15. Subscriptions: Properly sign out users and cache state (#2520)

Task/Issue URL: https://app.asana.com/0/0/1206707680638927/f

Description:
If the subscription has become inactive, the user may still see the options in settings. This forces a signout in that case and caches the subscription state data properly.

DuckDuckGo/SettingsViewModel.swift

@@ -340,15 +340,14 @@ extension SettingsViewModel {
         // Fetch available subscriptions from the backend (or sign out)
         switch await SubscriptionService.getSubscriptionDetails(token: token) {
         case .success(let response) where !response.isSubscriptionActive:
-            AccountManager().signOut()
-            setupSubscriptionPurchaseOptions()
+
+            // Account is active but there's not a valid subscription
+            signOutUser()
 
         case .success(let response):
 
             // Cache Subscription state
-            self.state.subscription.hasActiveSubscription = true
-            Self.cachedHasActiveSubscription = self.state.subscription.hasActiveSubscription
-
+            cacheSubscriptionState(active: true)
 
             // Check entitlements and update UI accordingly
             let entitlements: [AccountManager.Entitlement] = [.identityTheftRestoration, .dataBrokerProtection, .networkProtection]
@@ -364,19 +363,27 @@ extension SettingsViewModel {
                     }
                 }
             }
-
-            // Enable Subscription purchase if there's no active subscription
-            if !self.state.subscription.hasActiveSubscription {
-                setupSubscriptionPurchaseOptions()
-            }
+
         default:
-            setupSubscriptionPurchaseOptions()
+            signOutUser()
         }
     }
 
+    @available(iOS 15.0, *)
+    private func signOutUser() {
+        AccountManager().signOut()
+        cacheSubscriptionState(active: false)
+        setupSubscriptionPurchaseOptions()
+    }
+
+    private func cacheSubscriptionState(active: Bool) {
+        self.state.subscription.hasActiveSubscription = active
+        Self.cachedHasActiveSubscription = active
+    }
+
     @available(iOS 15.0, *)
     private func setupSubscriptionPurchaseOptions() {
-        self.state.subscription.hasActiveSubscription = false
+        cacheSubscriptionState(active: false)
         PurchaseManager.shared.$availableProducts
             .receive(on: RunLoop.main)
             .sink { [weak self] products in