package jmri.util;

import java.awt.event.ActionEvent;
import java.lang.reflect.InvocationTargetException;

import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.ThreadSafe;

import jmri.JmriException;
import jmri.Reference;

/**
 * Utilities for handling JMRI's threading conventions.
 * <p>
 * For background, see
 * <a href="http://jmri.org/help/en/html/doc/Technical/Threads.shtml">http://jmri.org/help/en/html/doc/Technical/Threads.shtml</a>
 * <p>
 * Note this distinguishes "on layout", for example, Setting a sensor, from "on
 * GUI", for example, manipulating the Swing GUI. That may not be an important
 * distinction now, but it might be later, so we build it into the calls.
 *
 * @author Bob Jacobsen Copyright 2015
 */
@ThreadSafe
public class ThreadingUtil {

    /**
     * Run some layout-specific code before returning.
     * <p>
     * Typical uses:
     * <p> {@code
     * ThreadingUtil.runOnLayout(() -> {
     *     sensor.setState(value);
     * }); 
     * }
     *
     * @param ta What to run, usually as a lambda expression
     */
    static public void runOnLayout(@Nonnull ThreadAction ta) {
        runOnGUI(ta);
    }

    /**
     * Run some layout-specific code before returning.
     * This method catches and rethrows JmriException and RuntimeException.
     * <p>
     * Typical uses:
     * <p> {@code
     * ThreadingUtil.runOnLayout(() -> {
     *     sensor.setState(value);
     * }); 
     * }
     *
     * @param ta What to run, usually as a lambda expression
     * @throws JmriException when an exception occurs
     * @throws RuntimeException when an exception occurs
     */
    static public void runOnLayoutWithJmriException(
            @Nonnull ThreadActionWithJmriException ta)
            throws JmriException, RuntimeException {
        runOnGUIWithJmriException(ta);
    }

    /**
     * Run some layout-specific code at some later point.
     * <p>
     * Please note the operation may have happened before this returns. Or
     * later. No long-term guarantees.
     * <p>
     * Typical uses:
     * <p> {@code
     * ThreadingUtil.runOnLayoutEventually(() -> {
     *     sensor.setState(value);
     * }); 
     * }
     *
     * @param ta What to run, usually as a lambda expression
     */
    static public void runOnLayoutEventually(@Nonnull ThreadAction ta) {
        runOnGUIEventually(ta);
    }

    /**
     * Run some layout-specific code at some later point, at least a known time
     * in the future.
     * <p>
     * There is no long-term guarantee about the accuracy of the interval.
     * <p>
     * Typical uses:
     * <p> {@code
     * ThreadingUtil.runOnLayoutDelayed(() -> {
     *     sensor.setState(value);
     * }, 1000); 
     * }
     *
     * @param ta    what to run, usually as a lambda expression
     * @param delay interval in milliseconds
     * @return reference to timer object handling delay so you can cancel if desired; note that operation may have already taken place.
     */
    @Nonnull 
    static public Timer runOnLayoutDelayed(@Nonnull ThreadAction ta, int delay) {
        return runOnGUIDelayed(ta, delay);
    }

    /**
     * Check if on the layout-operation thread.
     *
     * @return true if on the layout-operation thread
     */
    static public boolean isLayoutThread() {
        return isGUIThread();
    }

    /**
     * Run some GUI-specific code before returning
     * <p>
     * Typical uses:
     * <p> {@code
     * ThreadingUtil.runOnGUI(() -> {
     *     mine.setVisible();
     * });
     * }
     * <p>
     * If an InterruptedException is encountered, it'll be deferred to the 
     * next blocking call via Thread.currentThread().interrupt()
     * 
     * @param ta What to run, usually as a lambda expression
     */
    static public void runOnGUI(@Nonnull ThreadAction ta) {
        if (isGUIThread()) {
            // run now
            ta.run();
        } else {
            // dispatch to Swing
            warnLocks();
            try {
                SwingUtilities.invokeAndWait(ta);
            } catch (InterruptedException e) {
                log.debug("Interrupted while running on GUI thread");
                Thread.currentThread().interrupt();
            } catch (InvocationTargetException e) {
                log.error("Error while on GUI thread", e.getCause());
                log.error("   Came from call to runOnGUI:", e);
                // should have been handled inside the ThreadAction
            }
        }
    }

