package jmri.jmrix;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.*;
import javax.swing.SwingUtilities;

import jmri.InstanceManager;
import jmri.ShutDownManager;
import jmri.ShutDownTask;

/**
 * Abstract base for TrafficControllers in a Message/Reply protocol.
 * <p>
 * Two threads are used for the actual communication. The "Transmit" thread
 * handles pushing characters to the port, and also changing the mode. The
 * "Receive" thread converts characters from the input stream into replies.
 * <p>
 * The constructor registers a shutdown task to
 * trigger the necessary cleanup code
 * <p>
 * The internal state machine handles changes of mode, automatic retry of
 * certain messages, time outs, and sending poll messages when otherwise idle.
 * <p>
 * "Mode" refers to the state of the command station communications. "Normal"
 * and "Programming" are the two modes, used if the command station requires
 * messages to go back and forth between them. <br>
 *
 * <img src="doc-files/AbstractMRTrafficController-StateDiagram.png" alt="UML State diagram">
 *
 * <p>
 * The key methods for the basic operation are:
 * <ul>
 * <li>If needed for formatting outbound messages, {@link #addHeaderToOutput(byte[], AbstractMRMessage)} and {@link #addTrailerToOutput(byte[], int, AbstractMRMessage)}
 * <li> {@link #newReply()} creates an empty reply message (of the proper concrete type) to fill with incoming data
 * <li>The {@link #endOfMessage(AbstractMRReply) } method is used to parse incoming messages. If it needs
 *      information on e.g. the last message sent, that can be stored in member variables
 *      by {@link #forwardToPort(AbstractMRMessage, AbstractMRListener)}.
 *  <li>{@link #forwardMessage(AbstractMRListener, AbstractMRMessage)} and {@link #forwardReply(AbstractMRListener, AbstractMRReply) } handle forwarding of specific types of objects
 * </ul>
 * <p>
 * If your command station requires messages to go in and out of
 * "programming mode", those should be provided by
 * {@link #enterProgMode()} and {@link #enterNormalMode()}.
 * <p>
 * If you want to poll for information when the line is otherwise idle,
 * implement {@link #pollMessage()} and {@link #pollReplyHandler()}.
 *
 * @author Bob Jacobsen Copyright (C) 2003
 * @author Paul Bender Copyright (C) 2004-2010
 */

/*
@startuml jmri/jmrix/doc-files/AbstractMRTrafficController-StateDiagram.png

    [*] --> IDLESTATE
    IDLESTATE --> NOTIFIEDSTATE : sendMessage()
    NOTIFIEDSTATE --> IDLESTATE : queue empty

    NOTIFIEDSTATE --> WAITMSGREPLYSTATE : transmitLoop()\nwake, send message

    WAITMSGREPLYSTATE --> WAITREPLYINPROGMODESTATE : transmitLoop()\nnot in PROGRAMINGMODE,\nmsg for PROGRAMINGMODE
    WAITMSGREPLYSTATE --> WAITREPLYINNORMMODESTATE : transmitLoop()\nnot in NORMALMODE,\nmsg for NORMALMODE

    WAITMSGREPLYSTATE --> NOTIFIEDSTATE : handleOneIncomingReply()

    WAITREPLYINPROGMODESTATE --> OKSENDMSGSTATE : handleOneIncomingReply()\nentered PROGRAMINGMODE
    WAITREPLYINNORMMODESTATE --> OKSENDMSGSTATE : handleOneIncomingReply()\nentered NORMALMODE
    OKSENDMSGSTATE --> WAITMSGREPLYSTATE : send original pended message

    IDLESTATE --> POLLSTATE : transmitLoop()\nno work
    POLLSTATE --> WAITMSGREPLYSTATE : transmitLoop()\npoll msg exists, send it
    POLLSTATE --> IDLESTATE : transmitLoop()\nno poll msg to send

    WAITMSGREPLYSTATE --> AUTORETRYSTATE : handleOneIncomingReply()\nwhen tagged as error reply
    AUTORETRYSTATE --> IDLESTATE : to drive a repeat of a message

NOTIFIEDSTATE : Transmit thread wakes up and processes
POLLSTATE : Transient while deciding to send poll
OKSENDMSGSTATE : Transient while deciding to send\noriginal message after mode change
AUTORETRYSTATE : Transient while deciding to resend auto-retry message
WAITREPLYINPROGMODESTATE : Sent request to go to programming mode,\nwaiting reply
WAITREPLYINNORMMODESTATE : Sent request to go to normal mode,\nwaiting reply
WAITMSGREPLYSTATE : Have sent message, waiting a\nresponse from layout

Note left of AUTORETRYSTATE : This state handles timeout of\nmessages marked for autoretry
Note left of OKSENDMSGSTATE : Transient internal state\nwill transition when going back\nto send message that\nwas deferred for mode change.

@enduml
 */

public abstract class AbstractMRTrafficController {

    private final Runnable shutDownTask = this::terminate; // retain for possible removal.

    /**
     * Create a new unnamed MRTrafficController.
     */
    public AbstractMRTrafficController() {
        log.debug("Creating AbstractMRTrafficController instance");
        mCurrentMode = NORMALMODE;
        mCurrentState = IDLESTATE;
        allowUnexpectedReply = false;


        // We use a shutdown task here to make sure the connection is left
        // in a clean state prior to exiting.  This is required on systems
        // which have a service mode to ensure we don't leave the system
        // in an unusable state. Once the shutdown task executes, the connection
        // must be considered permanently closed.

