Iterator.cs :  » 2.6.4-mono-.net-core » System.Xml » System » Xml » XPath » C# / CSharp Open Source

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C# / CSharp Open Source » 2.6.4 mono .net core » System.Xml 
System.Xml » System » Xml » XPath » Iterator.cs
//
// System.Xml.XPath.BaseIterator
//
// Author:
//   Piers Haken (piersh@friskit.com)
//   Atsushi Enomoto (atsushi@ximian.com)
//
// (C) 2002 Piers Haken
// (C) 2003 Atsushi Enomoto
//

//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using System.Collections;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;

#if NET_2_0
using NSResolverSystem.Xml.IXmlNamespaceResolver;
#else
using NSResolverSystem.Xml.XmlNamespaceManager;
#endif

namespace System.Xml.XPath{
  internal abstract class BaseIterator : XPathNodeIterator
  {
    NSResolver _nsm;
    int position;

    internal BaseIterator (BaseIterator other)
    {
      _nsm = other._nsm;
      position = other.position;
    }
    internal BaseIterator (NSResolver nsm)
    {
      _nsm = nsm;
    }

    public NSResolver NamespaceManager
    {
      get { return _nsm; }
      set { _nsm = value; }
    }

    public virtual bool ReverseAxis {
      get { return false; }
    }

    public int ComparablePosition {
      get {
        if (ReverseAxis) {
          int diff = Count - CurrentPosition + 1;
          return diff < 1 ? 1 : diff;
        }
        else
          return CurrentPosition;
      }
    }

    public override int CurrentPosition {
      get { return position; }
    }

    internal void SetPosition (int pos)
    {
      position = pos;
    }

    public override bool MoveNext ()
    {
// FIXME: enable this line once I found the culprit of a breakage in WrapperIterator. And remove it again in the final stage.
//if (CurrentPosition == 0 && Current != null) throw new Exception (GetType ().FullName);
      if (!MoveNextCore ())
        return false;
      position++;
      return true;
    }

    public abstract bool MoveNextCore ();

    internal XPathNavigator PeekNext ()
    {
      XPathNodeIterator i = Clone ();
      return i.MoveNext () ? i.Current : null;
    }

    public override string ToString ()
    {
      if (Current != null)
        return Current.NodeType.ToString () + "[" + CurrentPosition + "] : " + Current.Name + " = " + Current.Value;
      else
        return this.GetType().ToString () + "[" + CurrentPosition + "]";
    }
  }

  internal class WrapperIterator : BaseIterator
  {
    XPathNodeIterator iter;

    public WrapperIterator (XPathNodeIterator iter, NSResolver nsm)
      : base (nsm)
    {
      this.iter = iter;
    }

    private WrapperIterator (WrapperIterator other)
      : base (other)
    {
      iter = other.iter.Clone ();
    }

    public override XPathNodeIterator Clone ()
    {
      return new WrapperIterator (this);
    }

    public override bool MoveNextCore ()
    {
      return iter.MoveNext ();
    }

    public override XPathNavigator Current {
      get { return iter.Current; }
    }
  }

  internal abstract class SimpleIterator : BaseIterator
  {
    protected readonly XPathNavigator _nav;
    protected XPathNavigator _current;
    bool skipfirst;

    public SimpleIterator (BaseIterator iter) : base (iter.NamespaceManager)
    {
      if (iter.CurrentPosition == 0) {
        skipfirst = true;
        iter.MoveNext ();
      }
      if (iter.CurrentPosition > 0)
        _nav = iter.Current.Clone ();
    }
    protected SimpleIterator (SimpleIterator other, bool clone) : base (other)
    {
      if (other._nav != null)
        _nav = clone ? other._nav.Clone () : other._nav;
      skipfirst = other.skipfirst;
    }
    public SimpleIterator (XPathNavigator nav, NSResolver nsm) : base (nsm)
    {
      _nav = nav.Clone ();
    }

    public override bool MoveNext ()
    {
      if (skipfirst) {
        if (_nav == null)
          return false; // empty
        skipfirst = false;
        base.SetPosition (1);
        return true;
      } else {
        return base.MoveNext ();
      }
    }

