export string to csv file web api umbraco

csv-file-export.cs

public class ExportController
{
    [HttpGet]
    public HttpResponseMessage AllUsers()
    {
        var csv = new StringBuilder();
        var fileName = $"export {DateTime.Now.ToString("yyyy-MM-dd--HH-mm-ss")}.csv";
        var result = new HttpResponseMessage(HttpStatusCode.OK);
        var excelDateTimeFormat = "yyyy-MM-dd HH:mm:ss"; // format datetimes so excel can parse them

        // headers
        csv.AppendLine("Name;Id;Last login");

        foreach (var user in ListOfUsers)
        {
            csv.AppendLine(string.Format("{0};{1};{2}",
                ToSafeCsvString(user.Name),
                ToSafeCsvString(user.Id),
                ToSafeCsvString(user.LastLoginDate.ToString(excelDateTimeFormat))
                ));
                
            // ALTERNATIVE way
            // var columns = new List<string>();
            // columns.Add(ToSafeCsvString(user.Name));
            // columns.Add(ToSafeCsvString(user.Id));
            // columns.Add(ToSafeCsvString(user.LastLoginDate.ToString("yyyy-MM-dd HH:mm:ss")));

            // and then
            // csv.AppendLine(string.Format(GetStringFormat(columns), columns.ToArray()));
        }
        
        // save file to disk
        //File.WriteAllText(HttpContext.Current.Request.MapPath("~/Content/ass.csv"), csv.ToString(), Encoding.UTF8);

        // utf-8 with BOM
        result.Content = new StreamContent(new MemoryStream(Encoding.UTF8.GetPreamble().Concat(Encoding.UTF8.GetBytes(csv.ToString())).ToArray()));

        result.Content.Headers.ContentType = new MediaTypeHeaderValue("text/csv");
        result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") { FileName = fileName };

        return result;
    }
}

private string GetStringFormat(List<string> list)
{
    var sf = "";
    for (int i = 0; i < list.Count; i++)
    {
        sf += "{" + i + "};";
    }

    return sf; // returns "{0};{1};{2};..."
}

private string ToSafeCsvString(string s)
{
    if (s == null) return "";

    // replace " with "" and wrap all whole text with "", so that excel can handle ,;" etc
    return $"\"{s.Replace("\"", "\"\"")}\"";
}