handler/src/handlers/presence.ts

import { concatMap, from, interval, of, map, scan, startWith, fromEvent, take } from "rxjs"
import { Presence  } from "../core/presences";
import { Services } from "../core/ioc";
import assert from "node:assert";
import * as Files from "../core/module-loading";
type SetPresence = (conf: Presence.Result) => Promise<unknown>

const parseConfig = async (conf: Promise<Presence.Result>) => {
    return conf.then(s => {
        if('repeat' in s) {
            const { onRepeat, repeat } = s;
            assert(repeat !== undefined, "repeat option is undefined");
            assert(onRepeat !== undefined, "onRepeat callback is undefined, but repeat exists");
            const src$ = typeof repeat === 'number' 
                ? interval(repeat)
                : fromEvent(...repeat);
                return src$.pipe(scan(onRepeat, s), 
                                 startWith(s));
        }
        return of(s).pipe(take(1));
    })
};

export const presenceHandler = (path: string, setPresence: SetPresence) => {
    const presence = Files
        .importModule<Presence.Config<(keyof Dependencies)[]>>(path)
        .then(({ module }) => {
            //fetch services with the order preserved, passing it to the execute fn 
            const fetchedServices = Services(...module.inject ?? []);
            return async () => module.execute(...fetchedServices);
        })
    const module$ = from(presence);
    return module$.pipe(
        //compose:
        //call the execute function, passing that result into parseConfig.
        //concatMap resolves the promise, and passes it to the next concatMap.
        concatMap(fn => parseConfig(fn())),
        // subscribe to the observable parseConfig yields, and set the presence.
        concatMap(conf => conf.pipe(map(setPresence))));
}