    public override XPathNavigator Current {
      get {
        if (CurrentPosition == 0)
          return null;
        _current = _nav;
        return _current;
      }
    }
  }

  internal class SelfIterator : SimpleIterator
  {
    public SelfIterator (BaseIterator iter) : base (iter) {}
    public SelfIterator (XPathNavigator nav, NSResolver nsm) : base (nav, nsm) {}
    protected SelfIterator (SelfIterator other, bool clone) : base (other, true) 
    {
    }

    public override XPathNodeIterator Clone () { return new SelfIterator (this, true); }
    public override bool MoveNextCore ()
    {
      if (CurrentPosition == 0)
      {
        return true;
      }
      return false;
    }

    public override XPathNavigator Current {
      get { return CurrentPosition == 0 ? null : _nav; }
    }
  }

  internal class NullIterator : SelfIterator
  {
    public NullIterator (BaseIterator iter) : base (iter) {}
    public NullIterator (XPathNavigator nav) : this (nav, null) {}
    public NullIterator (XPathNavigator nav, NSResolver nsm) : base (nav, nsm) {}
    private NullIterator (NullIterator other) : base (other, true) {}
    public override XPathNodeIterator Clone () { return new NullIterator (this); }
    public override bool MoveNextCore ()
    {
      return false;
    }

    public override int CurrentPosition {
      get { return 1; }
    }

    public override XPathNavigator Current {
      get { return _nav; }
    }
  }

  internal class ParensIterator : BaseIterator
  {
    BaseIterator _iter;

    public ParensIterator (BaseIterator iter) : base (iter.NamespaceManager) 
    {
      _iter = iter;
    }
    private ParensIterator (ParensIterator other) : base (other) 
    {
      _iter = (BaseIterator) other._iter.Clone ();
    }
    public override XPathNodeIterator Clone () { return new ParensIterator (this); }
    public override bool MoveNextCore ()
    {
      return _iter.MoveNext ();
    }

    public override XPathNavigator Current { get { return _iter.Current; }}

    public override int Count { get { return _iter.Count; } }
  }

  internal class ParentIterator : SimpleIterator
  {
    bool canMove;
    public ParentIterator (BaseIterator iter) : base (iter)
    {
      canMove = _nav.MoveToParent ();
      //_current = _nav;
    }
    private ParentIterator (ParentIterator other, bool dummy) : base (other, true)
    {
      //_current = _nav;
      canMove = other.canMove;
    }
    public ParentIterator (XPathNavigator nav, NSResolver nsm) : base (nav, nsm) {}
    public override XPathNodeIterator Clone () { return new ParentIterator (this, true); }
    public override bool MoveNextCore ()
    {
      if (!canMove)
        return false;
      canMove = false;
      return true;
    }
  }

  internal class ChildIterator : BaseIterator
  {
    XPathNavigator _nav;

    public ChildIterator (BaseIterator iter) : base (iter.NamespaceManager) 
    {
      _nav = iter.CurrentPosition == 0 ? iter.PeekNext () : iter.Current;
      if (_nav != null && _nav.HasChildren)
        _nav = _nav.Clone ();
      else
        _nav = null;
    }
    private ChildIterator (ChildIterator other) : base (other)
    {
      _nav = other._nav == null ? null : other._nav.Clone ();
    }

    public override XPathNodeIterator Clone () { return new ChildIterator (this); }

    public override bool MoveNextCore ()
    {
      if (_nav == null)
        return false;

      return (CurrentPosition == 0) ? _nav.MoveToFirstChild () : _nav.MoveToNext ();
    }

    public override XPathNavigator Current {
      get {
        if (CurrentPosition == 0)
          return null;
        return _nav;
      }
    }
  }

