Add custom operation queue, conditions and observers

6 files changed, 548 insertions, 22 deletions

diff --git a/ios/MullvadVPN.xcodeproj/project.pbxproj b/ios/MullvadVPN.xcodeproj/project.pbxproj
index fad611075f..61d4e38245 100644
--- a/ios/MullvadVPN.xcodeproj/project.pbxproj
+++ b/ios/MullvadVPN.xcodeproj/project.pbxproj
@@ -8,6 +8,7 @@
 
 /* Begin PBXBuildFile section */
 		5801C9A527A14B2A0031566A /* TunnelManagerState.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5801C9A427A14B2A0031566A /* TunnelManagerState.swift */; };
+		58059DE228468255002B1049 /* ResultOperation+Fallible.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58059DE128468255002B1049 /* ResultOperation+Fallible.swift */; };
 		5806767C27048E9B00C858CB /* PacketTunnelProvider.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58CE5E7B224146470008646E /* PacketTunnelProvider.swift */; };
 		5807483B27DB8A980020ECBF /* WireGuardKitTypes in Frameworks */ = {isa = PBXBuildFile; productRef = 5807483A27DB8A980020ECBF /* WireGuardKitTypes */; };
 		5807E2C02432038B00F5FF30 /* String+Split.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5807E2BF2432038B00F5FF30 /* String+Split.swift */; };
@@ -70,6 +71,7 @@
 		5835B7CC233B76CB0096D79F /* TunnelManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5835B7CB233B76CB0096D79F /* TunnelManager.swift */; };
 		5838318B27C40A3900000571 /* Pinger.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5838318A27C40A3900000571 /* Pinger.swift */; };
 		583DA21425FA4B5C00318683 /* LocationDataSource.swift in Sources */ = {isa = PBXBuildFile; fileRef = 583DA21325FA4B5C00318683 /* LocationDataSource.swift */; };
+		583E1E1B2848DE1C004838B3 /* ResultOperation+Fallible.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58059DE128468255002B1049 /* ResultOperation+Fallible.swift */; };
 		5840250122B1124600E4CFEC /* IPAddress+Codable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5840250022B1124600E4CFEC /* IPAddress+Codable.swift */; };
 		5840250222B1124600E4CFEC /* IPAddress+Codable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5840250022B1124600E4CFEC /* IPAddress+Codable.swift */; };
 		5840250422B11AB700E4CFEC /* MullvadEndpoint.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5840250322B11AB700E4CFEC /* MullvadEndpoint.swift */; };
@@ -194,6 +196,9 @@
 		5896AE86246D6AD8005B36CB /* CustomDateComponentsFormattingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5896AE85246D6AD8005B36CB /* CustomDateComponentsFormattingTests.swift */; };
 		5896AE88246D7FAF005B36CB /* CustomDateComponentsFormatting.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5896AE83246D5889005B36CB /* CustomDateComponentsFormatting.swift */; };
 		5896CEF226972DEB00B0FAE8 /* AccountContentView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5896CEF126972DEB00B0FAE8 /* AccountContentView.swift */; };
+		589D287A2846250500F9A7B3 /* OperationCondition.swift in Sources */ = {isa = PBXBuildFile; fileRef = 589D28772846250500F9A7B3 /* OperationCondition.swift */; };
+		589D287B2846250500F9A7B3 /* AsyncOperationQueue.swift in Sources */ = {isa = PBXBuildFile; fileRef = 589D28782846250500F9A7B3 /* AsyncOperationQueue.swift */; };
+		589D287C2846250500F9A7B3 /* OperationObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 589D28792846250500F9A7B3 /* OperationObserver.swift */; };
 		58A1AA8C23F5584C009F7EA6 /* ConnectionPanelView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58A1AA8B23F5584B009F7EA6 /* ConnectionPanelView.swift */; };
 		58A8055E2716EA6700681642 /* AnyIPAddress.swift in Sources */ = {isa = PBXBuildFile; fileRef = 584D26BE270C550B004EA533 /* AnyIPAddress.swift */; };
 		58A8BE81239FBE62006B74AC /* IPEndpoint.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58561C98239A5D1500BD6B5E /* IPEndpoint.swift */; };
@@ -327,6 +332,7 @@
 