        InstanceManager.getDefault(ShutDownManager.class).register(shutDownTask);
    }

    private boolean synchronizeRx = true;

    protected void setSynchronizeRx(boolean val) {
        synchronizeRx = val;
    }

    protected boolean getSynchronizeRx() {
        return synchronizeRx;
    }

    // The methods to implement the abstract Interface

    protected final Vector<AbstractMRListener> cmdListeners = new Vector<>();

    protected synchronized void addListener(AbstractMRListener l) {
        // add only if not already registered
        if (l == null) {
            throw new NullPointerException();
        }
        if (!cmdListeners.contains(l)) {
            cmdListeners.addElement(l);
        }
    }

    protected synchronized void removeListener(AbstractMRListener l) {
        if (cmdListeners.contains(l)) {
            cmdListeners.removeElement(l);
        }
    }

    /**
     * Forward a Message to registered listeners.
     *
     * @param m     Message to be forwarded intact
     * @param notMe One (optional) listener to be skipped, usually because it's
     *              the originating object.
     */
    @SuppressWarnings("unchecked")
    protected void notifyMessage(AbstractMRMessage m, AbstractMRListener notMe) {
        // make a copy of the listener vector to synchronized not needed for transmit
        Vector<AbstractMRListener> v;
        synchronized (this) {
            // FIXME: unnecessary synchronized; the Vector IS already thread-safe.
            v = (Vector<AbstractMRListener>) cmdListeners.clone();
        }
        // forward to all listeners
        int cnt = v.size();
        for (int i = 0; i < cnt; i++) {
            AbstractMRListener client = v.elementAt(i);
            if (notMe != client) {
                log.debug("notify message, client: {}", client);
                try {
                    forwardMessage(client, m);
                } catch (RuntimeException e) {
                    log.warn("notify: During message dispatch to {}", client, e);
                }
            }
        }
    }

    /**
     * Implement this to forward a specific message type to a protocol-specific
     * listener interface.
     * This puts the casting into the concrete class.
     * @param client abstract listener.
     * @param m message to forward.
     */
    protected abstract void forwardMessage(AbstractMRListener client, AbstractMRMessage m);

    /**
     * Invoked if it's appropriate to do low-priority polling of the command
     * station, this should return the next message to send, or null if the
     * TrafficController should just sleep.
     * @return Formatted poll message
     */
    protected abstract AbstractMRMessage pollMessage();

    protected abstract AbstractMRListener pollReplyHandler();

    protected AbstractMRListener mLastSender = null;

    protected volatile int mCurrentMode;
    public static final int NORMALMODE = 1;
    public static final int PROGRAMINGMODE = 4;

    /**
     * Set the system to programming mode.
     * @see #enterNormalMode()
     *
     * @return any message that needs to be returned to the Command Station
     * to change modes. If no message is needed, returns null.
     */
    protected abstract AbstractMRMessage enterProgMode();

    /**
     * Sets the system to normal mode during programming while in IDLESTATE.
     * If {@link #programmerIdle()} returns true, enterNormalMode() is
     * called after a timeout.
     * @see #enterProgMode()
     *
     * @return any message that needs to be returned to the Command Station
     * to change modes. If no message is needed, returns null.
     */
    protected abstract AbstractMRMessage enterNormalMode();

    /**
     * Check if the programmer is idle.
     * Override in the system specific code if necessary (see notes for
     * {@link #enterNormalMode()}.
     *
     * @return true if not busy programming
     */
    protected boolean programmerIdle() {
        return true;
    }

    /**
     * Get the delay (wait time) after enabling the programming track.
     * Override in subclass to add a longer delay.
     *
     * @return 0 as default delay
     */
    protected int enterProgModeDelayTime() {
        return 0;
    }

    protected volatile int mCurrentState;
    public static final int IDLESTATE = 10;        // nothing happened
    public static final int NOTIFIEDSTATE = 15;    // xmt notified, will next wake
    public static final int WAITMSGREPLYSTATE = 25;  // xmt has sent, await reply to message
    public static final int WAITREPLYINPROGMODESTATE = 30;  // xmt has done mode change, await reply
    public static final int WAITREPLYINNORMMODESTATE = 35;  // xmt has done mode change, await reply
    public static final int OKSENDMSGSTATE = 40;        // mode change reply here, send original msg
    public static final int AUTORETRYSTATE = 45;        // received message where automatic recovery may occur with a retransmission, re-send original msg
    public static final int POLLSTATE = 50;   // Send program mode or poll message

    protected boolean allowUnexpectedReply;

    /**
     * Set whether the command station may send messages without a request
     * sent to it.
     *
     * @param expected true to allow messages without a prior request
     */
    protected void setAllowUnexpectedReply(boolean expected) {
        allowUnexpectedReply = expected;
    }

    /**
     * Forward a "Reply" from layout to registered listeners.
     *
     * @param r    Reply to be forwarded intact
     * @param dest One (optional) listener to be skipped, usually because it's
     *             the originating object.
     */
    @SuppressWarnings("unchecked")
    protected void notifyReply(AbstractMRReply r, AbstractMRListener dest) {
        // make a copy of the listener vector to synchronized (not needed for transmit?)
        Vector<AbstractMRListener> v;
        synchronized (this) {
            // FIXME: unnecessary synchronized; the Vector IS already thread-safe.
            v = (Vector<AbstractMRListener>) cmdListeners.clone();
        }
        // forward to all listeners
        int cnt = v.size();
        for (int i = 0; i < cnt; i++) {
            AbstractMRListener client = v.elementAt(i);
            log.debug("notify reply, client: {}", client);
            try {
                //skip dest for now, we'll send the message to there last.
                if (dest != client) {
                    forwardReply(client, r);
                }
            } catch (RuntimeException e) {
                log.warn("notify: During reply dispatch to {}", client, e);
            }
        }