  internal class FollowingSiblingIterator : SimpleIterator
  {
    public FollowingSiblingIterator (BaseIterator iter) : base (iter) {}
    private FollowingSiblingIterator (FollowingSiblingIterator other) : base (other, true) {}
    public override XPathNodeIterator Clone () { return new FollowingSiblingIterator (this); }
    public override bool MoveNextCore ()
    {
      switch (_nav.NodeType) {
      case XPathNodeType.Attribute:
      case XPathNodeType.Namespace:
        // They have no siblings.
        return false;
      }
      if (_nav.MoveToNext ())
      {
//        Current.MoveTo (_nav);
        return true;
      }
      return false;
    }
  }

  internal class PrecedingSiblingIterator : SimpleIterator
  {
    bool finished;
    bool started;
    XPathNavigator startPosition;

    public PrecedingSiblingIterator (BaseIterator iter) : base (iter)
    {
      startPosition = iter.Current.Clone ();
    }
    private PrecedingSiblingIterator (PrecedingSiblingIterator other) : base (other, true) 
    {
      startPosition = other.startPosition;
      started = other.started;
      finished = other.finished;
    }

    public override XPathNodeIterator Clone () { return new PrecedingSiblingIterator (this); }
    public override bool MoveNextCore ()
    {
      if (finished)
        return false;
      if (!started) {
        started = true;
        switch (_nav.NodeType) {
        case XPathNodeType.Attribute:
        case XPathNodeType.Namespace:
          // They have no siblings.
          finished = true;
          return false;
        }

        _nav.MoveToFirst ();
        if (!_nav.IsSamePosition (startPosition)) {
//          Current.MoveTo (_nav);
          return true;
        }
      } else {
        if (!_nav.MoveToNext ()) {
          finished = true;
          return false;
        }
      }
      if (_nav.ComparePosition (startPosition) != XmlNodeOrder.Before) {
        // Note that if _nav contains only 1 node, it won't be Same.
        finished = true;
        return false;
      } else {
//        Current.MoveTo (_nav);
        return true;
      }
    }
    public override bool ReverseAxis {
      get { return true; }
    }
  }

  internal class AncestorIterator : SimpleIterator
  {
    int currentPosition;
    ArrayList navigators;
    XPathNavigator startPosition;

    public AncestorIterator (BaseIterator iter) : base (iter)
    {
      startPosition = iter.Current.Clone ();
    }

    private AncestorIterator (AncestorIterator other)
      : base (other, true)
    {
      startPosition = other.startPosition;
      if (other.navigators != null)
        navigators = (ArrayList) other.navigators;
      currentPosition = other.currentPosition;
    }

    public override XPathNodeIterator Clone ()
    {
      return new AncestorIterator (this);
    }

    private void CollectResults ()
    {
      navigators = new ArrayList ();

      XPathNavigator ancestors = startPosition.Clone ();
      while (ancestors.NodeType != XPathNodeType.Root && ancestors.MoveToParent ())
        navigators.Add (ancestors.Clone ());
      currentPosition = navigators.Count;
    }

    public override bool MoveNextCore ()
    {
      if (navigators == null)
        CollectResults ();
      if (currentPosition == 0)
        return false;
      _nav.MoveTo ((XPathNavigator) navigators [--currentPosition]);
//      Current.MoveTo (_nav);
      return true;
    }

    public override bool ReverseAxis {
      get { return true; }
    }

    public override int Count {
      get {
        if (navigators == null)
          CollectResults ();
        return navigators.Count;
      }
    }
  }

  internal class AncestorOrSelfIterator : SimpleIterator
  {
    int currentPosition;
    ArrayList navigators;
    XPathNavigator startPosition;

    public AncestorOrSelfIterator (BaseIterator iter) : base (iter)
    {
      startPosition = iter.Current.Clone ();
    }

    private AncestorOrSelfIterator (AncestorOrSelfIterator other)
      : base (other, true)
    {
      startPosition = other.startPosition;
      if (other.navigators != null)
        navigators = (ArrayList) other.navigators.Clone ();
      currentPosition = other.currentPosition;
    }

    public override XPathNodeIterator Clone ()
    {
      return new AncestorOrSelfIterator (this);
    }

    private void CollectResults ()
    {
      navigators = new ArrayList ();

