UnionIterator.cs

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using System.ComponentModel;
using System.Xml.XPath;
 
namespace System.Xml.Xsl.Runtime;
 
[EditorBrowsable(EditorBrowsableState.Never)]
public struct UnionIterator
{
    private enum IteratorState
    {
        InitLeft,
        NeedLeft,
        NeedRight,
        LeftIsCurrent,
        RightIsCurrent
    }
 
    private XmlQueryRuntime _runtime;
 
    private XPathNavigator _navCurr;
 
    private XPathNavigator _navOther;
 
    private IteratorState _state;
 
    public XPathNavigator Current => _navCurr;
 
    public void Create(XmlQueryRuntime runtime)
    {
        _runtime = runtime;
        _state = IteratorState.InitLeft;
    }
 
    public SetIteratorResult MoveNext(XPathNavigator nestedNavigator)
    {
        switch (_state)
        {
        case IteratorState.InitLeft:
            _navOther = nestedNavigator;
            _state = IteratorState.NeedRight;
            return SetIteratorResult.InitRightIterator;
        case IteratorState.NeedLeft:
            _navCurr = nestedNavigator;
            _state = IteratorState.LeftIsCurrent;
            break;
        case IteratorState.NeedRight:
            _navCurr = nestedNavigator;
            _state = IteratorState.RightIsCurrent;
            break;
        case IteratorState.LeftIsCurrent:
            _state = IteratorState.NeedLeft;
            return SetIteratorResult.NeedLeftNode;
        case IteratorState.RightIsCurrent:
            _state = IteratorState.NeedRight;
            return SetIteratorResult.NeedRightNode;
        }
        if (_navCurr == null)
        {
            if (_navOther == null)
            {
                return SetIteratorResult.NoMoreNodes;
            }
            Swap();
        }
        else if (_navOther != null)
        {
            int num = _runtime.ComparePosition(_navOther, _navCurr);
            if (num == 0)
            {
                if (_state == IteratorState.LeftIsCurrent)
                {
                    _state = IteratorState.NeedLeft;
                    return SetIteratorResult.NeedLeftNode;
                }
                _state = IteratorState.NeedRight;
                return SetIteratorResult.NeedRightNode;
            }
            if (num < 0)
            {
                Swap();
            }
        }
        return SetIteratorResult.HaveCurrentNode;
    }
 
    private void Swap()
    {
        XPathNavigator navCurr = _navCurr;
        _navCurr = _navOther;
        _navOther = navCurr;
        if (_state == IteratorState.LeftIsCurrent)
        {
            _state = IteratorState.RightIsCurrent;
        }
        else
        {
            _state = IteratorState.LeftIsCurrent;
        }
    }
}