type Current = null | (() => void);

let current: Current = null;

export function createSignal<T>(value: T): [() => T, (value: T) => void] {
	let innerValue = value;
	const observers: Array<Current> = [];
	const indices = new Map<Current, number>();

	const getter = () => {
		if (current !== null && !indices.has(current)) {
			observers.push(current);
			indices.set(current, observers.length);
		}

		return innerValue;
	};

	const setter = (value: T) => {
		innerValue = value;
		for (let i = 0; i < observers.length; i++) {
			observers[i]!();
		}
	};

	return [getter, setter];
}

export function createEffect(callback: () => void): void {
	current = callback;
	callback();
	current = null;
}