export type LazyResource<T> = {
	load: () => Promise<T>;
	unload: () => void;
	isLoaded: () => boolean;
};

export function createLazyResource<T>(
	loader: () => Promise<T>,
	dispose?: (value: T) => void
): LazyResource<T> {
	let cached: T | null = null;
	let inflight: Promise<T> | null = null;

	const load = async (): Promise<T> => {
		if (cached) return cached;
		if (inflight) return inflight;

		inflight = (async () => {
			const value = await loader();
			cached = value;
			inflight = null;
			return value;
		})();

		return inflight;
	};

	const unload = () => {
		if (cached && dispose) {
			try {
				dispose(cached);
			} catch (error) {
				console.error("[lazy-resource] failed to dispose resource", error);
			}
		}
		cached = null;
		inflight = null;
	};

	return {
		load,
		unload,
		isLoaded: () => cached !== null
	};
}