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+/* DomIterator.java --
+   Copyright (C) 1999, 2000, 2001, 2006 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath 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 the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+package gnu.xml.dom;
+
+import org.w3c.dom.DOMException;
+import org.w3c.dom.Node;
+import org.w3c.dom.events.Event;
+import org.w3c.dom.events.EventListener;
+import org.w3c.dom.events.EventTarget;
+import org.w3c.dom.events.MutationEvent;
+import org.w3c.dom.traversal.NodeFilter;
+import org.w3c.dom.traversal.NodeIterator;
+
+/**
+ * <p> "NodeIterator" implementation, usable with any L2 DOM which
+ * supports MutationEvents. </p>
+ *
+ * @author David Brownell
+ */
+public final class DomIterator
+  implements NodeIterator, EventListener
+{
+
+  private Node reference;
+  private boolean right;
+  private boolean done;
+
+  private final Node root;
+  private final int whatToShow;
+  private final NodeFilter filter;
+  private final boolean expandEntityReferences;
+
+  /**
+   * Constructs and initializes an iterator.
+   */
+  protected DomIterator(Node root,
+                        int whatToShow,
+                        NodeFilter filter,
+                        boolean entityReferenceExpansion)
+  {
+    if (!root.isSupported("MutationEvents", "2.0"))
+      {
+        throw new DomDOMException(DOMException.NOT_SUPPORTED_ERR,
+                        "Iterator needs mutation events", root, 0);
+      }
+
+    this.root = root;
+    this.whatToShow = whatToShow;
+    this.filter = filter;
+    this.expandEntityReferences = entityReferenceExpansion;
+
+    // start condition:  going right, seen nothing yet.
+    reference = null;
+    right = true;
+
+    EventTarget target = (EventTarget) root;
+    target.addEventListener("DOMNodeRemoved", this, false);
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Flags the iterator as done, unregistering its event listener so
+   * that the iterator can be garbage collected without relying on weak
+   * references (a "Java 2" feature) in the event subsystem.
+   */
+  public void detach()
+  {
+    EventTarget target = (EventTarget) root;
+    target.removeEventListener("DOMNodeRemoved", this, false);
+    done = true;
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Returns the flag controlling whether iteration descends
+   * through entity references.
+   */
+  public boolean getExpandEntityReferences()
+  {
+    return expandEntityReferences;
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Returns the filter provided during construction.
+   */
+  public NodeFilter getFilter()
+  {
+    return filter;
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Returns the root of the tree this is iterating through.
+   */
+  public Node getRoot()
+  {
+    return root;
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Returns the mask of flags provided during construction.
+   */
+  public int getWhatToShow()
+  {
+    return whatToShow;
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Returns the next node in a forward iteration, masked and filtered.
+   * Note that the node may be read-only due to entity expansions.
+   * A null return indicates the iteration is complete, but may still
+   * be processed backwards.
+   */
+  public Node nextNode()
+  {
+    if (done)
+      {
+        throw new DomDOMException(DOMException.INVALID_STATE_ERR);
+      }
+    right = true;
+    return walk(true);
+  }
+
+  /**
+   * <b>DOM L2</b>
+   * Returns the next node in a backward iteration, masked and filtered.
+   * Note that the node may be read-only due to entity expansions.
+   * A null return indicates the iteration is complete, but may still
+   * be processed forwards.
+   */
+  public Node previousNode()
+  {
+    if (done)
+      {
+        throw new DomDOMException(DOMException.INVALID_STATE_ERR);
+      }
+    Node previous = reference;
+    right = false;
+    walk(false);
+    return previous;
+  }
+
+  private boolean shouldShow(Node node)
+    // raises Runtime exceptions indirectly, via acceptNode()
+  {
+    if ((whatToShow & (1 << (node.getNodeType() - 1))) == 0)
+      {
+        return false;
+      }
+    if (filter == null)
+      {
+        return true;
+      }
+    return filter.acceptNode(node) == NodeFilter.FILTER_ACCEPT;
+  }
+
+  //
+  // scenario:  root = 1, sequence = 1 2 ... 3 4
+  // forward walk: 1 2 ... 3 4 null
+  // then backward: 4 3 ... 2 1 null
+  //
+  // At the leftmost end, "previous" == null
+  // At the rightmost end, "previous" == 4
+  //
+  // The current draft spec really seem to make no sense re the
+  // role of the reference node, so what it says is ignored here.
