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Generic Backend class
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| import Foundation | |
| public enum BackendError: Error { | |
| case invalid(String) | |
| case notFound(String) | |
| } | |
| public protocol Backend { | |
| var baseURL: String { get } | |
| var urlSession: URLSession { get } | |
| @discardableResult | |
| func perform(_ request: Request, completion: ((Result<Data>) -> Void)?) -> URLSessionTask? | |
| } | |
| public extension Backend { | |
| @discardableResult | |
| public func perform(_ request: Request, completion: ((Result<Data>) -> Void)? = nil) -> URLSessionTask? { | |
| let urlString = baseURL + request.path | |
| guard let url = URLComponents(string: urlString)?.url else { | |
| completion?(Result.failure(BackendError.invalid("Invalid url \(urlString)"))) | |
| return nil | |
| } | |
| var urlRequest = URLRequest(url: url) | |
| urlRequest.httpMethod = request.httpMethod | |
| urlRequest.httpBody = request.httpBody | |
| // set custom headers if there is any | |
| if let customHeaders = request.headers { | |
| customHeaders.forEach { urlRequest.addValue($0.value, forHTTPHeaderField: $0.key) } | |
| } | |
| let task = urlSession.dataTask(with: urlRequest) { (data, response, error) in | |
| do { | |
| if let error = error { | |
| throw error | |
| } | |
| guard let httpURLResponse = response as? HTTPURLResponse else { | |
| throw BackendError.invalid("Invalid API response \(String(describing: response))") | |
| } | |
| guard httpURLResponse.isValidResponse else { | |
| throw BackendError.invalid("Invalid statusCode: \(httpURLResponse.statusCode)") | |
| } | |
| guard let data = data else { | |
| throw BackendError.notFound("Data can't be found") | |
| } | |
| completion?(.success(data)) | |
| } catch { | |
| completion?(.failure(error)) | |
| } | |
| } | |
| task.resume() | |
| return task | |
| } | |
| @discardableResult | |
| public func perform<T>(_ request: Request, type: T.Type, keyPath: String? = nil, completion: ((Result<T>) -> Void)?) -> URLSessionTask? where T: Decodable { | |
| let decoder = JSONDecoder() | |
| return perform(request) { result in | |
| do { | |
| switch result { | |
| case .success(let data): | |
| let object: T | |
| if let keyPath = keyPath { | |
| let topLevelObject = try decoder.decode([String: T].self, from: data) | |
| guard let value = topLevelObject[keyPath] else { | |
| throw BackendError.notFound("Data can't be found at keyPath: \(keyPath)") | |
| } | |
| object = value | |
| } else { | |
| object = try decoder.decode(T.self, from: data) | |
| } | |
| completion?(Result.success(object)) | |
| case .failure(let error): | |
| throw error | |
| } | |
| } catch { | |
| completion?(Result.failure(error)) | |
| } | |
| } | |
| } | |
| } | |
| public enum Result<T> { | |
| case success(T) | |
| case failure(Error) | |
| } | |
| public struct Request { | |
| public let httpMethod: String | |
| public let path: String | |
| public var headers: [String: String]? | |
| public var httpBody: Data? | |
| public init(httpMethod: String, path: String, headers: [String: String]? = nil, httpBody: Data? = nil) { | |
| self.httpMethod = httpMethod | |
| self.path = path | |
| self.headers = headers | |
| self.httpBody = httpBody | |
| } | |
| } | |
| public extension HTTPURLResponse { | |
| public var isValidResponse: Bool { | |
| switch statusCode { | |
| case 200 ... 299: | |
| return true | |
| default: | |
| return false | |
| } | |
| } | |
| } |
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