/*
 * 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.xerces.dom;

import java.util.ArrayList;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

This class implements the DOM's NodeList behavior for
Element.getElementsByTagName()

The DOM describes NodeList as follows:

1) It may represent EITHER nodes scattered through a subtree (when
returned by Element.getElementsByTagName), or just the immediate
children (when returned by Node.getChildNodes). The latter is easy,
but the former (which this class addresses) is more challenging.

2) Its behavior is "live" -- that is, it always reflects the
current state of the document tree. To put it another way, the
NodeLists obtained before and after a series of insertions and
deletions are effectively identical (as far as the user is
concerned, the former has been dynamically updated as the changes
have been made).

3) Its API accesses individual nodes via an integer index, with the
listed nodes numbered sequentially in the order that they were
found during a preorder depth-first left-to-right search of the tree.
(Of course in the case of getChildNodes, depth is not involved.) As
nodes are inserted or deleted in the tree, and hence the NodeList,
the numbering of nodes that follow them in the NodeList will
change.

It is rather painful to support the latter two in the
getElementsByTagName case. The current solution is for Nodes to
maintain a change count (eventually that may be a Digest instead),
which the NodeList tracks and uses to invalidate itself.

Unfortunately, this does _not_ respond efficiently in the case that
the dynamic behavior was supposed to address: scanning a tree while
it is being extended. That requires knowing which subtrees have
changed, which can become an arbitrarily complex problem.

We save some work by filling the ArrayList only as we access the
item()s... but I suspect the same users who demanded index-based
access will also start by doing a getLength() to control their loop,
blowing this optimization out of the water.

NOTE: Level 2 of the DOM will probably _not_ use NodeList for its
extended search mechanisms, partly for the reasons just discussed.
@xerces.internal
Version:
$Id: DeepNodeListImpl.java 778245 2009-05-24 22:27:32Z mrglavas $
Since:
 PR-DOM-Level-1-19980818./**
 * This class implements the DOM's NodeList behavior for
 * Element.getElementsByTagName()
 * <P>
 * The DOM describes NodeList as follows:
 * <P>
 * 1) It may represent EITHER nodes scattered through a subtree (when
 * returned by Element.getElementsByTagName), or just the immediate
 * children (when returned by Node.getChildNodes). The latter is easy,
 * but the former (which this class addresses) is more challenging.
 * <P>
 * 2) Its behavior is "live" -- that is, it always reflects the
 * current state of the document tree. To put it another way, the
 * NodeLists obtained before and after a series of insertions and
 * deletions are effectively identical (as far as the user is
 * concerned, the former has been dynamically updated as the changes
 * have been made).
 * <P>
 * 3) Its API accesses individual nodes via an integer index, with the
 * listed nodes numbered sequentially in the order that they were
 * found during a preorder depth-first left-to-right search of the tree.
 * (Of course in the case of getChildNodes, depth is not involved.) As
 * nodes are inserted or deleted in the tree, and hence the NodeList,
 * the numbering of nodes that follow them in the NodeList will
 * change.
 * <P>
 * It is rather painful to support the latter two in the
 * getElementsByTagName case. The current solution is for Nodes to
 * maintain a change count (eventually that may be a Digest instead),
 * which the NodeList tracks and uses to invalidate itself.
 * <P>
 * Unfortunately, this does _not_ respond efficiently in the case that
 * the dynamic behavior was supposed to address: scanning a tree while
 * it is being extended. That requires knowing which subtrees have
 * changed, which can become an arbitrarily complex problem.
 * <P>
 * We save some work by filling the ArrayList only as we access the
 * item()s... but I suspect the same users who demanded index-based
 * access will also start by doing a getLength() to control their loop,
 * blowing this optimization out of the water.
 * <P>
 * NOTE: Level 2 of the DOM will probably _not_ use NodeList for its
 * extended search mechanisms, partly for the reasons just discussed.
 * 
 * @xerces.internal

 *
 * @version $Id: DeepNodeListImpl.java 778245 2009-05-24 22:27:32Z mrglavas $
 * @since  PR-DOM-Level-1-19980818.
 */
public class DeepNodeListImpl 
    implements NodeList {

    //
    // Data
    //

    protected NodeImpl rootNode; // Where the search started
    protected String tagName;   // Or "*" to mean all-tags-acceptable
    protected int changes=0;
    protected ArrayList nodes;
    
    protected String nsName;
    protected boolean enableNS = false;

