Design pattern for an email notification service which monitors workflow/state

I'm sorry this question is going to be a bit vague because I'm not entirely sure what I'm looking for.

Basically in my (Asp.net MVC) web app I have some basic (manually coded) workflow triggered by my various user inputs.

I need to send email configurable notifications when certain events happen.

For example, there is an update status method in my controller, which I could write something like this:

public ActionResult UpdateStatus(int id, Status status)
{
    Orders order = _orders.GetById(id);
    order.Status = status;

    if (status = Status.AwaitingApproval)
    {
        SendAwaitingApprovalNotification(_roles.GetApproverForDept(order.Department));
    }

    else if (status = Status.Approved && order.Department = someDept) { ... }

    else if (status = Status.Approved && order.Department = someOtherDept) { ... }

    else if // ... etc
}

As you can see, this is all going to get messy very quickly. And also, the logic for when/what notifications are sent is coded into the controller, which doesn't fe开发者_StackOverflowel right to me.

Also, there are various other actions which can change the state without specifically calling the UpdateStatus method. eg

public ActionResult ChangeOrderCost(int id, decimal newCost)
{
    Orders order = _orders.GetById(id);
    order.Cost = newCost;
    order.Status = Status.AwaitingCustomerApproval;
}

These are just made up examples but I hope you get the idea.

What I'm really thinking is that all my notification rules should be self-contained in some kind of configurable notication class, which basically monitors state changes on my object and does whatever it needs to do, so it acts like a plugin to the main application and maintains loose coupling. At the same time, I don't really feel like my underlying data objects should have dependencies on things like notification services, I kind of think this should plug-in to my main controller classes.

I can't really think how to achieve this, but I'm guessing it must be a common problem. Is there a specific design pattern I can read up on to give some clues? Has anyone done something like this before? Am I even thinking about this problem correctly? I'm pretty new to all this stuff but trying to think and code the correct way.

I would advise Chain-Of-Responsibility pattern: http://en.wikipedia.org/wiki/Chain-of-responsibility_pattern

It is basically a chain in which each element acts/doesn't act based on the test condition implemented by it. These conditions can be made configurable but it is down to your implementation.