/*******************************************************************************
 * Copyright (c) 2000, 2003 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.jface.viewers;

import java.util.*;
import java.util.List;

import org.eclipse.core.runtime.Platform;
import org.eclipse.jface.util.*;
import org.eclipse.swt.SWT;
import org.eclipse.swt.custom.BusyIndicator;
import org.eclipse.swt.events.*;
import org.eclipse.swt.widgets.*;

/**
 * Abstract base implementation for tree-structure-oriented viewers (trees and
 * table trees).
 * <p>
 * Nodes in the tree can be in either an expanded or a collapsed state,
 * depending on whether the children on a node are visible. This class
 * introduces public methods for controlling the expanding and collapsing of
 * nodes.
 * </p>
 * <p>
 * Content providers for abstract tree viewers must implement the <code>ITreeContentProvider</code>
 * interface.
 * </p>
 * 
 * @see TreeViewer
 * @see TableTreeViewer
 */
public abstract class AbstractTreeViewer extends StructuredViewer {

	/**
	 * Constant indicating that all levels of the tree should be expanded or
	 * collapsed.
	 * 
	 * @see #expandToLevel
	 * @see #collapseToLevel
	 */
	public static final int ALL_LEVELS = -1;

	/**
	 * List of registered tree listeners (element type: <code>TreeListener</code>). */
	private ListenerList treeListeners = new ListenerList(1);

	/**
	 * The level to which the tree is automatically expanded each time the
	 * viewer's input is changed (that is, by <code>setInput</code>). A
	 * value of 0 means that auto-expand is off.
	 * 
	 * @see #setAutoExpandLevel
	 */
	private int expandToLevel = 0;

	/**
	 * The safe runnable used to call the label provider. */
	private UpdateItemSafeRunnable safeUpdateItem =
		new UpdateItemSafeRunnable();

	class UpdateItemSafeRunnable extends SafeRunnable {
		Object element;
		Item item;
		boolean exception = false;
		public void run() {
			if (exception)
				return;
			doUpdateItem(item, element);
		}
		public void handleException(Throwable e) {
			super.handleException(e);
			//If and unexpected exception happens, remove it
			//to make sure the application keeps running.
			exception = true;
		}
	}

	/**
	 * Creates an abstract tree viewer. The viewer has no input, no content
	 * provider, a default label provider, no sorter, no filters, and has
	 * auto-expand turned off.
	 */
	protected AbstractTreeViewer() {
	}
	/**
	 * Adds the given child elements to this viewer as children of the given
	 * parent element. If this viewer does not have a sorter, the elements are
	 * added at the end of the parent's list of children in the order given;
	 * otherwise, the elements are inserted at the appropriate positions.
	 * <p>
	 * This method should be called (by the content provider) when elements
	 * have been added to the model, in order to cause the viewer to accurately
	 * reflect the model. This method only affects the viewer, not the model.
	 * </p>
	 * 
	 * @param parentElement
	 *           the parent element
	 * @param childElements
	 *           the child elements to add
	 */
	public void add(Object parentElement, Object[] childElements) {
		Assert.isNotNull(parentElement);
		Assert.isNotNull(childElements);
		Widget widget = findItem(parentElement);
		// If parent hasn't been realized yet, just ignore the add.
		if (widget == null)
			return;

		Control tree = getControl();

		// optimization!
		// if the widget is not expanded we just invalidate the subtree
		if (widget instanceof Item) {
			Item ti = (Item) widget;
			if (!getExpanded(ti)) {
				boolean needDummy = isExpandable(parentElement);
				boolean haveDummy = false;
				// remove all children
				Item[] items = getItems(ti);
				for (int i = 0; i < items.length; i++) {
					if (items[i].getData() != null) {
						disassociate(items[i]);
						items[i].dispose();
					} else {
						if (needDummy && !haveDummy) {
							haveDummy = true;
						} else {
							items[i].dispose();
						}
					}
				}
				// append a dummy if necessary
				if (needDummy && !haveDummy) {
					newItem(ti, SWT.NULL, -1);
				} else {
					// XXX: Workaround (PR missing)
					tree.redraw();
				}

				return;
			}
		}

		if (childElements.length > 0) {
			Object[] filtered = filter(childElements);
			for (int i = 0; i < filtered.length; i++) {
				createAddedElement(widget,filtered[i]);				
			}
		}
	}
	
	/**
	 * Create the new element in the parent widget. If the
	 * child already exists do nothing.
	 * @param widget
	 * @param element
	 */
	private void createAddedElement(Widget widget, Object element){
		
		if(equals(element,widget.getData()))
			return;
		
		Item[] items = getChildren(widget); 
		for(int i = 0; i < items.length; i++){
			if(items[i].getData().equals(element))
				return;
		}				
		
		int index = indexForElement(widget, element);
		createTreeItem(widget, element, index);
	}

	/**
	 * Returns the index where the item should be inserted.
	 * 
	 * @param parent
	 *           The parent widget the element will be inserted into.
	 * @param element
	 *           The element to insert.
	 */
	protected int indexForElement(Widget parent, Object element) {
		ViewerSorter sorter = getSorter();
		Item[] items = getChildren(parent);

		if (sorter == null)
			return items.length;
		int count = items.length;
		int min = 0, max = count - 1;

