using System;
using System.ComponentModel;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;

namespace WindowsFormsApplication1
{
    static class NativeMethods
    {
        private static readonly IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);

        private const uint FILE_READ_EA = 0x0008;
        private const uint FILE_FLAG_BACKUP_SEMANTICS = 0x2000000;

        [DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        private static extern uint GetFinalPathNameByHandle(IntPtr hFile, [MarshalAs(UnmanagedType.LPTStr)] StringBuilder filePath, uint length, uint flags);

        [DllImport("kernel32.dll", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool CloseHandle(IntPtr hObject);

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr CreateFile(
                [MarshalAs(UnmanagedType.LPTStr)] string filename,
                [MarshalAs(UnmanagedType.U4)] uint access,
                [MarshalAs(UnmanagedType.U4)] FileShare share,
                IntPtr securityAttributes, // optional SECURITY_ATTRIBUTES struct or IntPtr.Zero
                [MarshalAs(UnmanagedType.U4)] FileMode creationDisposition,
                [MarshalAs(UnmanagedType.U4)] uint flagsAndAttributes,
                IntPtr templateFile);

        /// <summary>
        /// Gibt von einem gemappten Verzeichnis das ursprüngliche Verzeichnis zurück.
        /// Funktioniert beim System "C:\Dokumente und Einstellungen\All Users\LID\Data\"
        /// und beim Server "P:\Themen\LID\".
        /// </summary>
        /// <param name="path">das zu untersuchende Verzeichnis</param>
        /// <returns>das ursprüngliche Verzeichnis in der Notation des Systems</returns>
        public static string GetFinalPathName(string path)
        {
            IntPtr h = NativeMethods.CreateFile(path,
                NativeMethods.FILE_READ_EA,
                FileShare.ReadWrite | FileShare.Delete,
                IntPtr.Zero,
                FileMode.Open,
                NativeMethods.FILE_FLAG_BACKUP_SEMANTICS,
                IntPtr.Zero);

            if (h == NativeMethods.INVALID_HANDLE_VALUE)
            {
                // Pfad existiert nicht
                throw new Win32Exception();
            }

            try
            {
                StringBuilder sb = new StringBuilder(1024);
                uint res = NativeMethods.GetFinalPathNameByHandle(h, sb, 1024, 0);
                if (res == 0)
                {
                    throw new Win32Exception();
                }

                string finalPath = sb.ToString();
                if (finalPath.StartsWith("\\\\?\\"))
                {
                    return finalPath.Substring(4);
                }

                return finalPath;
            }
            finally
            {
                NativeMethods.CloseHandle(h);
            }
        }
    }
}