      XPathNavigator ancestors = startPosition.Clone ();
      if (!ancestors.MoveToParent ())
        return;
      while (ancestors.NodeType != XPathNodeType.Root) {
        navigators.Add (ancestors.Clone ());
        ancestors.MoveToParent ();
      }
      currentPosition = navigators.Count;
    }

    public override bool MoveNextCore ()
    {
      if (navigators == null) {
        CollectResults ();
        if (startPosition.NodeType != XPathNodeType.Root) {
          // First time it returns Root
          _nav.MoveToRoot ();
//          Current.MoveTo (_nav);
          return true;
        }
      }
      if (currentPosition == -1)
        return false;
      if (currentPosition-- == 0) {
        _nav.MoveTo (startPosition);
//        Current.MoveTo (_nav);
        return true; // returns self.
      }
      _nav.MoveTo ((XPathNavigator) navigators [currentPosition]);
//      Current.MoveTo (_nav);
      return true;
    }

    public override bool ReverseAxis {
      get { return true; }
    }

    public override int Count {
      get {
        if (navigators == null)
          CollectResults ();
        return navigators.Count + 1;
      }
    }
  }

  internal class DescendantIterator : SimpleIterator
  {
    private int _depth;
    private bool _finished;

    public DescendantIterator (BaseIterator iter) : base (iter) {}

    private DescendantIterator (DescendantIterator other) : base (other, true)
    {
      _depth = other._depth;
      _finished = other._finished;
    }

    public override XPathNodeIterator Clone () { return new DescendantIterator (this); }

    public override bool MoveNextCore ()
    {
      if (_finished)
        return false;

      if (_nav.MoveToFirstChild ())
      {
        _depth ++;
//        Current.MoveTo (_nav);
        return true;
      }
      while (_depth != 0)
      {
        if (_nav.MoveToNext ())
        {
//          Current.MoveTo (_nav);
          return true;
        }
        if (!_nav.MoveToParent ())  // should NEVER fail!
          throw new XPathException ("Current node is removed while it should not be, or there are some bugs in the XPathNavigator implementation class: " + _nav.GetType ());
        _depth --;
      }
      _finished = true;
      return false;
    }
  }

  internal class DescendantOrSelfIterator : SimpleIterator
  {
    private int _depth;
    private bool _finished;

    public DescendantOrSelfIterator (BaseIterator iter) : base (iter) {}

    private DescendantOrSelfIterator (DescendantOrSelfIterator other) : base (other, true)
    {
      _depth = other._depth;
    }

    public override XPathNodeIterator Clone () { return new DescendantOrSelfIterator (this); }

    public override bool MoveNextCore ()
    {
      if (_finished)
        return false;

      if (CurrentPosition == 0)
      {
        // self
//        Current.MoveTo (_nav);
        return true;
      }
      if (_nav.MoveToFirstChild ())
      {
        _depth ++;
//        Current.MoveTo (_nav);
        return true;
      }
      while (_depth != 0)
      {
        if (_nav.MoveToNext ())
        {
//          Current.MoveTo (_nav);
          return true;
        }
        if (!_nav.MoveToParent ())  // should NEVER fail!
          throw new XPathException ("Current node is removed while it should not be, or there are some bugs in the XPathNavigator implementation class: " + _nav.GetType ());
        _depth --;
      }
      _finished = true;
      return false;
    }
  }

  internal class FollowingIterator : SimpleIterator
  {
    private bool _finished = false;
    public FollowingIterator (BaseIterator iter) : base (iter) {}
    private FollowingIterator (FollowingIterator other) : base (other, true) {}
    public override XPathNodeIterator Clone () { return new FollowingIterator (this); }
    public override bool MoveNextCore ()
    {
      if (_finished)
        return false;
      bool checkChildren = true;
      if (CurrentPosition == 0)
      {
        checkChildren = false;
        switch (_nav.NodeType) {
        case XPathNodeType.Attribute:
        case XPathNodeType.Namespace:
          _nav.MoveToParent ();
          checkChildren = true;
          break;
        default:
          if (_nav.MoveToNext ())
          {
//            Current.MoveTo (_nav);
            return true;
          } else {
            while (_nav.MoveToParent ()) {
              if (_nav.MoveToNext ()) {
//                Current.MoveTo (_nav);
                return true;
              }
            }
          }
          break;
        }
      }
      if (checkChildren)
      {
        if (_nav.MoveToFirstChild ())
        {
//          Current.MoveTo (_nav);
          return true;
        }
        do
        {
          if (_nav.MoveToNext ())
          {
//            Current.MoveTo (_nav);
            return true;
          }
        }
        while (_nav.MoveToParent ());
      }
      _finished = true;
      return false;
    }
  }

