumentsToCommand(commandUsock, clientPid, argCount, argFD, err)

	err = sendTTYToCommand(commandUsock, clientFile, err)

	cmdPid, err := receivePidFromCommand(commandUsock, err)

	err = sendCommandPidToClient(usock, cmdPid, err)

	exitStatus, err := receiveExitStatus(commandUsock, err)

	err = sendExitStatus(usock, exitStatus, err)

	if err != nil {
		slog.Error(err)
	}
	// Done! Hooray!
}

// see docs/client_master_handshake.md
func handleClientConnection(tree *processtree.ProcessTree, usock *unixsocket.Usock) {
	defer usock.Close()
	// we have established first contact to the client.

	command, clientPid, arguments, err := receiveCommandArgumentsAndPid(usock, nil)
	commandNode, slaveNode, err := findCommandAndSlaveNodes(tree, command, err)
	if err != nil {
		// connection was established, no data was sent. Ignore.
		return
	}
	command = commandNode.Name // resolve aliases

	clientFile, err := receiveTTY(usock, err)
	defer clientFile.Close()

	if err == nil && slaveNode.Error != "" {
		// we can skip steps 3-5 as they deal with the command process we're not spawning.
		// Write a fake pid (step 6)
		usock.WriteMessage("0")
		// Write the error message to the terminal
		clientFile.Write([]byte(slaveNode.Error))
		// Skip step 7, and write an exit code to the client (step 8)
		usock.WriteMessage("1")
		return
	}

	commandUsock, err := bootNewCommand(slaveNode, command, err)
	defer commandUsock.Close()

	err = sendClientPidAndArgumentsToCommand(commandUsock, clientPid, arguments, err)

	err = sendTTYToCommand(commandUsock, clientFile, err)

	cmdPid, err := receivePidFromCommand(commandUsock, err)

	err = sendCommandPidToClient(usock, cmdPid, err)

	exitStatus, err := receiveExitStatus(commandUsock, err)

	err = sendExitStatus(usock, exitStatus, err)

	if err != nil {
		slog.Error(err)
	}
	// Done! Hooray!
}

func Start(tree *processtree.ProcessTree, done chan bool) chan bool {
	quit := make(chan bool)
	go func() {
		theChart = &StatusChart{}
		theChart.RootSlave = tree.Root
		theChart.numberOfSlaves = len(tree.SlavesByName)
		theChart.Commands = tree.Commands
		theChart.update = make(chan bool, 10)
		theChart.directLogger = slog.NewShinyLogger(os.Stdout, os.Stderr)

		scw := &StringChannelWriter{make(chan string, 10)}
		slog.DefaultLogger = slog.NewShinyLogger(scw, scw)

		termios, err := ttyutils.NoEcho(uintptr(os.Stdout.Fd()))
		if err != nil {
			slog.Error(err)
		}

		ticker := time.Tick(1000 * time.Millisecond)
		for {
			select {
			case <-quit:
				ttyutils.RestoreTerminalState(uintptr(os.Stdout.Fd()), termios)
				done <- true
				return
			case <-ticker:
				theChart.draw()
			case output := <-scw.Notif:
				theChart.L.Lock()
				if theChart.drawnInitial {
					print(output)
				}
				theChart.extraOutput += output
				theChart.L.Unlock()
				theChart.draw()
			case <-tree.StateChanged:
				theChart.draw()
			case <-theChart.update:
				theChart.draw()
			}
		}
	}()
	return quit
}

func (s *StatusChart) lengthOfOutput() int {
	ts, err := ttyutils.Winsize(os.Stdout)
	if err != nil {
		slog.Error(err)
	}
	width := int(ts.Columns)

	lines := strings.Split(s.extraOutput, "\n")

	numLines := 0
	for _, line := range lines {
		n := (len(line) + width - 1) / width
		if n == 0 {
			n = 1
		}
		numLines += n
	}

	return numLines - 1
}

func StartSlaveMonitor(tree *ProcessTree, quit chan bool) {
	localMasterFile, remoteMasterFile, err := unixsocket.Socketpair(syscall.SOCK_DGRAM)
	if err != nil {
		Error("Couldn't create socketpair")
	}

	monitor := &SlaveMonitor{tree, remoteMasterFile}

	localMasterSocket, err := unixsocket.NewUsockFromFile(localMasterFile)
	if err != nil {
		Error("Couldn't Open UNIXSocket")
	}

	// We just want this unix socket to be a channel so we can select on it...
	registeringFds := make(chan int, 3)
	go func() {
		for {
			fd, err := localMasterSocket.ReadFD()
			if err != nil {
				slog.Error(err)
			}
			registeringFds <- fd
		}
	}()

	for _, slave := range monitor.tree.SlavesByName {
		go slave.Run(monitor)
	}

	for {
		select {
		case <-quit:
			monitor.cleanupChildren()
			quit <- true
			return
		case fd := <-registeringFds:
			go monitor.slaveDidBeginRegistration(fd)
		}
	}
}

func startWatchingFile(file string) {
	_, err := watcherIn.Write([]byte(file + "\n"))
	if err != nil {
		slog.Error(err)
	}
}