feat: beta background sync (#21243)

* feat: ios background sync

# Conflicts:
#	mobile/ios/Runner/Info.plist

* feat: Android sync

* add local sync worker and rename stuff

* group upload notifications

* uncomment onresume beta handling

* rename methods

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/ios/Runner/Background/BackgroundWorkerApiImpl.swift

@@ -0,0 +1,155 @@
+import BackgroundTasks
+
+class BackgroundWorkerApiImpl: BackgroundWorkerFgHostApi {
+  func enableSyncWorker() throws {
+    BackgroundWorkerApiImpl.scheduleLocalSync()
+    print("BackgroundUploadImpl:enableSyncWorker Local Sync worker scheduled")
+  }
+  
+  func enableUploadWorker(callbackHandle: Int64) throws {
+    BackgroundWorkerApiImpl.updateUploadEnabled(true)
+    // Store the callback handle for later use when starting background Flutter isolates
+    BackgroundWorkerApiImpl.updateUploadCallbackHandle(callbackHandle)
+    
+    BackgroundWorkerApiImpl.scheduleRefreshUpload()
+    BackgroundWorkerApiImpl.scheduleProcessingUpload()
+    print("BackgroundUploadImpl:enableUploadWorker Scheduled background upload tasks")
+  }
+  
+  func disableUploadWorker() throws {
+    BackgroundWorkerApiImpl.updateUploadEnabled(false)
+    BackgroundWorkerApiImpl.cancelUploadTasks()
+    print("BackgroundUploadImpl:disableUploadWorker Disabled background upload tasks")
+  }
+  
+  public static let backgroundUploadEnabledKey = "immich:background:backup:enabled"
+  public static let backgroundUploadCallbackHandleKey = "immich:background:backup:callbackHandle"
+  
+  private static let localSyncTaskID = "app.alextran.immich.background.localSync"
+  private static let refreshUploadTaskID = "app.alextran.immich.background.refreshUpload"
+  private static let processingUploadTaskID = "app.alextran.immich.background.processingUpload"
+
+  private static func updateUploadEnabled(_ isEnabled: Bool) {
+    return UserDefaults.standard.set(isEnabled, forKey: BackgroundWorkerApiImpl.backgroundUploadEnabledKey)
+  }
+
+  private static func updateUploadCallbackHandle(_ callbackHandle: Int64) {
+    return UserDefaults.standard.set(String(callbackHandle), forKey: BackgroundWorkerApiImpl.backgroundUploadCallbackHandleKey)
+  }
+
+  private static func cancelUploadTasks() {
+    BackgroundWorkerApiImpl.updateUploadEnabled(false)
+    BGTaskScheduler.shared.cancel(taskRequestWithIdentifier: refreshUploadTaskID);
+    BGTaskScheduler.shared.cancel(taskRequestWithIdentifier: processingUploadTaskID);
+  }
+
+  public static func registerBackgroundProcessing() {
+      BGTaskScheduler.shared.register(
+          forTaskWithIdentifier: processingUploadTaskID, using: nil) { task in
+          if task is BGProcessingTask {
+            handleBackgroundProcessing(task: task as! BGProcessingTask)
+          }
+      }
+
+      BGTaskScheduler.shared.register(
+          forTaskWithIdentifier: refreshUploadTaskID, using: nil) { task in
+          if task is BGAppRefreshTask {
+            handleBackgroundRefresh(task: task as! BGAppRefreshTask, taskType: .refreshUpload)
+          }
+      }
+    
+    BGTaskScheduler.shared.register(
+        forTaskWithIdentifier: localSyncTaskID, using: nil) { task in
+        if task is BGAppRefreshTask {
+          handleBackgroundRefresh(task: task as! BGAppRefreshTask, taskType: .localSync)
+        }
+    }
+  }
+  
+  private static func scheduleLocalSync() {
+    let backgroundRefresh = BGAppRefreshTaskRequest(identifier: localSyncTaskID)
+      backgroundRefresh.earliestBeginDate = Date(timeIntervalSinceNow: 5 * 60) // 5 mins
+
+      do {
+          try BGTaskScheduler.shared.submit(backgroundRefresh)
+      } catch {
+          print("Could not schedule the local sync task \(error.localizedDescription)")
+      }
+  }
+  
+  private static func scheduleRefreshUpload() {
+    let backgroundRefresh = BGAppRefreshTaskRequest(identifier: refreshUploadTaskID)
+      backgroundRefresh.earliestBeginDate = Date(timeIntervalSinceNow: 5 * 60) // 5 mins
+
+      do {
+          try BGTaskScheduler.shared.submit(backgroundRefresh)
+      } catch {
+          print("Could not schedule the refresh upload task \(error.localizedDescription)")
+      }
+  }
+
+  private static func scheduleProcessingUpload() {
+    let backgroundProcessing = BGProcessingTaskRequest(identifier: processingUploadTaskID)
+    
+    backgroundProcessing.requiresNetworkConnectivity = true
+    backgroundProcessing.earliestBeginDate = Date(timeIntervalSinceNow: 15 * 60) // 15 mins
+    
+    do {
+        try BGTaskScheduler.shared.submit(backgroundProcessing)
+    } catch {
+        print("Could not schedule the processing upload task \(error.localizedDescription)")
+    }
+  }
+  
+  private static func handleBackgroundRefresh(task: BGAppRefreshTask, taskType: BackgroundTaskType) {
+    scheduleRefreshUpload()
+    // Restrict the refresh task to run only for a maximum of 20 seconds
+    runBackgroundWorker(task: task, taskType: taskType, maxSeconds: 20)
+  }
+  
+  private static func handleBackgroundProcessing(task: BGProcessingTask) {
+    scheduleProcessingUpload()
+    // There are no restrictions for processing tasks. Although, the OS could signal expiration at any time
+    runBackgroundWorker(task: task, taskType: .processingUpload, maxSeconds: nil)
+  }
+  
+  /**
+   * Executes the background worker within the context of a background task.
+   * This method creates a BackgroundWorker, sets up task expiration handling,
+   * and manages the synchronization between the background task and the Flutter engine.
+   *
+   * - Parameters:
+   *   - task: The iOS background task that provides the execution context
+   *   - taskType: The type of background operation to perform (refresh or processing)
+   *   - maxSeconds: Optional timeout for the operation in seconds
+   */
+  private static func runBackgroundWorker(task: BGTask, taskType: BackgroundTaskType, maxSeconds: Int?) {
+    let semaphore = DispatchSemaphore(value: 0)
+    var isSuccess = true
+    
+    let backgroundWorker = BackgroundWorker(taskType: taskType, maxSeconds: maxSeconds) { success in
+      isSuccess = success
+      semaphore.signal()
+    }
+
+    task.expirationHandler = {
+      DispatchQueue.main.async {
+        backgroundWorker.cancel()
+      }
+      isSuccess = false
+      
+      // Schedule a timer to signal the semaphore after 2 seconds
+      Timer.scheduledTimer(withTimeInterval: 2, repeats: false) { _ in
+        semaphore.signal()
+      }
+    }
+
+    DispatchQueue.main.async {
+      backgroundWorker.run()
+    }
+
+    semaphore.wait()
+    task.setTaskCompleted(success: isSuccess)
+    print("Background task completed with success: \(isSuccess)")
+  }
+}