import { merge, Observable } from "kefir";

export const transform = <
	T,
	Mutations extends [Observable<any, any>, (prev: T, evt: any) => T][]
>(
	initValue: T,
	...mutations: Mutations
): Observable<T, unknown> =>
	merge(
		mutations.map(([source, mutation]) =>
			source.map((event) => ({ event, mutation }))
		)
	).scan((prev, { event, mutation }) => mutation(prev, event), initValue);

export const partition =
	<C extends readonly [...string[]], T, E>(
		classes: C,
		partitionFn: (v: T) => C[number]
	) =>
	(obs: Observable<T, E>) => {
		const assigned = obs.map((obj) => ({ obj, cls: partitionFn(obj) }));
		return Object.fromEntries(
			classes.map((C) => [
				C,
				assigned.filter(({ cls }) => cls == C).map(({ obj }) => obj),
			])
		);
	};