  internal class PrecedingIterator : SimpleIterator
  {
    bool finished;
    bool started;
    XPathNavigator startPosition;

    public PrecedingIterator (BaseIterator iter) : base (iter) 
    {
      startPosition = iter.Current.Clone ();
    }
    private PrecedingIterator (PrecedingIterator other) : base (other, true) 
    {
      startPosition = other.startPosition;
      started = other.started;
      finished = other.finished;
    }
    public override XPathNodeIterator Clone () { return new PrecedingIterator (this); }
    public override bool MoveNextCore ()
    {
      if (finished)
        return false;
      if (!started) {
        started = true;
        _nav.MoveToRoot ();
      }
      bool loop = true;
      while (loop) {
        while (!_nav.MoveToFirstChild ()) {
          while (!_nav.MoveToNext ()) {
            if (!_nav.MoveToParent ()) { // Should not finish, at least before startPosition.
              finished = true;
              return false;
            }
          }
          break;
        }
        if (_nav.IsDescendant (startPosition))
          continue;
        loop = false;
        break;
      }
      if (_nav.ComparePosition (startPosition) != XmlNodeOrder.Before) {
        // Note that if _nav contains only 1 node, it won't be Same.
        finished = true;
        return false;
      } else {
//        Current.MoveTo (_nav);
        return true;
      }
    }
    public override bool ReverseAxis {
      get { return true; }
    }
  }

  internal class NamespaceIterator : SimpleIterator
  {
    public NamespaceIterator (BaseIterator iter) : base (iter) {}
    private NamespaceIterator (NamespaceIterator other) : base (other, true) {}
    public override XPathNodeIterator Clone () { return new NamespaceIterator (this); }
    public override bool MoveNextCore ()
    {
      if (CurrentPosition == 0)
      {
        if (_nav.MoveToFirstNamespace ())
        {
//          Current.MoveTo (_nav);
          return true;
        }
      }
      else if (_nav.MoveToNextNamespace ())
      {
//        Current.MoveTo (_nav);
        return true;
      }
      return false;
    }
  }

  internal class AttributeIterator : SimpleIterator
  {
    public AttributeIterator (BaseIterator iter) : base (iter) {}
    private AttributeIterator (AttributeIterator other) : base (other, true) {}
    public override XPathNodeIterator Clone () { return new AttributeIterator (this); }
    public override bool MoveNextCore ()
    {
      if (CurrentPosition == 0)
      {
        if (_nav.MoveToFirstAttribute ())
        {
//          Current.MoveTo (_nav);
          return true;
        }
      }
      else if (_nav.MoveToNextAttribute ())
      {
//        Current.MoveTo (_nav);
        return true;
      }
      return false;      
    }
  }

  internal class AxisIterator : BaseIterator
  {
    private BaseIterator _iter;
    private NodeTest _test;
      
    //string name, ns;
    //XPathNodeType matchType;

    public AxisIterator (BaseIterator iter, NodeTest test) : base (iter.NamespaceManager)
    {
      _iter = iter;
      _test = test;
      //test.GetInfo (out name, out ns, out matchType, NamespaceManager);
//      if (name != null)
//        name = Current.NameTable.Add (name);

