IStorage.cs

public interface IStorage
{
  Uri Save(Stream data, string name);
  Task<Stream> LoadAsync(Uri dataUri);
}

Storage.cs

public static class Storage
{
  public static bool SaveDownloadedFile(WebResponse response, ref string fileName)
  {
    using (var stream = response.GetResponseStream())
    {
      if (stream == null)
        return false;

      using (var file = File.Create(fileName))
      {
        fileName = file.Name;
        stream.CopyTo(file);
        file.Close();
      }
    }
    return true;
  }
}