storePath

import { storePath } from "@solidjs/signals";

interface StorePath {
  <T>(setter: PathSetter<T>): (state: T) => void;
  <T, K extends keyof T>(
    key: Part<T, K>,
    setter: PathSetter<T[K]>
  ): (state: T) => void;
  readonly DELETE: typeof DELETE;
}

const storePath: StorePath;

const [state, setState] = createStore({ user: { name: "Ada" }, todos: [] });

setState(storePath("user", "name", "Grace"));
setState(storePath("todos", (t) => !t.done, "done", true)); // mark all undone as done
setState(storePath("user", "nickname", storePath.DELETE));

setState(storePath("user", "name", "Grace"));
setState(storePath("todos", (todo) => !todo.done, "done", true));
setState(storePath("user", "nickname", storePath.DELETE));

type ArrayFilterFn<T> = (item: T, index: number) => boolean;

type CustomPartial<T> = T extends readonly unknown[]
  ? "0" extends keyof T
    ? { [K in Extract<keyof T, `${number}`>]?: T[K] }
    : { [x: number]: T[number] }
  : Partial<T>;

type Part<T, K extends KeyOf<T> = KeyOf<T>> =
  | K
  | ([K] extends [never] ? never : readonly K[])
  | ([T] extends [readonly unknown[]]
      ? ArrayFilterFn<T[number]> | StorePathRange
      : never);

type PathSetter<T> =
  T | CustomPartial<T> | ((prev: T) => T | CustomPartial<T>) | typeof DELETE;

type StorePathRange = { from?: number; to?: number; by?: number };