A helper class to nicely wrap service calls and provide JSON responses back.

Helper.cs

private class Helper<T> : IDisposable where T : CheckoutInformation
{
    private readonly T _input;
    private readonly IOrderService _orderService;
    private readonly Func<object, JsonResult> _jsonResultSelector;

    private object _data;

    public CheckoutHelper(T input, IOrderService orderService, Func<object, JsonResult> jsonResultSelector)
    {
        _input = input;
        _orderService = orderService;
        _jsonResultSelector = jsonResultSelector;
    }

    public ActionResult Response { get; private set; }

    public void Dispose()
    {
        Response = _jsonResultSelector(_data);
    }

    public void Action(Action<T, IOrderService, Order> action)
    {
        try
        {
            var order = _orderService.GetOrder();

            if (order == null)
            {
                _data = new { success = false, redirect = "/cart" };
                return;
            }

            if (_input.ClientId != order.Id)
            {
                Response = new HttpStatusCodeResult((int) HttpStatusCode.Unauthorized);
                return;
            }

            action(_input, _orderService, order);
            _data = order;
        }
        catch (Exception ex)
        {
            _data = new { success = false, message = ex.Message };
        }
    }
}