        // forward to the last listener who sent a message
        // this is done _second_ so monitoring can have already stored the reply
        // before a response is sent
        if (dest != null) {
            log.debug("notify reply, dest: {}", dest);
            forwardReply(dest, r);
        }
    }

    protected abstract void forwardReply(AbstractMRListener client, AbstractMRReply m);

    /**
     * Messages to be transmitted.
     */
    protected LinkedList<AbstractMRMessage> msgQueue = new LinkedList<>();
    protected LinkedList<AbstractMRListener> listenerQueue = new LinkedList<>();

    /**
     * Forward message to the port. Messages are queued and then the
     * transmission thread is notified.
     * @see #forwardToPort(AbstractMRMessage, AbstractMRListener)
     *
     * @param m the message to send
     * @param reply the Listener sending the message, often provided as 'this'
     */
    protected synchronized void sendMessage(AbstractMRMessage m, AbstractMRListener reply) {
        msgQueue.addLast(m);
        listenerQueue.addLast(reply);
        synchronized (xmtRunnable) {
            if (mCurrentState == IDLESTATE) {
                mCurrentState = NOTIFIEDSTATE;
                xmtRunnable.notify();
            }
        }
        if (m != null) {
            log.debug("just notified transmit thread with message {}", m);
        }
    }

    /**
     * Permanent loop for the transmit thread.
     */
    protected void transmitLoop() {
        log.debug("transmitLoop starts in {}", this);

        // loop forever
        while (!connectionError && !threadStopRequest) {
            AbstractMRMessage m = null;
            AbstractMRListener l = null;
            // check for something to do
            synchronized (this) {
                if (!msgQueue.isEmpty()) {
                    // yes, something to do
                    m = msgQueue.getFirst();
                    msgQueue.removeFirst();
                    l = listenerQueue.getFirst();
                    listenerQueue.removeFirst();
                    mCurrentState = WAITMSGREPLYSTATE;
                    log.debug("transmit loop has something to do: {}", m);
                }  // release lock here to proceed in parallel
            }
            // if a message has been extracted, process it
            if (m != null) {
                // check for need to change mode
                log.debug("Start msg, state = {}", mCurrentMode);
                if (m.getNeededMode() != mCurrentMode) {
                    AbstractMRMessage modeMsg;
                    if (m.getNeededMode() == PROGRAMINGMODE) {
                        // change state to programming mode and send message
                        modeMsg = enterProgMode();
                        if (modeMsg != null) {
                            mCurrentState = WAITREPLYINPROGMODESTATE;
                            log.debug("Enter Programming Mode");
                            forwardToPort(modeMsg, null);
                            // wait for reply
                            transmitWait(m.getTimeout(), WAITREPLYINPROGMODESTATE, "enter programming mode interrupted");
                        }
                    } else {
                        // change state to normal and send message
                        modeMsg = enterNormalMode();
                        if (modeMsg != null) {
                            mCurrentState = WAITREPLYINNORMMODESTATE;
                            log.debug("Enter Normal Mode");
                            forwardToPort(modeMsg, null);
                            // wait for reply
                            transmitWait(m.getTimeout(), WAITREPLYINNORMMODESTATE, "enter normal mode interrupted");
                        }
                    }
                    if (modeMsg != null) {
                        checkReplyInDispatch();
                        if (mCurrentState != OKSENDMSGSTATE) {
                            handleTimeout(modeMsg, l);
                        }
                        mCurrentState = WAITMSGREPLYSTATE;
                    } else {
                        // no mode message required, but the message
                        // needs a different mode
                        log.debug("Setting mode to: {}", m.getNeededMode());
                        mCurrentMode = m.getNeededMode();
                    }
                }
                forwardToPort(m, l);
                // reply expected?
                if (m.replyExpected()) {
                    log.debug("reply expected is true for message {}",m);
                    // wait for a reply, or eventually timeout
                    transmitWait(m.getTimeout(), WAITMSGREPLYSTATE, "transmitLoop interrupted");
                    checkReplyInDispatch();
                    if (mCurrentState == WAITMSGREPLYSTATE) {
                        handleTimeout(m, l);
                    } else if (mCurrentState == AUTORETRYSTATE) {
                        log.info("Message added back to queue: {}", m);
                        msgQueue.addFirst(m);
                        listenerQueue.addFirst(l);
                        synchronized (xmtRunnable) {
                            mCurrentState = IDLESTATE;
                        }
                    } else {
                        resetTimeout(m);
                    }
                } // just continue to the next message from here
            } else {
                // nothing to do
                if (mCurrentState != IDLESTATE) {
                    log.debug("Setting IDLESTATE");
                    log.debug("Current Mode {}", mCurrentMode);
                    mCurrentState = IDLESTATE;
                }
                // wait for something to send
                if (mWaitBeforePoll > waitTimePoll || mCurrentMode == PROGRAMINGMODE) {
                    try {
                        long startTime = Calendar.getInstance().getTimeInMillis();
                        synchronized (xmtRunnable) {
                            xmtRunnable.wait(mWaitBeforePoll);
                        }
                        long endTime = Calendar.getInstance().getTimeInMillis();
                        waitTimePoll = waitTimePoll + endTime - startTime;
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt(); // retain if needed later
                        // end of transmit loop
                        break;
                    }
                }
                // once we decide that mCurrentState is in the IDLESTATE and there's an xmt msg we must guarantee
                // the change of mCurrentState to one of the waiting for reply states.  Therefore we need to synchronize.
                synchronized (this) {
                    if (mCurrentState != NOTIFIEDSTATE && mCurrentState != IDLESTATE) {
                        log.error("left timeout in unexpected state: {}", mCurrentState);
                    }
                    if (mCurrentState == IDLESTATE) {
                        mCurrentState = POLLSTATE; // this prevents other transitions from the IDLESTATE
                    }
                }
                // went around with nothing to do; leave programming state if in it
                if (mCurrentMode == PROGRAMINGMODE) {
                    log.debug("Timeout - in service mode");
                }
                if (mCurrentState == POLLSTATE && mCurrentMode == PROGRAMINGMODE && programmerIdle()) {
                    log.debug("timeout causes leaving programming mode");
                    mCurrentState = WAITREPLYINNORMMODESTATE;
                    AbstractMRMessage msg = enterNormalMode();
                    // if the enterNormalMode() message is null, we
                    // don't want to try to send it to the port.
                    if (msg != null) {
                        forwardToPort(msg, null);
                        // wait for reply
                        transmitWait(msg.getTimeout(), WAITREPLYINNORMMODESTATE, "interrupted while leaving programming mode");
                        checkReplyInDispatch();
                        // exit program mode timeout?
                        if (mCurrentState == WAITREPLYINNORMMODESTATE) {
                            // entering normal mode via timeout
                            handleTimeout(msg, l);
                            mCurrentMode = NORMALMODE;
                        }
                        // and go around again
                    }
                } else if (mCurrentState == POLLSTATE && mCurrentMode == NORMALMODE) {
                    // We may need to poll
                    AbstractMRMessage msg = pollMessage();
                    if (msg != null) {
                        // yes, send that
                        log.debug("Sending poll, wait time {}", waitTimePoll);
                        mCurrentState = WAITMSGREPLYSTATE;
                        forwardToPort(msg, pollReplyHandler());
                        // wait for reply
                        log.debug("Still waiting for reply");
                        transmitWait(msg.getTimeout(), WAITMSGREPLYSTATE, "interrupted while waiting poll reply");
                        checkReplyInDispatch();
                        // and go around again
                        if (mCurrentState == WAITMSGREPLYSTATE) {
                            handleTimeout(msg, l);
                        } else {
                            resetTimeout(msg);
                        }
                    }
                    waitTimePoll = 0;
                }
                // no messages, so back to idle
                if (mCurrentState == POLLSTATE) {
                    mCurrentState = IDLESTATE;
                }
            }
        }
    }   // end of transmit loop; go around again

