Package org.apache.wicket.markup.html.tree

Source Code of org.apache.wicket.markup.html.tree.AbstractTree

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.wicket.markup.html.tree;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreeNode;

import org.apache.wicket.Component;
import org.apache.wicket.IRequestTarget;
import org.apache.wicket.ResourceReference;
import org.apache.wicket.ajax.AjaxRequestTarget;
import org.apache.wicket.behavior.HeaderContributor;
import org.apache.wicket.behavior.IBehavior;
import org.apache.wicket.markup.ComponentTag;
import org.apache.wicket.markup.MarkupStream;
import org.apache.wicket.markup.html.WebMarkupContainer;
import org.apache.wicket.markup.html.internal.HtmlHeaderContainer;
import org.apache.wicket.markup.html.panel.Panel;
import org.apache.wicket.markup.html.resources.JavascriptResourceReference;
import org.apache.wicket.model.IDetachable;
import org.apache.wicket.model.IModel;
import org.apache.wicket.model.Model;
import org.apache.wicket.util.string.AppendingStringBuffer;


/**
* This class encapsulates the logic for displaying and (partial) updating the tree. Actual
* presentation is out of scope of this class. User should derive they own tree (if needed) from
* {@link BaseTree} (recommended).
*
* @author Matej Knopp
*/
public abstract class AbstractTree extends Panel
  implements
    ITreeStateListener,
    TreeModelListener,
    AjaxRequestTarget.ITargetRespondListener
{

  /**
   *
   */
  private static final long serialVersionUID = 1L;

  /**
   * Interface for visiting individual tree items.
   */
  private static interface IItemCallback
  {
    /**
     * Visits the tree item.
     *
     * @param item
     *            the item to visit
     */
    void visitItem(TreeItem item);
  }

  /**
   * This class represents one row in rendered tree (TreeNode). Only TreeNodes that are visible
   * (all their parent are expanded) have TreeItem created for them.
   */
  private final class TreeItem extends WebMarkupContainer
  {
    /**
     * whether this tree item should also render it's children to response. this is set if we
     * need the whole subtree rendered as one component in ajax response, so that we can replace
     * it in one step (replacing individual rows is very slow in javascript, therefore we
     * replace the whole subtree)
     */
    private final static int FLAG_RENDER_CHILDREN = FLAG_RESERVED8;

    private static final long serialVersionUID = 1L;

    /**
     * tree item children - we need this to traverse items in correct order when rendering
     */
    private List children = null;

    /** tree item level - how deep is this item in tree */
    private final int level;

    /**
     * Construct.
     *
     * @param id
     *            The component id
     * @param node
     *            tree node
     * @param level
     *            current level
     */
    public TreeItem(String id, final TreeNode node, int level)
    {
      super(id, new Model((Serializable)node));

      nodeToItemMap.put(node, this);
      this.level = level;
      setOutputMarkupId(true);

      // if this isn't a root item in rootless mode
      if (level != -1)
      {
        populateTreeItem(this, level);
      }
    }

    /**
     * @return The children
     */
    public List getChildren()
    {
      return children;
    }

    /**
     * @return The current level
     */
    public int getLevel()
    {
      return level;
    }

    /**
     * @see org.apache.wicket.Component#getMarkupId()
     */
    public String getMarkupId()
    {
      // this is overridden to produce id that begins with id of tree
      // if the tree has set (shorter) id in markup, we can use it to
      // shorten the id of individual TreeItems
      return AbstractTree.this.getMarkupId() + "_" + getId();
    }

    /**
     * @return parent item
     */
    public TreeItem getParentItem()
    {
      return (TreeItem)nodeToItemMap.get(((TreeNode)getModelObject()).getParent());
    }

    /**
     * Sets the children.
     *
     * @param children
     *            The children
     */
    public void setChildren(List children)
    {
      this.children = children;
    }

    /**
     * Whether to render children.
     *
     * @return whether to render children
     */
    protected final boolean isRenderChildren()
    {
      return getFlag(FLAG_RENDER_CHILDREN);
    }

    /**
     * @see org.apache.wicket.MarkupContainer#onRender(org.apache.wicket.markup.MarkupStream)
     */
    protected void onRender(final MarkupStream markupStream)
    {
      // is this root and tree is in rootless mode?
      if (this == rootItem && isRootLess() == true)
      {
        // yes, write empty div with id
        // this is necessary for createElement js to work correctly
        String tagName = ((ComponentTag)markupStream.get()).getName();
        getResponse().write(
          "<" + tagName + " style=\"display:none\" id=\"" + getMarkupId() + "\"></" +
            tagName + ">");
        markupStream.skipComponent();
      }
      else
      {
        // remember current index
        final int index = markupStream.getCurrentIndex();

