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

export function keepFocusWithin(event: KeyboardEvent, container: HTMLElement) {
  if (event.key !== "Tab") return;

  const focusable = Array.from(container.querySelectorAll<HTMLElement>(focusableSelector))
    .filter((element) => element.getAttribute("aria-hidden") !== "true" && element.offsetParent !== null);
  const first = focusable[0];
  const last = focusable[focusable.length - 1];
  if (!first || !last) return;

  if (event.shiftKey && document.activeElement === first) {
    event.preventDefault();
    last.focus();
  } else if (!event.shiftKey && document.activeElement === last) {
    event.preventDefault();
    first.focus();
  }
}