    protected void transmitWait(int waitTime, int state, String interruptMessage) {
        // wait() can have spurious wakeup!
        // so we protect by making sure the entire timeout time is used
        long currentTime = Calendar.getInstance().getTimeInMillis();
        long endTime = currentTime + waitTime;
        while (endTime > (currentTime = Calendar.getInstance().getTimeInMillis())) {
            long wait = endTime - currentTime;
            try {
                synchronized (xmtRunnable) {
                    // Do not wait if the current state has changed since we
                    // last set it.
                    if (mCurrentState != state) {
                        return;
                    }
                    xmtRunnable.wait(wait); // rcvr normally ends this w state change
                }
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt(); // retain if needed later
                String[] packages = this.getClass().getName().split("\\.");
                String name = (packages.length>=2 ? packages[packages.length-2]+"." :"")
                        +(packages.length>=1 ? packages[packages.length-1] :"");
                if (!threadStopRequest) {
                    log.error("{} in transmitWait(..) of {}", interruptMessage, name);
                } else {
                    log.debug("during shutdown, {}  in transmitWait(..) of {}", interruptMessage, name);
                }
            }
        }
        log.debug("Timeout in transmitWait, mCurrentState: {}", mCurrentState);
    }

    // Dispatch control and timer
    protected boolean replyInDispatch = false;          // true when reply has been received but dispatch not completed
    private int maxDispatchTime = 0;
    private int warningMessageTime = DISPATCH_WARNING_TIME;
    private static final int DISPATCH_WAIT_INTERVAL = 100;
    private static final int DISPATCH_WARNING_TIME = 12000; // report warning when max dispatch time exceeded
    private static final int WARN_NEXT_TIME = 1000;         // report every second

    private void checkReplyInDispatch() {
        int loopCount = 0;
        while (replyInDispatch) {
            try {
                synchronized (xmtRunnable) {
                    xmtRunnable.wait(DISPATCH_WAIT_INTERVAL);
                }
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt(); // retain if needed later
                if (threadStopRequest) return; // don't log an error if closing.
                String[] packages = this.getClass().getName().split("\\.");
                String name = (packages.length>=2 ? packages[packages.length-2]+"." :"")
                        +(packages.length>=1 ? packages[packages.length-1] :"");
                log.error("transmitLoop interrupted in class {}", name);
            }
            loopCount++;
            int currentDispatchTime = loopCount * DISPATCH_WAIT_INTERVAL;
            if (currentDispatchTime > maxDispatchTime) {
                maxDispatchTime = currentDispatchTime;
                if (currentDispatchTime >= warningMessageTime) {
                    warningMessageTime = warningMessageTime + WARN_NEXT_TIME;
                    log.debug("Max dispatch time is now {}", currentDispatchTime);
                }
            }
        }
    }