        // render the item
        super.onRender(markupStream);

        // should we also render children (ajax response)
        if (isRenderChildren())
        {
          // visit every child
          visitItemChildren(this, new IItemCallback()
          {
            public void visitItem(TreeItem item)
            {
              // rewind markupStream
              markupStream.setCurrentIndex(index);
              // render child
              item.onRender(markupStream);

              // go through the behaviors and invoke IBehavior.afterRender
              List behaviors = item.getBehaviors();
              for (Iterator i = behaviors.iterator(); i.hasNext();)
              {
                IBehavior behavior = (IBehavior)i.next();
                behavior.afterRender(item);
              }
            }
          });
          //
        }
      }
    }

    public void renderHead(final HtmlHeaderContainer container)
    {
      super.renderHead(container);

      if (isRenderChildren())
      {
        // visit every child
        visitItemChildren(this, new IItemCallback()
        {
          public void visitItem(TreeItem item)
          {
            // write header contributions from the children of item
            item.visitChildren(new Component.IVisitor()
            {
              public Object component(Component component)
              {
                if (component.isVisible())
                {
                  component.renderHead(container);
                  return CONTINUE_TRAVERSAL;
                }
                else
                {
                  return CONTINUE_TRAVERSAL_BUT_DONT_GO_DEEPER;
                }
              }
            });
          }
        });
      }
    }

    protected final void setRenderChildren(boolean value)
    {
      setFlag(FLAG_RENDER_CHILDREN, value);
    }

    protected void onDetach()
    {
      super.onDetach();
      Object object = getModelObject();
      if (object instanceof IDetachable)
      {
        ((IDetachable)object).detach();
      }

      if (isRenderChildren())
      {
        // visit every child
        visitItemChildren(this, new IItemCallback()
        {
          public void visitItem(TreeItem item)
          {
            item.detach();
          }
        });
      }

      // children are rendered, clear the flag
      setRenderChildren(false);
    }

    protected void onBeforeRender()
    {
      onBeforeRenderInternal();
      super.onBeforeRender();

      if (isRenderChildren())
      {
        // visit every child
        visitItemChildren(this, new IItemCallback()
        {
          public void visitItem(TreeItem item)
          {
            item.prepareForRender();
          }
        });
      }
    }

    protected void onAfterRender()
    {
      super.onAfterRender();
      if (isRenderChildren())
      {
        // visit every child
        visitItemChildren(this, new IItemCallback()
        {
          public void visitItem(TreeItem item)
          {
            item.afterRender();
          }
        });
      }
    }
  }

  /**
   * Components that holds tree items. This is similar to ListView, but it renders tree items in
   * the right order.
   */
  private class TreeItemContainer extends WebMarkupContainer
  {
    private static final long serialVersionUID = 1L;

    /**
     * Construct.
     *
     * @param id
     *            The component id
     */
    public TreeItemContainer(String id)
    {
      super(id);
    }

    /**
     * @see org.apache.wicket.MarkupContainer#remove(org.apache.wicket.Component)
     */
    public void remove(Component component)
    {
      // when a treeItem is removed, remove reference to it from
      // nodeToItemMAp
      if (component instanceof TreeItem)
      {
        nodeToItemMap.remove(((TreeItem)component).getModelObject());
      }
      super.remove(component);
    }

    /**
     * renders the tree items, making sure that items are rendered in the order they should be
     *
     * @param markupStream
     */
    protected void onRender(final MarkupStream markupStream)
    {
      // Save position in markup stream
      final int markupStart = markupStream.getCurrentIndex();

      // have we rendered at least one item?
      final class Rendered
      {
        boolean rendered = false;
      }
      ;
      final Rendered rendered = new Rendered();

      // is there a root item? (non-empty tree)
      if (rootItem != null)
      {
        IItemCallback callback = new IItemCallback()
        {
          public void visitItem(TreeItem item)
          {
            // rewind markup stream
            markupStream.setCurrentIndex(markupStart);

            // render component
            item.render(markupStream);

            rendered.rendered = true;
          }
        };

        // visit item and it's children
        visitItemAndChildren(rootItem, callback);
      }

      if (rendered.rendered == false)
      {
        // tree is empty, just move the markupStream
        markupStream.skipComponent();
      }
    }
  }

