Finding a relative Path

[RowTest()]

[Row(@"c:\fred.txt", @"c:\", "fred.txt")]

[Row(@"c:\fred.txt", @"C:\", "fred.txt")]

[Row(@"c:\fred\Tom\Bill\fred.txt", @"c:\fred\Tom\Bill", "fred.txt")]

[Row(@"c:\fred\Tom\Bill\fred.txt", @"c:\fred\Tom\Bill\", "fred.txt")]

[Row(@"c:\fred\Tom\fred.txt", @"c:\fred\Tom\Bill\", @"..\fred.txt")]

[Row(@"c:\fred\fred.txt", @"c:\fred\Tom\Bill\", @"..\..\fred.txt")]

[Row(@"c:\fred.txt", @"c:\fred\Tom\Bill\", @"..\..\..\fred.txt")]

[Row(@"c:\fred\Tom\Bill\fred.txt", @"c:\fred\", @"Tom\Bill\fred.txt")]

[Row(@"c:\fred\Tom\Bill\fred.txt", @"c:\fred", @"Tom\Bill\fred.txt")]

[Row(@"c:\fred\Tom\Bill\fred.txt", @"c:\fred\Tom\", @"Bill\fred.txt")]

[Row(@"c:\fred\Tom\Bill\fred.txt", @"c:\fred\Tom", @"Bill\fred.txt")]

[Row(@"c:\Harry\Tom\Bill\fred.txt", @"c:\fred\Tom\Bill\", @"..\..\..\Harry\Tom\Bill\fred.txt")]

[Row(@"c:\Harry\Tom\Bill\fred.txt", @"c:\fred\Tom\Bill", @"..\..\..\Harry\Tom\Bill\fred.txt")]

public void RelativePaths(string path, string root, string expected)

{

    Assert.AreEqual(expected, Centivus.Net.PathExtensions.CalculateRelative(path, root));

}

public static string CalculateRelative(string path, string root)

{

    string[] relativeParts = root.Split(

         new char[1] { Path.DirectorySeparatorChar},

         StringSplitOptions.RemoveEmptyEntries);

    string[] pathParts = Path.GetDirectoryName(path).Split(

         new char[1] { Path.DirectorySeparatorChar }, 

         StringSplitOptions.RemoveEmptyEntries);

    System.Collections.IEnumerator rootEnumerator = relativeParts.GetEnumerator();

    System.Collections.IEnumerator pathEnumerator = pathParts.GetEnumerator();

    StringBuilder result = new StringBuilder();

    string rootPart = null;

    string pathPart = null;

    bool haveNextRoot = true;

    bool haveNextPath = true;

    do //first is the drive or UNC root

    {

        haveNextRoot &= rootEnumerator.MoveNext();

        haveNextPath &= pathEnumerator.MoveNext();

        if (haveNextRoot)

            rootPart = (string)rootEnumerator.Current;

        if (haveNextPath)

            pathPart = (string) pathEnumerator.Current;

    }

    while (haveNextRoot

        && haveNextPath

        && String.Compare(rootPart, pathPart, true) == 0);       

    while (haveNextRoot)

    {

        result.Append("..");

        result.Append(Path.DirectorySeparatorChar);

        haveNextRoot = rootEnumerator.MoveNext();

    }

    while (haveNextPath)

    {

        if (String.IsNullOrEmpty((string) pathEnumerator.Current) == false)

        {

            result.Append((string)pathEnumerator.Current);

            result.Append(Path.DirectorySeparatorChar);

        }

        haveNextPath = pathEnumerator.MoveNext();

    }            

    return Path.Combine(result.ToString(), Path.GetFileName(path));

}