forgejo/web_src/js/modules/fomantic/dropdown.js

import $ from 'jquery';
import {generateAriaId} from './base.js';

const ariaPatchKey = '_giteaAriaPatchDropdown';
const fomanticDropdownFn = $.fn.dropdown;

// use our own `$().dropdown` function to patch Fomantic's dropdown module
export function initAriaDropdownPatch() {
  if ($.fn.dropdown === ariaDropdownFn) throw new Error('initAriaDropdownPatch could only be called once');
  $.fn.dropdown = ariaDropdownFn;
  ariaDropdownFn.settings = fomanticDropdownFn.settings;
}

// the patched `$.fn.dropdown` function, it passes the arguments to Fomantic's `$.fn.dropdown` function, and:
// * it does the one-time attaching on the first call
// * it delegates the `onLabelCreate` to the patched `onLabelCreate` to add necessary aria attributes
function ariaDropdownFn(...args) {
  const ret = fomanticDropdownFn.apply(this, args);

  // if the `$().dropdown()` call is without arguments, or it has non-string (object) argument,
  // it means that this call will reset the dropdown internal settings, then we need to re-delegate the callbacks.
  const needDelegate = (!args.length || typeof args[0] !== 'string');
  for (const el of this) {
    const $dropdown = $(el);
    if (!el[ariaPatchKey]) {
      attachInit($dropdown);
    }
    if (needDelegate) {
      delegateOne($dropdown);
    }
  }
  return ret;
}

// make the item has role=option/menuitem, add an id if there wasn't one yet, make items as non-focusable
// the elements inside the dropdown menu item should not be focusable, the focus should always be on the dropdown primary element.
function updateMenuItem(dropdown, item) {
  if (!item.id) item.id = generateAriaId();
  item.setAttribute('role', dropdown[ariaPatchKey].listItemRole);
  item.setAttribute('tabindex', '-1');
  for (const a of item.querySelectorAll('a')) a.setAttribute('tabindex', '-1');
}

// make the label item and its "delete icon" has correct aria attributes
function updateSelectionLabel($label) {
  // the "label" is like this: "<a|div class="ui label" data-value="1">the-label-name <i|svg class="delete icon"/></a>"
  if (!$label.attr('id')) $label.attr('id', generateAriaId());
  $label.attr('tabindex', '-1');
  $label.find('.delete.icon').attr({
    'aria-hidden': 'false',
    'aria-label': window.config.i18n.remove_label_str.replace('%s', $label.attr('data-value')),
    'role': 'button',
  });
}

// delegate the dropdown's template functions and callback functions to add aria attributes.
function delegateOne($dropdown) {
  const dropdownCall = fomanticDropdownFn.bind($dropdown);

  // If there is a "search input" in the "menu", Fomantic will only "focus the input" but not "toggle the menu" when the "dropdown icon" is clicked.
  // Actually, Fomantic UI doesn't support such layout/usage. It needs to patch the "focusSearch" / "blurSearch" functions to make sure it toggles the menu.
  const oldFocusSearch = dropdownCall('internal', 'focusSearch');
  const oldBlurSearch = dropdownCall('internal', 'blurSearch');
  // * If the "dropdown icon" is clicked, Fomantic calls "focusSearch", so show the menu
  dropdownCall('internal', 'focusSearch', function () { dropdownCall('show'); oldFocusSearch.call(this) });
  // * If the "dropdown icon" is clicked again when the menu is visible, Fomantic calls "blurSearch", so hide the menu
  dropdownCall('internal', 'blurSearch', function () { oldBlurSearch.call(this); dropdownCall('hide') });

  // the "template" functions are used for dynamic creation (eg: AJAX)
  const dropdownTemplates = {...dropdownCall('setting', 'templates'), t: performance.now()};
  const dropdownTemplatesMenuOld = dropdownTemplates.menu;
  dropdownTemplates.menu = function(response, fields, preserveHTML, className) {
    // when the dropdown menu items are loaded from AJAX requests, the items are created dynamically
    const menuItems = dropdownTemplatesMenuOld(response, fields, preserveHTML, className);
    const $wrapper = $('<div>').append(menuItems);
    const $items = $wrapper.find('> .item');
    $items.each((_, item) => updateMenuItem($dropdown[0], item));
    $dropdown[0][ariaPatchKey].deferredRefreshAriaActiveItem();
    return $wrapper.html();
  };
  dropdownCall('setting', 'templates', dropdownTemplates);