  /**
   * Returns an iterator that iterates trough the enumeration.
   *
   * @param enumeration
   *            The enumeration to iterate through
   * @return The iterator
   */
  private static final Iterator toIterator(final Enumeration enumeration)
  {
    return new Iterator()
    {
      private final Enumeration e = enumeration;

      public boolean hasNext()
      {
        return e.hasMoreElements();
      }

      public Object next()
      {
        return e.nextElement();
      }

      public void remove()
      {
        throw new UnsupportedOperationException("Remove is not supported on enumeration.");
      }
    };
  }

  private boolean attached = false;

  /** comma separated list of ids of elements to be deleted. */
  private final AppendingStringBuffer deleteIds = new AppendingStringBuffer();

  /**
   * whether the whole tree is dirty (so the whole tree needs to be refreshed).
   */
  private boolean dirtyAll = false;

  /**
   * list of dirty items. if children property of these items is null, the children will be
   * rebuild.
   */
  private final List dirtyItems = new ArrayList();

  /**
   * list of dirty items which need the DOM structure to be created for them (added items)
   */
  private final List dirtyItemsCreateDOM = new ArrayList();

  /** counter for generating unique ids of every tree item. */
  private int idCounter = 0;

  /** Component whose children are tree items. */
  private TreeItemContainer itemContainer;

  /**
   * map that maps TreeNode to TreeItem. TreeItems only exists for TreeNodes, that are visible
   * (their parents are not collapsed).
   */
  private final Map nodeToItemMap = new HashMap();

  /**
   * we need to track previous model. if the model changes, we unregister the tree from listeners
   * of old model and register the tree as listener of new model.
   */
  private TreeModel previousModel = null;

  /** root item of the tree. */
  private TreeItem rootItem = null;

  /** whether the tree root is shown. */
  private boolean rootLess = false;

  /** stores reference to tree state. */
  private ITreeState state;

  /**
   * Tree constructor
   *
   * @param id
   *            The component id
   */
  public AbstractTree(String id)
  {
    super(id);
    init();
  }

  /**
   * Tree constructor
   *
   * @param id
   *            The component id
   * @param model
   *            The tree model
   */
  public AbstractTree(String id, IModel model)
  {
    super(id, model);
    init();
  }

  /** called when all nodes are collapsed. */
  public final void allNodesCollapsed()
  {
    invalidateAll();
  }

  /** called when all nodes are expanded. */
  public final void allNodesExpanded()
  {
    invalidateAll();
  }

  /**
   * Returns the TreeState of this tree.
   *
   * @return Tree state instance
   */
  public ITreeState getTreeState()
  {
    if (state == null)
    {
      state = newTreeState();

      // add this object as listener of the state
      state.addTreeStateListener(this);
      // FIXME: Where should we remove the listener?
    }
    return state;
  }

  /**
   * This method is called before the onAttach is called. Code here gets executed before the items
   * have been populated.
   */
  protected void onBeforeAttach()
  {
  }

  // This is necessary because MarkupContainer.onBeforeRender involves calling
  // beforeRender on children, which results in stack overflow when called from TreeItem
  private void onBeforeRenderInternal()
  {
    if (attached == false)
    {
      onBeforeAttach();

      checkModel();

      // Do we have to rebuild the whole tree?
      if (dirtyAll && rootItem != null)
      {
        clearAllItem();
      }
      else
      {
        // rebuild children of dirty nodes that need it
        rebuildDirty();
      }

      // is root item created? (root item is null if the items have not
      // been created yet, or the whole tree was dirty and clearAllITem
      // has been called
      if (rootItem == null)
      {
        TreeNode rootNode = (TreeNode)((TreeModel)getModelObject()).getRoot();
        if (rootNode != null)
        {
          if (isRootLess())
          {
            rootItem = newTreeItem(rootNode, -1);
          }
          else
          {
            rootItem = newTreeItem(rootNode, 0);
          }
          itemContainer.add(rootItem);
          buildItemChildren(rootItem);
        }
      }

      attached = true;
    }
  }

  /**
   * Called at the beginning of the request (not ajax request, unless we are rendering the entire
   * component)
   */
  public void onBeforeRender()
  {
    onBeforeRenderInternal();
    super.onBeforeRender();
  }

  /**
   * @see org.apache.wicket.MarkupContainer#onDetach()
   */
  public void onDetach()
  {
    attached = false;
    super.onDetach();
  }

