The Mediator class is responsible for coordinating the overall application state, and the interactions between our various UI classes. As such, it really needs to have three key ingredients. Firstly, it needs to have the concrete implementation of the IMediatorImpl interface, so that it can call the various functions it needs to when the UI needs updating. We have just implemented the IMediatorImpl interface in our AppComponent class, so we will need to pass a reference to the AppComponent instance to the Mediator class.
Secondly, the Mediator class needs a concrete instance of each of our State classes, so that it can recreate both the current state of the application, as well as the desired next state. It can then compare ...