    //
    // Constructors
    //

    
Constructor. /** Constructor. */
    public DeepNodeListImpl(NodeImpl rootNode, String tagName) {
        this.rootNode = rootNode;
        this.tagName  = tagName;
        nodes = new ArrayList();
    }  

    
Constructor for Namespace support. /** Constructor for Namespace support. */
    public DeepNodeListImpl(NodeImpl rootNode,
                            String nsName, String tagName) {
        this(rootNode, tagName);
        this.nsName = (nsName != null && nsName.length() != 0) ? nsName : null;
        enableNS = true;
    }
    
    //
    // NodeList methods
    //

    
Returns the length of the node list. /** Returns the length of the node list. */
    public int getLength() {
        // Preload all matching elements. (Stops when we run out of subtree!)
        item(java.lang.Integer.MAX_VALUE);
        return nodes.size();
    }  

    
Returns the node at the specified index. /** Returns the node at the specified index. */
    public Node item(int index) {
    	Node thisNode;

        // Tree changed. Do it all from scratch!
    	if (rootNode.changes() != changes) {
            nodes   = new ArrayList();     
            changes = rootNode.changes();
    	}
    
        // In the cache
    	final int currentSize = nodes.size();
    	if (index < currentSize) {
    	    return (Node)nodes.get(index);
    	}
        // Not yet seen
    	else {
    
            // Pick up where we left off (Which may be the beginning)
    		if (currentSize == 0) { 
    		    thisNode = rootNode;
    		}
    		else {
    		    thisNode = (NodeImpl)(nodes.get(currentSize - 1));
    		}
    
    		// Add nodes up to the one we're looking for
    		while (thisNode != null && index >= nodes.size()) {
    		    thisNode = nextMatchingElementAfter(thisNode);
    		    if (thisNode != null) {
    		        nodes.add(thisNode);
    		    }
    		}

            // Either what we want, or null (not avail.)
		    return thisNode;           
	    }

    } // item(int):Node

    //
    // Protected methods (might be overridden by an extending DOM)
    //

    
Iterative tree-walker. When you have a Parent link, there's often no
need to resort to recursion. NOTE THAT only Element nodes are matched
since we're specifically supporting getElementsByTagName().
/** 
     * Iterative tree-walker. When you have a Parent link, there's often no
     * need to resort to recursion. NOTE THAT only Element nodes are matched
     * since we're specifically supporting getElementsByTagName().
     */
    protected Node nextMatchingElementAfter(Node current) {

	    Node next;
	    while (current != null) {
		    // Look down to first child.
		    if (current.hasChildNodes()) {
			    current = (current.getFirstChild());
		    }

		    // Look right to sibling (but not from root!)
		    else if (current != rootNode && null != (next = current.getNextSibling())) {
				current = next;
			}

			// Look up and right (but not past root!)
			else {
				next = null;
				for (; current != rootNode; // Stop when we return to starting point
					current = current.getParentNode()) {

					next = current.getNextSibling();
					if (next != null)
						break;
				}
				current = next;
			}

			// Have we found an Element with the right tagName?
			// ("*" matches anything.)
		    if (current != rootNode 
		        && current != null
		        && current.getNodeType() ==  Node.ELEMENT_NODE) {
			if (!enableNS) {
			    if (tagName.equals("*") ||
				((ElementImpl) current).getTagName().equals(tagName))
			    {
				return current;
			    }
			} else {
			    // DOM2: Namespace logic. 
			    if (tagName.equals("*")) {
				if (nsName != null && nsName.equals("*")) {
				    return current;
				} else {
				    ElementImpl el = (ElementImpl) current;
				    if ((nsName == null
					 && el.getNamespaceURI() == null)
					|| (nsName != null
					    && nsName.equals(el.getNamespaceURI())))
				    {
					return current;
				    }
				}
			    } else {
				ElementImpl el = (ElementImpl) current;
				if (el.getLocalName() != null
				    && el.getLocalName().equals(tagName)) {
				    if (nsName != null && nsName.equals("*")) {
					return current;
				    } else {
					if ((nsName == null
					     && el.getNamespaceURI() == null)
					    || (nsName != null &&
						nsName.equals(el.getNamespaceURI())))
					{
					    return current;
					}
				    }
				}
			    }
			}
		    }

		// Otherwise continue walking the tree
	    }

	    // Fell out of tree-walk; no more instances found
	    return null;

    } // nextMatchingElementAfter(int):Node

} // class DeepNodeListImpl