  /**
   * Call to refresh the whole tree. This should only be called when the roodNode has been
   * replaced or the entiry tree model changed.
   */
  public final void invalidateAll()
  {
    updated();
    dirtyAll = true;
  }

  /**
   * @return whether the tree root is shown
   */
  public final boolean isRootLess()
  {
    return rootLess;
  };

  /**
   * @see org.apache.wicket.markup.html.tree.ITreeStateListener#nodeCollapsed(javax.swing.tree.TreeNode)
   */
  public final void nodeCollapsed(TreeNode node)
  {
    if (isNodeVisible(node) == true)
    {
      invalidateNodeWithChildren(node);
    }
  }

  /**
   * @see org.apache.wicket.markup.html.tree.ITreeStateListener#nodeExpanded(javax.swing.tree.TreeNode)
   */
  public final void nodeExpanded(TreeNode node)
  {
    if (isNodeVisible(node) == true)
    {
      invalidateNodeWithChildren(node);
    }
  }

  /**
   * @see org.apache.wicket.markup.html.tree.ITreeStateListener#nodeSelected(javax.swing.tree.TreeNode)
   */
  public final void nodeSelected(TreeNode node)
  {
    if (isNodeVisible(node))
    {
      invalidateNode(node, isForceRebuildOnSelectionChange());
    }
  }

  /**
   * @see org.apache.wicket.markup.html.tree.ITreeStateListener#nodeUnselected(javax.swing.tree.TreeNode)
   */
  public final void nodeUnselected(TreeNode node)
  {
    if (isNodeVisible(node))
    {
      invalidateNode(node, isForceRebuildOnSelectionChange());
    }
  }

  /**
   * Determines whether the TreeNode needs to be rebuilt if it is selected or deselected
   *
   * @return true if the node should be rebuilt after (de)selection, false otherwise
   */
  protected boolean isForceRebuildOnSelectionChange()
  {
    return true;
  }

  /**
   * Sets whether the root of the tree should be visible.
   *
   * @param rootLess
   *            whether the root should be visible
   */
  public void setRootLess(boolean rootLess)
  {
    if (this.rootLess != rootLess)
    {
      this.rootLess = rootLess;
      invalidateAll();

      // if the tree is in rootless mode, make sure the root node is
      // expanded
      if (rootLess == true && getModelObject() != null)
      {
        getTreeState().expandNode((TreeNode)((TreeModel)getModelObject()).getRoot());
      }
    }
  }

  /**
   * @see javax.swing.event.TreeModelListener#treeNodesChanged(javax.swing.event.TreeModelEvent)
   */
  public final void treeNodesChanged(TreeModelEvent e)
  {
    // has root node changed?
    if (e.getChildren() == null)
    {
      if (rootItem != null)
      {
        invalidateNode((TreeNode)rootItem.getModelObject(), true);
      }
    }
    else
    {
      // go through all changed nodes
      Object[] children = e.getChildren();
      if (children != null)
      {
        for (int i = 0; i < children.length; i++)
        {
          TreeNode node = (TreeNode)children[i];
          if (isNodeVisible(node))
          {
            // if the nodes is visible invalidate it
            invalidateNode(node, true);
          }
        }
      }
    }
  };

  /**
   * Marks the last but one visible child node of the given item as dirty, if give child is the
   * last item of parent.
   *
   * We need this to refresh the previous visible item in case the inserted / deleted item was
   * last. The reason is that the line shape of previous item changes from L to |- .
   *
   * @param parent
   * @param child
   */
  private void markTheLastButOneChildDirty(TreeItem parent, TreeItem child)
  {
    if (parent.getChildren().indexOf(child) == parent.getChildren().size() - 1)
    {
      // go through the children backwards, start at the last but one
      // item
      for (int i = parent.getChildren().size() - 2; i >= 0; --i)
      {
        TreeItem item = (TreeItem)parent.getChildren().get(i);

        // invalidate the node and it's children, so that they are
        // redrawn
        invalidateNodeWithChildren((TreeNode)item.getModelObject());

