source: trunk/src/org/expeditee/items/widgets/WidgetCacheManager.java@ 919

/**
 *    WidgetCacheManager.java
 *    Copyright (C) 2010 New Zealand Digital Library, http://expeditee.org
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation, either version 3 of the License, or
 *    (at your option) any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.expeditee.items.widgets;

import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Set;

import org.expeditee.gui.DisplayIOObserver;
import org.expeditee.gui.FrameIO;


/**
 * Some heavy duty widgets can hold alot of data and must only be in Expeditee memory for
 * a little while ... e.g. Not cached once the user has traversed 50 or so frames after
 * where the widget was first loaded.
 * 
 * @author Brook Novak
 *
 */
public final class WidgetCacheManager implements DisplayIOObserver {
        
        private static HashMap<HeavyDutyInteractiveWidget, Integer> transientWidgets = new HashMap<HeavyDutyInteractiveWidget, Integer>();
        
        private static WidgetCacheManager _instance = new WidgetCacheManager();
        
        private WidgetCacheManager() {
        }
        
        public static WidgetCacheManager getInstance() {
                return _instance;
        }
        
        /**
         * @return
         *              An unmodifiable set of the current transientWidgets that are registered.
         */
        public static Set<HeavyDutyInteractiveWidget> getTransientWidgets() {
                return Collections.unmodifiableSet(transientWidgets.keySet());
        }
        
        public static void cacheWidget(HeavyDutyInteractiveWidget widget) {
                if (widget == null) throw new NullPointerException("widget");
                
                if (widget.getCacheDepth() > FrameIO.MAX_CACHE ||
                                widget.getCacheDepth() <= 0) return;
                
                // If widget already exists, then the current count will be reset (overriden to zero)
                transientWidgets.put(widget, new Integer(0));
                
        }
        
        public static void uncacheWidget(HeavyDutyInteractiveWidget widget) {
                if (widget == null) throw new NullPointerException("widget");
                transientWidgets.remove(widget);
        }


        /**
         * invoked when the frame changes. After the new frame is actually set.
         * Expires heavy duty widgets that have been cached for to long....
         * 
         * Intention: to be called from the DisplayIO frame change code...
         *
         */
        public void frameChanged() {

                // Increment all cache counters
                Collection<HeavyDutyInteractiveWidget> toCheck = new LinkedList<HeavyDutyInteractiveWidget>(
                                transientWidgets.keySet());
                
                // Check all heavyduty widgets that have limited cache
                for (HeavyDutyInteractiveWidget tw : toCheck) {
                        
                        Integer count = transientWidgets.remove(tw); // get rid of reference
                        if (count == null) continue;
                        
                        int newCount = count;
                        newCount++;

                        if (tw.isVisible()) { // Reset cache counter if visible
                                
                                transientWidgets.put(tw, new Integer(0));
                                
                        } else if (newCount >= tw.getCacheDepth()) { // Expire if stale
        
                                // Ensure that the heavy duty widgets data is handled correctly (i.e. saving)
                                tw.expire();
                                
                        } else { // keep reference, with new count
                                
                                transientWidgets.put(tw, newCount);
                                
                        }
                        
                }
        }
        
        
}