import type { ReadonlyStore } from "./computedStore.js";
import type { Store } from "./store.js";

/**
 * Run a function whenever dependencies change
 * @param effectFn - Side effect function to run
 * @param dependencies - The stores it depends on
 * @param runOnMount - Whether to run the effect function immediately or not
 * @example
 * ```ts
 * const foo = computed(() => bar.getValue() + baz.getValue(), [bar, baz]);
 * ```
 * @returns A function to stop listening to changes in the dependencies
 */
export function effect<T>(
  // pass the values of the dependencies to the computation function
  effectFn: () => T,
  // biome-ignore lint/suspicious/noExplicitAny: library function that accepts any store type
  dependencies: (Store<any> | ReadonlyStore<any>)[],
  runOnMount = true,
) {
  if (runOnMount) {
    effectFn();
  }

  // when any of the dependencies change, recompute the value and set it
  const unsubscribeList = dependencies.map((store) => {
    return store.subscribe(() => {
      effectFn();
    });
  });

  return () => {
    for (const fn of unsubscribeList) {
      fn();
    }
  };
}