 /* Begin PBXFileReference section */
 		5801C9A427A14B2A0031566A /* TunnelManagerState.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelManagerState.swift; sourceTree = "<group>"; };
+		58059DE128468255002B1049 /* ResultOperation+Fallible.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "ResultOperation+Fallible.swift"; sourceTree = "<group>"; };
 		5807E2BF2432038B00F5FF30 /* String+Split.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "String+Split.swift"; sourceTree = "<group>"; };
 		5807E2C1243203D000F5FF30 /* StringTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = StringTests.swift; sourceTree = "<group>"; };
 		5808273928487E3E006B77A4 /* Base.xcconfig */ = {isa = PBXFileReference; lastKnownFileType = text.xcconfig; path = Base.xcconfig; sourceTree = "<group>"; };
@@ -463,6 +469,9 @@
 		5896AE83246D5889005B36CB /* CustomDateComponentsFormatting.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CustomDateComponentsFormatting.swift; sourceTree = "<group>"; };
 		5896AE85246D6AD8005B36CB /* CustomDateComponentsFormattingTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CustomDateComponentsFormattingTests.swift; sourceTree = "<group>"; };
 		5896CEF126972DEB00B0FAE8 /* AccountContentView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AccountContentView.swift; sourceTree = "<group>"; };
+		589D28772846250500F9A7B3 /* OperationCondition.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = OperationCondition.swift; sourceTree = "<group>"; };
+		589D28782846250500F9A7B3 /* AsyncOperationQueue.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AsyncOperationQueue.swift; sourceTree = "<group>"; };
+		589D28792846250500F9A7B3 /* OperationObserver.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = OperationObserver.swift; sourceTree = "<group>"; };
 		58A1AA8623F43901009F7EA6 /* Location.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Location.swift; sourceTree = "<group>"; };
 		58A1AA8B23F5584B009F7EA6 /* ConnectionPanelView.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ConnectionPanelView.swift; sourceTree = "<group>"; };
 		58A94AE326CFD945001CB97C /* TunnelErrorNotificationProvider.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TunnelErrorNotificationProvider.swift; sourceTree = "<group>"; };
@@ -608,11 +617,15 @@
 				580EE22324B3243100F9D8A1 /* AsyncBlockOperation.swift */,
 				58E973DD24850EB600096F90 /* AsyncOperation.swift */,
 				580EE20524B3222200F9D8A1 /* ExclusivityController.swift */,
+				589D28782846250500F9A7B3 /* AsyncOperationQueue.swift */,
 				5840BE34279EDB16002836BA /* OperationCompletion.swift */,
+				589D28772846250500F9A7B3 /* OperationCondition.swift */,
+				589D28792846250500F9A7B3 /* OperationObserver.swift */,
 				5820675D26E6839900655B05 /* PresentAlertOperation.swift */,
 				5846226426E0D9630035F7C2 /* ProductsRequestOperation.swift */,
 				58F7D26427EB50A300E4D821 /* ResultOperation.swift */,
 				5842102D282D3FC200F24E46 /* ResultBlockOperation.swift */,