    /**
     *  Determine if the interface is down.
     *
     *  @return timeoutFlag
     */
    public boolean hasTimeouts() {
        return timeoutFlag;
    }

    private boolean timeoutFlag = false;
    private int timeouts = 0;
    protected boolean flushReceiveChars = false;

    protected void handleTimeout(AbstractMRMessage msg, AbstractMRListener l) {
        //log.debug("Timeout mCurrentState: {}", mCurrentState);
        String[] packages = this.getClass().getName().split("\\.");
        String name = (packages.length>=2 ? packages[packages.length-2]+"." :"")
                +(packages.length>=1 ? packages[packages.length-1] :"");

        log.warn("Timeout on reply to message: {} consecutive timeouts = {} in {}", msg, timeouts, name);
        timeouts++;
        timeoutFlag = true;
        flushReceiveChars = true;
    }

    protected void resetTimeout(AbstractMRMessage msg) {
        if (timeouts > 0) {
            log.debug("Reset timeout after {} timeouts", timeouts);
        }
        timeouts = 0;
        timeoutFlag = false;
    }

    /**
     * Add header to the outgoing byte stream.
     *
     * @param msg the output byte stream
     * @param m Message results
     * @return next location in the stream to fill
     */
    protected int addHeaderToOutput(byte[] msg, AbstractMRMessage m) {
        return 0;
    }

    protected int mWaitBeforePoll = 100;
    protected long waitTimePoll = 0;

    /**
     * Add trailer to the outgoing byte stream.
     *
     * @param msg    the output byte stream
     * @param offset the first byte not yet used
     * @param m   output message to extend
     */
    protected void addTrailerToOutput(byte[] msg, int offset, AbstractMRMessage m) {
        if (!m.isBinary()) {
            msg[offset] = 0x0d;
        }
    }

    /**
     * Determine how many bytes the entire message will take, including
     * space for header and trailer.
     *
     * @param m the message to be sent
     * @return number of bytes
     */
    protected int lengthOfByteStream(AbstractMRMessage m) {
        int len = m.getNumDataElements();
        int cr = 0;
        if (!m.isBinary()) {
            cr = 1;  // space for return char
        }
        return len + cr;
    }

    protected boolean xmtException = false;

    /**
     * Actually transmit the next message to the port.
     * @see #sendMessage(AbstractMRMessage, AbstractMRListener)
     *
     * @param m the message to send
     * @param reply the Listener sending the message, often provided as 'this'
     */
    @SuppressFBWarnings(value = {"TLW_TWO_LOCK_WAIT"},
            justification = "Two locks needed for synchronization here, this is OK")
    protected synchronized void forwardToPort(AbstractMRMessage m, AbstractMRListener reply) {
        log.debug("forwardToPort message: [{}]", m);
        // remember who sent this
        mLastSender = reply;

        // forward the message to the registered recipients,
        // which includes the communications monitor, except the sender.
        // Schedule notification via the Swing event queue to ensure order
        Runnable r = new XmtNotifier(m, mLastSender, this);
        SwingUtilities.invokeLater(r);

        // stream to port in single write, as that's needed by serial
        int byteLength = lengthOfByteStream(m);
        byte[]  msg= new byte[byteLength];
        log.debug("copying message, length = {}", byteLength);
        // add header
        int offset = addHeaderToOutput(msg, m);

        // add data content
        int len = m.getNumDataElements();
        log.debug("copying data to message, length = {}", len);
        if (len > byteLength) { // happens somehow
            log.warn("Invalid message array size {} for {} elements, truncated", byteLength, len);
        }
        for (int i = 0; (i < len && i < byteLength); i++) {
            msg[i + offset] = (byte) m.getElement(i);
        }
        // add trailer
        addTrailerToOutput(msg, len + offset, m);
        // and stream the bytes
        try {
            if (ostream != null) {
                if (log.isDebugEnabled()) {
                    StringBuilder f = new StringBuilder();
                    for (int i = 0; i < msg.length; i++) {
                        f.append(String.format("%02X ",0xFF & msg[i]));
                    }
                    log.debug("formatted message: {}", f.toString() );
                }
                while (m.getRetries() >= 0) {
                    if (portReadyToSend(controller)) {
                        ostream.write(msg);
                        ostream.flush();
                        log.debug("written, msg timeout: {} mSec", m.getTimeout());
                        break;
                    } else if (m.getRetries() >= 0) {
                        log.debug("Retry message: {} attempts remaining: {}", m, m.getRetries());
                        m.setRetries(m.getRetries() - 1);
                        try {
                            synchronized (xmtRunnable) {
                                xmtRunnable.wait(m.getTimeout());
                            }
                        } catch (InterruptedException e) {
                            Thread.currentThread().interrupt(); // retain if needed later
                            log.error("retry wait interrupted");
                        }
                    } else {
                        log.warn("sendMessage: port not ready for data sending: {}", Arrays.toString(msg));
                    }
                }
            } else {  // ostream is null
                // no stream connected
                connectionWarn();
            }
        } catch (IOException | RuntimeException e) {
            // TODO Currently there's no port recovery if an exception occurs
            // must restart JMRI to clear xmtException.
            xmtException = true;
            portWarn(e);
        }
    }

    protected void connectionWarn() {
        log.warn("sendMessage: no connection established for {}", this.getClass().getName(), new Exception());
    }

    protected void portWarn(Exception e) {
        log.warn("sendMessage: Exception: In {} port warn: ", this.getClass().getName(), e);
    }

    protected boolean connectionError = false;

    protected void portWarnTCP(Exception e) {
        log.warn("Exception java net: ", e);
        connectionError = true;
    }
    // methods to connect/disconnect to a source of data in an AbstractPortController

    public AbstractPortController controller = null;

    public boolean status() {
        return (ostream != null && istream != null);
    }

    protected volatile Thread xmtThread = null;
    protected volatile Thread rcvThread = null;

    protected volatile Runnable xmtRunnable = null;

