// SPDX-License-Identifier: AGPL-3.0-or-later

const singletonClearers: Array<() => void> = [];

export function singleton<T>(factory: () => T, teardown?: (instance: T) => void): () => T {
	let instance: T | undefined;
	singletonClearers.push(() => {
		if (instance !== undefined) {
			teardown?.(instance);
		}
		instance = undefined;
	});
	return () => {
		if (instance === undefined) {
			instance = factory();
		}
		return instance;
	};
}

export function clearSingletonsForTesting(): void {
	for (const clear of singletonClearers) {
		clear();
	}
}