The class library contains several classes :

Config - the data have to come externally from places like web.config .

Repository - simulates DataSource. Instead of database it conatains lists which we manipulate with LINQ.

Model Classes

All the low level data manipulation is done in the ....Model classes.
If we decide to change the DataSource only these classes have to be changed.
We can implement a base model class that implements database or xml interaction depending on the DataSource.
All the logic in the other classes stays the same.

Handler Classes

More specialised classes that handle specific routine tasks.
Payment, Courier , Email, HttpRequests etc.
There may be several Payment handlers ( PayPal, WorldsPay ... ) and Courier handlers classes ( Royal Mail, Dx .... ) .
We instantiate the one needed for the specific transaction based on web.config defined strings or Provider web definitions and pass them when needed.

Action Classes

All the application logic manipulation is done in the ....Action classes .
Most of the Action classes inherit from AuthenticatedAction to ensure they are used only when there is a logged in user .

External library RazorEngine is used utilise email template. The email template for this example is kept in memory but can be held in a file and read on demamnd.

The parameters for the SmtpClient used to send the email should be available in the web.config .