/*!
 * Adapted from jQuery UI core
 *
 * http://jqueryui.com
 *
 * Copyright 2014 jQuery Foundation and other contributors
 * Released under the MIT license.
 * http://jquery.org/license
 *
 * http://api.jqueryui.com/category/ui-core/
 */

const tabbableNode = /input|select|textarea|button|object/

function hidesContents(element: HTMLElement) {
  const zeroSize = element.offsetWidth <= 0 && element.offsetHeight <= 0

  // If the node is empty, this is good enough
  if (zeroSize && !element.innerHTML) return true

  // Otherwise we need to check some styles
  const style = window.getComputedStyle(element)
  return (
    style.getPropertyValue("display") === "none" ||
    (zeroSize && style.getPropertyValue("overflow") !== "visible")
  )
}

function visible(element: any) {
  let parentElement = element
  while (parentElement) {
    if (parentElement === document.body) break
    if (hidesContents(parentElement)) return false
    parentElement = parentElement.parentNode
  }
  return true
}

export function focusable(element: HTMLElement, isTabIndexNotNaN: boolean) {
  const nodeName = element.nodeName.toLowerCase()
  const res =
    //@ts-ignore
    (tabbableNode.test(nodeName) && !element.disabled) ||
    //@ts-ignore
    (nodeName === "a" ? element.href || isTabIndexNotNaN : isTabIndexNotNaN)
  return res && visible(element)
}

export function tabbable(element: HTMLElement) {
  const tabIndexAttr = element.getAttribute("tabindex")
  const tabIndex = tabIndexAttr !== null ? Number(tabIndexAttr) : undefined
  const isTabIndexNaN = tabIndex === undefined || isNaN(tabIndex)

  return (isTabIndexNaN || tabIndex >= 0) && focusable(element, !isTabIndexNaN)
}

export default function findTabbableDescendants(
  element: HTMLElement | null | undefined
): HTMLElement[] {
  if (!(element instanceof HTMLElement)) {
    return []
  }

  return Array.from(element.querySelectorAll("*"))
    .filter((el): el is HTMLElement => el instanceof HTMLElement)
    .filter(tabbable)
}