// Copyright 2004 Adam Megacz, see the COPYING file for licensing [GPL]
package org.xwt;

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

/** Implements cooperative multitasking */
public class Scheduler {

    // Public API Exposed to org.xwt /////////////////////////////////////////////////

    private static Scheduler singleton;
    public static interface Task { public abstract void perform() throws Exception; }
    public static void add(Task t) { singleton.runnable.append(t); }
    public static void init() { if (singleton == null) (singleton = Platform.getScheduler()).run(); }

    private static Task current = null;

    private static volatile boolean rendering = false;
    private static volatile boolean again = false;

    /** synchronizd so that we can safely call it from an event-delivery thread, in-context */
    public static void renderAll() {
        if (rendering) { again = true; return; }
        synchronized(Scheduler.class) {
            try {
                rendering = true;
                do {
                    // FEATURE: this could be cleaner
                    again = false;
                    for(int i=0; i<Surface.allSurfaces.size(); i++) {
                        Surface s = ((Surface)Surface.allSurfaces.elementAt(i));
                        do { s.render(); } while(s.abort);
                    }
                } while(again);
            } finally {
                rendering = false;
            }
        }
    }

    

    // API which must be supported by subclasses /////////////////////////////////////

    /**
     *  SCHEDULER INVARIANT: all scheduler implementations MUST invoke
     *  Surface.renderAll() after performing a Task if no tasks remain
     *  in the queue.  A scheduler may choose to invoke
     *  Surface.renderAll() more often than that if it so chooses.
     */
    public void run() { defaultRun(); }
    protected Scheduler() { }


    // Default Implementation //////////////////////////////////////////////////////

    protected static Queue runnable = new Queue(50);
    public void defaultRun() {
        while(true) {
            current = (Task)runnable.remove(true);
            try {
                // FIXME hideous
                synchronized(this) {
                    for(int i=0; i<Surface.allSurfaces.size(); i++) {
                        Surface s = (Surface)Surface.allSurfaces.elementAt(i);
                        if (current instanceof JS) {
                            s._mousex = Integer.MAX_VALUE;
                            s._mousey = Integer.MAX_VALUE;
                        } else {
                            s._mousex = s.mousex;
                            s._mousey = s.mousey;
                        }
                    }
                    current.perform();
                }
                renderAll();
            } catch (JSExn e) {
                Log.info(Scheduler.class, "a JavaScript thread spawned with xwt.thread() threw an exception:");
                Log.info(Scheduler.class, "JS Exception: " + e.getObject() + "\n" + e.backtrace());
                Log.info(Scheduler.class,e);
            } catch (Exception e) {
                Log.info(Scheduler.class, "a Task threw an exception which was caught by the scheduler:");
                Log.info(Scheduler.class, e);
            }
            // if an Error is thrown it will cause the engine to quit
        }
    }
}