  // the `onLabelCreate` is used to add necessary aria attributes for dynamically created selection labels
  const dropdownOnLabelCreateOld = dropdownCall('setting', 'onLabelCreate');
  dropdownCall('setting', 'onLabelCreate', function(value, text) {
    const $label = dropdownOnLabelCreateOld.call(this, value, text);
    updateSelectionLabel($label);
    return $label;
  });
}

// for static dropdown elements (generated by server-side template), prepare them with necessary aria attributes
function attachStaticElements($dropdown, $focusable, $menu) {
  const dropdown = $dropdown[0];

  // prepare static dropdown menu list popup
  if (!$menu.attr('id')) $menu.attr('id', generateAriaId());
  $menu.find('> .item').each((_, item) => updateMenuItem(dropdown, item));
  // this role could only be changed after its content is ready, otherwise some browsers+readers (like Chrome+AppleVoice) crash
  $menu.attr('role', dropdown[ariaPatchKey].listPopupRole);

  // prepare selection label items
  $dropdown.find('.ui.label').each((_, label) => updateSelectionLabel($(label)));

  // make the primary element (focusable) aria-friendly
  $focusable.attr({
    'role': $focusable.attr('role') ?? dropdown[ariaPatchKey].focusableRole,
    'aria-haspopup': dropdown[ariaPatchKey].listPopupRole,
    'aria-controls': $menu.attr('id'),
    'aria-expanded': 'false',
  });

  // use tooltip's content as aria-label if there is no aria-label
  const tooltipContent = $dropdown.attr('data-tooltip-content');
  if (tooltipContent && !$dropdown.attr('aria-label')) {
    $dropdown.attr('aria-label', tooltipContent);
  }
}

function attachInit($dropdown) {
  const dropdown = $dropdown[0];
  dropdown[ariaPatchKey] = {};
  if ($dropdown.hasClass('custom')) return;

  // Dropdown has 2 different focusing behaviors
  // * with search input: the input is focused, and it works with aria-activedescendant pointing another sibling element.
  // * without search input (but the readonly text), the dropdown itself is focused. then the aria-activedescendant points to the element inside dropdown
  // Some desktop screen readers may change the focus, but dropdown requires that the focus must be on its primary element, then they don't work well.

  // Expected user interactions for dropdown with aria support:
  // * user can use Tab to focus in the dropdown, then the dropdown menu (list) will be shown
  // * user presses Tab on the focused dropdown to move focus to next sibling focusable element (but not the menu item)
  // * user can use arrow key Up/Down to navigate between menu items
  // * when user presses Enter:
  //    - if the menu item is clickable (eg: <a>), then trigger the click event
  //    - otherwise, the dropdown control (low-level code) handles the Enter event, hides the dropdown menu

  // TODO: multiple selection is only partially supported. Check and test them one by one in the future.

  const $textSearch = $dropdown.find('input.search').eq(0);
  const $focusable = $textSearch.length ? $textSearch : $dropdown; // the primary element for focus, see comment above
  if (!$focusable.length) return;

  // as a combobox, the input should not have autocomplete by default
  if ($textSearch.length && !$textSearch.attr('autocomplete')) {
    $textSearch.attr('autocomplete', 'off');
  }

  let $menu = $dropdown.find('> .menu');
  if (!$menu.length) {
    // some "multiple selection" dropdowns don't have a static menu element in HTML, we need to pre-create it to make it have correct aria attributes
    $menu = $('<div class="menu"></div>').appendTo($dropdown);
  }

  // There are 2 possible solutions about the role: combobox or menu.
  // The idea is that if there is an input, then it's a combobox, otherwise it's a menu.
  // Since #19861 we have prepared the "combobox" solution, but didn't get enough time to put it into practice and test before.
  const isComboBox = $dropdown.find('input').length > 0;

  dropdown[ariaPatchKey].focusableRole = isComboBox ? 'combobox' : 'menu';
  dropdown[ariaPatchKey].listPopupRole = isComboBox ? 'listbox' : '';
  dropdown[ariaPatchKey].listItemRole = isComboBox ? 'option' : 'menuitem';

  attachDomEvents($dropdown, $focusable, $menu);
  attachStaticElements($dropdown, $focusable, $menu);
}

function attachDomEvents($dropdown, $focusable, $menu) {
  const dropdown = $dropdown[0];
  // when showing, it has class: ".animating.in"
  // when hiding, it has class: ".visible.animating.out"
  const isMenuVisible = () => ($menu.hasClass('visible') && !$menu.hasClass('out')) || $menu.hasClass('in');

