func createTempDirectory() -> String? {
    let tempDirectoryTemplate = NSTemporaryDirectory().stringByAppendingPathComponent("XXXXX")

    let fileManager = NSFileManager.defaultManager()

    var err: NSErrorPointer = nil
    if fileManager.createDirectoryAtPath(tempDirectoryTemplate, withIntermediateDirectories: true, attributes: nil, error: err) {
        return tempDirectoryTemplate
    } else {
        return nil
    }
}