		while (min <= max) {
			int mid = (min + max) / 2;
			Object data = items[mid].getData();
			int compare = sorter.compare(this, data, element);
			if (compare == 0) {
				// find first item > element
				while (compare == 0) {
					++mid;
					if (mid >= count) {
						break;
					}
					data = items[mid].getData();
					compare = sorter.compare(this, data, element);
				}
				return mid;
			}
			if (compare < 0)
				min = mid + 1;
			else
				max = mid - 1;
		}
		return min;
	}
	/**
	 * Adds the given child element to this viewer as a child of the given
	 * parent element. If this viewer does not have a sorter, the element is
	 * added at the end of the parent's list of children; otherwise, the
	 * element is inserted at the appropriate position.
	 * <p>
	 * This method should be called (by the content provider) when a single
	 * element has been added to the model, in order to cause the viewer to
	 * accurately reflect the model. This method only affects the viewer, not
	 * the model. Note that there is another method for efficiently processing
	 * the simultaneous addition of multiple elements.
	 * </p>
	 * 
	 * @param parentElement
	 *           the parent element
	 * @param childElement
	 *           the child element
	 */
	public void add(Object parentElement, Object childElement) {
		add(parentElement, new Object[] { childElement });
	}
	/**
	 * Adds the given SWT selection listener to the given SWT control.
	 * 
	 * @param control
	 *           the SWT control
	 * @param listener
	 *           the SWT selection listener
	 * @deprecated
	 */
	protected void addSelectionListener(
		Control control,
		SelectionListener listener) {
	}
	/**
	 * Adds a listener for expand and collapse events in this viewer. Has no
	 * effect if an identical listener is already registered.
	 * 
	 * @param listener
	 *           a tree viewer listener
	 */
	public void addTreeListener(ITreeViewerListener listener) {
		treeListeners.add(listener);
	}
	/**
	 * Adds the given SWT tree listener to the given SWT control.
	 * 
	 * @param control
	 *           the SWT control
	 * @param listener
	 *           the SWT tree listener
	 */
	protected abstract void addTreeListener(
		Control control,
		TreeListener listener);

	/* (non-Javadoc) @see StructuredViewer#associate(Object, Item) */
	protected void associate(Object element, Item item) {
		Object data = item.getData();
		if (data != null && data != element && equals(data, element)) {
			// workaround for PR 1FV62BT
			// assumption: elements are equal but not identical
			// -> remove from map but don't touch children
			unmapElement(data, item);
			item.setData(element);
			mapElement(element, item);
		} else {
			// recursively disassociate all
			super.associate(element, item);
		}
	}

	/**
	 * Collapses all nodes of the viewer's tree, starting with the root. This
	 * method is equivalent to <code>collapseToLevel(ALL_LEVELS)</code>.
	 */
	public void collapseAll() {
		Object root = getRoot();
		if (root != null) {
			collapseToLevel(root, ALL_LEVELS);
		}
	}
	/**
	 * Collapses the subtree rooted at the given element to the given level.
	 * 
	 * @param element
	 *           the element
	 * @param level
	 *           non-negative level, or <code>ALL_LEVELS</code> to collapse
	 *           all levels of the tree
	 */
	public void collapseToLevel(Object element, int level) {
		Widget w = findItem(element);
		if (w != null)
			internalCollapseToLevel(w, level);
	}
	/**
	 * Creates all children for the given widget.
	 * <p>
	 * The default implementation of this framework method assumes that <code>widget.getData()</code>
	 * returns the element corresponding to the node. Note: the node is not
	 * visually expanded! You may have to call <code>parent.setExpanded(true)</code>.
	 * </p>
	 * 
	 * @param widget
	 *           the widget
	 */
	protected void createChildren(final Widget widget) {
		final Item[] tis = getChildren(widget);
		if (tis != null && tis.length > 0) {
			Object data = tis[0].getData();
			if (data != null)
				return; // children already there!
		}

		BusyIndicator.showWhile(widget.getDisplay(), new Runnable() {
			public void run() {
				// fix for PR 1FW89L7:
				// don't complain and remove all "dummies" ...
				if (tis != null) {
					for (int i = 0; i < tis.length; i++) {
						tis[i].dispose();
					}
				}
				Object d = widget.getData();
				if (d != null) {
					Object parentElement = d;
					Object[] children = getSortedChildren(parentElement);
					for (int i = 0; i < children.length; i++) {
						createTreeItem(widget, children[i], -1);
					}
				}
			}
		});
	}
	/**
	 * Creates a single item for the given parent and synchronizes it with the
	 * given element.
	 * 
	 * @param parent
	 *           the parent widget
	 * @param element
	 *           the element
	 * @param index
	 *           if non-negative, indicates the position to insert the item
	 *           into its parent
	 */
	protected void createTreeItem(Widget parent, Object element, int index) {
		Item item = newItem(parent, SWT.NULL, index);
		updateItem(item, element);
		updatePlus(item, element);
	}
	/**
	 * The <code>AbstractTreeViewer</code> implementation of this method also
	 * recurses over children of the corresponding element.
	 */
	protected void disassociate(Item item) {
		super.disassociate(item);
		// recursively unmapping the items is only required when
		// the hash map is used. In the other case disposing
		// an item will recursively dispose its children.
		if (usingElementMap())
			disassociateChildren(item);
	}
	/**
	 * Disassociates the children of the given SWT item from their
	 * corresponding elements.
	 * 
	 * @param item
	 *           the widget
	 */
	private void disassociateChildren(Item item) {
		Item[] items = getChildren(item);
		for (int i = 0; i < items.length; i++) {
			if (items[i].getData() != null)
				disassociate(items[i]);
		}
	}
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected Widget doFindInputItem(Object element) {
		// compare with root
		Object root = getRoot();
		if (root == null)
			return null;

		if (equals(root, element))
			return getControl();
		return null;
	}
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected Widget doFindItem(Object element) {
		// compare with root
		Object root = getRoot();
		if (root == null)
			return null;

