DelayedStorage to optimize data saving

1Weather.xcodeproj/project.pbxproj

@@ -209,6 +209,7 @@
 		CEDE4E8925EEFFEF007457E9 /* WdtDayNight.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEDE4E8825EEFFEF007457E9 /* WdtDayNight.swift */; };
 		CEDE4F0B25EFA3A7007457E9 /* UpdatableModelObject.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEDE4F0A25EFA3A7007457E9 /* UpdatableModelObject.swift */; };
 		CEDE4F0F25EFA3B4007457E9 /* UpdatableModelObjectInTime.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEDE4F0E25EFA3B4007457E9 /* UpdatableModelObjectInTime.swift */; };
+		CEE0A179262FA9650044C257 /* DelayedSaveStorage.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEE0A178262FA9650044C257 /* DelayedSaveStorage.swift */; };
 		CEF959652600C2F900975FAA /* AnalyticsService.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF959642600C2F900975FAA /* AnalyticsService.swift */; };
 		CEF959692600C30500975FAA /* Global.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF959682600C30500975FAA /* Global.swift */; };
 		CEF9596C2600C32E00975FAA /* AnalyticsEvent.swift in Sources */ = {isa = PBXBuildFile; fileRef = CEF9596B2600C32E00975FAA /* AnalyticsEvent.swift */; };
@@ -443,6 +444,7 @@
 		CEDE4E8825EEFFEF007457E9 /* WdtDayNight.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WdtDayNight.swift; sourceTree = "<group>"; };
 		CEDE4F0A25EFA3A7007457E9 /* UpdatableModelObject.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UpdatableModelObject.swift; sourceTree = "<group>"; };
 		CEDE4F0E25EFA3B4007457E9 /* UpdatableModelObjectInTime.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UpdatableModelObjectInTime.swift; sourceTree = "<group>"; };
+		CEE0A178262FA9650044C257 /* DelayedSaveStorage.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DelayedSaveStorage.swift; sourceTree = "<group>"; };
 		CEF959642600C2F900975FAA /* AnalyticsService.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AnalyticsService.swift; sourceTree = "<group>"; };
 		CEF959682600C30500975FAA /* Global.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Global.swift; sourceTree = "<group>"; };
 		CEF9596B2600C32E00975FAA /* AnalyticsEvent.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AnalyticsEvent.swift; sourceTree = "<group>"; };
@@ -1236,6 +1238,7 @@
 			children = (
 				CEFB857126174F7A00C5CDD2 /* Storage.swift */,
 				CEFB8577261750DF00C5CDD2 /* CoreData */,
+				CEE0A178262FA9650044C257 /* DelayedSaveStorage.swift */,
 			);
 			path = Storage;
 			sourceTree = "<group>";
@@ -1593,6 +1596,7 @@
 				CD593BD32608BC3F00C93428 /* ForecastDayCell.swift in Sources */,
 				CD4742D0261200500061AC95 /* TodayAlertCell.swift in Sources */,
 				CD15DB4225DA806C00024727 /* TodayForecastTimePeriodCell.swift in Sources */,
+				CEE0A179262FA9650044C257 /* DelayedSaveStorage.swift in Sources */,
 				CE0456242629C04C003D252B /* NWSAlertsManager.swift in Sources */,
 				CE8962AB26175DF500CA274A /* CorePollutant.swift in Sources */,
 				CEC5276025E92DDA00DA58A5 /* WdtHourlySummary.swift in Sources */,

1Weather/Model/LocationManager.swift

@@ -150,7 +150,12 @@ public class LocationManager {
         }
     }
     
-    public static let shared = LocationManager(weatherUpdateSource: WdtWeatherSource(), healthSource: BlendHealthSource(), nwsAlertsManager: NWSAlertsManager(), storage: CoreDataStorage())
+    public static let shared = LocationManager(
+        weatherUpdateSource: WdtWeatherSource(),
+        healthSource: BlendHealthSource(),
+        nwsAlertsManager: NWSAlertsManager(),
+        storage: DelayedSaveStorage(storage: CoreDataStorage(), delay: 2))
+    
     public let maxLocationsCount = 12
     
     public init(weatherUpdateSource: WeatherSource, healthSource: HealthSource, nwsAlertsManager: NWSAlertsManager, storage: Storage) {

1Weather/Model/ModelObjects/Location.swift

@@ -74,6 +74,7 @@ public struct Location {
         guard self == other else { return false }
         guard self.lastWeatherUpdateDate == other.lastWeatherUpdateDate else { return false }
         guard self.health?.lastUpdateTime == other.health?.lastUpdateTime else { return false }
+        guard self.notifications?.updatedAt == other.notifications?.updatedAt else { return false }
         return true
     }
 }

1Weather/Storage/CoreData/CoreDataStorage.swift

@@ -103,10 +103,8 @@ public class CoreDataStorage: Storage {
     }
     
     private func save(context: NSManagedObjectContext) throws {
-        log.info("Context save: start")
         if context.hasChanges {
             try context.save()
-            log.info("Context save: success")
         }
         else {
             log.info("Context save: no need")

1Weather/Storage/DelayedSaveStorage.swift

+//
+//  DelayedSaveStorage.swift
+//  1Weather
+//
+//  Created by Demid Merzlyakov on 21.04.2021.
+//
+
+import Foundation
+
+/// 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 = {
+        let queue = OperationQueue()
+        queue.name = "DelayedSaveStorageSavingQueue"
+        queue.maxConcurrentOperationCount = 1
+        return queue
+    }()
+    
+    /// A "cache" to allow for loading after saving without waiting.
+    private var latestKnownAppData: AppData?
+    private let latestKnownAppDataSynchronizationQueue: OperationQueue = {
+        let queue = OperationQueue()
+        queue.name = "DelayedSaveStorageVariableAccessQueue"
+        queue.maxConcurrentOperationCount = 1
+        return queue
+    }()
+    
+    public init(storage: Storage, delay: TimeInterval) {
+        self.delay = delay
+        self.storage = storage
+    }
+    
+    public func save(locations: [Location], selectedIndex: Int?) {
+        latestKnownAppDataSynchronizationQueue.addOperation {
+            self.latestKnownAppData = AppData(selectedIndex: selectedIndex, locations: locations)
+        }
+        savingQueue.cancelAllOperations()
+        let saveOperation = BlockOperation()
+        saveOperation.addExecutionBlock { [weak saveOperation, weak self] in
+            guard saveOperation?.isCancelled == false else {
+                return
+            }
+            if let delay = self?.delay, delay > 0 {
+                Thread.sleep(forTimeInterval: delay)
+            }
+            guard saveOperation?.isCancelled == false else {
+                return
+            }
+            self?.storage.save(locations: locations, selectedIndex: selectedIndex)
+        }
+        savingQueue.addOperation(saveOperation)
+    }
+    
+    public func load(completion: @escaping StorageCompletion) {
+        latestKnownAppDataSynchronizationQueue.addOperation { [weak self] in
+            if let lastKnownData = self?.latestKnownAppData {
+                completion(lastKnownData.locations, lastKnownData.selectedIndex, nil)
+                return
+            }
+            else {
+                self?.storage.load(completion: completion)
+            }
+        }
+    }
+}

1Weather/Storage/Storage.swift

@@ -7,6 +7,7 @@
 
 import Foundation
 
+/// locations list, selectedIndex, error
 public typealias StorageCompletion = ([Location]?, Int?, Error?) -> ()
 
 public protocol Storage {