[Feature]: Import external backup, Restore n-1 backup if current backup is corrupted by importing wrong directory

SideStore/Utils/importexport/ImportExport.swift

@@ -0,0 +1,135 @@
+//
+//  ImportExport.swift
+//  AltStore
+//
+//  Created by Magesh K on 07/01/25.
+//  Copyright © 2025 SideStore. All rights reserved.
+//
+
+
+import UIKit
+import AltStoreCore
+
+class ImportExport {
+    
+    private static var documentPickerHandler: DocumentPickerHandler?
+    
+    public static func getPreviousBackupURL(_ backupURL: URL) -> URL {
+        let backupParentDirectory = backupURL.deletingLastPathComponent()
+        let backupName = backupURL.lastPathComponent
+        let backupBakURL = backupParentDirectory.appendingPathComponent("\(backupName).bak")
+        return backupBakURL
+    }
+    
+    /// Renames the existing backup contents at `backupURL` to `<foldername>.bak`.
+    private static func renameBackupContents(at backupURL: URL) throws {
+        
+        // rename backup to backup.bak dir only if backup dir exists
+        guard FileManager.default.fileExists(atPath: backupURL.path) else { return }
+        
+        let backupBakURL = getPreviousBackupURL(backupURL)
+        
+        let fileManager = FileManager.default
+        if fileManager.fileExists(atPath: backupBakURL.path) {
+            try fileManager.removeItem(at: backupBakURL) // Remove any existing .bak directory
+        }
+        
+        try fileManager.moveItem(at: backupURL, to: backupBakURL)
+    }
+    
+    /// Handles importing new backup data into the designated backup directory.
+    private static func importBackupContents(from documentPickerURL: URL, to backupURL: URL) throws {
+        let fileManager = FileManager.default
+        
+        // Ensure the backup directory exists.
+        if !fileManager.fileExists(atPath: backupURL.path) {
+            try fileManager.createDirectory(at: backupURL, withIntermediateDirectories: true, attributes: nil)
+        }
+        
+        print("Backup URL: \(backupURL)")
+        print("Document Picker URL: \(documentPickerURL)")
+        
+        // Enumerate the contents of the selected directory and copy them to the backup directory.
+        let selectedContents = try fileManager.contentsOfDirectory(
+            at: documentPickerURL,
+            includingPropertiesForKeys: nil,
+            options: .skipsHiddenFiles
+        )
+        for itemURL in selectedContents {
+            let destinationURL = backupURL.appendingPathComponent(itemURL.lastPathComponent)
+            
+            // Remove the existing file if it exists at the destination.
+            if fileManager.fileExists(atPath: destinationURL.path) {
+                try fileManager.removeItem(at: destinationURL)
+            }
+            
+            // Copy the item.
+            try fileManager.copyItem(at: itemURL, to: destinationURL)
+        }
+    }
+    
+    public static func importBackup(presentingViewController: UIViewController,
+                                    for installedApp: InstalledApp,
+                                    completionHandler: @escaping (Result<Void, Error>) -> Void){
+        guard let backupURL = FileManager.default.backupDirectoryURL(for: installedApp) else {
+            return completionHandler(.failure(OperationError.invalidParameters("Error: Backup directory URL not found.")))
+        }
+        
+        let documentPicker = UIDocumentPickerViewController(forOpeningContentTypes: [.folder], asCopy: false)
+        documentPicker.allowsMultipleSelection = false
+                
+        // Create a handler and set it as the delegate
+        Self.documentPickerHandler = DocumentPickerHandler { selectedURL in
+            guard let selectedURL = selectedURL else {
+                return completionHandler(.failure( OperationError.cancelled))
+            }
+            
+            // resolve symlinks if any, so that prefix match works
+            let appUserDataDir = FileManager.default.documentsDirectory.resolvingSymlinksInPath()
+            guard selectedURL.resolvingSymlinksInPath().path.hasPrefix(appUserDataDir.path) else {
+                return completionHandler(.failure(
+                    OperationError.forbidden(failureReason: "Selected backup data directory is not within the app's user data directory"))
+                )
+            }
+            
+            do {
+                // Rename existing backup contents to `<foldername>.bak`.
+                try Self.renameBackupContents(at: backupURL)
+                
+                // Import the contents of the selected folder into the backup directory.
+                try Self.importBackupContents(from: selectedURL, to: backupURL)
+                
+                print("Backup imported successfully to:", backupURL.path)
+                return completionHandler(.success(()))
+            } catch {
+                print("Backup Error:", error)
+                return completionHandler(.failure( OperationError.invalidParameters(error.localizedDescription)))
+            }
+        }
+        
+        documentPicker.delegate = Self.documentPickerHandler
+        // Present the picker
+        presentingViewController.present(documentPicker, animated: true, completion: nil)
+    }
+}
+
+private struct AssociatedKeys {
+    static var documentPickerHandler = "documentPickerHandler"
+}
+
+
+class DocumentPickerHandler: NSObject, UIDocumentPickerDelegate {
+    private let completion: (URL?) -> Void
+
+    init(completion: @escaping (URL?) -> Void) {
+        self.completion = completion
+    }
+
+    func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
+        completion(urls.first)
+    }
+
+    func documentPickerWasCancelled(_ controller: UIDocumentPickerViewController) {
+        completion(nil)
+    }
+}