Deleting folders is a risky business

Deleting folder programmatically is extremely dangerous. It is enough for somebody else to change a configuration file or constant variable including the target folder's name to, say C:\, and that's it: the workstation is paralyzed!

Following suggested methods are to prevent such a situation. Their aim is to wrap the low level, possibly recursive file system operation with the necessary validation and clear facade - look twice, delete once.

Delete temporary directory created by current user (non recursive!)

    /// <summary>
    /// carefully remove directory and its files
    /// verify the directory is located under the %temp%
    /// and it is not e.g. C:\
    /// </summary>
    /// <param name="dir"></param>

    public static void DeleteTempDirShallow(string dir)
    {
        // check if it is an invalid directory path,
        // e.g. a disk drive or just a bad string

        if (! Directory.Exists(dir)) return;
 
        DirectoryInfo userTempDirInfo = new DirectoryInfo(Path.GetTempPath());
        DirectoryInfo dirInfo = new DirectoryInfo(dir);
 
        if (dirInfo.FullName.Contains(userTempDirInfo.FullName))
        {
            foreach (FileInfo file in dirInfo.GetFiles())
                file.Delete();
 
            dirInfo.Delete(); // just clean up the empty dir
        }
    }

Delete temporary directory created by current user (recursive!)

    public static void DeleteTempDirRecursive(string dir)
    {
        // check if it is an invalid directory path,
        // e.g. a disk drive or just a bad string
        if (! Directory.Exists(dir)) return;
 
        DirectoryInfo userTempDirInfo = new DirectoryInfo(Path.GetTempPath());
        DirectoryInfo dirInfo = new DirectoryInfo(dir);
 
        if (dirInfo.FullName.Contains(userTempDirInfo.FullName))
        {
            dirInfo.Delete(recursive: true);
        }
    }

Do I try to delete any root or system folder?

    static List<string> systemDirs = new List<string>
    {
        Environment.GetFolderPath(Environment.SpecialFolder.CommonProgramFiles),
        Environment.GetFolderPath(Environment.SpecialFolder.CommonProgramFilesX86),
        Environment.GetFolderPath(Environment.SpecialFolder.CommonPrograms),
        Environment.GetFolderPath(Environment.SpecialFolder.CommonStartMenu),
        Environment.GetFolderPath(Environment.SpecialFolder.CommonStartup),
        Environment.GetFolderPath(Environment.SpecialFolder.Fonts),
        Environment.GetFolderPath(Environment.SpecialFolder.NetworkShortcuts),
        Environment.GetFolderPath(Environment.SpecialFolder.PrinterShortcuts),
        Environment.GetFolderPath(Environment.SpecialFolder.ProgramFiles),
        Environment.GetFolderPath(Environment.SpecialFolder.ProgramFilesX86),
        Environment.GetFolderPath(Environment.SpecialFolder.Resources),
        Environment.GetFolderPath(Environment.SpecialFolder.StartMenu),
        Environment.GetFolderPath(Environment.SpecialFolder.Startup),
        Environment.GetFolderPath(Environment.SpecialFolder.System),
        Environment.GetFolderPath(Environment.SpecialFolder.SystemX86),
        Environment.GetFolderPath(Environment.SpecialFolder.Templates),
        Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
        Environment.GetFolderPath(Environment.SpecialFolder.Windows),
    };
 
    /// <summary>
    /// check if the argument dir is a disk drive,
    /// is a system (sub-)folder
    /// and should not be erased
    /// </summary>
    /// <param name="dir"></param>
    /// <returns></returns>
    public static bool IsSystemOrRootDir(string dir)
    {
        // check if it is an invalid directory path,
        // or just a bad string
        if (! Directory.Exists(dir)) return true;
 
        DirectoryInfo dirInfo = new DirectoryInfo(dir);
 
        // is it a root (disk drive)? 
        if (dirInfo.Parent == null) return true;
 
        bool result = false;
        systemDirs.ForEach(sysDir => { result = result ||
                                       dirInfo.FullName.Contains(sysDir); } );
        return result;
    }