Backend refactoring

[jamilraichouni]

Move backend app from data class in explorer.py to a global app in
main.py and launch with uvicorn command.

[Wuestengecko]

Thanks for doing this work! I already have some general comments, just from a first brief look at the diff (so I might have missed something):

• It seems the middleware updating the last_interaction_time got lost in the process

• The /metrics endpoint was moved into the app.router (i.e. below $ROUTE_PREFIX), which will probably break monitoring

• It feels a bit odd to have the app.state setup at the end of the file, and all the rest of the app initialization somewhere further up (not even at the top, right after the imports, just somewhere in the middle between some standalone functions and all the routes). I think we should at least move that first part up to the other globals.

• In the interest of type safety (read: helping the linters understand what's going on), it might be a good idea to define a dummy dataclass for the app.state, and cast to that instead of using app.state directly.

  If FastAPI doesn't have something clever that we can use built-in, doing it ourselves should be as simple as this:

  @dataclasses.dataclass
  class AppState:
      model: capellambse.MelodyModel
      env: jinja2.Environment
      # etc.
  
  @app.router.get(...)
  def some_route(...):
      state: AppState = app.state

[jamilraichouni]

Thanks for doing this work! I already have some general comments, just from a first brief look at the diff (so I might have missed something):

• It seems the middleware updating the last_interaction_time got lost in the process
• The /metrics endpoint was moved into the app.router (i.e. below $ROUTE_PREFIX), which will probably break monitoring
• It feels a bit odd to have the app.state setup at the end of the file, and all the rest of the app initialization somewhere further up (not even at the top, right after the imports, just somewhere in the middle between some standalone functions and all the routes). I think we should at least move that first part up to the other globals.
• In the interest of type safety (read: helping the linters understand what's going on), it might be a good idea to define a dummy dataclass for the app.state, and cast to that instead of using app.state directly.
  If FastAPI doesn't have something clever that we can use built-in, doing it ourselves should be as simple as this:

  @dataclasses.dataclass
  class AppState:
      model: capellambse.MelodyModel
      env: jinja2.Environment
      # etc.
  
  @app.router.get(...)
  def some_route(...):
      state: AppState = app.state

Hi @Wuestengecko , thank you for this review comment!

I considered it and after our discussion I introduced a separate state.py module to handle the application state in a manner that helps mypy to infer the type of state variables.

[Wuestengecko]

Could you please rebase on top of latest master (at your convenience)? Should be straight forward, as there are no conflicts and no tool changes that should affect formatting of this PR.

[jamilraichouni]

Could you please rebase on top of latest master (at your convenience)? Should be straight forward, as there are no conflicts and no tool changes that should affect formatting of this PR.

done