CategoryDetector.java

package org.limewire.ui.swing.filter;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.SwingUtilities;
import javax.swing.Timer;

import org.limewire.core.api.Category;

import ca.odell.glazedlists.event.ListEvent;
import ca.odell.glazedlists.event.ListEventListener;

/**
 * Support class to detect the category with the most search results.
 */
class CategoryDetector<E extends FilterableItem> {
    /** Number of results needed to trigger category detection. */
    private static final int RESULTS_COUNT = 25;
    /** Delay in milliseconds needed to trigger category detection. */
    private static final int TIMER_DELAY = 10000;

    private final FilterableSource<E> filterableSource;
    private final CategoryFilter categoryFilter;
    
    private CategoryDetectorListener detectorListener;
    private ListEventListener<E> resultsListener;
    private ActionListener timerListener;
    private Timer timer;
    
    /**
     * Constructs a CategoryDetector using the specified search results model
     * and category filter.
     */
    public CategoryDetector(FilterableSource<E> filterableSource, CategoryFilter categoryFilter) {
        this.filterableSource = filterableSource;
        this.categoryFilter = categoryFilter;
    }
    
    /**
     * Starts category detection.  When the default category is found, the 
     * specified listener is notified.
     */
    public void start(CategoryDetectorListener listener) {
        detectorListener = listener;
        
        // Create results listener to detect the category when enough results 
        // are received.
        resultsListener = new ListEventListener<E>() {
            @Override
            public void listChanged(ListEvent listChanges) {
                int size = listChanges.getSourceList().size();
                if (size >= RESULTS_COUNT) {
                    fireDelayedCategoryFound();
                }
            }
        };
        filterableSource.getUnfilteredList().addListEventListener(resultsListener);
        
        // Create timer listener to detect the category after enough time has 
        // passed.
        timerListener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                fireDelayedCategoryFound();
            }
        };
        timer = new Timer(TIMER_DELAY, timerListener);
        timer.start();
    }
    
    /**
     * Stops category detection.  This method removes all listeners.
     */
    public void stop() {
        // Remove listener from list.
        if (resultsListener != null) {
            filterableSource.getUnfilteredList().removeListEventListener(resultsListener);
            resultsListener = null;
        }
        
        // Stop timer and remove listener.
        if (timer != null) {
            timer.stop();
            timer.removeActionListener(timerListener);
            timerListener = null;
            timer = null;
        }
    }
    
    /**
     * Notifies the detector listener with the default category, and stops 
     * category detection.  Delayed notification is performed by posting a new 
     * event on the event queue.  We do this because the method may be invoked 
     * in response to an EventList change, and we want to delay category 
     * notification since further processing of the EventList chain in the same
     * event can cause issues.
     */
    private void fireDelayedCategoryFound() {
        // Perform delayed notification by posting Runnable on event queue.
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                if (detectorListener != null) {
                    Category category = categoryFilter.getDefaultCategory();
                    detectorListener.categoryFound(category);
                    detectorListener = null;
                }
            }
        });
        
        // Stop category detection.
        stop();
    }

    /**
     * Defines a listener for category found events. 
     */
    public static interface CategoryDetectorListener {
        
        /**
         * Invoked when the category is found.
         */
        void categoryFound(Category category);
        
    }
}