Add ResultOperation

1 files changed, 77 insertions, 0 deletions

diff --git a/ios/MullvadVPN/Operations/ResultOperation.swift b/ios/MullvadVPN/Operations/ResultOperation.swift
new file mode 100644
index 0000000000..ba2cd59c4e
--- /dev/null
+++ b/ios/MullvadVPN/Operations/ResultOperation.swift
@@ -0,0 +1,77 @@
+//
+//  ResultOperation.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 23/03/2022.
+//  Copyright © 2022 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+/// Base class for operations producing result.
+class ResultOperation<Success, Failure: Error>: AsyncOperation {
+    typealias Completion = OperationCompletion<Success, Failure>
+    typealias CompletionHandler = (Completion) -> Void
+
+    private let stateLock = NSLock()
+    private var completionValue: Completion?
+    private let completionQueue: DispatchQueue?
+    private var completionHandler: CompletionHandler?
+
+    var completion: Completion? {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+        return completionValue
+    }
+
+    init(completionQueue: DispatchQueue?, completionHandler: CompletionHandler?) {
+        self.completionQueue = completionQueue
+        self.completionHandler = completionHandler
+
+        super.init()
+    }
+
+    override func finish() {
+        // Propagate cancellation if finish() is called directly from start().
+        if isCancelled {
+            finish(completion: .cancelled)
+        } else {
+            preconditionFailure("Use finish(completion:) to finish operation.")
+        }
+    }
+
+    func finish(completion: Completion) {
+        stateLock.lock()
+
+        // Bail if operation is already finishing.
+        guard completionValue == nil else {
+            stateLock.unlock()
+            return
+        }
+
+        // Store completion value.
+        completionValue = completion
+
+        // Copy completion handler.
+        let completionHandler: CompletionHandler? = self.completionHandler
+
+        // Unset completion handler.
+        self.completionHandler = nil
+
+        stateLock.unlock()
+
+        let block = {
+            // Call completion handler.
+            completionHandler?(completion)
+
+            // Finish operation.
+            super.finish()
+        }
+
+        if let completionQueue = completionQueue {
+            completionQueue.async(execute: block)
+        } else {
+            block()
+        }
+    }
+}