import { merge, Observable } from "kefir";
import Bus from "kefir-bus";

export type ValueWithin<O extends Observable<any, any>> = Parameters<
	Parameters<O["map"]>[0]
>[0];

type Mutation<A, O extends Observable<any, any>> = [
	O,
	(prev: A, value: ValueWithin<O>) => A
];

export const multiScan = <A, M extends Mutation<A, any>[]>(
	initValue: A,
	...mutations: M
): Observable<A, any> =>
	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 extends { [key: string]: any },
	E
>(
	classes: C,
	obs: Observable<T, E>
) => {
	const classBuses = Object.fromEntries(classes.map((c) => [c, Bus()]));
	obs.onValue((v) => {
		for (const _class of classes) {
			if (_class in v) {
				classBuses[_class].emit(v);
				return;
			}
		}
	});
	return classBuses;
};

export const isEmpty = (container: { length: number }) => container.length == 0;

export const setDiff = <T>(
	sets: [Set<T>, s2: Set<T>]
): { added: T[]; removed: T[] } => ({
	added: [...sets[1].difference(sets[0])],
	removed: [...sets[0].difference(sets[1])],
});

export const set = <T>(arr: T[]) => new Set<T>(arr);

export const invert = <E>(obs: Observable<boolean, E>) => obs.map((o) => !o);