deduplicate code to persist data

deltachat-ios/Helper/ImageFormat.swift

@@ -81,62 +81,7 @@ extension ImageFormat {
             return nil
         }
 
-        return saveImage(data: data, name: name, suffix: suffix)
-    }
-
-    // implementation is following Apple's recommendations
-    // https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/AccessingFilesandDirectories/AccessingFilesandDirectories.html
-    public static func saveImage(data: Data, name: String? = nil, suffix: String, directory: FileManager.SearchPathDirectory = .applicationSupportDirectory) -> String? {
-        var path: URL?
-
-        // ensure directory exists (application support dir doesn't exist per default)
-        let fileManager = FileManager.default
-        let urls = fileManager.urls(for: directory, in: .userDomainMask) as [URL]
-        guard let identifier = Bundle.main.bundleIdentifier else {
-            print("err: Could not find bundle identifier")
-            return nil
-        }
-        guard let directoryURL = urls.first else {
-            print("err: Could not find directory url for \(String(describing: directory)) in .userDomainMask")
-            return nil
-        }
-        var subdirectoryURL = directoryURL.appendingPathComponent(identifier)
-        do {
-            if !fileManager.fileExists(atPath: subdirectoryURL.path) {
-                try fileManager.createDirectory(at: subdirectoryURL, withIntermediateDirectories: true, attributes: nil)
-            }
-        } catch {
-            print("err: \(error.localizedDescription)")
-            return nil
-        }
-
-        // Opt out from iCloud backup
-        var resourceValues: URLResourceValues = URLResourceValues()
-        resourceValues.isExcludedFromBackup = true
-        do {
-            try subdirectoryURL.setResourceValues(resourceValues)
-        } catch {
-            print("err: \(error.localizedDescription)")
-            return nil
-        }
-
-        // add file name to path
-        if let name = name {
-            path = subdirectoryURL.appendingPathComponent("\(name).\(suffix)")
-        } else {
-            let timestamp = Double(Date().timeIntervalSince1970)
-            path = subdirectoryURL.appendingPathComponent("\(timestamp).\(suffix)")
-        }
-        guard let path = path else { return nil }
-
-        // write data
-        do {
-            try data.write(to: path)
-            return path.relativePath
-        } catch {
-            print("err: \(error.localizedDescription)")
-            return nil
-        }
+        return FileHelper.saveData(data: data, name: name, suffix: suffix)
     }
 
     // This scaling method is more memory efficient than UIImage.scaleDownImage(toMax: CGFloat)