/**
 * Roving-tabindex keyboard helpers shared by the composite widgets in the admin
 * (radiogroups and the section tablist).
 *
 * A composite widget exposes exactly one tab stop: the selected item carries
 * `tabIndex={0}` and every other item carries `tabIndex={-1}`. Arrow keys move
 * between items inside the widget, so the helpers here only need to answer
 * "which index does this key land on".
 */

/** Which arrow keys a widget claims. Unclaimed keys must keep their default behavior. */
export type RovingOrientation = 'horizontal' | 'vertical' | 'both';

/**
 * Resolve the writing direction that applies to `element`.
 *
 * The nearest explicit `dir` attribute wins (this is also the only signal jsdom
 * reports), otherwise fall back to the computed style so a direction inherited
 * from CSS is still honored.
 */
export function isRtlElement(element: Element | null | undefined): boolean {
  if (!element) {
    return false;
  }

  const explicitDir = element.closest('[dir]')?.getAttribute('dir')?.toLowerCase();

  if (explicitDir === 'rtl') {
    return true;
  }

  if (explicitDir === 'ltr') {
    return false;
  }

  try {
    const view = element.ownerDocument?.defaultView;

    return view ? view.getComputedStyle(element).direction === 'rtl' : false;
  } catch {
    return false;
  }
}

/**
 * Map a key press onto the index it should move to, or `null` when the widget
 * does not claim the key. Callers must only call `preventDefault()` for a
 * non-null result, otherwise a horizontal tablist would swallow page scrolling.
 *
 * Movement wraps at both ends, matching the WAI-ARIA radiogroup and tablist
 * patterns.
 */
export function resolveRovingIndex(
  key: string,
  currentIndex: number,
  count: number,
  orientation: RovingOrientation,
  rtl: boolean,
): number | null {
  if (count <= 0) {
    return null;
  }

  const origin = currentIndex >= 0 && currentIndex < count ? currentIndex : 0;
  const step = (delta: number): number => (origin + delta + count) % count;
  const claimsHorizontal = orientation !== 'vertical';
  const claimsVertical = orientation !== 'horizontal';

  switch (key) {
    case 'ArrowRight':
      return claimsHorizontal ? step(rtl ? -1 : 1) : null;
    case 'ArrowLeft':
      return claimsHorizontal ? step(rtl ? 1 : -1) : null;
    case 'ArrowDown':
      return claimsVertical ? step(1) : null;
    case 'ArrowUp':
      return claimsVertical ? step(-1) : null;
    case 'Home':
      return 0;
    case 'End':
      return count - 1;
    default:
      return null;
  }
}

/**
 * The tab stop of a composite widget. The selected item owns it; when nothing is
 * selected the first item does, so the widget always stays reachable by Tab.
 */
export function rovingTabIndex(isSelected: boolean, index: number, selectedIndex: number): 0 | -1 {
  if (isSelected) {
    return 0;
  }

  return selectedIndex < 0 && index === 0 ? 0 : -1;
}