/** Returns a given tab index for an element, defaulting to zero. */
export const getTabIndex = (node: Element): number => {
  const index = parseInt(node.getAttribute('tabindex')!, 10);
  return (
    index === index &&
    !(node as HTMLElement).isContentEditable &&
    index
  ) || 0;
};

/** Returns whether an element is visible in the context of focusability. */
export const isVisible = (node: Element): boolean => !!(
  (node as HTMLElement).offsetWidth &&
  (node as HTMLElement).offsetHeight &&
  node.getClientRects().length &&
  getComputedStyle(node).visibility !== 'hidden'
);

/** Returns whether an element accepts text input. */
export const isInputElement = (node: Element): boolean => !!(
  node.tagName === 'INPUT'
    || node.tagName === 'TEXTAREA'
    || (node as HTMLElement).isContentEditable
);

export const contains = (owner: Element | null, node: Element | EventTarget | null) =>
  !!(node && owner && (owner === node || owner.contains(node as Element)));