		Item[] items = getChildren(getControl());
		if (items != null) {
			for (int i = 0; i < items.length; i++) {
				Widget o = internalFindItem(items[i], element);
				if (o != null)
					return o;
			}
		}
		return null;
	}
	/**
	 * Copies the attributes of the given element into the given SWT item.
	 * 
	 * @param item
	 *           the SWT item
	 * @param element
	 *           the element
	 */
	protected abstract void doUpdateItem(Item item, Object element);
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected void doUpdateItem(
		Widget widget,
		Object element,
		boolean fullMap) {
		if (widget instanceof Item) {
			Item item = (Item) widget;

			// ensure that backpointer is correct
			if (fullMap) {
				associate(element, item);
			} else {
				item.setData(element);
				mapElement(element, item);
			}

			// update icon and label
			safeUpdateItem.item = item;
			safeUpdateItem.element = element;
			try {
				Platform.run(safeUpdateItem);
			} finally {
				safeUpdateItem.item = null;
				safeUpdateItem.element = null;
			}
		}
	}
	/**
	 * Expands all nodes of the viewer's tree, starting with the root. This
	 * method is equivalent to <code>expandToLevel(ALL_LEVELS)</code>.
	 */
	public void expandAll() {
		expandToLevel(ALL_LEVELS);
	}
	/**
	 * Expands the root of the viewer's tree to the given level.
	 * 
	 * @param level
	 *           non-negative level, or <code>ALL_LEVELS</code> to expand all
	 *           levels of the tree
	 */
	public void expandToLevel(int level) {
		expandToLevel(getRoot(), level);
	}
	/**
	 * Expands all ancestors of the given element so that the given element
	 * becomes visible in this viewer's tree control, and then expands the
	 * subtree rooted at the given element to the given level.
	 * 
	 * @param element
	 *           the element
	 * @param level
	 *           non-negative level, or <code>ALL_LEVELS</code> to expand all
	 *           levels of the tree
	 */
	public void expandToLevel(Object element, int level) {
		Widget w = internalExpand(element, true);
		if (w != null)
			internalExpandToLevel(w, level);
	}
	/**
	 * Fires a tree collapsed event. Only listeners registered at the time this
	 * method is called are notified.
	 * 
	 * @param event
	 *           the tree expansion event
	 * @see ITreeViewerListener#treeCollapsed
	 */
	protected void fireTreeCollapsed(final TreeExpansionEvent event) {
		Object[] listeners = treeListeners.getListeners();
		for (int i = 0; i < listeners.length; ++i) {
			final ITreeViewerListener l = (ITreeViewerListener) listeners[i];
			Platform.run(new SafeRunnable() {
				public void run() {
					l.treeCollapsed(event);
				}
				public void handleException(Throwable e) {
					super.handleException(e);
					//If and unexpected exception happens, remove it
					//to make sure the application keeps running.
					removeTreeListener(l);
				}
			});
		}
	}
	/**
	 * Fires a tree expanded event. Only listeners registered at the time this
	 * method is called are notified.
	 * 
	 * @param event
	 *           the tree expansion event
	 * @see ITreeViewerListener#treeExpanded
	 */
	protected void fireTreeExpanded(final TreeExpansionEvent event) {
		Object[] listeners = treeListeners.getListeners();
		for (int i = 0; i < listeners.length; ++i) {
			final ITreeViewerListener l = (ITreeViewerListener) listeners[i];
			Platform.run(new SafeRunnable() {
				public void run() {
					l.treeExpanded(event);
				}
				public void handleException(Throwable e) {
					super.handleException(e);
					//If and unexpected exception happens, remove it
					//to make sure the application keeps running.
					removeTreeListener(l);
				}
			});
		}

	}
	/**
	 * Returns the auto-expand level.
	 * 
	 * @return non-negative level, or <code>ALL_LEVELS</code> if all levels
	 *         of the tree are expanded automatically
	 * @see #setAutoExpandLevel
	 */
	public int getAutoExpandLevel() {
		return expandToLevel;
	}
	/**
	 * Returns the SWT child items for the given SWT widget.
	 * 
	 * @param widget
	 *           the widget
	 * @return the child items
	 */
	protected abstract Item[] getChildren(Widget widget);
	/**
	 * Returns whether the given SWT item is expanded or collapsed.
	 * 
	 * @param item
	 *           the item
	 * @return <code>true</code> if the item is considered expanded and
	 *         <code>false</code> if collapsed
	 */
	protected abstract boolean getExpanded(Item item);
	/**
	 * Returns a list of elements corresponding to expanded nodes in this
	 * viewer's tree, including currently hidden ones that are marked as
	 * expanded but are under a collapsed ancestor.
	 * <p>
	 * This method is typically used when preserving the interesting state of a
	 * viewer; <code>setExpandedElements</code> is used during the restore.
	 * </p>
	 * 
	 * @return the array of expanded elements
	 * @see #setExpandedElements
	 */
	public Object[] getExpandedElements() {
		ArrayList v = new ArrayList();
		internalCollectExpanded(v, getControl());
		return v.toArray();
	}
	/**
	 * Returns whether the node corresponding to the given element is expanded
	 * or collapsed.
	 * 
	 * @param element
	 *           the element
	 * @return <code>true</code> if the node is expanded, and <code>false</code>
	 *         if collapsed
	 */
	public boolean getExpandedState(Object element) {
		Widget item = findItem(element);
		if (item instanceof Item)
			return getExpanded((Item) item);
		return false;
	}
	/**
	 * Returns the number of child items of the given SWT control.
	 * 
	 * @param control
	 *           the control
	 * @return the number of children
	 */
	protected abstract int getItemCount(Control control);
	/**
	 * Returns the number of child items of the given SWT item.
	 * 
	 * @param item
	 *           the item
	 * @return the number of children
	 */
	protected abstract int getItemCount(Item item);
	/**
	 * Returns the child items of the given SWT item.
	 * 
	 * @param item
	 *           the item
	 * @return the child items
	 */
	protected abstract Item[] getItems(Item item);
	/**
	 * Returns the item after the given item in the tree, or <code>null</code>
	 * if there is no next item.
	 * 
	 * @param item
	 *           the item
	 * @param includeChildren
	 *           <code>true</code> if the children are considered in
	 *           determining which item is next, and <code>false</code> if
	 *           subtrees are ignored
	 * @return the next item, or <code>null</code> if none
	 */
	protected Item getNextItem(Item item, boolean includeChildren) {
		if (item == null) {
			return null;
		}
		if (includeChildren && getExpanded(item)) {
			Item[] children = getItems(item);
			if (children != null && children.length > 0) {
				return children[0];
			}
		}