    /**
     * Make connection to an existing PortController object.
     *
     * @param p the PortController
     */
    public void connectPort(AbstractPortController p) {
        rcvException = false;
        connectionError = false;
        xmtException = false;
        threadStopRequest = false;
        try {
            istream = p.getInputStream();
            ostream = p.getOutputStream();
            if (controller != null) {
                log.warn("connectPort: connect called while connected");
            } else {
                log.debug("connectPort invoked");
            }
            controller = p;
            // and start threads
            xmtThread = jmri.util.ThreadingUtil.newThread(
                xmtRunnable = new Runnable() {
                    @Override
                    public void run() {
                        try {
                            transmitLoop();
                        } catch (ThreadDeath td) {
                            if (!threadStopRequest) log.error("Transmit thread terminated prematurely by: {}", td, td);
                            // ThreadDeath must be thrown per Java API Javadocs
                            throw td;
                        } catch (Throwable e) {
                            if (!threadStopRequest) log.error("Transmit thread terminated prematurely by: {}", e, e);
                        }
                }
            });

            String[] packages = this.getClass().getName().split("\\.");
            xmtThread.setName(
                (packages.length>=2 ? packages[packages.length-2]+"." :"")
                +(packages.length>=1 ? packages[packages.length-1] :"")
                +" Transmit thread");

            xmtThread.setDaemon(true);
            xmtThread.setPriority(Thread.MAX_PRIORITY-1);      //bump up the priority
            xmtThread.start();

            rcvThread = jmri.util.ThreadingUtil.newThread(
                new Runnable() {
                    @Override
                    public void run() {
                        receiveLoop();
                    }
                });
            rcvThread.setName(
                (packages.length>=2 ? packages[packages.length-2]+"." :"")
                +(packages.length>=1 ? packages[packages.length-1] :"")
                +" Receive thread");

            rcvThread.setPriority(Thread.MAX_PRIORITY);      //bump up the priority
            rcvThread.setDaemon(true);
            rcvThread.start();

        } catch (RuntimeException e) {
            log.error("Failed to start up communications. Error was: ", e);
            log.debug("Full trace:", e);
        }
    }

    /**
     * Get the port name for this connection from the TrafficController.
     *
     * @return the name of the port
     */
    public String getPortName() {
        return controller.getCurrentPortName();
    }

    /**
     * Break connection to existing PortController object. Once broken, attempts
     * to send via "message" member will fail.
     *
     * @param p the PortController
     */
    public void disconnectPort(AbstractPortController p) {
        istream = null;
        ostream = null;
        if (controller != p) {
            log.warn("disconnectPort: disconnect called from non-connected AbstractPortController");
        }
        controller = null;
        threadStopRequest = true;
    }

    /**
     * Check if PortController object can be sent to.
     *
     * @param p the PortController
     * @return true if ready, false otherwise May throw an Exception.
     */
    public boolean portReadyToSend(AbstractPortController p) {
        if (p != null && !xmtException && !rcvException) {
            return true;
        } else {
            return false;
        }
    }

    // data members to hold the streams
    protected DataInputStream istream = null;
    protected OutputStream ostream = null;

    protected boolean rcvException = false;

    protected int maxRcvExceptionCount = 100;

    /**
     * Handle incoming characters. This is a permanent loop, looking for input
     * messages in character form on the stream connected to the PortController
     * via {@link #connectPort(AbstractPortController)}.
     * <p>
     * Each turn of the loop is the receipt of a single message.
     */
    public void receiveLoop() {
        log.debug("receiveLoop starts in {}", this);
        int errorCount = 0;
        while (errorCount < maxRcvExceptionCount && !threadStopRequest) { // stream close will exit via exception
            try {
                handleOneIncomingReply();
                errorCount = 0;
            } catch (java.io.InterruptedIOException e) {
                // related to InterruptedException, catch first
                break;
            } catch (IOException e) {
                rcvException = true;
                reportReceiveLoopException(e);
                break;
            } catch (RuntimeException e1) {
                log.error("Exception in receive loop: {}", e1.toString(), e1);
                errorCount++;
                if (errorCount == maxRcvExceptionCount) {
                    rcvException = true;
                    reportReceiveLoopException(e1);
                }
            }
        }
        if (!threadStopRequest) { // if e.g. unexpected end
            ConnectionStatus.instance().setConnectionState(controller.getUserName(), controller.getCurrentPortName(), ConnectionStatus.CONNECTION_DOWN);
            log.error("Exit from rcv loop in {}", this.getClass());
            recovery(); // see if you can restart
        }
    }

    /**
     * Disconnect and reset the current PortController.
     * Invoked at abnormal ending of receiveLoop.
     */
    protected final void recovery() {
        AbstractPortController adapter = controller;
        disconnectPort(controller);
        adapter.recover();
    }

    /**
     * Report an error on the receive loop. Separated so tests can suppress, even
     * though message is asynchronous.
     * @param e Exception encountered at lower level to trigger error, or null
     */
    protected void reportReceiveLoopException(Exception e) {
        log.error("run: Exception: {} in {}", e.toString(), this.getClass().toString(), e);
        jmri.jmrix.ConnectionStatus.instance().setConnectionState(controller.getUserName(), controller.getCurrentPortName(), jmri.jmrix.ConnectionStatus.CONNECTION_DOWN);
        if (controller instanceof AbstractNetworkPortController) {
            portWarnTCP(e);
        }
    }

    protected abstract AbstractMRReply newReply();

    protected abstract boolean endOfMessage(AbstractMRReply r);

