[Feature] Enforce/describe State Meta Data with TS

[semopz]

Bug or feature request?

Feature

Description:

Currently metadata is of any/unknown type but in the case of actors, I need to be able to lock down what kind of metadata each event can or should have. I'm not sure if this is wading too much into context (extended state) territory but if states can be configured to only accept certain events, they should also be able to emit only a certain type of metadata.

(Feature) Potential implementation:

This is what the API might look like

type Locales = 'en-US' | 'en-GB' | 'fr-CA';
enum EventIntendedFor {
  NoOneOrSilent,
  User,
  Console,
  EventLog,
  System,
}

type Translations = { [code in Locales]: string };
type EventInfo = {
  for: EventIntendedFor,
  message: Translations
};

interface MachineMeta {
  // Tells the app what the machine state is in the local language (if the app wants to display that info)
  strings: {
    label: Translations;
    desc: Translations;
  },
  info?: EventInfo;
}

interface Color extends MachineMeta {
  rgb: number;
  // Different beeps and chirps or instructions
  audio?: number[];
};


interface LightStateSchema {
  states: {
    green: {
      meta: Color
    };
    yellow: {
      meta: Color
    };
    red: {
      meta: Color
      states: {
        walk: {
          meta?: MachineMeta | any
        };
        wait: {
          meta?: MachineMeta | any
        };
        stop: {
          meta?: MachineMeta | any
        };
      };
    };
  };
}

It shouldn't be a breaking change as omitting the meta definition should just imply meta can be any.

Leaving the flexibility in makes the definition a bit verbose (maybe I don't care what the nested states have as metadata but if I decide to put it in, I'd still like some intellisense).

Would be nice if you could define a meta inside the states definition so that all nested states inherit the meta definition. But would that also apply to the nested states within (might break builtin states like onDone)?

Link to reproduction or proof-of-concept:

Sorry, not sure how to implement this

[jamiehaywood]

any movement on this?

[Allaoua9]

It would be nice to have this 👍 !

[nstadigs]

I have a use case where the UI elements and the states of my physical devices in my automated home is driven by the metadata of the states of an xstate machine. So I use metadata extensively. Being able to enforce the type of the meta property would really improve my workflow!

[davidkpiano]

I have a use case where the UI elements and the states of my physical devices in my automated home is driven by the metadata of the states of an xstate machine. So I use metadata extensively. Being able to enforce the type of the meta property would really improve my workflow!

Thanks for sharing the use-case! I have some ideas around typing this and other properties that I will share soon in https://github.com/statelyai/rfcs

[Andarist]

@nstadigs do u need for all states to have the same type of metadata or would you like for it to be per-state information?

[nstadigs]

@Andarist having all states share the type of metadata would suit my use case best :)