//      if (ns != null)
//        ns = Current.NameTable.Add (ns);
    }

    private AxisIterator (AxisIterator other) : base (other)
    {
      _iter = (BaseIterator) other._iter.Clone ();
      _test = other._test;
      //name = other.name;
      //ns = other.ns;
      //matchType = other.matchType;
    }
    public override XPathNodeIterator Clone () { return new AxisIterator (this); }

    public override bool MoveNextCore ()
    {
      while (_iter.MoveNext ())
      {
        if (_test.Match (NamespaceManager, _iter.Current))
        {
          return true;
        }
      }
      return false;
    }
    public override XPathNavigator Current { get { return CurrentPosition == 0 ? null : _iter.Current; }}

    public override bool ReverseAxis {
      get { return _iter.ReverseAxis; }
    }
  }

  internal class SimpleSlashIterator : BaseIterator
  {
    private NodeSet _expr;
    private BaseIterator _left, _right;
    private XPathNavigator _current;

    public SimpleSlashIterator (BaseIterator left, NodeSet expr)
      : base (left.NamespaceManager)
    {
      this._left = left;
      this._expr = expr;
    }

    private SimpleSlashIterator (SimpleSlashIterator other)
      : base (other)
    {
      _expr = other._expr;
      _left = (BaseIterator) other._left.Clone ();
      if (other._right != null)
        _right = (BaseIterator) other._right.Clone ();
    }

    public override XPathNodeIterator Clone () { return new SimpleSlashIterator (this); }

    public override bool MoveNextCore ()
    {
      while (_right == null || !_right.MoveNext ()) {
        if (!_left.MoveNext ())
          return false;
        _right = _expr.EvaluateNodeSet (_left);
      }
      if (_current == null)
        _current = _right.Current.Clone ();
      else
        if (! _current.MoveTo (_right.Current) )
          _current = _right.Current.Clone ();
      return true;
    }

    public override XPathNavigator Current {
      get { return _current; }
    }
  }

  internal class SortedIterator : BaseIterator
  {
    ArrayList list;

    public SortedIterator (BaseIterator iter) : base (iter.NamespaceManager)
    {
      list = new ArrayList ();
      while (iter.MoveNext ())
        list.Add (iter.Current.Clone ());

      // sort
      if (list.Count == 0)
        return;
      XPathNavigator prev = (XPathNavigator) list [0];
      list.Sort (XPathNavigatorComparer.Instance);
      for (int i = 1; i < list.Count; i++) {
        XPathNavigator n = (XPathNavigator) list [i];
        if (prev.IsSamePosition (n)) {
          list.RemoveAt (i);
          i--;
        }
        else
          prev = n;
      }
    }

    public SortedIterator (SortedIterator other) : base (other)
    {
      this.list = other.list;
      SetPosition (other.CurrentPosition);
    }

    public override XPathNodeIterator Clone () { return new SortedIterator (this); }

    public override bool MoveNextCore ()
    {
      return CurrentPosition < list.Count;
    }

    public override XPathNavigator Current {
      get { return CurrentPosition == 0 ? null : (XPathNavigator) list [CurrentPosition - 1]; }
    }

    public override int Count {
      get { return list.Count; }
    }
  }

  // NOTE: it is *not* sorted. Do not directly use it without checking sorting requirement.
  internal class SlashIterator : BaseIterator
  {
    private BaseIterator _iterLeft;
    private BaseIterator _iterRight;
    private NodeSet _expr;
    SortedList _iterList;
    bool _finished;
    BaseIterator _nextIterRight;

    public SlashIterator (BaseIterator iter, NodeSet expr) : base (iter.NamespaceManager)
    {
      _iterLeft = iter;
      _expr = expr;
    }

    private SlashIterator (SlashIterator other) : base (other)
    {
      _iterLeft = (BaseIterator) other._iterLeft.Clone ();
      if (other._iterRight != null)
        _iterRight = (BaseIterator) other._iterRight.Clone ();
      _expr = other._expr;
      if (other._iterList != null)
        _iterList = (SortedList) other._iterList.Clone ();
      _finished = other._finished;
      if (other._nextIterRight != null)
        _nextIterRight = (BaseIterator) other._nextIterRight.Clone ();
    }
    public override XPathNodeIterator Clone () { return new SlashIterator (this); }

    public override bool MoveNextCore ()
    {
      if (_finished)
        return false;

