PrecedingQuery.cs

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using System.Xml.XPath;
 
namespace MS.Internal.Xml.XPath;
 
internal sealed class PrecedingQuery : BaseAxisQuery
{
    private XPathNodeIterator _workIterator;
 
    private readonly ClonableStack<XPathNavigator> _ancestorStk;
 
    public override QueryProps Properties => base.Properties | QueryProps.Reverse;
 
    public PrecedingQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest)
        : base(qyInput, name, prefix, typeTest)
    {
        _ancestorStk = new ClonableStack<XPathNavigator>();
    }
 
    private PrecedingQuery(PrecedingQuery other)
        : base(other)
    {
        _workIterator = Query.Clone(other._workIterator);
        _ancestorStk = other._ancestorStk.Clone();
    }
 
    public override void Reset()
    {
        _workIterator = null;
        _ancestorStk.Clear();
        base.Reset();
    }
 
    public override XPathNavigator Advance()
    {
        if (_workIterator == null)
        {
            XPathNavigator xPathNavigator = qyInput.Advance();
            if (xPathNavigator == null)
            {
                return null;
            }
            XPathNavigator xPathNavigator2 = xPathNavigator.Clone();
            do
            {
                xPathNavigator2.MoveTo(xPathNavigator);
            }
            while ((xPathNavigator = qyInput.Advance()) != null);
            if (xPathNavigator2.NodeType == XPathNodeType.Attribute || xPathNavigator2.NodeType == XPathNodeType.Namespace)
            {
                xPathNavigator2.MoveToParent();
            }
            do
            {
                _ancestorStk.Push(xPathNavigator2.Clone());
            }
            while (xPathNavigator2.MoveToParent());
            _workIterator = xPathNavigator2.SelectDescendants(XPathNodeType.All, matchSelf: true);
        }
        while (_workIterator.MoveNext())
        {
            currentNode = _workIterator.Current;
            if (currentNode.IsSamePosition(_ancestorStk.Peek()))
            {
                _ancestorStk.Pop();
                if (_ancestorStk.Count == 0)
                {
                    currentNode = null;
                    _workIterator = null;
                    return null;
                }
            }
            else if (matches(currentNode))
            {
                position++;
                return currentNode;
            }
        }
        return null;
    }
 
    public override XPathNodeIterator Clone()
    {
        return new PrecedingQuery(this);
    }
}