		//next item is either next sibling or next sibling of first
		//parent that has a next sibling.
		Item parent = getParentItem(item);
		if (parent == null) {
			return null;
		}
		Item[] siblings = getItems(parent);
		if (siblings != null && siblings.length <= 1) {
			return getNextItem(parent, false);
		}
		for (int i = 0; i < siblings.length; i++) {
			if (siblings[i] == item && i < (siblings.length - 1)) {
				return siblings[i + 1];
			}
		}
		return getNextItem(parent, false);
	}
	/**
	 * Returns the parent item of the given item in the tree, or <code>null</code>
	 * if there is parent item.
	 * 
	 * @param item
	 *           the item
	 * @return the parent item, or <code>null</code> if none
	 */
	protected abstract Item getParentItem(Item item);
	/**
	 * Returns the item before the given item in the tree, or <code>null</code>
	 * if there is no previous item.
	 * 
	 * @param item
	 *           the item
	 * @return the previous item, or <code>null</code> if none
	 */
	protected Item getPreviousItem(Item item) {
		//previous item is either right-most visible descendent of previous
		//sibling or parent
		Item parent = getParentItem(item);
		if (parent == null) {
			return null;
		}
		Item[] siblings = getItems(parent);
		if (siblings.length == 0 || siblings[0] == item) {
			return parent;
		}
		Item previous = siblings[0];
		for (int i = 1; i < siblings.length; i++) {
			if (siblings[i] == item) {
				return rightMostVisibleDescendent(previous);
			}
			previous = siblings[i];
		}
		return null;
	}
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected Object[] getRawChildren(Object parent) {
		if (parent != null) {
			if (equals(parent, getRoot()))
				return super.getRawChildren(parent);
			ITreeContentProvider cp =
				(ITreeContentProvider) getContentProvider();
			if (cp != null) {
				Object[] result = cp.getChildren(parent);
				if (result != null)
					return result;
			}
		}
		return new Object[0];
	}
	/**
	 * Returns all selected items for the given SWT control.
	 * 
	 * @param control
	 *           the control
	 * @return the list of selected items
	 */
	protected abstract Item[] getSelection(Control control);
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected List getSelectionFromWidget() {
		Widget[] items = getSelection(getControl());
		ArrayList list = new ArrayList(items.length);
		for (int i = 0; i < items.length; i++) {
			Widget item = items[i];
			Object e = item.getData();
			if (e != null)
				list.add(e);
		}
		return list;
	}
	/**
	 * Handles a tree collapse event from the SWT widget.
	 * 
	 * @param event
	 *           the SWT tree event
	 */
	protected void handleTreeCollapse(TreeEvent event) {
		if (event.item.getData() != null) {
			fireTreeCollapsed(
				new TreeExpansionEvent(this, event.item.getData()));
		}
	}
	/**
	 * Handles a tree expand event from the SWT widget.
	 * 
	 * @param event
	 *           the SWT tree event
	 */
	protected void handleTreeExpand(TreeEvent event) {
		createChildren(event.item);
		if (event.item.getData() != null) {
			fireTreeExpanded(
				new TreeExpansionEvent(this, event.item.getData()));
		}
	}
	/* (non-Javadoc) Method declared on Viewer. */
	protected void hookControl(Control control) {
		super.hookControl(control);
		addTreeListener(control, new TreeListener() {
			public void treeExpanded(TreeEvent event) {
				handleTreeExpand(event);
			}
			public void treeCollapsed(TreeEvent event) {
				handleTreeCollapse(event);
			}
		});
	}
	/*
	 * (non-Javadoc) Method declared on StructuredViewer. Builds the initial
	 * tree and handles the automatic expand feature.
	 */
	protected void inputChanged(Object input, Object oldInput) {
		preservingSelection(new Runnable() {
			public void run() {
				Control tree = getControl();
				boolean useRedraw = true;
				// (size > REDRAW_THRESHOLD) || (table.getItemCount() >
				// REDRAW_THRESHOLD);
				if (useRedraw)
					tree.setRedraw(false);
				removeAll(tree);
				tree.setData(getRoot());
				createChildren(tree);
				internalExpandToLevel(tree, expandToLevel);
				if (useRedraw)
					tree.setRedraw(true);
			}
		});
	}
	/**
	 * Recursively collapses the subtree rooted at the given widget to the
	 * given level.
	 * <p>
	 * </p>
	 * Note that the default implementation of this method does not call <code>setRedraw</code>.
	 * 
	 * @param widget
	 *           the widget
	 * @param level
	 *           non-negative level, or <code>ALL_LEVELS</code> to collapse
	 *           all levels of the tree
	 */
	protected void internalCollapseToLevel(Widget widget, int level) {
		if (level == ALL_LEVELS || level > 0) {

			if (widget instanceof Item)
				setExpanded((Item) widget, false);

