/**
 * Copyright (C) 2001-2017 by RapidMiner and the contributors
 * 
 * Complete list of developers available at our web site:
 * 
 * http://rapidminer.com
 * 
 * This program is free software: you can redistribute it and/or modify it under the terms of the
 * GNU Affero 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
 * Affero General Public License for more details.
 * 
 * You should have received a copy of the GNU Affero General Public License along with this program.
 * If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.tools;

import java.lang.ref.WeakReference;
import java.util.Map;
import java.util.WeakHashMap;

import com.rapidminer.ObjectVisualizer;
import com.rapidminer.example.ExampleSet;
import com.rapidminer.gui.DummyObjectVisualizer;
import com.rapidminer.gui.ExampleVisualizer;


/**
 * This class provides the management of {@link ObjectVisualizer}s. The visualizer are remembered
 * per object using a weak hash map and WeakReferences. Hence if the object isn't in ordinary use
 * any more, the visualizer will be discarded also.
 *
 * @author Ingo Mierswa, Sebastian Land
 */
public class ObjectVisualizerService {

	private static final DummyObjectVisualizer DUMMY_VISUALIZER = new DummyObjectVisualizer();

	private static final Map<Object, WeakReference<ObjectVisualizer>> visualizerMap = new WeakHashMap<>();

	/**
	 * This method adds the given visualizer for the target object. Please not that only one
	 * visualizer per object is allowed. The subsequent added visualizer will overwrite the first.
	 *
	 * The targets will be remembered using a weak reference, so that they don't pose a memory leak:
	 * If the object isn't referenced anywhere else, it will be deleted.
	 */
	public static void addObjectVisualizer(Object target, ObjectVisualizer visualizer) {
		visualizerMap.put(target, new WeakReference<>(visualizer));
	}

	/**
	 * Returns the object visualizer registered for this targetObject. If the targetObject is of
	 * type ExampleSet and there's no special visualizer registered, it will return an new
	 * ExampleVisualizer.
	 */
	public static ObjectVisualizer getVisualizerForObject(Object targetObject) {
		ObjectVisualizer capableVisualizer = null;
		WeakReference<ObjectVisualizer> visualizerReference = visualizerMap.get(targetObject);
		if (visualizerReference != null) {
			capableVisualizer = visualizerReference.get();
		}
		if (capableVisualizer == null) {
			if (targetObject instanceof ExampleSet) {
				ObjectVisualizer visualizer = new ExampleVisualizer((ExampleSet) targetObject);
				addObjectVisualizer(targetObject, visualizer);
				return visualizer;
			}
			return DUMMY_VISUALIZER;
		}
		return capableVisualizer;
	}
}