import { focusVisibleElement } from '@utils/helpers';

/**
 * This query string selects elements that
 * are eligible to receive focus. We select
 * interactive elements that meet the following
 * criteria:
 * 1. Element does not have a negative tabindex
 * 2. Element does not have `hidden`
 * 3. Element does not have `disabled` for non-Ionic components.
 * 4. Element does not have `disabled` or `disabled="true"` for Ionic components.
 * Note: We need this distinction because `disabled="false"` is
 * valid usage for the disabled property on ion-button.
 */
export const focusableQueryString =
  '[tabindex]:not([tabindex^="-"]):not([hidden]):not([disabled]), input:not([type=hidden]):not([tabindex^="-"]):not([hidden]):not([disabled]), textarea:not([tabindex^="-"]):not([hidden]):not([disabled]), button:not([tabindex^="-"]):not([hidden]):not([disabled]), select:not([tabindex^="-"]):not([hidden]):not([disabled]), ion-checkbox:not([tabindex^="-"]):not([hidden]):not([disabled]), ion-radio:not([tabindex^="-"]):not([hidden]):not([disabled]), .ion-focusable:not([tabindex^="-"]):not([hidden]):not([disabled]), .ion-focusable[disabled="false"]:not([tabindex^="-"]):not([hidden])';

/**
 * Focuses the first descendant in a context
 * that can receive focus. If none exists,
 * a fallback element will be focused.
 * This fallback is typically an ancestor
 * container such as a menu or overlay so focus does not
 * leave the container we are trying to trap focus in.
 *
 * If no fallback is specified then we focus the container itself.
 */
export const focusFirstDescendant = <R extends HTMLElement, T extends HTMLElement>(ref: R, fallbackElement?: T) => {
  const firstInput = ref.querySelector<HTMLElement>(focusableQueryString);

  focusElementInContext(firstInput, fallbackElement ?? ref);
};

/**
 * Focuses the last descendant in a context
 * that can receive focus. If none exists,
 * a fallback element will be focused.
 * This fallback is typically an ancestor
 * container such as a menu or overlay so focus does not
 * leave the container we are trying to trap focus in.
 *
 * If no fallback is specified then we focus the container itself.
 */
export const focusLastDescendant = <R extends HTMLElement, T extends HTMLElement>(ref: R, fallbackElement?: T) => {
  const inputs = Array.from(ref.querySelectorAll<HTMLElement>(focusableQueryString));
  const lastInput = inputs.length > 0 ? inputs[inputs.length - 1] : null;

  focusElementInContext(lastInput, fallbackElement ?? ref);
};

/**
 * Focuses a particular element in a context. If the element
 * doesn't have anything focusable associated with it then
 * a fallback element will be focused.
 *
 * This fallback is typically an ancestor
 * container such as a menu or overlay so focus does not
 * leave the container we are trying to trap focus in.
 * This should be used instead of the focus() method
 * on most elements because the focusable element
 * may not be the host element.
 *
 * For example, if an ion-button should be focused
 * then we should actually focus the native <button>
 * element inside of ion-button's shadow root, not
 * the host element itself.
 */
const focusElementInContext = <T extends HTMLElement>(
  hostToFocus: HTMLElement | null | undefined,
  fallbackElement: T
) => {
  let elementToFocus = hostToFocus;

  const shadowRoot = hostToFocus?.shadowRoot;
  if (shadowRoot) {
    // If there are no inner focusable elements, just focus the host element.
    elementToFocus = shadowRoot.querySelector<HTMLElement>(focusableQueryString) || hostToFocus;
  }

  if (elementToFocus) {
    const radioGroup = elementToFocus.closest('ion-radio-group');

    if (radioGroup) {
      radioGroup.setFocus();
    } else {
      focusVisibleElement(elementToFocus);
    }
  } else {
    // Focus fallback element instead of letting focus escape
    fallbackElement.focus();
  }
};