IOS-96: bugfix: force immediate save in DelayedSaveStorage, when the app…

IOS-96: bugfix: force immediate save in DelayedSaveStorage, when the app transitions to the background.

1Weather/Storage/DelayedSaveStorage.swift

@@ -6,14 +6,23 @@
 //
 
 import Foundation
+import UIKit
 
 /// A decorator Storage that adds delay before saving to the nested storage.
 public class DelayedSaveStorage: Storage {
     private let delay: TimeInterval
     private let storage: Storage
-    private let savingQueue: OperationQueue = {
+    private let log = Logger(componentName: "DelayedSaveStorage 💾")
+    private let saveDelayQueue: OperationQueue = {
         let queue = OperationQueue()
-        queue.name = "DelayedSaveStorageSavingQueue"
+        queue.name = "DelayedSaveStorageSaveDelayQueue"
+        queue.maxConcurrentOperationCount = 1
+        return queue
+    }()
+    
+    private let saveQueue: OperationQueue = {
+        let queue = OperationQueue()
+        queue.name = "DelayedSaveStorageSaveQueue"
         queue.maxConcurrentOperationCount = 1
         return queue
     }()
@@ -30,13 +39,19 @@ public class DelayedSaveStorage: Storage {
     public init(storage: Storage, delay: TimeInterval) {
         self.delay = delay
         self.storage = storage
+        
+        NotificationCenter.default.addObserver(self, selector: #selector(handleSwitchToBackground), name: UIApplication.didEnterBackgroundNotification, object: nil)
+    }
+    
+    deinit {
+        NotificationCenter.default.removeObserver(self)
     }
     
     public func save(locations: [Location], selectedIndex: Int?) {
-        latestKnownAppDataSynchronizationQueue.addOperation {
-            self.latestKnownAppData = AppData(selectedIndex: selectedIndex, locations: locations)
+        latestKnownAppDataSynchronizationQueue.addOperation { [weak self] in
+            self?.latestKnownAppData = AppData(selectedIndex: selectedIndex, locations: locations)
         }
-        savingQueue.cancelAllOperations()
+        saveDelayQueue.cancelAllOperations()
         let saveOperation = BlockOperation()
         saveOperation.addExecutionBlock { [weak saveOperation, weak self] in
             guard saveOperation?.isCancelled == false else {
@@ -48,9 +63,13 @@ public class DelayedSaveStorage: Storage {
             guard saveOperation?.isCancelled == false else {
                 return
             }
+            self?.saveQueue.addOperation {
+                if saveOperation?.isCancelled != true {
                     self?.storage.save(locations: locations, selectedIndex: selectedIndex)
                 }
-        savingQueue.addOperation(saveOperation)
+            }
+        }
+        saveDelayQueue.addOperation(saveOperation)
     }
     
     public func load(completion: @escaping StorageCompletion) {
@@ -64,4 +83,21 @@ public class DelayedSaveStorage: Storage {
             }
         }
     }
+    
+    @objc
+    private func handleSwitchToBackground() {
+        saveDelayQueue.cancelAllOperations()
+        self.saveQueue.addOperation { [weak self] in
+            self?.latestKnownAppDataSynchronizationQueue.addOperation {
+                guard let self = self else { return }
+                guard let appData = self.latestKnownAppData else {
+                    return
+                }
+                self.log.debug("Switch to background: force save")
+                self.storage.save(locations: appData.locations, selectedIndex: appData.selectedIndex)
+            }
+            self?.latestKnownAppDataSynchronizationQueue.waitUntilAllOperationsAreFinished()
+        }
+        self.saveQueue.waitUntilAllOperationsAreFinished()
+    }
 }