Possibly fix phantom local push subscription not alerting (#1800)

Refs #1799.

## Summary
I can't see too many cases where we'd drop a subscription, but this is one of them - basically, multiple connection info change notifications fire at once, and the invoked method isn't threadsafe.

## Any other notes
Also adds some more logging and discrete subscription cancelling when stopping to hopefully help debug this in the future if it continues.

Sources/Extensions/PushProvider/PushProvider.swift

@@ -102,6 +102,7 @@ import UserNotifications
 
     override func stop(with reason: NEProviderStopReason, completionHandler: @escaping () -> Void) {
         Current.Log.notify("stopping with reason \(reason)", log: .error)
+        localPushManager?.invalidate()
         localPushManager = nil
         Current.apiConnection.disconnect()
     }

Sources/Shared/Notifications/LocalPush/LocalPushManager.swift

@@ -80,18 +80,28 @@ public class LocalPushManager {
     }
 
     public init() {
+        updateSubscription()
+
         NotificationCenter.default.addObserver(
             self,
-            selector: #selector(updateSubscription),
+            selector: #selector(updateSubscriptionFromNotification),
             name: SettingsStore.connectionInfoDidChange,
             object: nil
         )
-
-        updateSubscription()
     }
 
     deinit {
-        subscription?.cancel()
+        invalidate()
+    }
+
+    public func invalidate() {
+        if let subscription = subscription {
+            Current.Log.info("cancelling")
+            subscription.cancel()
+        } else {
+            Current.Log.info("no active subscription")
+        }
+        NotificationCenter.default.removeObserver(self)
     }
 
     var add: (UNNotificationRequest) -> Promise<Void> = { request in
@@ -105,13 +115,20 @@ public class LocalPushManager {
         let webhookID: String
 
         func cancel() {
+            Current.Log.info("cancelling subscription")
             token.cancel()
         }
     }
 
     private var subscription: SubscriptionInstance?
 
-    @objc private func updateSubscription() {
+    @objc private func updateSubscriptionFromNotification() {
+        DispatchQueue.main.async { [self] in
+            updateSubscription()
+        }
+    }
+
+    private func updateSubscription() {
         guard let webhookID = Current.settingsStore.connectionInfo?.webhookID else {
             // webhook is invalid, if there is a subscription we remove it
             subscription?.cancel()

Tests/Shared/LocalPushManager.test.swift

@@ -39,6 +39,10 @@ class LocalPushManagerTests: XCTestCase {
         weak var weakManager = manager
         manager = nil
         XCTAssertNil(weakManager)
+
+        for sub in apiConnection.pendingSubscriptions {
+            XCTAssertTrue(sub.cancellable.wasCancelled)
+        }
     }
 
     private func setUpManager(webhookID: String?) {
@@ -67,6 +71,19 @@ class LocalPushManagerTests: XCTestCase {
         }
     }
 
+    private func fireConnectionChange() {
+        NotificationCenter.default.post(
+            name: SettingsStore.connectionInfoDidChange,
+            object: nil,
+            userInfo: nil
+        )
+        let expectation = self.expectation(description: "loop")
+        DispatchQueue.main.async {
+            expectation.fulfill()
+        }
+        wait(for: [expectation], timeout: 10)
+    }
+
     func testStateInitialUnavailable() {
         setUpManager(webhookID: nil)
         XCTAssertEqual(manager.state, .unavailable)
@@ -119,20 +136,12 @@ class LocalPushManagerTests: XCTestCase {
         sub1.initiated(.success(.empty))
 
         apiConnection.pendingSubscriptions.removeAll()
-        NotificationCenter.default.post(
-            name: SettingsStore.connectionInfoDidChange,
-            object: nil,
-            userInfo: nil
-        )
+        fireConnectionChange()
         XCTAssertTrue(apiConnection.pendingSubscriptions.isEmpty, "same id")
 
         // change webhookID
         Current.settingsStore.connectionInfo?.webhookID = "webhook2"
-        NotificationCenter.default.post(
-            name: SettingsStore.connectionInfoDidChange,
-            object: nil,
-            userInfo: nil
-        )
+        fireConnectionChange()
 
         XCTAssertTrue(sub1.cancellable.wasCancelled)
 
@@ -142,27 +151,26 @@ class LocalPushManagerTests: XCTestCase {
 
         // fail the subscription
         sub2.initiated(.failure(.internal(debugDescription: "unit-test")))
-        NotificationCenter.default.post(
-            name: SettingsStore.connectionInfoDidChange,
-            object: nil,
-            userInfo: nil
-        )
+        fireConnectionChange()
 
         // now succeed it (e.g. reconnect happened)
         sub2.initiated(.success(.empty))
 
         // kill off the connection info
         apiConnection.pendingSubscriptions.removeAll()
         Current.settingsStore.connectionInfo = nil
-        NotificationCenter.default.post(
-            name: SettingsStore.connectionInfoDidChange,
-            object: nil,
-            userInfo: nil
-        )
+        fireConnectionChange()
 
         XCTAssertTrue(sub2.cancellable.wasCancelled)
     }
 
+    func testInvalidate() throws {
+        setUpManager(webhookID: "webhook1")
+        let sub = try XCTUnwrap(apiConnection.pendingSubscriptions.first)
+        manager.invalidate()
+        XCTAssertTrue(sub.cancellable.wasCancelled)
+    }
+
     func testNoSubscriptionAtStart() throws {
         setUpManager(webhookID: nil)
         XCTAssertTrue(apiConnection.pendingSubscriptions.isEmpty)