Previously we would refresh all the views when download/cancel
button was clicked. This was done mainly to avoid zombie widget bugs
that would arise from shared state.
Now we still refresh all the background views but not the visible one.
Instead the widget has the reponsibility of recalculating it's state.
Add a ButtonState Machine which represents the state of total_size
label, play button, and download button. Also implemented the
update/determine_state function for ButtonState.
Also implemented required generic functions for MediaMachine<X,Y,Z>
that convert it to the desired state.
Instead of having a Wrapper of StateMachinesWrappers, use only the desired
possible states in A new struct with only 1 Wrapper that covers all 3 of
the embeded state machines.
I don't even know if the comment makes any sense. Sorry.
Currently it's required that you take mut self in order to manipulate
the internal state machines. This would not allow passing an Arc/Rc to
a callback since A/Rc<T> only derefs to &T and not T.
The take_mut crate allows the retrieval of ownership if you have a &mut refference
and as long you return T again. So Arc<Mutex<Machine> could work with
callbacks and embed Nested state machies without copying.
