import { id, registerSubscriptions, registerFire } from './util.js';

export function prop(store, hash = id) {
	let subscribers = [];
	let oldId = hash(store);

	const accessor = function _prop(newVal) {
		const newId = hash(newVal);
		if (newVal !== undefined && oldId !== newId) {
			oldId = newId;
			store = newVal;
			accessor.fire(store);
		}
		return store;
	};
	accessor.subscribe = registerSubscriptions(subscribers);
	accessor.fire = registerFire(subscribers);
	accessor.unsubscribeAll = () => (subscribers = []);

	return accessor;
}