/** Creates useful state for an infinite scroll subscription */
export function useColumnReverseInfiniteScroll(
	threshold: number,
	ends: { hasMoreBelow: boolean, hasMoreAbove: boolean } | null,
	loadMoreAbove: () => Promise<void>,
	loadMoreBelow: () => Promise<void>,
	setScrollRatio: Dispatch<SetStateAction<number>>
): [
	updateCallable: (event: UIEvent<HTMLElement>) => void,
	loadAboveRetry: () => Promise<void>,
	loadBelowRetry: () => Promise<void>
] {
	const isMounted = useIsMountedRef();

	const [ loadingAbove, setLoadingAbove ] = useState<boolean>(false);
	const [ loadingBelow, setLoadingBelow ] = useState<boolean>(false);

	const loadAbove = useCallback(async () => {
		if (loadingAbove) return;
		if (!ends || !ends.hasMoreAbove) return;
		setLoadingAbove(true);
		await loadMoreAbove();
		if (!isMounted.current) return;
		setLoadingAbove(false);
	}, [ loadingAbove, loadMoreAbove, ends ]);

	const loadBelow = useCallback(async () => {
		if (loadingBelow) return;
		if (!ends || !ends.hasMoreBelow) return;
		setLoadingBelow(true);
		await loadMoreBelow();
		if (!isMounted.current) return;
		setLoadingBelow(false);
	}, [ loadingBelow, loadMoreBelow, ends ]);

	const onScrollCallable = useCallback(async (event: UIEvent<HTMLElement>) => {
		const scrollTop = event.currentTarget.scrollTop;
		const scrollHeight = event.currentTarget.scrollHeight;
		const clientHeight = event.currentTarget.clientHeight;

		// WARNING
		// There's likely an inconsistency between browsers on this so have fun when you're working
		// on the cross-platform implementation of this
		// scrollTop apparantly is negative for column-reverse divs (this actually kindof makes sense if you flip your head upside down)
		// have to reverse this
		// I expect this was a change with some version of chromium.
		// MDN documentation issue: https://github.com/mdn/content/issues/10968

		setScrollRatio(Math.abs(scrollTop / scrollHeight));

		const distToTop = -(clientHeight - scrollHeight - scrollTop); // keep in mind scrollTop is negative >:]
		const distToBottom = -scrollTop;

		//LOG.debug(`scroll callable update. to top: ${distToTop}, to bottom: ${distToBottom}`)

		if (distToTop < threshold) {
			await loadAbove();
		}

		if (distToBottom < threshold) {
			await loadBelow();
		}
	}, [ setScrollRatio, loadAbove, loadBelow, threshold ]);

	return [ onScrollCallable, loadAbove, loadBelow ];
}