Request.swift

public typealias NetworkCompletion = ((_ result: Response<Data?>) -> Void)?

public enum Method: String {
    case OPTIONS, GET, HEAD, POST, PUT, PATCH, DELETE, TRACE, CONNECT
}

public class Request {

    fileprivate var headers: [String: String] = ["Content-Type": "application/json"]
    fileprivate var task   : URLSessionDataTask!

    public init() {
    }

    public func send(method: Method, url: String, parameter: [String: Any], completion: NetworkCompletion) {
        if method == .GET {
            requestData(method: method, url: url, queryParameters: parameter, completion: completion)
        } else {
            requestData(method: method, url: url, bodyParameters: parameter, completion: completion)
        }
    }

    public func setHeaders(key:String, value:String) {
        headers = [key: value]
    }

    public func cancelTask() {
        guard task != nil else {return}
        task.cancel()
    }

    /**
     MARK: - Private Methods
     */
    private func requestData(method: Method,
                             url:String,
                             queryParameters: [String: Any]? = nil,
                             bodyParameters: [String: Any]? = nil,
                             completion: NetworkCompletion) {

        let url = URL(string: url, relativeTo: URL(string:"https://api.github.com/"))!
        do {
            let request = try createURLRequest(url: url,
                                               method: method.rawValue,
                                               queryParameters: queryParameters,
                                               bodyParameters: bodyParameters,
                                               headers: headers)

            task = URLSession.sessionDefault.dataTask(with: request,
                                                        completionHandler: { (data, response, error) in
                return self.parseTo(data,
                                    request: request,
                                    response: response,
                                    error: error,
                                    completion: completion)
            })

            task.resume()
        } catch {
            completion?(Response(request: nil, response: nil, data: nil, result: Result.failure(error)))
        }
    }

    private func createURLRequest(url: URL, method: String,
                                  queryParameters: [String: Any]?,
                                  bodyParameters: [String: Any]?,
                                  headers: [String: String]?)
        throws -> URLRequest {

        var actualURL: URL = url
        if let queryParameters = queryParameters {
            var components = URLComponents(url: url, resolvingAgainstBaseURL: true)!
            components.queryItems = queryParameters.map { (key, value) in
                URLQueryItem(name: key, value: value as? String)
            }
            actualURL = components.url!
        }

            print(actualURL)
        var request = URLRequest(url: actualURL)
        request.httpMethod = method

        if let bodyParameters = bodyParameters {
            request.httpBody = try JSONSerialization.data(withJSONObject: bodyParameters, options: [])
        }

        if let headers = headers {
            for (field, value) in headers {
                request.addValue(value, forHTTPHeaderField: field)
            }
        }
        return request
    }

    private func parseTo(_ data: Data?,
                         request: URLRequest,
                         response:URLResponse?,
                         error: Error?,
                         completion: NetworkCompletion) {

        //todo: Não ficou bom isso
        guard error == nil else {
            completion?(Response(request: request,
                                 response: response as? HTTPURLResponse,
                                 data: nil,
                                 result: Result.failure(error!)))
            return
        }
        //todo: e nem isso
        guard data != nil else {
            completion?(Response(request: request,
                                 response: response as? HTTPURLResponse,
                                 data: nil,
                                 result: Result.failure(error!)))
            return
        }

        completion?(Response(request: request,
                             response: response as? HTTPURLResponse,
                             data: data,
                             result: Result.success(data)))
    }
}