+				58059DE128468255002B1049 /* ResultOperation+Fallible.swift */,
 			);
 			path = Operations;
 			sourceTree = "<group>";
@@ -1208,6 +1221,7 @@
 				585DA8A326B14E0D00B8C587 /* ServerRelaysResponse.swift in Sources */,
 				5820676226E75D8500655B05 /* REST.swift in Sources */,
 				58A8055E2716EA6700681642 /* AnyIPAddress.swift in Sources */,
+				583E1E1B2848DE1C004838B3 /* ResultOperation+Fallible.swift in Sources */,
 				5857F23024C843ED00CF6F47 /* ChainedError.swift in Sources */,
 				58A8BE81239FBE62006B74AC /* IPEndpoint.swift in Sources */,
 				5846227A26E24F1F0035F7C2 /* ExclusivityController.swift in Sources */,
@@ -1242,10 +1256,12 @@
 				58BA693123EADA6A009DC256 /* SimulatorTunnelProvider.swift in Sources */,
 				58F1311327E09B00007AC5BC /* Cancellable.swift in Sources */,
 				587C575326D2615F005EF767 /* PacketTunnelOptions.swift in Sources */,
+				589D287C2846250500F9A7B3 /* OperationObserver.swift in Sources */,
 				587B753B2666467500DEF7E9 /* NotificationBannerView.swift in Sources */,
 				58B993B12608A34500BA7811 /* LoginContentView.swift in Sources */,
 				58E6771F24ADFE7800AA26E7 /* SettingsNavigationController.swift in Sources */,
 				58A1AA8C23F5584C009F7EA6 /* ConnectionPanelView.swift in Sources */,
+				58059DE228468255002B1049 /* ResultOperation+Fallible.swift in Sources */,
 				582BB1B3229574F40055B6EF /* SettingsAccountCell.swift in Sources */,
 				588527B2276B3F0700BAA373 /* LoadTunnelConfigurationOperation.swift in Sources */,
 				58F1311527E0B2AB007AC5BC /* Result+Extensions.swift in Sources */,
@@ -1272,6 +1288,7 @@
 				58655DCE27DA0A5D00911834 /* TunnelMonitorConfiguration.swift in Sources */,
 				5850367F25A481D800A43E93 /* IPAddressRange+Codable.swift in Sources */,
 				58F2E14C276A61C000A79513 /* RotateKeyOperation.swift in Sources */,
+				589D287A2846250500F9A7B3 /* OperationCondition.swift in Sources */,
 				5871FB96254ADE4E0051A0A4 /* ConsolidatedApplicationLog.swift in Sources */,
 				58FEEB58260B662E00A621A8 /* AutomaticKeyboardResponder.swift in Sources */,
 				5846227326E22A160035F7C2 /* AppStorePaymentObserver.swift in Sources */,
@@ -1397,6 +1414,7 @@
 				58FD5BF22424F7D700112C88 /* UserInterfaceInteractionRestriction.swift in Sources */,
 				5811DE50239014550011EB53 /* NEVPNStatus+Debug.swift in Sources */,
 				58C3A4B222456F1B00340BDB /* AccountInputGroupView.swift in Sources */,
+				589D287B2846250500F9A7B3 /* AsyncOperationQueue.swift in Sources */,
 				58F840B22464491D0044E708 /* ChainedError.swift in Sources */,
 				588BCF24280FE43D009ADCEC /* RESTDevicesProxy.swift in Sources */,
 				58ACF64B26553C3F00ACE4B7 /* SettingsSwitchCell.swift in Sources */,
diff --git a/ios/MullvadVPN/Operations/AsyncOperation.swift b/ios/MullvadVPN/Operations/AsyncOperation.swift
index 898fc4b297..d3e13d2f81 100644
--- a/ios/MullvadVPN/Operations/AsyncOperation.swift
+++ b/ios/MullvadVPN/Operations/AsyncOperation.swift
@@ -8,28 +8,82 @@
 
