/*
 * Copyright (c) 2000 World Wide Web Consortium,
 * (Massachusetts Institute of Technology, Institut National de
 * Recherche en Informatique et en Automatique, Keio University). All
 * Rights Reserved. This program is distributed under the W3C's Software
 * Intellectual Property License. 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 W3C License http://www.w3.org/Consortium/Legal/ for more details.
 */

package org.w3c.dom.traversal;

import org.w3c.dom.Node;
import org.w3c.dom.DOMException;

/**
 * <code>TreeWalker</code> objects are used to navigate a document tree or
 * subtree using the view of the document defined by their
 * <code>whatToShow</code> flags and filter (if any). Any function which
 * performs navigation using a <code>TreeWalker</code> will automatically
 * support any view defined by a <code>TreeWalker</code>.
 * <p>
 * Omitting nodes from the logical view of a subtree can result in a structure
 * that is substantially different from the same subtree in the complete,
 * unfiltered document. Nodes that are siblings in the <code>TreeWalker</code>
 * view may be children of different, widely separated nodes in the original
 * view. For instance, consider a <code>NodeFilter</code> that skips all
 * nodes except for Text nodes and the root node of a document. In the logical
 * view that results, all text nodes will be siblings and appear as direct
 * children of the root node, no matter how deeply nested the structure of the
 * original document.
 * <p>
 * See also the <a
 * href='http://www.w3.org/TR/2000/REC-DOM-Level-2-Traversal-Range-20001113'>Document
 * Object Model (DOM) Level 2 Traversal and Range Specification</a>.
 * 
 * @since DOM Level 2
 */
public interface TreeWalker {
	/**
	 * The <code>root</code> node of the <code>TreeWalker</code>, as
	 * specified when it was created.
	 */
	public Node getRoot();

	/**
	 * This attribute determines which node types are presented via the
	 * <code>TreeWalker</code>. The available set of constants is defined
	 * in the <code>NodeFilter</code> interface. Nodes not accepted by
	 * <code>whatToShow</code> will be skipped, but their children may still
	 * be considered. Note that this skip takes precedence over the filter, if
	 * any.
	 */
	public int getWhatToShow();

	/**
	 * The filter used to screen nodes.
	 */
	public NodeFilter getFilter();

	/**
	 * The value of this flag determines whether the children of entity
	 * reference nodes are visible to the <code>TreeWalker</code>. If
	 * false, they and their descendants will be rejected. Note that this
	 * rejection takes precedence over <code>whatToShow</code> and the
	 * filter, if any. <br>
	 * To produce a view of the document that has entity references expanded
	 * and does not expose the entity reference node itself, use the
	 * <code>whatToShow</code> flags to hide the entity reference node and
	 * set <code>expandEntityReferences</code> to true when creating the
	 * <code>TreeWalker</code>. To produce a view of the document that has
	 * entity reference nodes but no entity expansion, use the
	 * <code>whatToShow</code> flags to show the entity reference node and
	 * set <code>expandEntityReferences</code> to false.
	 */
	public boolean getExpandEntityReferences();

	/**
	 * The node at which the <code>TreeWalker</code> is currently
	 * positioned. <br>
	 * Alterations to the DOM tree may cause the current node to no longer be
	 * accepted by the <code>TreeWalker</code>'s associated filter.
	 * <code>currentNode</code> may also be explicitly set to any node,
	 * whether or not it is within the subtree specified by the
	 * <code>root</code> node or would be accepted by the filter and
	 * <code>whatToShow</code> flags. Further traversal occurs relative to
	 * <code>currentNode</code> even if it is not part of the current view,
	 * by applying the filters in the requested direction; if no traversal is
	 * possible, <code>currentNode</code> is not changed.
	 * 
	 * @exception DOMException
	 *                NOT_SUPPORTED_ERR: Raised if an attempt is made to set
	 *                <code>currentNode</code> to <code>null</code>.
	 */
	public Node getCurrentNode();

	public void setCurrentNode(Node currentNode) throws DOMException;

	/**
	 * Moves to and returns the closest visible ancestor node of the current
	 * node. If the search for <code>parentNode</code> attempts to step
	 * upward from the <code>TreeWalker</code>'s <code>root</code> node,
	 * or if it fails to find a visible ancestor node, this method retains the
	 * current position and returns <code>null</code>.
	 * 
	 * @return The new parent node, or <code>null</code> if the current node
	 *         has no parent in the <code>TreeWalker</code>'s logical view.
	 */
	public Node parentNode();

	/**
	 * Moves the <code>TreeWalker</code> to the first visible child of the
	 * current node, and returns the new node. If the current node has no
	 * visible children, returns <code>null</code>, and retains the current
	 * node.
	 * 
	 * @return The new node, or <code>null</code> if the current node has no
	 *         visible children in the <code>TreeWalker</code>'s logical
	 *         view.
	 */
	public Node firstChild();

	/**
	 * Moves the <code>TreeWalker</code> to the last visible child of the
	 * current node, and returns the new node. If the current node has no
	 * visible children, returns <code>null</code>, and retains the current
	 * node.
	 * 
	 * @return The new node, or <code>null</code> if the current node has no
	 *         children in the <code>TreeWalker</code>'s logical view.
	 */
	public Node lastChild();

	/**
	 * Moves the <code>TreeWalker</code> to the previous sibling of the
	 * current node, and returns the new node. If the current node has no
	 * visible previous sibling, returns <code>null</code>, and retains the
	 * current node.
	 * 
	 * @return The new node, or <code>null</code> if the current node has no
	 *         previous sibling. in the <code>TreeWalker</code>'s logical
	 *         view.
	 */
	public Node previousSibling();

	/**
	 * Moves the <code>TreeWalker</code> to the next sibling of the current
	 * node, and returns the new node. If the current node has no visible next
	 * sibling, returns <code>null</code>, and retains the current node.
	 * 
	 * @return The new node, or <code>null</code> if the current node has no
	 *         next sibling. in the <code>TreeWalker</code>'s logical view.
	 */
	public Node nextSibling();

	/**
	 * Moves the <code>TreeWalker</code> to the previous visible node in
	 * document order relative to the current node, and returns the new node.
	 * If the current node has no previous node, or if the search for
	 * <code>previousNode</code> attempts to step upward from the
	 * <code>TreeWalker</code>'s <code>root</code> node, returns
	 * <code>null</code>, and retains the current node.
	 * 
	 * @return The new node, or <code>null</code> if the current node has no
	 *         previous node in the <code>TreeWalker</code>'s logical view.
	 */
	public Node previousNode();

	/**
	 * Moves the <code>TreeWalker</code> to the next visible node in
	 * document order relative to the current node, and returns the new node.
	 * If the current node has no next node, or if the search for nextNode
	 * attempts to step upward from the <code>TreeWalker</code>'s
	 * <code>root</code> node, returns <code>null</code>, and retains the
	 * current node.
	 * 
	 * @return The new node, or <code>null</code> if the current node has no
	 *         next node in the <code>TreeWalker</code>'s logical view.
	 */
	public Node nextNode();

}