			if (level == ALL_LEVELS || level > 1) {
				Item[] children = getChildren(widget);
				if (children != null) {
					int nextLevel =
						(level == ALL_LEVELS ? ALL_LEVELS : level - 1);
					for (int i = 0; i < children.length; i++)
						internalCollapseToLevel(children[i], nextLevel);
				}
			}
		}
	}
	/**
	 * Recursively collects all expanded elements from the given widget.
	 * 
	 * @param result
	 *           a list (element type: <code>Object</code>) into which to
	 *           collect the elements
	 * @param widget
	 *           the widget
	 */
	private void internalCollectExpanded(List result, Widget widget) {
		Item[] items = getChildren(widget);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			if (getExpanded(item)) {
				Object data = item.getData();
				if (data != null)
					result.add(data);
			}
			internalCollectExpanded(result, item);
		}
	}
	/**
	 * Tries to create a path of tree items for the given element. This method
	 * recursively walks up towards the root of the tree and assumes that
	 * <code>getParent</code> returns the correct parent of an element.
	 * 
	 * @param element
	 *           the element
	 * @param expand
	 *           <code>true</code> if all nodes on the path should be
	 *           expanded, and <code>false</code> otherwise
	 */
	protected Widget internalExpand(Object element, boolean expand) {

		if (element == null)
			return null;

		Widget w = findItem(element);
		if (w == null) {
			if (equals(element, getRoot())) { // stop at root
				return null;
			}
			// my parent has to create me
			ITreeContentProvider cp =
				(ITreeContentProvider) getContentProvider();
			if (cp == null) {
				return null;
			}
			Object parent = cp.getParent(element);
			if (parent != null) {
				Widget pw = internalExpand(parent, expand);
				if (pw != null) {
					// let my parent create me
					createChildren(pw);
					// expand parent and find me
					if (pw instanceof Item) {
						Item item = (Item) pw;
						if (expand)
							setExpanded(item, true);
						w = internalFindChild(item, element);
					}
				}
			}
		}
		return w;
	}
	/**
	 * Recursively expands the subtree rooted at the given widget to the given
	 * level.
	 * <p>
	 * </p>
	 * Note that the default implementation of this method does not call <code>setRedraw</code>.
	 * 
	 * @param widget
	 *           the widget
	 * @param level
	 *           non-negative level, or <code>ALL_LEVELS</code> to collapse
	 *           all levels of the tree
	 */
	protected void internalExpandToLevel(Widget widget, int level) {
		if (level == ALL_LEVELS || level > 0) {
			createChildren(widget);
			if (widget instanceof Item)
				setExpanded((Item) widget, true);
			if (level == ALL_LEVELS || level > 1) {
				Item[] children = getChildren(widget);
				if (children != null) {
					int newLevel =
						(level == ALL_LEVELS ? ALL_LEVELS : level - 1);
					for (int i = 0; i < children.length; i++)
						internalExpandToLevel(children[i], newLevel);
				}
			}
		}
	}
	/**
	 * Non-recursively tries to find the given element as a child of the given
	 * parent item.
	 * 
	 * @param parent
	 *           the parent item
	 * @param element
	 *           the element
	 */
	private Widget internalFindChild(Item parent, Object element) {
		Item[] items = getChildren(parent);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			Object data = item.getData();
			if (data != null && equals(data, element))
				return item;
		}
		return null;
	}
	/**
	 * Recursively tries to find the given element.
	 * 
	 * @param parent
	 *           the parent item
	 * @param element
	 *           the element
	 */
	private Widget internalFindItem(Item parent, Object element) {

		// compare with node
		Object data = parent.getData();
		if (data != null) {
			if (equals(data, element))
				return parent;
		}
		// recurse over children
		Item[] items = getChildren(parent);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			Widget o = internalFindItem(item, element);
			if (o != null)
				return o;
		}
		return null;
	}
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected void internalRefresh(Object element) {
		internalRefresh(element, true);
	}
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected void internalRefresh(Object element, boolean updateLabels) {
		// If element is null, do a full refresh.
		if (element == null) {
			internalRefresh(getControl(), getRoot(), true, updateLabels);
			return;
		}
		Widget item = findItem(element);
		if (item != null) {
			// pick up structure changes too
			internalRefresh(item, element, true, updateLabels);
		}
	}
	/**
	 * Refreshes the tree starting at the given widget.
	 * 
	 * @param widget
	 *           the widget
	 * @param element
	 *           the element
	 * @param doStruct
	 *           <code>true</code> if structural changes are to be picked up,
	 *           and <code>false</code> if only label provider changes are of
	 *           interest
	 * @param updateLabels
	 *           <code>true</code> to update labels for existing elements,
	 *           <code>false</code> to only update labels as needed, assuming
	 *           that labels for existing elements are unchanged.
	 */
	private void internalRefresh(
		Widget widget,
		Object element,
		boolean doStruct,
		boolean updateLabels) {

		if (widget instanceof Item) {
			if (doStruct) {
				updatePlus((Item) widget, element);
			}
			if (updateLabels || !equals(element, widget.getData())) {
				doUpdateItem(widget, element, true);
			} else {
				associate(element, (Item) widget);
			}
		}

		if (doStruct) {
			internalRefreshStruct(widget, element, updateLabels);
		} else {
			Item[] children = getChildren(widget);
			if (children != null) {
				for (int i = 0; i < children.length; i++) {
					Widget item = children[i];
					Object data = item.getData();
					if (data != null)
						internalRefresh(item, data, doStruct, updateLabels);
				}
			}
		}
	}

	/**
	 * Update the structure and recurse. Items are updated in updateChildren,
	 * as needed.
	 */
	private void internalRefreshStruct(
		Widget widget,
		Object element,
		boolean updateLabels) {
		updateChildren(widget, element, null, updateLabels);
		Item[] children = getChildren(widget);
		if (children != null) {
			for (int i = 0; i < children.length; i++) {
				Widget item = children[i];
				Object data = item.getData();
				if (data != null)
					internalRefreshStruct(item, data, updateLabels);
			}
		}
	}