 import Foundation
 
+@objc enum State: Int, Comparable, CustomStringConvertible {
+    case initialized
+    case pending
+    case evaluatingConditions
+    case ready
+    case executing
+    case finished
+
+    static func < (lhs: State, rhs: State) -> Bool {
+        return lhs.rawValue < rhs.rawValue
+    }
+
+    var description: String {
+        switch self {
+        case .initialized:
+            return "initialized"
+        case .pending:
+            return "pending"
+        case .evaluatingConditions:
+            return "evaluatingConditions"
+        case .ready:
+            return "ready"
+        case .executing:
+            return "executing"
+        case .finished:
+            return "finished"
+        }
+    }
+}
+
 /// A base implementation of an asynchronous operation
 class AsyncOperation: Operation {
+    private static var observerContext = 0
+
     /// A state lock used for manipulating the operation state flags in a thread safe fashion.
     private let stateLock = NSRecursiveLock()
 
-    /// Operation state flags.
-    private var _isExecuting = false
-    private var _isFinished = false
+    /// Operation state.
+    @objc private var state: State = .initialized
     private var _isCancelled = false
 
+    final override var isReady: Bool {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+
+        // super.isReady should turn true when all dependencies are satisfied.
+        guard super.isReady else {
+            return false
+        }
+
+        // Mark operation ready when cancelled, so that operation queue could flush it faster.
+        guard !_isCancelled else {
+            return true
+        }
+
+        switch state {
+        case .initialized, .pending, .evaluatingConditions:
+            return false
+
+        case .ready, .executing, .finished:
+            return true
+        }
+    }
+
     final override var isExecuting: Bool {
         stateLock.lock()
         defer { stateLock.unlock() }
 
-        return _isExecuting
+        return state == .executing
     }
 
     final override var isFinished: Bool {
         stateLock.lock()
         defer { stateLock.unlock() }
 
-        return _isFinished
+        return state == .finished
     }
 
     final override var isCancelled: Bool {
@@ -43,14 +97,145 @@ class AsyncOperation: Operation {
         return true
     }
 
+    // MARK: - Observers
+
+    private var _observers: [OperationObserver] = []
+
+    final var observers: [OperationObserver] {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+
+        return _observers
+    }
+
+    final func addObserver(_ observer: OperationObserver) {
+        stateLock.lock()
+        assert(state < .executing)
+        _observers.append(observer)
+        stateLock.unlock()
+        observer.didAttach(to: self)
+    }
+
+    // MARK: - Conditions
+
+    private var _conditions: [OperationCondition] = []
+
+    final var conditions: [OperationCondition] {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+
+        return _conditions
+    }
+
+    func addCondition(_ condition: OperationCondition) {
+        stateLock.lock()
+        assert(state < .evaluatingConditions)
+        _conditions.append(condition)
+        stateLock.unlock()
+    }
+
+    private func evaluateConditions() {
+        guard !_conditions.isEmpty else {
+            setState(.ready)
+            return
+        }
+
+        setState(.evaluatingConditions)
+
+        var results = [Bool](repeating: false, count: _conditions.count)
+        let group = DispatchGroup()
+
+        for (index, condition) in _conditions.enumerated() {
+            group.enter()
+            condition.evaluate(for: self) { [weak self] isSatisfied in
+                self?.dispatchQueue.async {
+                    results[index] = isSatisfied
+                    group.leave()
+                }
+            }
+        }
+
+        group.notify(queue: dispatchQueue) { [weak self] in
+            self?.didEvaluateConditions(results)
+        }
+    }
+
+    private func didEvaluateConditions(_ results: [Bool]) {
+        stateLock.lock()
+        defer { stateLock.unlock() }
+
+        guard state < .ready else { return }
+
+        let conditionsSatisfied = results.allSatisfy { $0 }
+        if !conditionsSatisfied {
+            cancel()
+        }
+
+        setState(.ready)
+    }
+
+    // MARK: -
+
     let dispatchQueue: DispatchQueue
+
     init(dispatchQueue: DispatchQueue? = nil) {
         self.dispatchQueue = dispatchQueue ?? DispatchQueue(label: "AsyncOperation.dispatchQueue")
         super.init()
+
+        addObserver(
+            self,
+            forKeyPath: #keyPath(isReady),
+            options: [],
+            context: &Self.observerContext
+        )
+    }
+
+    deinit {
+        removeObserver(
+            self,
+            forKeyPath: #keyPath(isReady),
+            context: &Self.observerContext
+        )
+    }
+
+    // MARK: - KVO
+
+    @objc class func keyPathsForValuesAffectingIsReady() -> Set<String> {
+        return ["state"]
+    }
+
+    @objc class func keyPathsForValuesAffectingIsExecuting() -> Set<String> {
+        return ["state"]
     }
 