+  //
+  private Node walk(boolean forward)
+  {
+    Node here = reference;
+
+    while ((here = successor(here, forward)) != null
+           && !shouldShow(here))
+      {
+        continue;
+      }
+    if (here != null || !forward)
+      {
+        reference = here;
+      }
+    return here;
+  }
+
+  private boolean isLeaf(Node here)
+  {
+    boolean leaf = !here.hasChildNodes();
+    if (!leaf && !expandEntityReferences)
+      {
+        leaf = (here.getNodeType() == Node.ENTITY_REFERENCE_NODE);
+      }
+    return leaf;
+  }
+
+  //
+  // Returns the immediate successor in a forward (or backward)
+  // document order walk, sans filtering ... except that it knows
+  // how to stop, returning null when done.  This is a depth first
+  // preorder traversal when run in the forward direction.
+  //
+  private Node successor(Node here, boolean forward)
+  {
+    Node next;
+
+    // the "leftmost" end is funky
+    if (here == null)
+      {
+        return forward ? root : null;
+      }
+
+    //
+    // Forward, this is preorder: children before siblings.
+    // Backward, it's postorder: we saw the children already.
+    //
+    if (forward && !isLeaf(here))
+      {
+        return here.getFirstChild();
+      }
+
+    // There's no way up or sideways from the root, so if we
+    // couldn't move down to a child, there's nowhere to go.
+    //
+    if (here == root)
+      return null;
+
+    //
+    // Siblings ... if forward, we visit them, if backwards
+    // we visit their children first.
+    //
+    if (forward)
+      {
+        if ((next = here.getNextSibling()) != null)
+          {
+            return next;
+          }
+      }
+    else if ((next = here.getPreviousSibling()) != null)
+      {
+        if (isLeaf(next))
+          {
+            return next;
+          }
+        next = next.getLastChild();
+        while (!isLeaf(next))
+          {
+            next = next.getLastChild();
+          }
+        return next;
+      }
+
+    //
+    // We can't go down or lateral -- it's up, then.  The logic is
+    // the converse of what's above:  backwards is easy (the parent
+    // is next), forwards isn't.
+    //
+    next = here.getParentNode();
+    if (!forward)
+      {
+        return next;
+      }
+
+    Node temp = null;
+    while (next != null
+           && next != root
+           && (temp = next.getNextSibling()) == null)
+      {
+        next = next.getParentNode();
+      }
+
+    // If we have exceeded the root node then stop traversing.
+    if (next == root.getParentNode())
+      {
+        return null;
+      }
+    return temp;
+  }
+
+  /**
+   * Not for public use.  This lets the iterator know when its
+   * reference node will be removed from the tree, so that a new
+   * one may be selected.
+   *
+   * <p> This version works by watching removal events as they
+   * bubble up.  So, don't prevent them from bubbling.
+   */
+  public void handleEvent(Event e)
+  {
+    MutationEvent event;
+    Node ancestor, removed;
+
+    if (reference == null
+        || !"DOMNodeRemoved".equals(e.getType())
+        || e.getEventPhase() != Event.BUBBLING_PHASE)
+      {
+        return;
+      }
+
+    event = (MutationEvent) e;
+    removed = (Node) event.getTarget();
+
+    // See if the removal will cause trouble for this iterator
+    // by being the reference node or an ancestor of it.
+    for (ancestor = reference;
+         ancestor != null && ancestor != root;
+         ancestor = ancestor.getParentNode())
+      {
+        if (ancestor == removed)
+          {
+            break;
+          }
+      }
+    if (ancestor != removed)
+      {
+        return;
+      }
+
+    // OK, it'll cause trouble.  We want to make the "next"
+    // node in our current traversal direction seem right.
+    // So we pick the nearest node that's not getting removed,
+    // but go in the _opposite_ direction from our current
+    // traversal ... so the "next" doesn't skip anything.
+    Node candidate;
+
+search:
+    while ((candidate = walk(!right)) != null)
+      {
+        for (ancestor = candidate;
+             ancestor != null && ancestor != root;
+             ancestor = ancestor.getParentNode())
+          {
+            if (ancestor == removed)
+              {
+                continue search;
+              }
+          }
+        return;
+      }
+
+    // The current DOM WD talks about a special case here;
+    // I've not yet seen it.
+    }
+
+}