XPathFollowingMergeIterator.cs

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using System.ComponentModel;
using System.Xml.XPath;
 
namespace System.Xml.Xsl.Runtime;
 
[EditorBrowsable(EditorBrowsableState.Never)]
public struct XPathFollowingMergeIterator
{
    private enum IteratorState
    {
        NeedCandidateCurrent,
        HaveCandidateCurrent,
        HaveCurrentNeedNext,
        HaveCurrentHaveNext,
        HaveCurrentNoNext
    }
 
    private XmlNavigatorFilter _filter;
 
    private IteratorState _state;
 
    private XPathNavigator _navCurrent;
 
    private XPathNavigator _navNext;
 
    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;
                return MoveFirst();
            }
            if (_navCurrent.IsDescendant(input))
            {
                goto case IteratorState.NeedCandidateCurrent;
            }
            _state = IteratorState.HaveCurrentNeedNext;
            goto case IteratorState.HaveCurrentNeedNext;
        case IteratorState.HaveCurrentNeedNext:
            if (input == null)
            {
                _state = IteratorState.HaveCurrentNoNext;
                return MoveFirst();
            }
            if (_navCurrent.ComparePosition(input) != XmlNodeOrder.Unknown)
            {
                return IteratorResult.NeedInputNode;
            }
            _navNext = XmlQueryRuntime.SyncToNavigator(_navNext, input);
            _state = IteratorState.HaveCurrentHaveNext;
            return MoveFirst();
        default:
            if (!_filter.MoveToFollowing(_navCurrent, null))
            {
                return MoveFailed();
            }
            return IteratorResult.HaveCurrentNode;
        }
    }
 
    private IteratorResult MoveFailed()
    {
        if (_state == IteratorState.HaveCurrentNoNext)
        {
            _state = IteratorState.NeedCandidateCurrent;
            return IteratorResult.NoMoreNodes;
        }
        _state = IteratorState.HaveCandidateCurrent;
        XPathNavigator navCurrent = _navCurrent;
        _navCurrent = _navNext;
        _navNext = navCurrent;
        return IteratorResult.NeedInputNode;
    }
 
    private IteratorResult MoveFirst()
    {
        if (!XPathFollowingIterator.MoveFirst(_filter, _navCurrent))
        {
            return MoveFailed();
        }
        return IteratorResult.HaveCurrentNode;
    }
}