const focusableSelector = [
	'a[href]',
	'button:not([disabled])',
	'input:not([disabled])',
	'select:not([disabled])',
	'textarea:not([disabled])',
	'[tabindex]:not([tabindex="-1"])'
].join(', ');

function focusableElements(container: HTMLElement): HTMLElement[] {
	return [...container.querySelectorAll<HTMLElement>(focusableSelector)].filter(
		(element) => element.getClientRects().length > 0
	);
}

export function focusTrap(container: HTMLElement) {
	const previouslyFocused = document.activeElement instanceof HTMLElement ? document.activeElement : null;
	(focusableElements(container)[0] ?? container).focus({ preventScroll: true });

	function handleKeydown(event: KeyboardEvent) {
		if (event.key !== 'Tab') return;

		const elements = focusableElements(container);
		const first = elements[0];
		const last = elements.at(-1);
		const active = document.activeElement;

		if (!first || !last) {
			event.preventDefault();
			container.focus({ preventScroll: true });
		} else if (!container.contains(active)) {
			event.preventDefault();
			first.focus();
		} else if (event.shiftKey && active === first) {
			event.preventDefault();
			last.focus();
		} else if (!event.shiftKey && active === last) {
			event.preventDefault();
			first.focus();
		}
	}

	document.addEventListener('keydown', handleKeydown);

	return {
		destroy() {
			document.removeEventListener('keydown', handleKeydown);
			if (previouslyFocused?.isConnected) previouslyFocused.focus({ preventScroll: true });
		}
	};
}