func getAllStocks(url: String, completion: @escaping (Result<[Stock]?,NetworkError>) -> Void) {

    guard let url = URL(string: url) else {
        DispatchQueue.main.async {
            completion(.failure(.invalidURL))
        }
        return
    }

    URLSession.shared.dataTask(with: url) { data, response, error in

        guard let data = data, error == nil else {
            DispatchQueue.main.async {
                completion(.failure(.unknownError))
            }

            return
        }

        let stocks = try? JSONDecoder().decode([Stock].self, from: data)
        DispatchQueue.main.async {
            completion(.success(stocks))
        }

    }.resume()
}