// Copyright 2003 Adam Megacz, see the COPYING file for licensing [GPL]
package org.xwt;

import java.util.*;
import org.xwt.util.*;


/** A simple interface that must be supported by any object inserted into the MessageQueue. */
public interface Message {

    /** Invoked when the Message is dequeued. */
    public void perform();


    /** 
     *  A singleton class (one instance per JVM) that implements a queue
     *  for XWT events and threads; this is the main action-scheduling
     *  loop for the engine.
     *
     *  This <i>is</i> the foreground thread -- it
     *  dequeues Messages when they arrive in the queue. Using this
     *  thread ensures that the messages are executed in a synchronous,
     *  in-order fashion.
     */
    public static class Q extends Thread {

        /** a do-nothing message enqueued to trigger Surfaces to refresh themselves */
        private static Message refreshMessage = new Message() { public void perform() { } };

        /** enqueues a do-nothing message to get the Surfaces to refresh themselves */
        public static void refresh() { add(refreshMessage); }

        /** true iff latency-sensitive UI work is being done; signals the networking code to yield */
        public static volatile boolean working = false;

        private Q() { }

        /** invoked by Main */
        public static void startQ() { singleton.start(); }

        /** pending events */
        private static Queue events = new Queue(50);

        /** the number of objects in the queue that are not subclasses of ThreadMessage */
        public static volatile int nonThreadEventsInQueue = 0;

        /** the message currently being performed */    
        static Message currentlyPerforming = null;

        private static Q singleton = new Q();
        private static Watcher watcher = new Watcher();

        /**
         *  The message loop. Note that non-ThreadMessage Messages get
         *  priority, and that the queue is emptied in passes -- first we
         *  look at how many events are in the queue, then perform that
         *  many events, then render. This has the effect of throttling
         *  render requests to the appropriate frequency -- when many
         *  messages are in the queue, refreshes happen less frequently.
         */
        public void run() {
            Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
            while(true) {
                try {
                    int size = events.size();
                    for(int i=0; i<Math.max(1, size); i++) {
                        Message e = (Message)events.remove();

                        // if there are non-ThreadMessage events, perform them first
                        // we check against Thread instead of ThreadMessage so we don't get link failures in the Shoehorn
                        if (!(e instanceof Thread)) nonThreadEventsInQueue--;
                        else if (nonThreadEventsInQueue > 0) {
                            add(e);
                            i--;
                            continue;
                        }
                        if (!(e instanceof Thread)) working = true;
                        currentlyPerforming = e;
                        e.perform();
                        currentlyPerforming = null;
                        working = false;
                    }
                    working = true;
                    for(int i=0; i<Surface.allSurfaces.size(); i++)
                        ((Surface)Surface.allSurfaces.elementAt(i)).render();
                    working = false;

                } catch (Throwable t) {
                    if (Log.on) Log.log(this, "caught throwable in Q.run(); this should never happen");
                    if (Log.on) Log.log(this, "    currentlyPerforming == " + currentlyPerforming);
                    if (Log.on) Log.log(this, "    working             == " + working);
                    if (Log.on) Log.log(this, t);
                    if (Log.on) Log.log(this, "resuming Q loop");
                }
            }
        }

        /** Adds an event to the queue */
        public static void add(Message e) {
            // Even though we don't synchronize around these two statements, it is not a race condition. In the worst case,
            // nonThreadEventsInQueue undercounts -- it never overcounts.
            events.append(e);
            if (!(e instanceof Thread)) nonThreadEventsInQueue++;
        }

        /** a simple thread that logs a warning if too much time is spent in any given message -- helpful for debugging infinite loops */
        private static class Watcher extends Thread {
            long t = System.currentTimeMillis();
            Message m = null;
            public Watcher() { start(); }
            public void run() {
                while(true) {
                    if ((m != null && m == Q.currentlyPerforming) || Q.working) {
                        String what, where;
                        if (m != null && m instanceof ThreadMessage) {
                            where = org.xwt.js.JS.Thread.fromJavaThread((ThreadMessage)m).getSourceName();
                            what = "background thread";
                        } else if (m != null) {
                            where = org.xwt.js.JS.Thread.fromJavaThread(Q.singleton).getSourceName();
                            what = "event trap";
                        } else {
                            where = org.xwt.js.JS.Thread.fromJavaThread(Q.singleton).getSourceName();
                            what = "script";
                        }
                        long howlong = (System.currentTimeMillis() - t) / 1000;
                        if (howlong >= 5)
                            if (Log.on) Log.log(this, "note: executing same " + what + " for " + howlong + "s" + " at " + where);
                    } else {
                        m = Q.currentlyPerforming;
                        t = System.currentTimeMillis();
                    }
                    try { Thread.sleep(1000); } catch (Exception e) { }
                }
            }
        }
    
    }

}