    /**
     * Run some GUI-specific code before returning.
     * This method catches and rethrows JmriException and RuntimeException.
     * <p>
     * Typical uses:
     * <p> {@code
     * ThreadingUtil.runOnGUI(() -> {
     *     mine.setVisible();
     * });
     * }
     * <p>
     * If an InterruptedException is encountered, it'll be deferred to the 
     * next blocking call via Thread.currentThread().interrupt()
     * 
     * @param ta What to run, usually as a lambda expression
     * @throws JmriException when an exception occurs
     * @throws RuntimeException when an exception occurs
     */
    static public void runOnGUIWithJmriException(
            @Nonnull ThreadActionWithJmriException ta)
            throws JmriException, RuntimeException {
        
        if (isGUIThread()) {
            // run now
            ta.run();
        } else {
            // dispatch to Swing
            warnLocks();
            try {
                Reference<JmriException> jmriException = new Reference<>();
                Reference<RuntimeException> runtimeException = new Reference<>();
                SwingUtilities.invokeAndWait(() -> {
                    try {
                        ta.run();
                    } catch (JmriException e) {
                        jmriException.set(e);
                    } catch (RuntimeException e) {
                        runtimeException.set(e);
                    }
                });
                JmriException je = jmriException.get();
                if (je != null) throw je;
                RuntimeException re = runtimeException.get();
                if (re != null) throw re;
            } catch (InterruptedException e) {
                log.debug("Interrupted while running on GUI thread");
                Thread.currentThread().interrupt();
            } catch (InvocationTargetException e) {
                log.error("Error while on GUI thread", e.getCause());
                log.error("   Came from call to runOnGUI:", e);
                // should have been handled inside the ThreadAction
            }
        }
    }

    /**
     * Run some GUI-specific code before returning a value.
     * <p>
     * Typical uses:
     * <p>
     * {@code
     * Boolean retval = ThreadingUtil.runOnGUIwithReturn(() -> {
     *     return mine.isVisible();
     * });
     * }
     * <p>
     * If an InterruptedException is encountered, it'll be deferred to the next
     * blocking call via Thread.currentThread().interrupt()
     * 
     * @param <E> generic
     * @param ta What to run, usually as a lambda expression
     * @return the value returned by ta
     */
    static public <E> E runOnGUIwithReturn(@Nonnull ReturningThreadAction<E> ta) {
        if (isGUIThread()) {
            // run now
            return ta.run();
        } else {
            warnLocks();
            // dispatch to Swing
            final Reference<E> result = new Reference<>();
            try {
                SwingUtilities.invokeAndWait(() -> {
                    result.set(ta.run());
                });
            } catch (InterruptedException e) {
                log.debug("Interrupted while running on GUI thread");
                Thread.currentThread().interrupt();
            } catch (InvocationTargetException e) {
                log.error("Error while on GUI thread", e.getCause());
                log.error("   Came from call to runOnGUIwithReturn:", e);
                // should have been handled inside the ThreadAction
            }
            return result.get();
        }
    }

    /**
     * Run some GUI-specific code at some later point.
     * <p>
     * If invoked from the GUI thread, the work is guaranteed to happen only
     * after the current routine has returned.
     * <p>
     * Typical uses:
     * <p> {@code 
     * ThreadingUtil.runOnGUIEventually( ()->{ 
     *      mine.setVisible();
     * } ); 
     * }
     *
     * @param ta What to run, usually as a lambda expression
     */
    static public void runOnGUIEventually(@Nonnull ThreadAction ta) {
        // dispatch to Swing
        SwingUtilities.invokeLater(ta);
    }

