Review rxv.py and refactor

[wuub]

TODO:

• tasks here
• and here

[sdague]

Here are some random ideas on breaking up the code a bit. They might be a bridge too far in refactoring.

1. The long list of command strings that are just at the beginning of the file could be turned into small class objects, in a dedicated file.

For instance:

class PlayGet(RXVRequest):
   zone_cmd = False
   method = "GET"

   def __init__(self, source):
       self.source = source

   def __str__(self, zone=None):
       return "<{src_name}><Play_Info>GetParam</Play_Info></{src_name}>".format(self.source)

Then calling code would look like:

resp = self._request(PlayGet(source))

We could have a PlayGetResponse class that's responsible for the parsing (and also a good place in the code to document what the return document is going to look like (I've been writing some notes locally, but a standard place to do that in code would be nice).

That takes a bunch of internal complexity out of the methods in the main class, and makes it more of high level flow:

def do_thing(self):
    if not can_do_thing(self.input):
        bail
    resp = self._request(Thing(self.input))
    return resp

2. move static discovery into a dedicated module, though I'm not sure I really have a good handle on the exposed interface because we both want it for safety checks in our methods, but we are also going to want a dump or something to support systems like HomeAssistant setting the capabilities on the receiver when that interface is active (which impacts the controls shown to the user).

[sdague]

Also, totally random bonus points if someone cracks the yamaha icon format that exists as part of the status. There is definitely a bitmap in there somewhere, as it's how both the app and the TV ui display an icon for net radio stations.