      }
    }
  }

  /**
   * @see javax.swing.event.TreeModelListener#treeNodesInserted(javax.swing.event.TreeModelEvent)
   */
  public final void treeNodesInserted(TreeModelEvent e)
  {
    // get the parent node of inserted nodes
    TreeNode parent = (TreeNode)e.getTreePath().getLastPathComponent();

    if (isNodeVisible(parent) && isNodeExpanded(parent))
    {
      TreeItem parentItem = (TreeItem)nodeToItemMap.get(parent);
      for (int i = 0; i < e.getChildren().length; ++i)
      {
        TreeNode node = (TreeNode)e.getChildren()[i];
        int index = e.getChildIndices()[i];
        TreeItem item = newTreeItem(node, parentItem.getLevel() + 1);
        itemContainer.add(item);
        parentItem.getChildren().add(index, item);

        markTheLastButOneChildDirty(parentItem, item);

        dirtyItems.add(item);
        dirtyItemsCreateDOM.add(item);
      }
    }
  }

  /**
   * @see javax.swing.event.TreeModelListener#treeNodesRemoved(javax.swing.event.TreeModelEvent)
   */
  public final void treeNodesRemoved(TreeModelEvent e)
  {
    // get the parent node of inserted nodes
    TreeNode parent = (TreeNode)e.getTreePath().getLastPathComponent();
    TreeItem parentItem = (TreeItem)nodeToItemMap.get(parent);

    if (isNodeVisible(parent) && isNodeExpanded(parent))
    {

      for (int i = 0; i < e.getChildren().length; ++i)
      {
        TreeNode node = (TreeNode)e.getChildren()[i];

        TreeItem item = (TreeItem)nodeToItemMap.get(node);
        if (item != null)
        {
          markTheLastButOneChildDirty(parentItem, item);

          parentItem.getChildren().remove(item);

          // go though item children and remove every one of them
          visitItemChildren(item, new IItemCallback()
          {
            public void visitItem(TreeItem item)
            {
              removeItem(item);

              // deselect the node
              getTreeState().selectNode((TreeNode)item.getModelObject(), false);
            }
          });

          getTreeState().selectNode((TreeNode)item.getModelObject(), false);

          removeItem(item);
        }
      }
    }
  }

  /**
   * @see javax.swing.event.TreeModelListener#treeStructureChanged(javax.swing.event.TreeModelEvent)
   */
  public final void treeStructureChanged(TreeModelEvent e)
  {
    // get the parent node of changed nodes
    TreeNode node = e.getTreePath() != null ? (TreeNode)e.getTreePath().getLastPathComponent()
      : null;

    // has the tree root changed?
    if (node == null || e.getTreePath().getPathCount() == 1)
    {
      invalidateAll();
    }
    else
    {
      invalidateNodeWithChildren(node);
    }
  }

  /**
   * Convenience method that updates changed portions on tree. You can call this method during
   * Ajax response, where calling {@link #updateTree(AjaxRequestTarget)} would be appropriate, but
   * you don't have the AjaxRequestTarget instance. However, it is also safe to call this method
   * outside Ajax response.
   */
  public final void updateTree()
  {
    IRequestTarget target = getRequestCycle().getRequestTarget();
    if (target instanceof AjaxRequestTarget)
    {
      updateTree((AjaxRequestTarget)target);
    }
  }

  /**
   * Allows to intercept adding dirty components to AjaxRequestTarget.
   *
   * @param target
   * @param component
   */
  protected void addComponent(AjaxRequestTarget target, Component component)
  {
    target.addComponent(component);
  }

  public void onTargetRespond(AjaxRequestTarget target)
  {
    // check whether the model hasn't changed
    checkModel();

    // is the whole tree dirty
    if (dirtyAll)
    {
      // render entire tree component
      addComponent(target, this);
    }
    else
    {
      // remove DOM elements that need to be removed
      if (deleteIds.length() != 0)
      {
        String js = getElementsDeleteJavascript();

        // add the javascript to target
        target.prependJavascript(js);
      }

      // We have to repeat this as long as there are any dirty items to be
      // created.
      // The reason why we can't do this in one pass is that some of the
      // items
      // may need to be inserted after items that has not been inserted
      // yet, so we have
      // to detect those and wait until the items they depend on are
      // inserted.
      while (dirtyItemsCreateDOM.isEmpty() == false)
      {
        for (Iterator i = dirtyItemsCreateDOM.iterator(); i.hasNext();)
        {
          TreeItem item = (TreeItem)i.next();
          TreeItem parent = item.getParentItem();
          int index = parent.getChildren().indexOf(item);
          TreeItem previous;
          // we need item before this (in dom structure)

          if (index == 0)
          {
            previous = parent;
          }
          else
          {
            previous = (TreeItem)parent.getChildren().get(index - 1);
            // get the last item of previous item subtree
            while (previous.getChildren() != null && previous.getChildren().size() > 0)
            {
              previous = (TreeItem)previous.getChildren().get(
                previous.getChildren().size() - 1);
            }
          }
          // check if the previous item isn't waiting to be inserted
          if (dirtyItemsCreateDOM.contains(previous) == false)
          {
            // it's already in dom, so we can use it as point of
            // insertion
            target.prependJavascript("Wicket.Tree.createElement(\"" +
              item.getMarkupId() + "\"," + "\"" + previous.getMarkupId() + "\")");