	/**
	 * Removes the given elements from this viewer.
	 * 
	 * @param elements
	 *           the elements to remove
	 */
	private void internalRemove(Object[] elements) {
		Object input = getInput();
		HashSet parentItems = new HashSet(5);
		for (int i = 0; i < elements.length; ++i) {
			if (equals(elements[i], input)) {
				setInput(null);
				return;
			}
			Widget childItem = findItem(elements[i]);
			if (childItem instanceof Item) {
				Item parentItem = getParentItem((Item) childItem);
				if (parentItem != null) {
					parentItems.add(parentItem);
				}
				disassociate((Item) childItem);
				childItem.dispose();
			}
		}
		Control tree = getControl();
		for (Iterator i = parentItems.iterator(); i.hasNext();) {
			Item parentItem = (Item) i.next();
			if (!getExpanded(parentItem) && getItemCount(parentItem) == 0) {
				// append a dummy if necessary
				if (isExpandable(parentItem.getData())) {
					newItem(parentItem, SWT.NULL, -1);
				} else {
					// XXX: Workaround (PR missing)
					tree.redraw();
				}
			}
		}
	}
	/**
	 * Sets the expanded state of all items to correspond to the given set of
	 * expanded elements.
	 * 
	 * @param expandedElements
	 *           the set (element type: <code>Object</code>) of elements
	 *           which are expanded
	 * @param widget
	 *           the widget
	 */
	private void internalSetExpanded(HashSet expandedElements, Widget widget) {
		Item[] items = getChildren(widget);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			Object data = item.getData();
			if (data != null) {
				// remove the element to avoid an infinite loop
				// if the same element appears on a child item
				boolean expanded = expandedElements.remove(data);
				if (expanded != getExpanded(item)) {
					if (expanded) {
						createChildren(item);
					}
					setExpanded(item, expanded);
				}
			}
			internalSetExpanded(expandedElements, item);
		}
	}
	/**
	 * Return whether the tree node representing the given element can be
	 * expanded.
	 * <p>
	 * The default implementation of this framework method calls <code>hasChildren</code>
	 * on this viewer's content provider. It may be overridden if necessary.
	 * </p>
	 * 
	 * @param element
	 *           the element
	 * @return <code>true</code> if the tree node representing the given
	 *         element can be expanded, or <code>false</code> if not
	 */
	public boolean isExpandable(Object element) {
		ITreeContentProvider cp = (ITreeContentProvider) getContentProvider();
		return cp != null && cp.hasChildren(element);
	}
	/* (non-Javadoc) Method declared on Viewer. */
	protected void labelProviderChanged() {
		// we have to walk the (visible) tree and update every item
		Control tree = getControl();
		tree.setRedraw(false);
		// don't pick up structure changes, but do force label updates
		internalRefresh(tree, getRoot(), false, true);
		tree.setRedraw(true);
	}
	/**
	 * Creates a new item.
	 * 
	 * @param parent
	 *           the parent widget
	 * @param style
	 *           SWT style bits
	 * @param index
	 *           if non-negative, indicates the position to insert the item
	 *           into its parent
	 * @return the newly-created item
	 */
	protected abstract Item newItem(Widget parent, int style, int index);
	/**
	 * Removes the given elements from this viewer. The selection is updated if
	 * required.
	 * <p>
	 * This method should be called (by the content provider) when elements
	 * have been removed from the model, in order to cause the viewer to
	 * accurately reflect the model. This method only affects the viewer, not
	 * the model.
	 * </p>
	 * 
	 * @param elements
	 *           the elements to remove
	 */
	public void remove(final Object[] elements) {
		preservingSelection(new Runnable() {
			public void run() {
				internalRemove(elements);
			}
		});
	}
	/**
	 * Removes the given element from the viewer. The selection is updated if
	 * necessary.
	 * <p>
	 * This method should be called (by the content provider) when a single
	 * element has been removed from the model, in order to cause the viewer to
	 * accurately reflect the model. This method only affects the viewer, not
	 * the model. Note that there is another method for efficiently processing
	 * the simultaneous removal of multiple elements.
	 * </p>
	 * 
	 * @param element
	 *           the element
	 */
	public void remove(Object element) {
		remove(new Object[] { element });
	}
	/**
	 * Removes all items from the given control.
	 * 
	 * @param control
	 *           the control
	 */
	protected abstract void removeAll(Control control);
	/**
	 * Removes a listener for expand and collapse events in this viewer. Has no
	 * affect if an identical listener is not registered.
	 * 
	 * @param listener
	 *           a tree viewer listener
	 */
	public void removeTreeListener(ITreeViewerListener listener) {
		treeListeners.remove(listener);
	}
	/* Non-Javadoc. Method defined on StructuredViewer. */
	public void reveal(Object element) {
		Widget w = internalExpand(element, true);
		if (w instanceof Item)
			showItem((Item) w);
	}
	/**
	 * Returns the rightmost visible descendent of the given item. Returns the
	 * item itself if it has no children.
	 * 
	 * @param item
	 *           the item to compute the descendent of
	 * @return the rightmost visible descendent or the item iself if it has no
	 *         children
	 */
	private Item rightMostVisibleDescendent(Item item) {
		Item[] children = getItems(item);
		if (getExpanded(item) && children != null && children.length > 0) {
			return rightMostVisibleDescendent(children[children.length - 1]);
		} else {
			return item;
		}
	}
	/* (non-Javadoc) Method declared on Viewer. */
	public Item scrollDown(int x, int y) {
		Item current = getItem(x, y);
		if (current != null) {
			Item next = getNextItem(current, true);
			showItem(next == null ? current : next);
			return next;
		}
		return null;
	}
	/* (non-Javadoc) Method declared on Viewer. */
	public Item scrollUp(int x, int y) {
		Item current = getItem(x, y);
		if (current != null) {
			Item previous = getPreviousItem(current);
			showItem(previous == null ? current : previous);
			return previous;
		}
		return null;
	}
	/**
	 * Sets the auto-expand level. The value 0 means that there is no
	 * auto-expand; 1 means that top-level elements are expanded, but not their
	 * children; 2 means that top-level elements are expanded, and their
	 * children, but not grandchildren; and so on.
	 * <p>
	 * The value <code>ALL_LEVELS</code> means that all subtrees should be
	 * expanded.
	 * </p>
	 * 
	 * @param level
	 *           non-negative level, or <code>ALL_LEVELS</code> to expand all
	 *           levels of the tree
	 */
	public void setAutoExpandLevel(int level) {
		expandToLevel = level;
	}
	/**
	 * The <code>AbstractTreeViewer</code> implementation of this method
	 * checks to ensure that the content provider is an <code>ITreeContentProvider</code>.
	 */
	public void setContentProvider(IContentProvider provider) {
		Assert.isTrue(provider instanceof ITreeContentProvider);
		super.setContentProvider(provider);
	}
	/**
	 * Sets the expand state of the given item.
	 * 
	 * @param item
	 *           the item
	 * @param expand
	 *           the expand state of the item
	 */
	protected abstract void setExpanded(Item item, boolean expand);
	/**
	 * Sets which nodes are expanded in this viewer's tree. The given list
	 * contains the elements that are to be expanded; all other nodes are to be
	 * collapsed.
	 * <p>
	 * This method is typically used when restoring the interesting state of a
	 * viewer captured by an earlier call to <code>getExpandedElements</code>.
	 * </p>
	 * 
	 * @param elements
	 *           the array of expanded elements
	 * @see #getExpandedElements
	 */
	public void setExpandedElements(Object[] elements) {
		HashSet expandedElements = new HashSet(elements.length * 2 + 1);
		for (int i = 0; i < elements.length; ++i) {
			// Ensure item exists for element
			internalExpand(elements[i], false);
			expandedElements.add(elements[i]);
		}
		internalSetExpanded(expandedElements, getControl());
	}
	/**
	 * Sets whether the node corresponding to the given element is expanded or
	 * collapsed.
	 * 
	 * @param element
	 *           the element
	 * @param expanded
	 *           <code>true</code> if the node is expanded, and <code>false</code>
	 *           if collapsed
	 */
	public void setExpandedState(Object element, boolean expanded) {
		Widget item = internalExpand(element, false);
		if (item instanceof Item) {
			if (expanded) {
				createChildren(item);
			}
			setExpanded((Item) item, expanded);
		}
	}
	/**
	 * Sets the selection to the given list of items.
	 * 
	 * @param items
	 *           list of items (element type: <code>org.eclipse.swt.widgets.Item</code>)
	 */
	protected abstract void setSelection(List items);
	/* (non-Javadoc) Method declared on StructuredViewer. */
	protected void setSelectionToWidget(List v, boolean reveal) {
		if (v == null) {
			setSelection(new ArrayList(0));
			return;
		}
		int size = v.size();
		List newSelection = new ArrayList(size);
		for (int i = 0; i < size; ++i) {
			// Use internalExpand since item may not yet be created. See
			// 1G6B1AR.
			Widget w = internalExpand(v.get(i), true);
			if (w instanceof Item) {
				newSelection.add(w);
			}
		}
		setSelection(newSelection);
		if (reveal && newSelection.size() > 0) {
			showItem((Item) newSelection.get(0));
		}
	}
	/**
	 * Shows the given item.
	 * 
	 * @param item
	 *           the item
	 */
	protected abstract void showItem(Item item);