    /**
     * Dummy routine, to be filled by protocols that have to skip some
     * start-of-message characters.
     * @param istream input source
     * @throws IOException from underlying operations
     */
    protected void waitForStartOfReply(DataInputStream istream) throws IOException {
    }

    /**
     * Read a single byte, protecting against various timeouts, etc.
     * <p>
     * When a port is set to have a receive timeout (via the
     * {@link purejavacomm.SerialPort#enableReceiveTimeout(int)} method), some will return
     * zero bytes or an EOFException at the end of the timeout. In that case, the read
     * should be repeated to get the next real character.
     *
     * @param istream stream to read
     * @return the byte read
     * @throws java.io.IOException if unable to read
     */
    protected byte readByteProtected(DataInputStream istream) throws IOException {
        if (istream == null) {
            throw new IOException("Input Stream NULL when reading");
        }
        while (true) { // loop will repeat until character found
            int nchars;
            nchars = istream.read(rcvBuffer, 0, 1);
            if (nchars == -1) {
                // No more bytes can be read from the channel
                throw new IOException("Connection not terminated normally");
            }
            if (nchars > 0) {
                return rcvBuffer[0];
            }
        }
    }

    // Defined this way to reduce new object creation
    private byte[] rcvBuffer = new byte[1];

    /**
     * Get characters from the input source, and file a message.
     * <p>
     * Returns only when the message is complete.
     * <p>
     * Only used in the Receive thread.
     * <p>
     * Handles timeouts on read by ignoring zero-length reads.
     *
     * @param msg     message to fill
     * @param istream character source.
     * @throws IOException when presented by the input source.
     */
    protected void loadChars(AbstractMRReply msg, DataInputStream istream)
            throws IOException {
        int i;
        for (i = 0; i < msg.maxSize(); i++) {
            byte char1 = readByteProtected(istream);
            log.trace("char: {} i: {}",(char1&0xFF),i);
            // if there was a timeout, flush any char received and start over
            if (flushReceiveChars) {
                log.warn("timeout flushes receive buffer: {}", msg);
                msg.flush();
                i = 0;  // restart
                flushReceiveChars = false;
            }
            if (canReceive()) {
                msg.setElement(i, char1);
                if (endOfMessage(msg)) {
                    break;
                }
            } else {
                i--; // flush char
                log.error("unsolicited character received: {}", Integer.toHexString(char1));
            }
        }
    }

    /**
     * Override in the system specific code if necessary
     *
     * @return true if it is okay to buffer receive characters into a reply
     *         message. When false, discard char received
     */
    protected boolean canReceive() {
        return true;
    }

    private int retransmitCount = 0;

    /**
     * Executes a reply distribution action on the appropriate thread for JMRI.
     * @param r a runnable typically encapsulating a MRReply and the iteration code needed to
     *          send it to all the listeners.
     */
    protected void distributeReply(Runnable r) {
        try {
            if (synchronizeRx) {
                SwingUtilities.invokeAndWait(r);
            } else {
                SwingUtilities.invokeLater(r);
            }
        } catch (InterruptedException ie) {
            if (threadStopRequest) return;
            log.error("Unexpected exception in invokeAndWait: {}{}", ie, ie.toString());
        } catch (java.lang.reflect.InvocationTargetException| RuntimeException e) {
            log.error("Unexpected exception in invokeAndWait: {}{}", e, e.toString());
            return;
        }
        log.debug("dispatch thread invoked");
    }

    /**
     * Handle each reply when complete.
     * <p>
     * (This is public for testing purposes) Runs in the "Receive" thread.
     *
     * @throws java.io.IOException on error.
     */
    public void handleOneIncomingReply() throws IOException {
        // we sit in this until the message is complete, relying on
        // threading to let other stuff happen

        // Create message off the right concrete class
        AbstractMRReply msg = newReply();

        // wait for start if needed
        waitForStartOfReply(istream);

        // message exists, now fill it
        loadChars(msg, istream);

        if (threadStopRequest) return;

        // message is complete, dispatch it !!
        replyInDispatch = true;
        log.debug("dispatch reply of length {} contains \"{}\", state {}", msg.getNumDataElements(), msg, mCurrentState);

        // forward the message to the registered recipients,
        // which includes the communications monitor
        // return a notification via the Swing event queue to ensure proper thread
        Runnable r = new RcvNotifier(msg, mLastSender, this);
        distributeReply(r);

        if (!msg.isUnsolicited()) {
            // effect on transmit:
            switch (mCurrentState) {
                case WAITMSGREPLYSTATE: {
                    // check to see if the response was an error message we want
                    // to automatically handle by re-queueing the last sent
                    // message, otherwise go on to the next message
                    if (msg.isRetransmittableErrorMsg()) {
                        log.error("Automatic Recovery from Error Message: {}.  Retransmitted {} times.", msg, retransmitCount);
                        synchronized (xmtRunnable) {
                            mCurrentState = AUTORETRYSTATE;
                            if (retransmitCount > 0) {
                                try {
                                    xmtRunnable.wait(retransmitCount * 100L);
                                } catch (InterruptedException e) {
                                    Thread.currentThread().interrupt(); // retain if needed later
                                }
                            }
                            replyInDispatch = false;
                            xmtRunnable.notify();
                            retransmitCount++;
                        }
                    } else {
                        // update state, and notify to continue
                        synchronized (xmtRunnable) {
                            mCurrentState = NOTIFIEDSTATE;
                            replyInDispatch = false;
                            xmtRunnable.notify();
                            retransmitCount = 0;
                        }
                    }
                    break;
                }
                case WAITREPLYINPROGMODESTATE: {
                    // entering programming mode
                    mCurrentMode = PROGRAMINGMODE;
                    replyInDispatch = false;