            // remove the item so we don't process it again
            i.remove();
          }
          else
          {
            // we don't do anything here, inserting this item will
            // have to wait
            // until the previous item gets inserted
          }
        }
      }

      // iterate through dirty items
      for (Iterator i = dirtyItems.iterator(); i.hasNext();)
      {
        TreeItem item = (TreeItem)i.next();
        // does the item need to rebuild children?
        if (item.getChildren() == null)
        {
          // rebuild the children
          buildItemChildren(item);

          // set flag on item so that it renders itself together with
          // it's children
          item.setRenderChildren(true);
        }

        // add the component to target
        addComponent(target, item);
      }

      // clear dirty flags
      updated();
    }
  }

  /**
   * Updates the changed portions of the tree using given AjaxRequestTarget. Call this method if
   * you modified the tree model during an ajax request target and you want to partially update
   * the component on page. Make sure that the tree model has fired the proper listener functions.
   * <p>
   * <b>You can only call this method once in a request.</b>
   *
   * @param target
   *            Ajax request target used to send the update to the page
   */
  public final void updateTree(final AjaxRequestTarget target)
  {
    if (target == null)
    {
      return;
    }

    target.registerRespondListener(this);
  }

  /**
   * Returns whether the given node is expanded.
   *
   * @param node
   *            The node to inspect
   * @return true if the node is expanded, false otherwise
   */
  protected final boolean isNodeExpanded(TreeNode node)
  {
    // In root less mode the root node is always expanded
    if (isRootLess() && rootItem != null && rootItem.getModelObject().equals(node))
    {
      return true;
    }

    return getTreeState().isNodeExpanded(node);
  }

  /**
   * Creates the TreeState, which is an object where the current state of tree (which nodes are
   * expanded / collapsed, selected, ...) is stored.
   *
   * @return Tree state instance
   */
  protected ITreeState newTreeState()
  {
    return new DefaultTreeState();
  }

  /**
   * Called after the rendering of tree is complete. Here we clear the dirty flags.
   */
  protected void onAfterRender()
  {
    super.onAfterRender();
    // rendering is complete, clear all dirty flags and items
    updated();
  }

  /**
   * This method is called after creating every TreeItem. This is the place for adding components
   * on item (junction links, labels, icons...)
   *
   * @param item
   *            newly created tree item. The node can be obtained as item.getModelObject()
   *
   * @param level
   *            how deep the component is in tree hierarchy (0 for root item)
   */
  protected abstract void populateTreeItem(WebMarkupContainer item, int level);

  /**
   * Builds the children for given TreeItem. It recursively traverses children of it's TreeNode
   * and creates TreeItem for every visible TreeNode.
   *
   * @param item
   *            The parent tree item
   */
  private final void buildItemChildren(TreeItem item)
  {
    List items;

    // if the node is expanded
    if (isNodeExpanded((TreeNode)item.getModelObject()))
    {
      // build the items for children of the items' treenode.
      items = buildTreeItems(nodeChildren((TreeNode)item.getModelObject()),
        item.getLevel() + 1);
    }
    else
    {
      // it's not expanded, just set children to an empty list
      items = new ArrayList(0);
    }

    item.setChildren(items);
  }

  /**
   * Builds (recursively) TreeItems for the given Iterator of TreeNodes.
   *
   * @param nodes
   *            The nodes to build tree items for
   * @param level
   *            The current level
   * @return List with new tree items
   */
  private final List buildTreeItems(Iterator nodes, int level)
  {
    List result = new ArrayList();

    // for each node
    while (nodes.hasNext())
    {
      TreeNode node = (TreeNode)nodes.next();
      // create tree item
      TreeItem item = newTreeItem(node, level);
      itemContainer.add(item);

      // builds it children (recursively)
      buildItemChildren(item);

