[wip] kefir cleanup

pkg/shared/kefir.ts

@@ -0,0 +1,29 @@
+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),
+			])
+		);
+	};