                    // check to see if we need to delay to allow decoders to become
                    // responsive
                    int warmUpDelay = enterProgModeDelayTime();
                    if (warmUpDelay != 0) {
                        try {
                            synchronized (xmtRunnable) {
                                xmtRunnable.wait(warmUpDelay);
                            }
                        } catch (InterruptedException e) {
                            Thread.currentThread().interrupt(); // retain if needed later
                        }
                    }
                    // update state, and notify to continue
                    synchronized (xmtRunnable) {
                        mCurrentState = OKSENDMSGSTATE;
                        xmtRunnable.notify();
                    }
                    break;
                }
                case WAITREPLYINNORMMODESTATE: {
                    // entering normal mode
                    mCurrentMode = NORMALMODE;
                    replyInDispatch = false;
                    // update state, and notify to continue
                    synchronized (xmtRunnable) {
                        mCurrentState = OKSENDMSGSTATE;
                        xmtRunnable.notify();
                    }
                    break;
                }
                default: {
                    replyInDispatch = false;
                    if (allowUnexpectedReply) {
                        log.debug("Allowed unexpected reply received in state: {} was {}", mCurrentState, msg);
                        synchronized (xmtRunnable) {
                            // The transmit thread sometimes gets stuck
                            // when unexpected replies are received.  Notify
                            // it to clear the block without a timeout.
                            // (do not change the current state)
                            //if(mCurrentState!=IDLESTATE)
                            xmtRunnable.notify();
                        }
                    } else {
                        unexpectedReplyStateError(mCurrentState, msg.toString());
                    }
                }
            }
            // Unsolicited message
        } else {
            log.debug("Unsolicited Message Received {}", msg);

            replyInDispatch = false;
        }
    }

    /**
     * Log an error message for a message received in an unexpected state.
     * @param State message state.
     * @param msgString message string.
     */
    protected void unexpectedReplyStateError(int State, String msgString) {
       String[] packages = this.getClass().getName().split("\\.");
       String name = (packages.length>=2 ? packages[packages.length-2]+"." :"")
                     +(packages.length>=1 ? packages[packages.length-1] :"");
       log.error("reply complete in unexpected state: {} was {} in class {}", State, msgString, name);
    }

    /**
     * for testing purposes, let us be able to find out
     * what the last sender was.
     * @return last sender, mLastSender.
     */
    public AbstractMRListener getLastSender() {
        return mLastSender;
    }

    protected void terminate() {
        log.debug("Cleanup Starts");
        if (ostream == null) {
            return;    // no connection established
        }
        AbstractMRMessage modeMsg = enterNormalMode();
        if (modeMsg != null) {
            modeMsg.setRetries(100); // set the number of retries
            // high, just in case the interface
            // is busy when we try to send
            forwardToPort(modeMsg, null);
            // wait for reply
            try {
                if (xmtRunnable != null) {
                    synchronized (xmtRunnable) {
                        xmtRunnable.wait(modeMsg.getTimeout());
                    }
                }
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt(); // retain if needed later
                log.error("transmit interrupted");
            }
        }
    }

    /**
     * Internal class to remember the Reply object and destination listener with
     * a reply is received.
     */
    protected static class RcvNotifier implements Runnable {

        AbstractMRReply mMsg;
        AbstractMRListener mDest;
        AbstractMRTrafficController mTc;

        public RcvNotifier(AbstractMRReply pMsg, AbstractMRListener pDest,
                AbstractMRTrafficController pTc) {
            mMsg = pMsg;
            mDest = pDest;
            mTc = pTc;
        }

        @Override
        public void run() {
            log.debug("Delayed rcv notify starts");
            mTc.notifyReply(mMsg, mDest);
        }
    } // end RcvNotifier

    // allow creation of object outside package
    protected RcvNotifier newRcvNotifier(AbstractMRReply pMsg, AbstractMRListener pDest,
            AbstractMRTrafficController pTc) {
        return new RcvNotifier(pMsg, pDest, pTc);
    }

    /**
     * Internal class to remember the Message object and destination listener
     * when a message is queued for notification.
     */
    protected static class XmtNotifier implements Runnable {

        AbstractMRMessage mMsg;
        AbstractMRListener mDest;
        AbstractMRTrafficController mTc;

        public XmtNotifier(AbstractMRMessage pMsg, AbstractMRListener pDest,
                AbstractMRTrafficController pTc) {
            mMsg = pMsg;
            mDest = pDest;
            mTc = pTc;
        }

        @Override
        public void run() {
            log.debug("Delayed xmt notify starts");
            mTc.notifyMessage(mMsg, mDest);
        }
    }  // end XmtNotifier

    /**
     * Terminate the receive and transmit threads.
     * <p>
     * This is intended to be used only by testing subclasses.
     */
    public void terminateThreads() {
        threadStopRequest = true;
        if (xmtThread != null) {
            xmtThread.interrupt();
            try {
                xmtThread.join();
            } catch (InterruptedException ie){
                // interrupted during cleanup.
            }
        }

        if (rcvThread != null) {
            rcvThread.interrupt();
            try {
                rcvThread.join();
            } catch (InterruptedException ie){
                // interrupted during cleanup.
            }
        }
        // we also need to remove the shutdown task.
        InstanceManager.getDefault(ShutDownManager.class).deregister(shutDownTask);
    }

    /**
     * Flag that threads should terminate as soon as they can.
     */
    protected volatile boolean threadStopRequest = false;

    private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(AbstractMRTrafficController.class);

}