[WIP] useDerivedState

Author: nDriaDev

packages/react-tools/src/hooks/useDerivedState.ts

@@ -0,0 +1,40 @@
+import { DependencyList, useRef, useReducer, useCallback, Dispatch, SetStateAction, useEffect } from "react";
+
+export const useDerivedState = <T>(initialState: T|(()=>T), compute: ()=>void|Promise<void>|(()=>void), deps?: DependencyList): [T, Dispatch<SetStateAction<T>>] => {
+	const [, update] = useReducer(t => !t, false);
+	const ref = useRef<{ init: boolean, localState?: T, deps?: DependencyList }>({
+		init: false
+	});
+
+	let localState: T;
+	if (!ref.current.init || (ref.current.deps || []).length !== (deps || []).length || !(ref.current.deps || []).every((dep, i) => (deps || [])[i] === dep)) {
+		localState = typeof initialState === "function" ? (initialState as ()=>T)() : initialState;
+		ref.current = {
+			init: true,
+			localState: localState,
+			deps
+		}
+		update();
+	} else {
+		localState = ref.current.localState!;
+	}
+
+	const updateLocalState = useCallback((state: T | ((state: T) => T)) => {
+		if (!ref.current.init) {
+			throw Error();
+		}
+		const localState = typeof state === "function"
+			? (state as ((state: T) => T))(ref.current.localState!)
+			: state;
+		ref.current.localState = localState;
+		update();
+	}, []) as Dispatch<SetStateAction<T>>;
+
+	useEffect(() => {
+		const cleanUp = compute();
+		return () => cleanUp && (cleanUp as ()=>void)();
+	}, [compute]);
+
+	return [localState, updateLocalState];
+
+}