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

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

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

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

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

    }.resume()
}