    /**
     * Run some GUI-specific code at some later point, at least a known time in
     * the future.
     * <p>
     * There is no long-term guarantee about the accuracy of the interval.
     * <p>
     * Typical uses:
     * <p>
     * {@code 
     * ThreadingUtil.runOnGUIDelayed( ()->{ 
     *  mine.setVisible(); 
     * }, 1000);
     * }
     *
     * @param ta    What to run, usually as a lambda expression
     * @param delay interval in milliseconds
     * @return reference to timer object handling delay so you can cancel if desired; note that operation may have already taken place.
     */
    @Nonnull 
    static public Timer runOnGUIDelayed(@Nonnull ThreadAction ta, int delay) {
        // dispatch to Swing via timer
        Timer timer = new Timer(delay, (ActionEvent e) -> {
            ta.run();
        });
        timer.setRepeats(false);
        timer.start();
        return timer;
    }

    /**
     * Check if on the GUI event dispatch thread.
     *
     * @return true if on the event dispatch thread
     */
    static public boolean isGUIThread() {
        return SwingUtilities.isEventDispatchThread();
    }

    /**
     * Create a new thread in the JMRI group
     * @param runner Runnable.
     * @return new Thread.
     */
    static public Thread newThread(Runnable runner) {
        return new Thread(getJmriThreadGroup(), runner);
    }
    
    /**
     * Create a new thread in the JMRI group.
     * @param runner Thread runnable.
     * @param name Thread name.
     * @return New Thread.
     */
    static public Thread newThread(Runnable runner, String name) {
        return new Thread(getJmriThreadGroup(), runner, name);
    }
    
    /**
     * Get the JMRI default thread group.
     * This should be passed to as the first argument to the {@link Thread} 
     * constructor so we can track JMRI-created threads.
     * @return JMRI default thread group.
     */
    static public ThreadGroup getJmriThreadGroup() {
        // we access this dynamically instead of keeping it in a static
        
        ThreadGroup main = Thread.currentThread().getThreadGroup();
        while (main.getParent() != null ) {main = main.getParent(); }        
        ThreadGroup[] list = new ThreadGroup[main.activeGroupCount()+2];  // space on end
        int max = main.enumerate(list);
        
        for (int i = 0; i<max; i++) { // usually just 2 or 3, quite quick
            if (list[i].getName().equals("JMRI")) return list[i];
        }
        return new ThreadGroup(main, "JMRI");
    }
    
    /**
     * Check whether a specific thread is running (or able to run) right now.
     *
     * @param t the thread to check
     * @return true is the specified thread is or could be running right now
     */
    static public boolean canThreadRun(@Nonnull Thread t) {
        Thread.State s = t.getState();
        return s.equals(Thread.State.RUNNABLE);
    }

    /**
     * Check whether a specific thread is currently waiting.
     * <p>
     * Note: This includes both waiting due to an explicit wait() call, and due
     * to being blocked attempting to synchronize.
     * <p>
     * Note: {@link #canThreadRun(Thread)} and {@link #isThreadWaiting(Thread)}
     * should never simultaneously be true, but it might look that way due to
     * sampling delays when checking on another thread.
     *
     * @param t the thread to check
     * @return true is the specified thread is or could be running right now
     */
    static public boolean isThreadWaiting(@Nonnull Thread t) {
        Thread.State s = t.getState();
        return s.equals(Thread.State.BLOCKED) || s.equals(Thread.State.WAITING) || s.equals(Thread.State.TIMED_WAITING);
    }

    /**
     * Check that a call is on the GUI thread. Warns (once) if not.
     * Intended to be the run-time check mechanism for {@code @InvokeOnGuiThread}
     * <p>
     * In this implementation, this is the same as {@link #requireLayoutThread(org.slf4j.Logger)}
     * @param logger The logger object from the calling class, usually "log"
     */
    static public void requireGuiThread(org.slf4j.Logger logger) {
        if (!isGUIThread()) {
            // fail, which can be a bit slow to do the right thing
            LoggingUtil.warnOnce(logger, "Call not on GUI thread", new Exception("traceback"));
        } 
    }
    
