Promise: add background task extension

1 files changed, 57 insertions, 0 deletions

diff --git a/ios/MullvadVPN/Promise/Promise+BackgroundTask.swift b/ios/MullvadVPN/Promise/Promise+BackgroundTask.swift
new file mode 100644
index 0000000000..1d7bfc3280
--- /dev/null
+++ b/ios/MullvadVPN/Promise/Promise+BackgroundTask.swift
@@ -0,0 +1,57 @@
+//
+//  Promise+BackgroundTask.swift
+//  Promise+BackgroundTask
+//
+//  Created by pronebird on 06/09/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import UIKit
+
+extension Promise {
+
+    /// Start the background task for the duration of the upstream execution.
+    func requestBackgroundTime(taskName: String? = nil) -> Promise<Value> {
+        return Promise<Value> { resolver in
+            var backgroundTaskIdentifier: UIBackgroundTaskIdentifier?
+
+            let beginBackgroundTask = {
+                backgroundTaskIdentifier = UIApplication.shared.beginBackgroundTask(withName: taskName) {
+                    resolver.resolve(completion: .cancelled)
+                }
+            }
+
+            let endBackgroundTask = {
+                guard let taskIdentifier = backgroundTaskIdentifier,
+                      taskIdentifier != .invalid else { return }
+
+                UIApplication.shared.endBackgroundTask(taskIdentifier)
+                backgroundTaskIdentifier = nil
+            }
+
+            let endBackgroundTaskOnMainQueue = {
+                if Thread.isMainThread {
+                    endBackgroundTask()
+                } else {
+                    DispatchQueue.main.async(execute: endBackgroundTask)
+                }
+            }
+
+            if Thread.isMainThread {
+                beginBackgroundTask()
+            } else {
+                DispatchQueue.main.async(execute: beginBackgroundTask)
+            }
+
+            resolver.setCancelHandler {
+                endBackgroundTaskOnMainQueue()
+            }
+
+            self.observe { completion in
+                resolver.resolve(completion: completion)
+
+                endBackgroundTaskOnMainQueue()
+            }
+        }
+    }
+}