import { Tracker } from 'meteor/tracker';
import { Subscription, Unsubscribe } from 'use-subscription';

interface ISubscriptionFactory<T> {
	(...args: any[]): Subscription<T>;
}

export const createReactiveSubscriptionFactory = <T>(
	computeCurrentValueWith: (...args: any[]) => T,
): ISubscriptionFactory<T> =>
	(...args: any[]): Subscription<T> => {
		const computeCurrentValue = (): T => computeCurrentValueWith(...args);

		const callbacks = new Set<Unsubscribe>();

		let currentValue: T;

		const computation = Tracker.autorun(() => {
			currentValue = computeCurrentValue();
			callbacks.forEach((callback) => {
				callback();
			});
		});

		return {
			getCurrentValue: (): T => currentValue,
			subscribe: (callback): Unsubscribe => {
				callbacks.add(callback);

				return (): void => {
					callbacks.delete(callback);

					if (callbacks.size === 0) {
						computation.stop();
					}
				};
			},
		};
	};