      if (_iterRight == null) { // First time
        if (!_iterLeft.MoveNext ())
          return false;
        _iterRight = _expr.EvaluateNodeSet (_iterLeft);
        _iterList = new SortedList (XPathIteratorComparer.Instance);
      }

      while (true) {
        while (!_iterRight.MoveNext ()) {
          if (_iterList.Count > 0) {
            int last = _iterList.Count - 1;
            _iterRight = (BaseIterator) _iterList.GetByIndex (last);
            _iterList.RemoveAt (last);
            break;
          } else if (_nextIterRight != null) {
            _iterRight = _nextIterRight;
            _nextIterRight = null;
            break;
          } else if (!_iterLeft.MoveNext ()) {
            _finished = true;
            return false;
          }
          else
            _iterRight = _expr.EvaluateNodeSet (_iterLeft);
        }
        bool loop = true;
        while (loop) {
          loop = false;
          if (_nextIterRight == null) {
            bool noMoreNext = false;
            while (_nextIterRight == null || !_nextIterRight.MoveNext ()) {
              if(_iterLeft.MoveNext ())
                _nextIterRight = _expr.EvaluateNodeSet (_iterLeft);
              else {
                noMoreNext = true;
                break;
              }
            }
            if (noMoreNext)
              _nextIterRight = null; // FIXME: More efficient code. Maybe making noMoreNext class scope would be better.
          }
          if (_nextIterRight != null) {
            switch (_iterRight.Current.ComparePosition (_nextIterRight.Current)) {
            case XmlNodeOrder.After:
              _iterList [_iterRight] = _iterRight;
              _iterRight = _nextIterRight;
              _nextIterRight = null;
              loop = true;
              break;
            case XmlNodeOrder.Same:
              if (!_nextIterRight.MoveNext ())
                _nextIterRight = null;

              else {
                int last = _iterList.Count;
                _iterList [_nextIterRight] = _nextIterRight;
                if (last != _iterList.Count) {
                  _nextIterRight = (BaseIterator) _iterList.GetByIndex (last);
                  _iterList.RemoveAt (last);
                }
              }

              loop = true;
              break;
            }
          }
        }
        return true;
      }
    }

    public override XPathNavigator Current { 
      get {
        return (CurrentPosition == 0) ? null : _iterRight.Current;
      }
    }
  }

  internal class PredicateIterator : BaseIterator
  {
    private BaseIterator _iter;
    private Expression _pred;
    private XPathResultType resType;
    private bool finished;

    public PredicateIterator (BaseIterator iter, Expression pred) : base (iter.NamespaceManager)
    {
      _iter = iter;
      _pred = pred;
      resType = pred.GetReturnType (iter);
    }

    private PredicateIterator (PredicateIterator other) : base (other)
    {
      _iter = (BaseIterator) other._iter.Clone ();
      _pred = other._pred;
      resType = other.resType;
      finished = other.finished;
    }
    public override XPathNodeIterator Clone () { return new PredicateIterator (this); }

    public override bool MoveNextCore ()
    {
      if (finished)
        return false;
      while (_iter.MoveNext ())
      {
        switch (resType) {
          case XPathResultType.Number:
            if (_pred.EvaluateNumber (_iter) != _iter.ComparablePosition)
              continue;
            break;
          case XPathResultType.Any: {
            object result = _pred.Evaluate (_iter);
            if (result is double)
            {
              if ((double) result != _iter.ComparablePosition)
                continue;
            }
            else if (!XPathFunctions.ToBoolean (result))
              continue;
          }
            break;
          default:
            if (!_pred.EvaluateBoolean (_iter))
              continue;
            break;
        }

        return true;
      }
      finished = true;
      return false;
    }
    public override XPathNavigator Current {
      get { return CurrentPosition == 0 ? null : _iter.Current; }}
    public override bool ReverseAxis {
      get { return _iter.ReverseAxis; }
    }
public override string ToString () { return _iter.GetType ().FullName; }
  }

  internal class ListIterator : BaseIterator
  {
    private IList _list;

