15. HasCodeBeenUsed.txt

        public ActionResult HasCodeBeenUsed(string customerCode)
        {
            var token = GetToken();
            if (token == null) return Unauthorized();

            var customerName = "";
            while (true)
            {
                var matches = searchService.Search(token, customerCode, "");
                var match = matches.FirstOrDefault();

                if (match == null)
                {
                    if (customerName == "")
                        // This is the first code we have tried and it's good.
                        return Json("");
                    else
                        // The original code failed,  but this one is ok
                        return Json(customerName + $" (Use {customerCode})");
                }
                else
                {
                    if (customerName == "")
                        // The supplied code has already been used
                        customerName = match.CustomerName;

		    // Increase the number on the end of the customer code by 1 and then try that
                    var numericPart = int.Parse(customerCode.Substring(5));
                    var nextOne = numericPart+1;
                    customerCode = customerCode.Substring(0, 5) + nextOne.ToString("000");
                }
            }
        }