      // add item to result
      result.add(item);
    }

    return result;
  }

  /**
   * Checks whether the model has been changed, and if so unregister and register listeners.
   */
  private final void checkModel()
  {
    // find out whether the model object (the TreeModel) has been changed
    TreeModel model = (TreeModel)getModelObject();
    if (model != previousModel)
    {
      if (previousModel != null)
      {
        previousModel.removeTreeModelListener(this);
      }

      previousModel = model;

      if (model != null)
      {
        model.addTreeModelListener(this);
      }
      // model has been changed, redraw whole tree
      invalidateAll();
    }
  }

  /**
   * Removes all TreeItem components.
   */
  private final void clearAllItem()
  {
    visitItemAndChildren(rootItem, new IItemCallback()
    {
      public void visitItem(TreeItem item)
      {
        item.remove();
      }
    });
    rootItem = null;
  }

  /**
   * Returns the javascript used to delete removed elements.
   *
   * @return The javascript
   */
  private String getElementsDeleteJavascript()
  {
    // build the javascript call
    final AppendingStringBuffer buffer = new AppendingStringBuffer(100);

    buffer.append("Wicket.Tree.removeNodes(\"");

    // first parameter is the markup id of tree (will be used as prefix to
    // build ids of child items
    buffer.append(getMarkupId() + "_\",[");

    // append the ids of elements to be deleted
    buffer.append(deleteIds);

    // does the buffer end if ','?
    if (buffer.endsWith(","))
    {
      // it does, trim it
      buffer.setLength(buffer.length() - 1);
    }

    buffer.append("]);");

    return buffer.toString();
  }

  //
  // State and Model callbacks
  //

  /**
   * returns the short version of item id (just the number part).
   *
   * @param item
   *            The tree item
   * @return The id
   */
  private String getShortItemId(TreeItem item)
  {
    // show much of component id can we skip? (to minimize the length of
    // javascript being sent)
    final int skip = getMarkupId().length() + 1; // the length of id of
    // tree and '_'.
    return item.getMarkupId().substring(skip);
  }

  private final static ResourceReference JAVASCRIPT = new JavascriptResourceReference(
    AbstractTree.class, "res/tree.js");

  /**
   * Initialize the component.
   */
  private final void init()
  {
    setVersioned(false);

    // we need id when we are replacing the whole tree
    setOutputMarkupId(true);

    // create container for tree items
    itemContainer = new TreeItemContainer("i");
    add(itemContainer);

    add(HeaderContributor.forJavaScript(JAVASCRIPT));

    checkModel();
  }

  /**
   * INTERNAL
   *
   * @param node
   */
  public final void markNodeDirty(TreeNode node)
  {
    invalidateNode(node, false);
  }

  /**
   * INTERNAL
   *
   * @param node
   */
  public final void markNodeChildrenDirty(TreeNode node)
  {
    TreeItem item = (TreeItem)nodeToItemMap.get(node);
    if (item != null)
    {
      visitItemChildren(item, new IItemCallback()
      {
        public void visitItem(TreeItem item)
        {
          invalidateNode((TreeNode)item.getModelObject(), false);
        }
      });
    }
  }

  /**
   * Invalidates single node (without children). On the next render, this node will be updated.
   * Node will not be rebuilt, unless forceRebuild is true.
   *
   * @param node
   *            The node to invalidate
   * @param forceRebuild
   */
  private final void invalidateNode(TreeNode node, boolean forceRebuild)
  {
    if (dirtyAll == false)
    {
      // get item for this node
      TreeItem item = (TreeItem)nodeToItemMap.get(node);

      if (item != null)
      {
        boolean createDOM = false;

        if (forceRebuild)
        {
          // recreate the item
          int level = item.getLevel();
          List children = item.getChildren();
          String id = item.getId();

          // store the parent of old item
          TreeItem parent = item.getParentItem();

          // if the old item has a parent, store it's index
          int index = parent != null ? parent.getChildren().indexOf(item) : -1;

          createDOM = dirtyItemsCreateDOM.contains(item);

          dirtyItems.remove(item);
          dirtyItemsCreateDOM.remove(item);

          item.remove();

          item = newTreeItem(node, level, id);
          itemContainer.add(item);

          item.setChildren(children);

          // was the item an root item?
          if (parent == null)
          {
            rootItem = item;
          }
          else
          {
            parent.getChildren().set(index, item);
          }
        }

        dirtyItems.add(item);
        if (createDOM)
        {
          dirtyItemsCreateDOM.add(item);
        }
      }
    }
  }

  /**
   * Invalidates node and it's children. On the next render, the node and children will be
   * updated. Node children will be rebuilt.
   *
   * @param node
   *            The node to invalidate
   */
  private final void invalidateNodeWithChildren(TreeNode node)
  {
    if (dirtyAll == false)
    {
      // get item for this node
      TreeItem item = (TreeItem)nodeToItemMap.get(node);