  // update aria attributes according to current active/selected item
  const refreshAriaActiveItem = () => {
    const menuVisible = isMenuVisible();
    $focusable.attr('aria-expanded', menuVisible ? 'true' : 'false');

    // if there is an active item, use it (the user is navigating between items)
    // otherwise use the "selected" for combobox (for the last selected item)
    const $active = $menu.find('> .item.active, > .item.selected');
    // if the popup is visible and has an active/selected item, use its id as aria-activedescendant
    if (menuVisible) {
      $focusable.attr('aria-activedescendant', $active.attr('id'));
    } else if (dropdown[ariaPatchKey].listPopupRole === 'menu') {
      // for menu, when the popup is hidden, no need to keep the aria-activedescendant, and clear the active/selected item
      $focusable.removeAttr('aria-activedescendant');
      $active.removeClass('active').removeClass('selected');
    }
  };

  $dropdown.on('keydown', (e) => {
    // here it must use keydown event before dropdown's keyup handler, otherwise there is no Enter event in our keyup handler
    if (e.key === 'Enter') {
      const dropdownCall = fomanticDropdownFn.bind($dropdown);
      let $item = dropdownCall('get item', dropdownCall('get value'));
      if (!$item) $item = $menu.find('> .item.selected'); // when dropdown filters items by input, there is no "value", so query the "selected" item
      // if the selected item is clickable, then trigger the click event.
      // we can not click any item without check, because Fomantic code might also handle the Enter event. that would result in double click.
      if ($item && ($item.is('a') || $item.hasClass('js-aria-clickable'))) $item[0].click();
    }
  });

  // use setTimeout to run the refreshAria in next tick (to make sure the Fomantic UI code has finished its work)
  // do not return any value, jQuery has return-value related behaviors.
  // when the popup is hiding, it's better to have a small "delay", because there is a Fomantic UI animation
  // without the delay for hiding, the UI will be somewhat laggy and sometimes may get stuck in the animation.
  const deferredRefreshAriaActiveItem = (delay = 0) => { setTimeout(refreshAriaActiveItem, delay) };
  dropdown[ariaPatchKey].deferredRefreshAriaActiveItem = deferredRefreshAriaActiveItem;
  $dropdown.on('keyup', (e) => { if (e.key.startsWith('Arrow')) deferredRefreshAriaActiveItem(); });

  // if the dropdown has been opened by focus, do not trigger the next click event again.
  // otherwise the dropdown will be closed immediately, especially on Android with TalkBack
  // * desktop event sequence: mousedown -> focus -> mouseup -> click
  // * mobile event sequence: focus -> mousedown -> mouseup -> click
  // Fomantic may stop propagation of blur event, use capture to make sure we can still get the event
  let ignoreClickPreEvents = 0, ignoreClickPreVisible = 0;
  dropdown.addEventListener('mousedown', () => {
    ignoreClickPreVisible += isMenuVisible() ? 1 : 0;
    ignoreClickPreEvents++;
  }, true);
  dropdown.addEventListener('focus', () => {
    ignoreClickPreVisible += isMenuVisible() ? 1 : 0;
    ignoreClickPreEvents++;
    deferredRefreshAriaActiveItem();
  }, true);
  dropdown.addEventListener('blur', () => {
    ignoreClickPreVisible = ignoreClickPreEvents = 0;
    deferredRefreshAriaActiveItem(100);
  }, true);
  dropdown.addEventListener('mouseup', () => {
    setTimeout(() => {
      ignoreClickPreVisible = ignoreClickPreEvents = 0;
      deferredRefreshAriaActiveItem(100);
    }, 0);
  }, true);
  dropdown.addEventListener('click', (e) => {
    if (isMenuVisible() &&
      ignoreClickPreVisible !== 2 && // dropdown is switch from invisible to visible
      ignoreClickPreEvents === 2 // the click event is related to mousedown+focus
    ) {
      e.stopPropagation(); // if the dropdown menu has been opened by focus, do not trigger the next click event again
    }
    ignoreClickPreEvents = ignoreClickPreVisible = 0;
  }, true);
}