	/**
	 * Updates the tree items to correspond to the child elements of the given
	 * parent element. If null is passed for the children, this method obtains
	 * them (only if needed).
	 * 
	 * @param widget
	 *           the widget
	 * @param parent
	 *           the parent element
	 * @param elementChildren
	 *           the child elements, or null
	 * @deprecated this is no longer called by the framework
	 */
	protected void updateChildren(
		Widget widget,
		Object parent,
		Object[] elementChildren) {
		updateChildren(widget, parent, elementChildren, true);
	}

	/**
	 * Updates the tree items to correspond to the child elements of the given
	 * parent element. If null is passed for the children, this method obtains
	 * them (only if needed).
	 * 
	 * @param widget
	 *           the widget
	 * @param parent
	 *           the parent element
	 * @param elementChildren
	 *           the child elements, or null
	 * @param updateLabels
	 *           <code>true</code> to update labels for existing elements,
	 *           <code>false</code> to only update labels as needed, assuming
	 *           that labels for existing elements are unchanged.
	 * @since 2.1
	 */
	private void updateChildren(
		Widget widget,
		Object parent,
		Object[] elementChildren,
		boolean updateLabels) {
		// optimization! prune collapsed subtrees
		if (widget instanceof Item) {
			Item ti = (Item) widget;
			if (!getExpanded(ti)) {
				// need a dummy node if element is expandable;
				// but try to avoid recreating the dummy node
				boolean needDummy = isExpandable(parent);
				boolean haveDummy = false;
				// remove all children
				Item[] items = getItems(ti);
				for (int i = 0; i < items.length; i++) {
					if (items[i].getData() != null) {
						disassociate(items[i]);
						items[i].dispose();
					} else {
						if (needDummy && !haveDummy) {
							haveDummy = true;
						} else {
							items[i].dispose();
						}
					}
				}
				if (needDummy && !haveDummy) {
					newItem(ti, SWT.NULL, -1);
				}

				return;
			}
		}

		// If the children weren't passed in, get them now since they're needed
		// below.
		if (elementChildren == null) {
			elementChildren = getSortedChildren(parent);
		}