    public ListIterator (BaseIterator iter, IList list) : base (iter.NamespaceManager)
    {
      _list = list;
    }
    
    public ListIterator (IList list, NSResolver nsm) : base (nsm)
    {
      _list = list;
    }

    private ListIterator (ListIterator other) : base (other)
    {
      _list = other._list;
    }
    public override XPathNodeIterator Clone () { return new ListIterator (this); }

    public override bool MoveNextCore ()
    {
      if (CurrentPosition >= _list.Count)
        return false;
      return true;
    }
    public override XPathNavigator Current {
      get {
        if (_list.Count == 0 || CurrentPosition == 0)
          return null;
        return (XPathNavigator) _list [CurrentPosition - 1]; 
      }
    }

    public override int Count { get { return _list.Count; } }
  }

  
  internal class UnionIterator : BaseIterator
  {
    private BaseIterator _left, _right;
    private bool keepLeft;
    private bool keepRight;
    XPathNavigator _current;

    public UnionIterator (BaseIterator iter, BaseIterator left, BaseIterator right) : base (iter.NamespaceManager)
    {
      _left = left;
      _right = right;
    }

    private UnionIterator (UnionIterator other) : base (other)
    {
      _left = (BaseIterator) other._left.Clone ();
      _right = (BaseIterator) other._right.Clone ();
      keepLeft = other.keepLeft;
      keepRight = other.keepRight;
      if (other._current != null)
        _current = other._current.Clone ();
    }
    public override XPathNodeIterator Clone () { return new UnionIterator (this); }

    public override bool MoveNextCore ()
    {
      if (!keepLeft)
        keepLeft = _left.MoveNext ();
      if (!keepRight)
        keepRight = _right.MoveNext ();

      if (!keepLeft && !keepRight)
        return false;

      if (!keepRight) {
        keepLeft = false;
        SetCurrent (_left);
        return true;
      } else if (!keepLeft) {
        keepRight = false;
        SetCurrent (_right);
        return true;
      }

      switch (_left.Current.ComparePosition (_right.Current)) {
      case XmlNodeOrder.Same:
        // consume both. i.e. don't output duplicate result.
        keepLeft = keepRight = false;
        SetCurrent (_right);
        return true;
      case XmlNodeOrder.Before:
      case XmlNodeOrder.Unknown: // Maybe happen because of "document(a) | document(b)"
        keepLeft = false;
        SetCurrent (_left);
        return true;
      case XmlNodeOrder.After:
        keepRight = false;
        SetCurrent (_right);
        return true;
      default:
        throw new InvalidOperationException ("Should not happen.");
      }
    }

    private void SetCurrent (XPathNodeIterator iter)
    {
      if (_current == null)
        _current = iter.Current.Clone ();
      else
        if (! _current.MoveTo (iter.Current) )
          _current = iter.Current.Clone ();
    }

    public override XPathNavigator Current
    {
      get { return CurrentPosition > 0 ? _current : null; }
    }
  }

  internal class OrderedIterator : BaseIterator
  {
    BaseIterator iter;
    ArrayList list;
    int index = -1;

    public OrderedIterator (BaseIterator iter)
      : base (iter.NamespaceManager)
    {
//      if (iter.Ordered)
//      if (false)
//        this.iter = iter;
//      else 
      {
        list = new ArrayList ();
        while (iter.MoveNext ())
          list.Add (iter.Current);
        list.Sort (XPathNavigatorComparer.Instance);
      }
    }

    private OrderedIterator (OrderedIterator other, bool dummy)
      : base (other)
    {
      if (other.iter != null)
        iter = (BaseIterator) other.iter.Clone ();
      list = other.list;
      index = other.index;
    }

    public override XPathNodeIterator Clone ()
    {
      return new OrderedIterator (this);
    }

    public override bool MoveNextCore ()
    {
      if (iter != null)
        return iter.MoveNext ();
      else if (index++ < list.Count)
        return true;
      index--;
      return false;
    }

    public override XPathNavigator Current {
      get { return iter != null ? iter.Current : index < 0 ? null : (XPathNavigator) list [index]; }
    }
  }
}
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