+    @objc class func keyPathsForValuesAffectingIsFinished() -> Set<String> {
+        return ["state"]
+    }
+
+    override func observeValue(
+        forKeyPath keyPath: String?,
+        of object: Any?,
+        change: [NSKeyValueChangeKey : Any]?,
+        context: UnsafeMutableRawPointer?
+    )
+    {
+        if context == &Self.observerContext {
+            checkReadiness()
+        } else {
+            super.observeValue(
+                forKeyPath: keyPath,
+                of: object,
+                change: change,
+                context: context
+            )
+        }
+    }
+
+    // MARK: - Lifecycle
+
     final override func start() {
-        let underlyingQueue = OperationQueue.current?.underlyingQueue
+        let currentQueue = OperationQueue.current
+        let underlyingQueue = currentQueue?.underlyingQueue
 
         if underlyingQueue == dispatchQueue {
             _start()
@@ -67,8 +252,13 @@ class AsyncOperation: Operation {
             stateLock.unlock()
             finish()
         } else {
-            setExecuting(true)
+            setState(.executing)
+
+            for observer in _observers {
+                observer.operationDidStart(self)
+            }
             stateLock.unlock()
+
             main()
         }
     }
@@ -95,6 +285,10 @@ class AsyncOperation: Operation {
         if notifyDidCancel {
             dispatchQueue.async {
                 self.operationDidCancel()
+
+                for observer in self.observers {
+                    observer.operationDidCancel(self)
+                }
             }
         }
     }
@@ -103,34 +297,46 @@ class AsyncOperation: Operation {
         var notifyDidFinish = false
 
         stateLock.lock()
-
-        if _isExecuting {
-           setExecuting(false)
-        }
-
-        if !_isFinished {
-            willChangeValue(for: \.isFinished)
-            _isFinished = true
-            didChangeValue(for: \.isFinished)
-
+        if state < .finished {
+            setState(.finished)
             notifyDidFinish = true
         }
-
         stateLock.unlock()
 
         if notifyDidFinish {
             dispatchQueue.async {
                 self.operationDidFinish()
+
+                for observer in self.observers {
+                    observer.operationDidFinish(self)
+                }
             }
         }
     }
 
-    private func setExecuting(_ value: Bool) {
-        willChangeValue(for: \.isExecuting)
-        _isExecuting = value
-        didChangeValue(for: \.isExecuting)
+    // MARK: - Private
+
+    private func setState(_ newState: State) {
+        willChangeValue(for: \.state)
+        assert(state < newState)
+        state = newState
+        didChangeValue(for: \.state)
+    }
+
+    private func checkReadiness() {
+        stateLock.lock()
+        if state == .pending && !_isCancelled && super.isReady {
+            evaluateConditions()
+        }
+        stateLock.unlock()
+    }
+
+    func didEnqueue() {
+        setState(.pending)
     }
 
