Refactor FXIOS-15851 WindowManager tabManager API should return an optional value (#33928)

* [FXIOS-15851] Refactor tabManager(for:) to return an optional value

* Unit test updates

* [FXIOS-15851] Comments

* Spacing

* [FXIOS-15851] Add unit tests

Author: mattreaganmozilla

firefox-ios/Client/Application/AppDelegate.swift

@@ -244,7 +244,7 @@ class AppDelegate: UIResponder,
         logger.log("Received memory warning", level: .info, category: .lifecycle)
         Task {
             for uuid in windowManager.allWindowUUIDs(includingReserved: false) {
-                await windowManager.tabManager(for: uuid).offloadBackgroundWebViews()
+                await windowManager.tabManager(for: uuid)?.offloadBackgroundWebViews()
             }
         }
     }

firefox-ios/Client/Application/SceneDelegate.swift

@@ -176,7 +176,7 @@ class SceneDelegate: UIResponder,
         // If so, we want to be sure that we select the tab in the correct iPad window.
         if shouldRerouteIncomingURLToSpecificWindow(url),
            let tabUUID = URLScanner(url: url)?.value(query: "uuid"),
-           let targetWindow = (AppContainer.shared.resolve() as WindowManager).window(for: tabUUID),
+           let targetWindow = (AppContainer.shared.resolve() as WindowManager).windowUUID(forTab: tabUUID),
            targetWindow != sceneCoordinator?.windowUUID {
             DefaultApplicationHelper().open(url, inWindow: targetWindow)
         } else {

firefox-ios/Client/Application/WindowManager+DebugUtilities.swift

@@ -15,7 +15,7 @@ extension WindowManagerImplementation {
         var result = "----------- Window Debug Info ------------\n"
         result.append("Open windows (\(windows.count)) & normal tabs (via TabManager):\n")
         for (idx, (uuid, _)) in windows.enumerated() {
-            let tabMgr = tabManager(for: uuid)
+            guard let tabMgr = tabManager(for: uuid) else { continue }
             let window = windows[uuid]?.sceneCoordinator?.window
             let frame = window?.frame ?? .zero
             result.append("    \(idx + 1): \(short(uuid)) (\(tabMgr.normalTabs.count) tabs) (frame: \(frame.debugDescription))\n")

firefox-ios/Client/Application/WindowManager.swift

@@ -30,7 +30,7 @@ protocol WindowManager {
     func newBrowserWindowConfigured(_ windowInfo: AppWindowInfo, uuid: WindowUUID)
 
     /// Convenience. Returns the TabManager for a specific window.
-    func tabManager(for windowUUID: WindowUUID) -> TabManager
+    func tabManager(for windowUUID: WindowUUID) -> TabManager?
 
     /// Convenience. Returns all TabManagers for all open windows.
     func allWindowTabManagers() -> [TabManager]
@@ -73,11 +73,7 @@ protocol WindowManager {
     /// - Parameter tab: the UUID of the tab.
     /// - Returns: the UUID of the window hosting it (if available and open).
     @MainActor
-    func window(for tab: TabUUID) -> WindowUUID?
-
-    /// Convenience. Provides opportunity for safety checks or window validation.
-    @MainActor
-    func windowExists(uuid: WindowUUID) -> Bool
+    func windowUUID(forTab tab: TabUUID) -> WindowUUID?
 }
 
 /// Captures state and coordinator references specific to one particular app window.
@@ -135,25 +131,21 @@ final class WindowManagerImplementation: WindowManager {
         clearReservedUUID(uuid)
     }
 
-    func tabManager(for windowUUID: WindowUUID) -> TabManager {
-        func unsafeAnyTabManager() -> TabManager {
-            // This is unsafe, but is the best fallback we have to try to handle non-fatally (but may crash anyway)
-            if let tabManager = windows.first?.value.tabManager {
-                logger.log("Unsafe tab manager with windowUUID: \(tabManager.windowUUID)", level: .fatal, category: .window)
-            }
-            return windows.first!.value.tabManager!
-        }
-
+    func tabManager(for windowUUID: WindowUUID) -> TabManager? {
         guard let window = window(for: windowUUID) else {
-            assertionFailure("No window for UUID: \(windowUUID). This is a client error.")
-            logger.log("No window for UUID: \(windowUUID)", level: .fatal, category: .window)
-            return unsafeAnyTabManager()
+            if !AppConstants.isRunningUnitTest {
+                assertionFailure("No window for UUID: \(windowUUID). This is a client error. It will return nil in production but querying a non-existent window is always indicative of a bug.")
+                logger.log("No window for UUID: \(windowUUID)", level: .fatal, category: .window)
+            }
+            return nil
         }
 
         guard let manager = window.tabManager else {
-            assertionFailure("Window alive, but no TabManager for UUID: \(windowUUID). This is a client error.")
-            logger.log("Window alive, but no TabManager for UUID: \(windowUUID)", level: .fatal, category: .window)
-            return unsafeAnyTabManager()
+            if !AppConstants.isRunningUnitTest {
+                assertionFailure("Valid window but no TabManager for UUID: \(windowUUID). This is a client error. It will return nil in production but is indicative of a bug.")
+                logger.log("Window alive, but no TabManager for UUID: \(windowUUID)", level: .fatal, category: .window)
+            }
+            return nil
         }
 
         return manager
@@ -285,15 +277,10 @@ final class WindowManagerImplementation: WindowManager {
         }
     }
 
-    func window(for tab: TabUUID) -> WindowUUID? {
+    func windowUUID(forTab tab: TabUUID) -> WindowUUID? {
         return allWindowTabManagers().first(where: { $0.tabs.contains(where: { $0.tabUUID == tab }) })?.windowUUID
     }
 
-    func windowExists(uuid: WindowUUID) -> Bool {
-        guard uuid != .unavailable else { return false }
-        return windows[uuid] != nil
-    }
-
     // MARK: - Internal Utilities
 
     private func clearReservedUUID(_ uuid: WindowUUID) {

firefox-ios/Client/Frontend/Browser/StartAtHome/StartAtHomeMiddleware.swift

@@ -45,7 +45,7 @@ final class StartAtHomeMiddleware {
     /// - Returns: `true` if a homepage tab was selected and displayed, `false` otherwise.
     @MainActor
     private func startAtHomeCheck(windowUUID: WindowUUID) -> Bool {
-        let tabManager = windowManager.tabManager(for: windowUUID)
+        guard let tabManager = windowManager.tabManager(for: windowUUID) else { return false }
         let startAtHomeManager = StartAtHomeHelper(
             prefs: prefs,
             isRestoringTabs: !tabManager.tabRestoreHasFinished