Azavea.NijPredictivePolicing.ACSAlchemistLibrary.Transfer.FileDownloader.GetFileByURL C# (CSharp) Method

        public static bool GetFileByURL(string desiredURL, string filePath, ref bool cancelled, bool workOffline = false)
        {
            bool preExists = false;
            if (File.Exists(filePath))
            {
                //don't keep harassing the server if the file is less than one week old, for Pete's sake.
                TimeSpan elapsed = (DateTime.Now - File.GetCreationTime(filePath));
                preExists = true;
                if (elapsed.TotalDays < 7)
                {
                    _log.DebugFormat("File {0} is less than 7 days old, skipping", Path.GetFileName(filePath));
                    System.Threading.Thread.Sleep(100); //give the disk a chance to catch up
                    return true;
                }
            }

            int retries = 0;

            while ((!File.Exists(filePath) || preExists) && retries < 4)
            {
                try
                {
                    if (workOffline && File.Exists(filePath))
                    {
                        _log.DebugFormat("Working Offline! - Skipping file stamp check");
                        return true;
                    }

                    _lastQuery = DateTime.Now;
                    System.Threading.Thread.Sleep(250); //just a little pre-nap so we don't hammer the server

                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(desiredURL);
                    request.KeepAlive = false;  //We're only doing this once
                    request.Credentials = CredentialCache.DefaultCredentials;
                    request.Timeout = Settings.TimeOutMs;
                    using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                    {
                        Stream downloadStream = response.GetResponseStream();
                        long expectedLength = response.ContentLength;
                        DateTime lastModified = response.LastModified;

                        if (File.Exists(filePath))
                        {
                            string srcDate = response.LastModified.ToShortDateString();
                            string localDate = File.GetLastWriteTime(filePath).ToShortDateString();
                            if (localDate == srcDate)
                            {
                                _log.DebugFormat("File {0} already exists, and date stamps match, skipping",
                                    Path.GetFileName(filePath));

                                FileUtilities.TryChangeCreationTime(filePath, DateTime.Now);
                                return true;
                            }
                        }

                        FileStream output = new FileStream(filePath, FileMode.Create);
                        Utilities.CopyToWithProgress(downloadStream, expectedLength, output, ref cancelled);

                        downloadStream.Close();
                        output.Close();
                        response.Close();
                        request.Abort();

                        if (cancelled)
                        {
                            //try to clean up after ourselves
                            FileUtilities.TryDelete(filePath);
                            _log.DebugFormat("Cancelling... Attempting to delete partially downloaded file {0}", Path.GetFileName(filePath));
                        }

                        if (!cancelled)
                        {
                            FileUtilities.TryChangeLastWriteTime(filePath, response.LastModified);
                            _log.DebugFormat("Downloaded of {0} was successful", Path.GetFileName(filePath));
                            if (Settings.ShowFilePaths)
                            {
                                _log.InfoFormat("Downloaded File {0} saved to {1}", Path.GetFileName(filePath), filePath);
                            }
                        }
                        else
                        {
                            return false;
                        }
                    }

                    return true;
                }
                catch (UnauthorizedAccessException cantWriteEx)
                {
                    string msg = "The importer couldn't save the file, please run this application as administrator, or set the output directory.";
                    _log.Error(msg);
                    _log.Fatal("The importer cannot continue.  Exiting...");
                    throw new ApplicationException(msg);
                }
                catch (Exception ex)
                {
                    _log.Error("Error downloading file, retrying", ex);

                    //This is to avoid the server blocking too many connection requests
                    if ((DateTime.Now - _lastQuery).Milliseconds < WaitTimeMs)
                    {
                        int nap = (int)Math.Pow(2, retries) * WaitTimeMs - (DateTime.Now - _lastQuery).Milliseconds;
                        if (nap > 0)
                        {
                            _log.DebugFormat("Sleeping for {0}ms before starting download", nap);
                            System.Threading.Thread.Sleep(nap);
                        }
                    }
                }

                retries++;
            }

            _log.FatalFormat("Could not download file at {0} to location {1} after {2} retries.  Please re-run the program to try again.  If this problem persists, you can try manually downloading the file and copying it to the above path.", desiredURL, filePath, retries);

            return false;
        }