DocumentOrderComparer.cs

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using System.Collections.Generic;
using System.Xml.XPath;
 
namespace System.Xml.Xsl.Runtime;
 
internal sealed class DocumentOrderComparer : IComparer<XPathNavigator>
{
    private List<XPathNavigator> _roots;
 
    public int Compare(XPathNavigator navThis, XPathNavigator navThat)
    {
        switch (navThis.ComparePosition(navThat))
        {
        case XmlNodeOrder.Before:
            return -1;
        case XmlNodeOrder.Same:
            return 0;
        case XmlNodeOrder.After:
            return 1;
        default:
            if (_roots == null)
            {
                _roots = new List<XPathNavigator>();
            }
            if (GetDocumentIndex(navThis) >= GetDocumentIndex(navThat))
            {
                return 1;
            }
            return -1;
        }
    }
 
    public int GetDocumentIndex(XPathNavigator nav)
    {
        if (_roots == null)
        {
            _roots = new List<XPathNavigator>();
        }
        XPathNavigator xPathNavigator = nav.Clone();
        xPathNavigator.MoveToRoot();
        for (int i = 0; i < _roots.Count; i++)
        {
            if (xPathNavigator.IsSamePosition(_roots[i]))
            {
                return i;
            }
        }
        _roots.Add(xPathNavigator);
        return _roots.Count - 1;
    }
}