File downloading in Swift 5 using URLSession

StorageManager.swift

import Foundation

class StorageManager {
    static let shared = StorageManager()
    
    private init() {}
}

// MARK: - Remote Config storage methods
extension StorageManager {
    func getFileLastDownloadedDate() -> Date {
		return UserDefaults.standard.object(forKey: "fileLastDownloadedDate") as? Date ?? Date(timeIntervalSince1970: 0)
	}
    
	func setFileLastDownloadedDate(_ date: Date) {
		UserDefaults.standard.set(date, forKey: "fileLastDownloadedDate")
	}
}

URLTask.swift

class URLTask {
    static let shared = URLTask()
    
    private init() {}
    
    // Checks if file at given URL is modified.
    // Using "Last-Modified" header value to compare it with given date.
    func checkFileModifiedAt(_ url: URL, completion: @escaping (Bool, Date?) -> Void) {
        var request = URLRequest(url: url)
        request.httpMethod = "HEAD"
        URLSession.shared.dataTask(with: request, completionHandler: { (_, response, error) in
            guard let httpURLResponse = response as? HTTPURLResponse,
            httpURLResponse.statusCode == 200,
            let modifiedDateString = httpURLResponse.allHeaderFields["Last-Modified"] as? String,
            let modifiedDate = modifiedDateString.toDate(),
            error == nil
            else {
                completion(false, nil)
                return
            }
            
            if modifiedDate > StorageManager.shared.getFileLastDownloadedDate() {
                completion(true, modifiedDate)
                return
            }
            
            completion(false, nil)
            
        }).resume()
    }
    
    // Downloads file from given URL and store it at temporary location.
    // It is possible that iOS will remove temp files very often so highly
    // recommended to move file to any permanent location. 
    func downloadFile(from url: URL, onSuccess: @escaping (URL) -> Void, onError: @escaping (Error?) -> Void) {
        URLSession.shared.downloadTask(with: url, completionHandler: { (downloadLocation, response, error) in
            guard let httpURLResponse = response as? HTTPURLResponse,
                httpURLResponse.statusCode == 200,
                let downloadLocation = downloadLocation,
                error == nil
                else {
                    onError(error)
                    return
                }
            onSuccess(downloadLocation)
        }).resume()
    }
}