		Control tree = getControl();

		// WORKAROUND
		int oldCnt = -1;
		if (widget == tree)
			oldCnt = getItemCount(tree);

		Item[] items = getChildren(widget);

		// save the expanded elements
		HashSet expanded = new HashSet(); // assume num expanded is small
		for (int i = 0; i < items.length; ++i) {
			if (getExpanded(items[i])) {
				Object element = items[i].getData();
				if (element != null) {
					expanded.add(element);
				}
			}
		}

		int min = Math.min(elementChildren.length, items.length);

		// Note: In the code below, doing disassociate calls before associate
		// calls is important,
		// since a later disassociate can undo an earlier associate,
		// if items are changing position.

		// dispose of all items beyond the end of the current elements
		for (int i = items.length; --i >= min;) {
			if (items[i].getData() != null) {
				disassociate(items[i]);
			}
			items[i].dispose();
		}

		// compare first min items, and update item if necessary
		// need to do it in two passes:
		// 1: disassociate old items
		// 2: associate new items
		// because otherwise a later disassociate can remove a mapping made for
		// a previous associate,
		// making the map inconsistent
		for (int i = 0; i < min; ++i) {
			Item item = items[i];
			Object oldElement = item.getData();
			if (oldElement != null) {
				Object newElement = elementChildren[i];
				if (newElement != oldElement) {
					if (equals(newElement, oldElement)) {
						// update the data to be the new element, since
						// although the elements
						// may be equal, they may still have different labels
						// or children
						item.setData(newElement);
						mapElement(newElement, item);
					} else {
						disassociate(item);
					}
				}
			}
		}
		for (int i = 0; i < min; ++i) {
			Item item = items[i];
			Object newElement = elementChildren[i];
			if (item.getData() == null) {
				// old and new elements are not equal
				associate(newElement, item);
				updatePlus(item, newElement);
				updateItem(item, newElement);
				// Restore expanded state for items that changed position.
				// Make sure setExpanded is called after updatePlus, since
				// setExpanded(false) fails if item has no children.
				// Need to call setExpanded for both expanded and unexpanded
				// cases
				// since the expanded state can change either way.
				setExpanded(item, expanded.contains(newElement));
			} else {
				// old and new elements are equal
				updatePlus(item, newElement);
				if (updateLabels) {
					updateItem(item, newElement);
				}
			}
		}

		// add any remaining elements
		if (min < elementChildren.length) {
			for (int i = min; i < elementChildren.length; ++i) {
				createTreeItem(widget, elementChildren[i], i);
			}

			// Need to restore expanded state in a separate pass
			// because createTreeItem does not return the new item.
			// Avoid doing this unless needed.
			if (!expanded.isEmpty()) {
				// get the items again, to include the new items
				items = getChildren(widget);
				for (int i = min; i < elementChildren.length; ++i) {
					// Restore expanded state for items that changed position.
					// Make sure setExpanded is called after updatePlus (called
					// in createTreeItem), since
					// setExpanded(false) fails if item has no children.
					// Only need to call setExpanded if element was expanded
					// since new items are initially unexpanded.
					if (expanded.contains(elementChildren[i])) {
						setExpanded(items[i], true);
					}
				}
			}
		}

		// WORKAROUND
		if (widget == tree && oldCnt == 0 && getItemCount(tree) != 0) {
			//System.out.println("WORKAROUND setRedraw");
			tree.setRedraw(false);
			tree.setRedraw(true);
		}
	}
	/**
	 * Updates the "+"/"-" icon of the tree node from the given element. It
	 * calls <code>isExpandable</code> to determine whether an element is
	 * expandable.
	 * 
	 * @param item
	 *           the item
	 * @param element
	 *           the element
	 */
	protected void updatePlus(Item item, Object element) {
		boolean hasPlus = getItemCount(item) > 0;
		boolean needsPlus = isExpandable(element);
		boolean removeAll = false;
		boolean addDummy = false;
		Object data = item.getData();
		if (data != null && equals(element, data)) {
			// item shows same element
			if (hasPlus != needsPlus) {
				if (needsPlus)
					addDummy = true;
				else
					removeAll = true;
			}
		} else {
			// item shows different element
			removeAll = true;
			addDummy = needsPlus;

			// we cannot maintain expand state so collapse it
			setExpanded(item, false);
		}
		if (removeAll) {
			// remove all children
			Item[] items = getItems(item);
			for (int i = 0; i < items.length; i++) {
				if (items[i].getData() != null)
					disassociate(items[i]);
				items[i].dispose();
			}
		}
		if (addDummy)
			newItem(item, SWT.NULL, -1); // append a dummy
	}

	/**
	 * Gets the expanded elements that are visible to the user. An expanded
	 * element is only visible if the parent is expanded.
	 * 
	 * @return the visible expanded elements
	 * @since 2.0
	 */
	public Object[] getVisibleExpandedElements() {
		ArrayList v = new ArrayList();
		internalCollectVisibleExpanded(v, getControl());
		return v.toArray();
	}

	private void internalCollectVisibleExpanded(
		ArrayList result,
		Widget widget) {
		Item[] items = getChildren(widget);
		for (int i = 0; i < items.length; i++) {
			Item item = items[i];
			if (getExpanded(item)) {
				Object data = item.getData();
				if (data != null)
					result.add(data);
				//Only recurse if it is expanded - if
				//not then the children aren't visible
				internalCollectVisibleExpanded(result, item);
			}
		}
	}
}