+    // MARK: - Subclass overrides
+
     func operationDidCancel() {
         // Override in subclasses.
     }
@@ -147,3 +353,19 @@ extension Operation {
         }
     }
 }
+
+extension Operation {
+    var operationName: String {
+        return name ?? "\(self)"
+    }
+}
+
+
+protocol OperationBlockObserverSupport {}
+extension AsyncOperation: OperationBlockObserverSupport {}
+
+extension OperationBlockObserverSupport where Self: AsyncOperation {
+    func addBlockObserver(_ observer: OperationBlockObserver<Self>) {
+        addObserver(observer)
+    }
+}
diff --git a/ios/MullvadVPN/Operations/AsyncOperationQueue.swift b/ios/MullvadVPN/Operations/AsyncOperationQueue.swift
new file mode 100644
index 0000000000..f89fd70841
--- /dev/null
+++ b/ios/MullvadVPN/Operations/AsyncOperationQueue.swift
@@ -0,0 +1,101 @@
+//
+//  AsyncOperationQueue.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 30/05/2022.
+//  Copyright © 2022 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+class AsyncOperationQueue: OperationQueue {
+    override func addOperation(_ operation: Operation) {
+        if let operation = operation as? AsyncOperation {
+            let categories = operation.conditions
+                .filter { condition in
+                    return condition.isMutuallyExclusive
+                }
+                .map { condition in
+                    return condition.name
+                }
+
+            if !categories.isEmpty {
+                ExclusivityManager.shared.addOperation(operation, categories: Set(categories))
+            }
+
+            super.addOperation(operation)
+
+            operation.didEnqueue()
+        } else {
+            super.addOperation(operation)
+        }
+    }
+
+    override func addOperations(_ operations: [Operation], waitUntilFinished wait: Bool) {
+        for operation in operations {
+            addOperation(operation)
+        }
+
+        if wait {
+            let blockOperation = BlockOperation()
+            blockOperation.addDependencies(operations)
+
+            addOperation(blockOperation)
+            blockOperation.waitUntilFinished()
+        }
+    }
+}
+
+private final class ExclusivityManager {
+    static let shared = ExclusivityManager()
+
+    private var operationsByCategory = [String: [Operation]]()
+    private let nslock = NSLock()
+
+    private init() {}
+
+    func addOperation(_ operation: AsyncOperation, categories: Set<String>) {
+        nslock.lock()
+        defer { nslock.unlock() }
+
+        for category in categories {
+            var operations = operationsByCategory[category] ?? []
+
+            if let lastOperation = operations.last {
+                operation.addDependency(lastOperation)
+            }
+
+            operations.append(operation)
+
+            operationsByCategory[category] = operations
+
+            let blockObserver = OperationBlockObserver(didFinish: { [weak self] op in
+                self?.removeOperation(op, categories: categories)
+            })
+
+            operation.addObserver(blockObserver)
+        }
+    }
+
+    private func removeOperation(_ operation: Operation, categories: Set<String>) {
+        nslock.lock()
+        defer { nslock.unlock() }
+
+        for category in categories {
+            guard var operations = operationsByCategory[category] else {
+                continue
+            }
+
+            if let index = operations.firstIndex(of: operation) {
+                operations.remove(at: index)
+            }
+
+            if operations.isEmpty {
+                operationsByCategory.removeValue(forKey: category)
+            } else {
+                operationsByCategory[category] = operations
+            }
+        }
+    }
+
+}
diff --git a/ios/MullvadVPN/Operations/OperationCondition.swift b/ios/MullvadVPN/Operations/OperationCondition.swift
new file mode 100644
index 0000000000..da3e5f56a1
--- /dev/null
+++ b/ios/MullvadVPN/Operations/OperationCondition.swift
@@ -0,0 +1,107 @@
+//
+//  OperationCondition.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 30/05/2022.
+//  Copyright © 2022 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+protocol FallibleOperation {
+    var error: Error? { get }
+}
+
+protocol OperationCondition {
+    var name: String { get }
+    var isMutuallyExclusive: Bool { get }
+
+    func evaluate(for operation: Operation, completion: @escaping (Bool) -> Void)
+}
+
+final class NoCancelledDependenciesCondition: OperationCondition {
+    var name: String {
+        return "NoCancelledDependenciesCondition"
+    }
