focus-management.ts

import { match } from './match'
import { getOwnerDocument } from './owner'

// Credit:
//  - https://stackoverflow.com/a/30753870
let focusableSelector = [
  '[contentEditable=true]',
  '[tabindex]',
  'a[href]',
  'area[href]',
  'button:not([disabled])',
  'iframe',
  'input:not([disabled])',
  'select:not([disabled])',
  'textarea:not([disabled])',
]
  .map(
    process.env.NODE_ENV === 'test'
      ? // TODO: Remove this once JSDOM fixes the issue where an element that is
        // "hidden" can be the document.activeElement, because this is not possible
        // in real browsers.
        (selector) => `${selector}:not([tabindex='-1']):not([style*='display: none'])`
      : (selector) => `${selector}:not([tabindex='-1'])`
  )
  .join(',')

export enum Focus {
  /** Focus the first non-disabled element */
  First = 1 << 0,

  /** Focus the previous non-disabled element */
  Previous = 1 << 1,

  /** Focus the next non-disabled element */
  Next = 1 << 2,

  /** Focus the last non-disabled element */
  Last = 1 << 3,

  /** Wrap tab around */
  WrapAround = 1 << 4,

  /** Prevent scrolling the focusable elements into view */
  NoScroll = 1 << 5,
}

export enum FocusResult {
  /** Something went wrong while trying to focus. */
  Error,

  /** When `Focus.WrapAround` is enabled, going from position `N` to `N+1` where `N` is the last index in the array, then we overflow. */
  Overflow,

  /** Focus was successful. */
  Success,

  /** When `Focus.WrapAround` is enabled, going from position `N` to `N-1` where `N` is the first index in the array, then we underflow. */
  Underflow,
}

enum Direction {
  Previous = -1,
  Next = 1,
}

export function getFocusableElements(container: HTMLElement | null = document.body) {
  if (container == null) return []
  return Array.from(container.querySelectorAll<HTMLElement>(focusableSelector))
}

export enum FocusableMode {
  /** The element itself must be focusable. */
  Strict,

  /** The element should be inside of a focusable element. */
  Loose,
}

export function isFocusableElement(
  element: HTMLElement,
  mode: FocusableMode = FocusableMode.Strict
) {
  if (element === getOwnerDocument(element)?.body) return false

  return match(mode, {
    [FocusableMode.Strict]() {
      return element.matches(focusableSelector)
    },
    [FocusableMode.Loose]() {
      let next: HTMLElement | null = element

      while (next !== null) {
        if (next.matches(focusableSelector)) return true
        next = next.parentElement
      }

      return false
    },
  })
}

export function focusElement(element: HTMLElement | null) {
  element?.focus({ preventScroll: true })
}

export function sortByDomNode<T>(
  nodes: T[],
  resolveKey: (item: T) => HTMLElement | null = (i) => i as unknown as HTMLElement | null
): T[] {
  return nodes.slice().sort((aItem, zItem) => {
    let a = resolveKey(aItem)
    let z = resolveKey(zItem)

    if (a === null || z === null) return 0

    let position = a.compareDocumentPosition(z)

    if (position & Node.DOCUMENT_POSITION_FOLLOWING) return -1
    if (position & Node.DOCUMENT_POSITION_PRECEDING) return 1
    return 0
  })
}

export function focusIn(container: HTMLElement | HTMLElement[], focus: Focus) {
  let ownerDocument = Array.isArray(container)
    ? container.length > 0
      ? container[0].ownerDocument
      : document
    : container.ownerDocument

  let elements = Array.isArray(container)
    ? sortByDomNode(container)
    : getFocusableElements(container)
  let active = ownerDocument.activeElement as HTMLElement

  let direction = (() => {
    if (focus & (Focus.First | Focus.Next)) return Direction.Next
    if (focus & (Focus.Previous | Focus.Last)) return Direction.Previous

    throw new Error('Missing Focus.First, Focus.Previous, Focus.Next or Focus.Last')
  })()

  let startIndex = (() => {
    if (focus & Focus.First) return 0
    if (focus & Focus.Previous) return Math.max(0, elements.indexOf(active)) - 1
    if (focus & Focus.Next) return Math.max(0, elements.indexOf(active)) + 1
    if (focus & Focus.Last) return elements.length - 1

    throw new Error('Missing Focus.First, Focus.Previous, Focus.Next or Focus.Last')
  })()

  let focusOptions = focus & Focus.NoScroll ? { preventScroll: true } : {}

  let offset = 0
  let total = elements.length
  let next = undefined
  do {
    // Guard against infinite loops
    if (offset >= total || offset + total <= 0) return FocusResult.Error

    let nextIdx = startIndex + offset

    if (focus & Focus.WrapAround) {
      nextIdx = (nextIdx + total) % total
    } else {
      if (nextIdx < 0) return FocusResult.Underflow
      if (nextIdx >= total) return FocusResult.Overflow
    }

    next = elements[nextIdx]

    // Try the focus the next element, might not work if it is "hidden" to the user.
    next?.focus(focusOptions)

    // Try the next one in line
    offset += direction
  } while (next !== ownerDocument.activeElement)

  // This is a little weird, but let me try and explain: There are a few scenario's
  // in chrome for example where a focused `<a>` tag does not get the default focus
  // styles and sometimes they do. This highly depends on whether you started by
  // clicking or by using your keyboard. When you programmatically add focus `anchor.focus()`
  // then the active element (document.activeElement) is this anchor, which is expected.
  // However in that case the default focus styles are not applied *unless* you
  // also add this tabindex.
  if (!next.hasAttribute('tabindex')) next.setAttribute('tabindex', '0')

  return FocusResult.Success
}