    /**
     * Check that a call is on the Layout thread. Warns (once) if not.
     * Intended to be the run-time check mechanism for {@code @InvokeOnLayoutThread}
     * <p>
     * In this implementation, this is the same as {@link #requireGuiThread(org.slf4j.Logger)}
     * @param logger The logger object from the calling class, usually "log"
     */
    static public void requireLayoutThread(org.slf4j.Logger logger) {
        if (!isLayoutThread()) {
            // fail, which can be a bit slow to do the right thing
            LoggingUtil.warnOnce(logger, "Call not on Layout thread", new Exception("traceback"));
        } 
    }
    
    /**
     * Interface for use in ThreadingUtil's lambda interfaces
     */
    @FunctionalInterface
    static public interface ThreadAction extends Runnable {

        /**
         * {@inheritDoc}
         * <p>
         * Must handle its own exceptions.
         */
        @Override
        public void run();
    }

    /**
     * Interface for use in ThreadingUtil's lambda interfaces
     */
    @FunctionalInterface
    static public interface ThreadActionWithJmriException {

        /**
         * When an object implementing interface <code>ThreadActionWithJmriException</code>
         * is used to create a thread, starting the thread causes the object's
         * <code>run</code> method to be called in that separately executing
         * thread.
         * <p>
         * The general contract of the method <code>run</code> is that it may
         * take any action whatsoever.
         *
         * @throws JmriException when an exception occurs
         * @throws RuntimeException when an exception occurs
         * @see     java.lang.Thread#run()
         */
        public void run() throws JmriException, RuntimeException;
    }

    /**
     * Interface for use in ThreadingUtil's lambda interfaces
     * 
     * @param <E> the type returned
     */
    @FunctionalInterface
    static public interface ReturningThreadAction<E> {
        public E run();
    }
    
    /**
     * Warn if a thread is holding locks. Used when transitioning to another context.
     */
    static public void warnLocks() {
        if ( log.isDebugEnabled() ) {
            try {
                java.lang.management.ThreadInfo threadInfo = java.lang.management.ManagementFactory
                                                    .getThreadMXBean()
                                                        .getThreadInfo(new long[]{Thread.currentThread().getId()}, true, true)[0];

                java.lang.management.MonitorInfo[] monitors = threadInfo.getLockedMonitors();
                for (java.lang.management.MonitorInfo mon : monitors) {
                    log.warn("Thread was holding monitor {} from {}", mon, mon.getLockedStackFrame(), LoggingUtil.shortenStacktrace(new Exception("traceback"))); // yes, warn - for re-enable later
                }

                java.lang.management.LockInfo[] locks = threadInfo.getLockedSynchronizers();
                for (java.lang.management.LockInfo lock : locks) {
                    // certain locks are part of routine Java API operations
                    if (lock.toString().startsWith("java.util.concurrent.ThreadPoolExecutor$Worker") ) {
                        log.debug("Thread was holding java lock {}", lock, LoggingUtil.shortenStacktrace(new Exception("traceback")));  // yes, warn - for re-enable later
                    } else {
                        log.warn("Thread was holding lock {}", lock, LoggingUtil.shortenStacktrace(new Exception("traceback")));  // yes, warn - for re-enable later
                    }
                }
            } catch (RuntimeException ex) {
                // just record exceptions for later pick up during debugging
                if (!lastWarnLocksLimit) log.warn("Exception in warnLocks", ex);
                lastWarnLocksLimit = true;
                lastWarnLocksException = ex;
            }
        }
    }
    private static boolean lastWarnLocksLimit = false;
    private static RuntimeException lastWarnLocksException = null; 
    public RuntimeException getlastWarnLocksException() { // public for script and test access
        return lastWarnLocksException;
    }
    
    private final static org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(ThreadingUtil.class);

}