+
+    var isMutuallyExclusive: Bool {
+        return false
+    }
+
+    func evaluate(for operation: Operation, completion: @escaping (Bool) -> Void) {
+        let satisfy = operation.dependencies.allSatisfy { operation in
+            return !operation.isCancelled
+        }
+
+        completion(satisfy)
+    }
+}
+
+final class NoFailedDependenciesCondition: OperationCondition {
+    var name: String {
+        return "NoFailedDependenciesCondition"
+    }
+
+    var isMutuallyExclusive: Bool {
+        return false
+    }
+
+    let ignoreCancellations: Bool
+    init(ignoreCancellations: Bool) {
+        self.ignoreCancellations = ignoreCancellations
+    }
+
+    func evaluate(for operation: Operation, completion: @escaping (Bool) -> Void) {
+        let satisfy = operation.dependencies.allSatisfy { operation in
+            if let fallibleOperation = operation as? FallibleOperation,
+                fallibleOperation.error != nil {
+                return false
+            }
+
+            if operation.isCancelled && !self.ignoreCancellations {
+                return false
+            }
+
+            return true
+        }
+
+        completion(satisfy)
+    }
+}
+
+final class BlockCondition: OperationCondition {
+    typealias HandlerBlock = (Operation, @escaping (Bool) -> Void) -> Void
+
+    var name: String {
+        return "BlockCondition"
+    }
+
+    var isMutuallyExclusive: Bool {
+        return false
+    }
+
+    let block: HandlerBlock
+    init(block: @escaping HandlerBlock) {
+        self.block = block
+    }
+
+    func evaluate(for operation: Operation, completion: @escaping (Bool) -> Void) {
+        block(operation, completion)
+    }
+}
+
+final class MutuallyExclusive: OperationCondition {
+    let name: String
+
+    var isMutuallyExclusive: Bool {
+        return true
+    }
+
+    init(category: String) {
+        name = "MutuallyExclusive<\(category)>"
+    }
+
+    func evaluate(for operation: Operation, completion: @escaping (Bool) -> Void) {
+        completion(true)
+    }
+}
diff --git a/ios/MullvadVPN/Operations/OperationObserver.swift b/ios/MullvadVPN/Operations/OperationObserver.swift
new file mode 100644
index 0000000000..28ce7ee348
--- /dev/null
+++ b/ios/MullvadVPN/Operations/OperationObserver.swift
@@ -0,0 +1,63 @@
+//
+//  OperationObserver.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 30/05/2022.
+//  Copyright © 2022 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+protocol OperationObserver {
+    func didAttach(to operation: Operation)
+    func operationDidStart(_ operation: Operation)
+    func operationDidCancel(_ operation: Operation)
+    func operationDidFinish(_ operation: Operation)
+}
+
+/// Block based operation observer.
+class OperationBlockObserver<OperationType: Operation>: OperationObserver {
+    typealias VoidBlock = (OperationType) -> Void
+
+    private let _didAttach: VoidBlock?
+    private let _didStart: VoidBlock?
+    private let _didCancel: VoidBlock?
+    private let _didFinish: VoidBlock?
+
+    init(
+        didAttach: VoidBlock? = nil,
+        didStart: VoidBlock? = nil,
+        didCancel: VoidBlock? = nil,
+        didFinish: VoidBlock? = nil
+    )
+    {
+        _didAttach = didAttach
+        _didStart = didStart
+        _didCancel = didCancel
+        _didFinish = didFinish
+    }
+
+    func didAttach(to operation: Operation) {
+        if let operation = operation as? OperationType {
+            _didAttach?(operation)
+        }
+    }
+
+    func operationDidStart(_ operation: Operation) {
+        if let operation = operation as? OperationType {
+            _didStart?(operation)
+        }
+    }
+
+    func operationDidCancel(_ operation: Operation) {
+        if let operation = operation as? OperationType {
+            _didCancel?(operation)
+        }
+    }
+
+    func operationDidFinish(_ operation: Operation) {
+        if let operation = operation as? OperationType {
+            _didFinish?(operation)
+        }
+    }
+}
diff --git a/ios/MullvadVPN/Operations/ResultOperation+Fallible.swift b/ios/MullvadVPN/Operations/ResultOperation+Fallible.swift
new file mode 100644
index 0000000000..fac45cbf93
--- /dev/null
+++ b/ios/MullvadVPN/Operations/ResultOperation+Fallible.swift
@@ -0,0 +1,15 @@
+//
+//  ResultOperation+Fallible.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 31/05/2022.
+//  Copyright © 2022 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+extension ResultOperation: FallibleOperation {
+    var error: Error? {
+        return completion?.error
+    }
+}