/** Sequentially focusable descendants in DOM order, including in DOM test shims. */
export function focusableElements(container: Element): HTMLElement[] {
  return Array.from(container.querySelectorAll<HTMLElement>(
    'button:not(:disabled), input:not(:disabled), select:not(:disabled), textarea:not(:disabled), [href], [tabindex]:not([tabindex="-1"])',
  )).filter(element => element.tabIndex >= 0 && element.getAttribute('type') !== 'hidden' &&
    !element.closest('[hidden], [inert], [aria-hidden="true"]'))
    .sort((a, b) => a.compareDocumentPosition(b) & Node.DOCUMENT_POSITION_FOLLOWING ? -1 : 1)
}

/** App popups are portaled; DOM order alone may disagree with their overlay z-index. */
export function topmostDialog(): HTMLElement | undefined {
  const dialogs = document.querySelectorAll<HTMLElement>('[role="dialog"]')
  let top: HTMLElement | undefined
  let highest = -Infinity
  for (const dialog of dialogs) {
    let layer = 0
    for (let element: HTMLElement | null = dialog; element; element = element.parentElement) {
      const z = Number.parseInt(getComputedStyle(element).zIndex, 10)
      if (Number.isFinite(z)) layer = Math.max(layer, z)
    }
    // Later DOM order wins only when overlay layers are equal.
    if (layer >= highest) { top = dialog; highest = layer }
  }
  return top
}