XPathPrecedingMergeIterator.cs

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using System.ComponentModel;
using System.Xml.XPath;
 
namespace System.Xml.Xsl.Runtime;
 
[EditorBrowsable(EditorBrowsableState.Never)]
public struct XPathPrecedingMergeIterator
{
    private enum IteratorState
    {
        NeedCandidateCurrent,
        HaveCandidateCurrent,
        HaveCurrentHaveNext,
        HaveCurrentNoNext
    }
 
    private XmlNavigatorFilter _filter;
 
    private IteratorState _state;
 
    private XPathNavigator _navCurrent;
 
    private XPathNavigator _navNext;
 
    private XmlNavigatorStack _navStack;
 
    public XPathNavigator Current => _navCurrent;
 
    public void Create(XmlNavigatorFilter filter)
    {
        _filter = filter;
        _state = IteratorState.NeedCandidateCurrent;
    }
 
    public IteratorResult MoveNext(XPathNavigator input)
    {
        switch (_state)
        {
        case IteratorState.NeedCandidateCurrent:
            if (input == null)
            {
                return IteratorResult.NoMoreNodes;
            }
            _navCurrent = XmlQueryRuntime.SyncToNavigator(_navCurrent, input);
            _state = IteratorState.HaveCandidateCurrent;
            return IteratorResult.NeedInputNode;
        case IteratorState.HaveCandidateCurrent:
            if (input == null)
            {
                _state = IteratorState.HaveCurrentNoNext;
            }
            else
            {
                if (_navCurrent.ComparePosition(input) != XmlNodeOrder.Unknown)
                {
                    _navCurrent = XmlQueryRuntime.SyncToNavigator(_navCurrent, input);
                    return IteratorResult.NeedInputNode;
                }
                _navNext = XmlQueryRuntime.SyncToNavigator(_navNext, input);
                _state = IteratorState.HaveCurrentHaveNext;
            }
            PushAncestors();
            break;
        }
        if (!_navStack.IsEmpty)
        {
            do
            {
                if (_filter.MoveToFollowing(_navCurrent, _navStack.Peek()))
                {
                    return IteratorResult.HaveCurrentNode;
                }
                _navCurrent.MoveTo(_navStack.Pop());
            }
            while (!_navStack.IsEmpty);
        }
        if (_state == IteratorState.HaveCurrentNoNext)
        {
            _state = IteratorState.NeedCandidateCurrent;
            return IteratorResult.NoMoreNodes;
        }
        _navCurrent = XmlQueryRuntime.SyncToNavigator(_navCurrent, _navNext);
        _state = IteratorState.HaveCandidateCurrent;
        return IteratorResult.HaveCurrentNode;
    }
 
    private void PushAncestors()
    {
        _navStack.Reset();
        do
        {
            _navStack.Push(_navCurrent.Clone());
        }
        while (_navCurrent.MoveToParent());
        _navStack.Pop();
    }
}