/*******************************************************************************
 * Copyright (c) 2008, 2012 Oracle. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0, which accompanies this distribution
 * and is available at http://www.eclipse.org/legal/epl-v10.html.
 *
 * Contributors:
 *     Oracle - initial API and implementation
 ******************************************************************************/
package org.eclipse.jpt.common.ui.jface;

import java.io.Serializable;
import org.eclipse.jpt.common.utility.internal.StringTools;

/**
 * Implementations of this interface can be used to maintain the elements
 * of a specific input element. The implementation will monitor
 * the item for any changes that affect the elements and forward them
 * appropriately to the {@link Manager}.
 * <p>
 * Provisional API: This interface is part of an interim API that is still
 * under development and expected to change significantly before reaching
 * stability. It is available at this early stage to solicit feedback from
 * pioneering adopters on the understanding that any code that uses this API
 * will almost certainly be broken (repeatedly) as the API evolves.
 * 
 * @see org.eclipse.jface.viewers.IContentProvider
 * @see org.eclipse.jface.viewers.IStructuredContentProvider
 */
public interface ItemStructuredContentProvider {
	/**
	 * Return the input element's elements.
	 * <strong>NB:</strong>
	 * When this method is called, the item is an <em>input</em> element.
	 * 
	 * @see org.eclipse.jface.viewers.IContentProvider#inputChanged(org.eclipse.jface.viewers.Viewer, Object, Object)
	 * @see org.eclipse.jface.viewers.IStructuredContentProvider#getElements(Object)
	 * @see org.eclipse.jface.viewers.ITreeContentProvider#getElements(Object)
	 * @see org.eclipse.jface.viewers.ITreeContentProvider#getChildren(Object)
	 */
	Object[] getElements();

	/**
	 * Dispose the item content provider.
	 * Remove any item listeners as appropriate.
	 */
	void dispose();


	/**
	 * Convenience constant for when no children are present.
	 */
	Object[] EMPTY_ARRAY = new Object[0];


	/**
	 * An item structured content provider's manager is notified whenever the
	 * input element's elements have changed.
	 */
	interface Manager {
		/**
		 * The elements for the specified input element have changed.
		 * Update appropriately.
		 */
		void updateElements(Object inputElement);

		/**
		 * The specified element has been removed from the input element.
		 * Dispose of the element's providers, if necessary.
		 */
		void dispose(Object element);
	}


	/**
	 * A "null" item structured content provider that has no elements.
	 */
	final class Null
		implements ItemStructuredContentProvider, Serializable
	{
		public static final ItemStructuredContentProvider INSTANCE = new Null();
		public static ItemStructuredContentProvider instance() {
			return INSTANCE;
		}
		// ensure single instance
		private Null() {
			super();
		}
		public Object[] getElements() {
			return EMPTY_ARRAY;
		}
		public void dispose() {
			// NOP
		}
		@Override
		public String toString() {
			return StringTools.buildSingletonToString(this);
		}
		private static final long serialVersionUID = 1L;
		private Object readResolve() {
			// replace this object with the singleton
			return INSTANCE;
		}
	}
}