import { Observable, interval, InteropObservable, Subscribable } from "rxjs"; // types: 7.5.2

declare const obs1: Observable<number>;
const obs2 = interval(100);

type Test1 = typeof obs1 extends InteropObservable<infer T> ? T : never;
//   ^?
type Test2 = typeof obs2 extends InteropObservable<infer T> ? T : never;
//   ^?

declare class MyObservable<T> {
  subscribe(cb: (a: T) => void): void;
  // just make this class nominal to avoid relying on structural subtyping with the Observable from RxJS
  private tag: string;
}

// strategy based on the one in RxJS itself
// https://github.com/ReactiveX/rxjs/blob/5d0e41ee46337f56dba6d9a1ef938002b261ccac/src/internal/types.ts#L90
type ObservableInput<T> = MyObservable<T> | InteropObservable<T>;

// https://github.com/ReactiveX/rxjs/blob/5d0e41ee46337f56dba6d9a1ef938002b261ccac/src/internal/types.ts
type ObservedValueOf<O> = O extends ObservableInput<infer T> ? T : never;

// https://github.com/ReactiveX/rxjs/blob/888c753e272443bbb879f9ffb1a8145a7773c865/src/internal/observable/from.ts#L6
declare function from<O extends ObservableInput<any>>(
  input: O
): MyObservable<ObservedValueOf<O>>;

// actual
const converted1 = from(obs1);
const converted2 = from(obs2);

// expected result (without having to cast this)
const converted3 = from(obs1 as typeof obs1 & { [Symbol.observable]: () => Subscribable<number> });
//    ^?
const converted4 = from(obs2 as typeof obs2 & { [Symbol.observable]: () => Subscribable<number> });
//    ^?