Combine examples

Other Projects/Combine using GitHub API/SwiftUI-Combine-Example/FoundationExtensions.swift

@@ -1,34 +1,57 @@
 import SwiftUI
 import Combine
 
-enum RequestError: Error {
-    case request(code: Int, error: Error?)
-    case unknown
+enum URLSessionError: Error {
+    case invalidResponse
+    case serverErrorMessage(statusCode: Int, data: Data)
+    case urlError(URLError)
 }
 
 extension URLSession {
-    func send(request: URLRequest) -> AnyPublisher<(data: Data, response: HTTPURLResponse), RequestError> {
-        AnyPublisher<(data: Data, response: HTTPURLResponse), RequestError> { subscriber in
-            let task = self.dataTask(with: request) { data, response, error in
-                DispatchQueue.main.async {
-                    let httpReponse = response as? HTTPURLResponse
-                    if let data = data, let httpReponse = httpReponse, 200..<300 ~= httpReponse.statusCode {
-                        _ = subscriber.receive((data, httpReponse))
-                        subscriber.receive(completion: .finished)
-                    }
-                    else if let httpReponse = httpReponse {
-                        subscriber.receive(completion: .failure(.request(code: httpReponse.statusCode, error: error)))
-                    }
-                    else {
-                        subscriber.receive(completion: .failure(.unknown))
-                    }
-                }
-            }
+    func send(request: URLRequest) -> AnyPublisher<Data, URLSessionError> {
 
-            subscriber.receive(subscription: AnySubscription(task.cancel))
-            task.resume()
-        }
+        dataTaskPublisher(for: request)
+            .mapError { URLSessionError.urlError($0) }
+            .flatMap { data, response -> AnyPublisher<Data, URLSessionError> in
+                guard let response = response as? HTTPURLResponse else {
+                    return .fail(.invalidResponse)
+                }
+
+                guard 200..<300 ~= response.statusCode else {
+                    return .fail(.serverErrorMessage(statusCode: response.statusCode,
+                                                     data: data))
+                }
+
+                return .just(data)
+        }.eraseToAnyPublisher()
     }
 }
 
 extension JSONDecoder: TopLevelDecoder {}
+
+extension Publisher {
+
+    /// - seealso: https://twitter.com/peres/status/1136132104020881408
+    func flatMapLatest<T: Publisher>(_ transform: @escaping (Self.Output) -> T) -> Publishers.SwitchToLatest<T, Publishers.Map<Self, T>> where T.Failure == Self.Failure {
+        map(transform).switchToLatest()
+    }
+}
+
+extension Publisher {
+
+    static func empty() -> AnyPublisher<Output, Failure> {
+        return Publishers.Empty()
+            .eraseToAnyPublisher()
+    }
+
+    static func just(_ output: Output) -> AnyPublisher<Output, Failure> {
+        return Just(output)
+            .catch { _ in AnyPublisher<Output, Failure>.empty() }
+            .eraseToAnyPublisher()
+    }
+
+    static func fail(_ error: Failure) -> AnyPublisher<Output, Failure> {
+        return Publishers.Fail(error: error)
+            .eraseToAnyPublisher()
+    }
+}