func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
    guard let url = downloadTask.originalRequest?.url else { return }
    let documentsPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
    let destinationURL = documentsPath.appendingPathComponent(url.lastPathComponent)
    let booksPath = documentsPath.appendingPathComponent(self.saveTo, isDirectory: true).appendingPathComponent(url.lastPathComponent)

    let pattern = "_\.\+-=!@#\$\%\^\&\*()!"
    let title   = url.lastPathComponent.replacingOccurrences(of: pattern, with: " ", options: .regularExpression, range: nil)

    let _ = CoreDataHelper.shared.create(params: ["title" : title], objectType: Book.self)

    // delete original copy
    try? FileManager.default.removeItem(at: destinationURL)

    // copy from temp to Document
    do {
        try FileManager.default.copyItem(at: location, to: booksPath)
    } catch let error {
        print("Copy Error: (error.localizedDescription)")
    }
}