CacheChildrenQuery.cs

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using System.Xml;
using System.Xml.XPath;
 
namespace MS.Internal.Xml.XPath;
 
internal sealed class CacheChildrenQuery : ChildrenQuery
{
    private XPathNavigator _nextInput;
 
    private readonly ClonableStack<XPathNavigator> _elementStk;
 
    private readonly ClonableStack<int> _positionStk;
 
    private bool _needInput;
 
    public CacheChildrenQuery(Query qyInput, string name, string prefix, XPathNodeType type)
        : base(qyInput, name, prefix, type)
    {
        _elementStk = new ClonableStack<XPathNavigator>();
        _positionStk = new ClonableStack<int>();
        _needInput = true;
    }
 
    private CacheChildrenQuery(CacheChildrenQuery other)
        : base(other)
    {
        _nextInput = Query.Clone(other._nextInput);
        _elementStk = other._elementStk.Clone();
        _positionStk = other._positionStk.Clone();
        _needInput = other._needInput;
    }
 
    public override void Reset()
    {
        _nextInput = null;
        _elementStk.Clear();
        _positionStk.Clear();
        _needInput = true;
        base.Reset();
    }
 
    public override XPathNavigator Advance()
    {
        do
        {
            IL_0000:
            if (_needInput)
            {
                if (_elementStk.Count == 0)
                {
                    currentNode = GetNextInput();
                    if (currentNode == null)
                    {
                        return null;
                    }
                    if (!currentNode.MoveToFirstChild())
                    {
                        goto IL_0000;
                    }
                    position = 0;
                }
                else
                {
                    currentNode = _elementStk.Pop();
                    position = _positionStk.Pop();
                    if (!DecideNextNode())
                    {
                        goto IL_0000;
                    }
                }
                _needInput = false;
            }
            else if (!currentNode.MoveToNext() || !DecideNextNode())
            {
                _needInput = true;
                goto IL_0000;
            }
        }
        while (!matches(currentNode));
        position++;
        return currentNode;
    }
 
    private bool DecideNextNode()
    {
        _nextInput = GetNextInput();
        if (_nextInput != null && Query.CompareNodes(currentNode, _nextInput) == XmlNodeOrder.After)
        {
            _elementStk.Push(currentNode);
            _positionStk.Push(position);
            currentNode = _nextInput;
            _nextInput = null;
            if (!currentNode.MoveToFirstChild())
            {
                return false;
            }
            position = 0;
        }
        return true;
    }
 
    private XPathNavigator GetNextInput()
    {
        XPathNavigator xPathNavigator;
        if (_nextInput != null)
        {
            xPathNavigator = _nextInput;
            _nextInput = null;
        }
        else
        {
            xPathNavigator = qyInput.Advance();
            if (xPathNavigator != null)
            {
                xPathNavigator = xPathNavigator.Clone();
            }
        }
        return xPathNavigator;
    }
 
    public override XPathNodeIterator Clone()
    {
        return new CacheChildrenQuery(this);
    }
}