      // is the item visible?
      if (item != null)
      {
        // go though item children and remove every one of them
        visitItemChildren(item, new IItemCallback()
        {
          public void visitItem(TreeItem item)
          {
            removeItem(item);
          }
        });

        // set children to null so that they get rebuild
        item.setChildren(null);

        // add item to dirty items
        dirtyItems.add(item);
      }
    }
  }

  /**
   * Returns whether the given node is visible, e.g. all it's parents are expanded.
   *
   * @param node
   *            The node to inspect
   * @return true if the node is visible, false otherwise
   */
  private final boolean isNodeVisible(TreeNode node)
  {
    while (node.getParent() != null)
    {
      if (isNodeExpanded(node.getParent()) == false)
      {
        return false;
      }
      node = node.getParent();
    }
    return true;
  }

  /**
   * Creates a tree item for given node.
   *
   * @param node
   *            The tree node
   * @param level
   *            The level
   * @return The new tree item
   */
  private final TreeItem newTreeItem(TreeNode node, int level)
  {
    return new TreeItem("" + idCounter++, node, level);
  }

  /**
   * Creates a tree item for given node with specified id.
   *
   * @param node
   *            The tree node
   * @param level
   *            The level
   * @param id
   *            the component id
   * @return The new tree item
   */
  private final TreeItem newTreeItem(TreeNode node, int level, String id)
  {
    return new TreeItem(id, node, level);
  }

  /**
   * Return the representation of node children as Iterator interface.
   *
   * @param node
   *            The tree node
   * @return iterable presentation of node children
   */
  private final Iterator nodeChildren(TreeNode node)
  {
    return toIterator(node.children());
  }

  /**
   * Rebuilds children of every item in dirtyItems that needs it. This method is called for
   * non-partial update.
   */
  private final void rebuildDirty()
  {
    // go through dirty items
    for (Iterator i = dirtyItems.iterator(); i.hasNext();)
    {
      TreeItem item = (TreeItem)i.next();
      // item children need to be rebuilt
      if (item.getChildren() == null)
      {
        buildItemChildren(item);
      }
    }
  }

  /**
   * Removes the item, appends it's id to deleteIds. This is called when a items parent is being
   * deleted or rebuilt.
   *
   * @param item
   *            The item to remove
   */
  private void removeItem(TreeItem item)
  {
    // even if the item is dirty it's no longer necessary to update id
    dirtyItems.remove(item);

    // if the item was about to be created
    if (dirtyItemsCreateDOM.contains(item))
    {
      // we needed to create DOM element, we no longer do
      dirtyItemsCreateDOM.remove(item);
    }
    else
    {
      // add items id (it's short version) to ids of DOM elements that
      // will be
      // removed
      deleteIds.append(getShortItemId(item));
      deleteIds.append(",");
    }

    // remove the id
    // note that this doesn't update item's parent's children list
    item.remove();
  }

  /**
   * Calls after the tree has been rendered. Clears all dirty flags.
   */
  private final void updated()
  {
    dirtyAll = false;
    dirtyItems.clear();
    dirtyItemsCreateDOM.clear();
    deleteIds.clear(); // FIXME: Recreate it to save some space?
  }

  /**
   * Call the callback#visitItem method for the given item and all it's children.
   *
   * @param item
   *            The tree item
   * @param callback
   *            item call back
   */
  private final void visitItemAndChildren(TreeItem item, IItemCallback callback)
  {
    callback.visitItem(item);
    visitItemChildren(item, callback);
  }

  /**
   * Call the callback#visitItem method for every child of given item.
   *
   * @param item
   *            The tree item
   * @param callback
   *            The callback
   */
  private final void visitItemChildren(TreeItem item, IItemCallback callback)
  {
    if (item.getChildren() != null)
    {
      for (Iterator i = item.getChildren().iterator(); i.hasNext();)
      {
        TreeItem child = (TreeItem)i.next();
        visitItemAndChildren(child, callback);
      }
    }
  }

  /**
   * Returns the component associated with given node, or null, if node is not visible. This is
   * useful in situations when you want to touch the node element in html.
   *
   * @param node
   *            Tree node
   * @return Component associated with given node, or null if node is not visible.
   */
  public Component getNodeComponent(TreeNode node)
  {
    return (Component)nodeToItemMap.get(node);
  }
}
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