class FieldUiTable

class FieldUiTable extends Table {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        $info = parent::getInfo();
        $info['#regions'] = [
            '' => [],
        ];
        $info['#theme'] = 'field_ui_table';
        // Prepend FieldUiTable's prerender callbacks.
        array_unshift($info['#pre_render'], [
            $this,
            'tablePreRender',
        ], [
            $this,
            'preRenderRegionRows',
        ]);
        return $info;
    }
    
    /**
     * Performs pre-render tasks on field_ui_table elements.
     *
     * @param array $elements
     *   A structured array containing two sub-levels of elements. Properties
     *   used:
     *   - #tabledrag: The value is a list of $options arrays that are passed to
     *     drupal_attach_tabledrag(). The HTML ID of the table is added to each
     *     $options array.
     *
     * @return array
     *   The $element with prepared variables ready for field-ui-table.html.twig.
     *
     * @see \Drupal\Core\Render\RendererInterface::render()
     * @see \Drupal\Core\Render\Element\Table::preRenderTable()
     */
    public static function tablePreRender($elements) {
        $js_settings = [];
        // For each region, build the tree structure from the weight and parenting
        // data contained in the flat form structure, to determine row order and
        // indentation.
        $regions = $elements['#regions'];
        $tree = [
            '' => [
                'name' => '',
                'children' => [],
            ],
        ];
        $trees = array_fill_keys(array_keys($regions), $tree);
        $parents = [];
        $children = Element::children($elements);
        $list = array_combine($children, $children);
        // Iterate on rows until we can build a known tree path for all of them.
        while ($list) {
            foreach ($list as $name) {
                $row =& $elements[$name];
                $parent = $row['parent_wrapper']['parent']['#value'];
                // Proceed if parent is known.
                if (empty($parent) || isset($parents[$parent])) {
                    // Grab parent, and remove the row from the next iteration.
                    $parents[$name] = $parent ? array_merge($parents[$parent], [
                        $parent,
                    ]) : [];
                    unset($list[$name]);
                    // Determine the region for the row.
                    $region_name = call_user_func_array($row['#region_callback'], [
                        &$row,
                    ]);
                    // Add the element in the tree.
                    $target =& $trees[$region_name][''];
                    foreach ($parents[$name] as $key) {
                        $target =& $target['children'][$key];
                    }
                    $target['children'][$name] = [
                        'name' => $name,
                        'weight' => $row['weight']['#value'],
                    ];
                    // Add tabledrag indentation to the first row cell.
                    if ($depth = count($parents[$name])) {
                        $children = Element::children($row);
                        $cell = current($children);
                        $indentation = [
                            '#theme' => 'indentation',
                            '#size' => $depth,
                            '#suffix' => isset($row[$cell]['#prefix']) ? $row[$cell]['#prefix'] : '',
                        ];
                        $row[$cell]['#prefix'] = \Drupal::service('renderer')->render($indentation);
                    }
                    // Add row id and associate JS settings.
                    $id = Html::getClass($name);
                    $row['#attributes']['id'] = $id;
                    if (isset($row['#js_settings'])) {
                        $row['#js_settings'] += [
                            'rowHandler' => $row['#row_type'],
                            'name' => $name,
                            'region' => $region_name,
                        ];
                        $js_settings[$id] = $row['#js_settings'];
                    }
                }
            }
        }
        // Determine rendering order from the tree structure.
        foreach ($regions as $region_name => $region) {
            $elements['#regions'][$region_name]['rows_order'] = array_reduce($trees[$region_name], [
                static::class,
                'reduceOrder',
            ]);
        }
        $elements['#attached']['drupalSettings']['fieldUIRowsData'] = $js_settings;
        // If the custom #tabledrag is set and there is a HTML ID, add the table's
        // HTML ID to the options and attach the behavior.
        // @see \Drupal\Core\Render\Element\Table::preRenderTable()
        if (!empty($elements['#tabledrag']) && isset($elements['#attributes']['id'])) {
            foreach ($elements['#tabledrag'] as $options) {
                $options['table_id'] = $elements['#attributes']['id'];
                drupal_attach_tabledrag($elements, $options);
            }
        }
        return $elements;
    }
    
    /**
     * Performs pre-render to move #regions to rows.
     *
     * @param array $elements
     *   A structured array containing two sub-levels of elements. Properties
     *   used:
     *   - #tabledrag: The value is a list of $options arrays that are passed to
     *     drupal_attach_tabledrag(). The HTML ID of the table is added to each
     *     $options array.
     *
     * @return array
     *   The $element with prepared variables ready for field-ui-table.html.twig.
     */
    public static function preRenderRegionRows($elements) {
        // Determine the colspan to use for region rows, by checking the number of
        // columns in the headers.
        $columns_count = 0;
        foreach ($elements['#header'] as $header) {
            $columns_count += is_array($header) && isset($header['colspan']) ? $header['colspan'] : 1;
        }
        $rows = [];
        foreach (Element::children($elements) as $key) {
            $rows[$key] = $elements[$key];
            unset($elements[$key]);
        }
        // Render rows, region by region.
        foreach ($elements['#regions'] as $region_name => $region) {
            $region_name_class = Html::getClass($region_name);
            // Add region rows.
            if (isset($region['title']) && empty($region['invisible'])) {
                $elements['#rows'][] = [
                    'class' => [
                        'region-title',
                        'region-' . $region_name_class . '-title',
                    ],
                    'no_striping' => TRUE,
                    'data' => [
                        [
                            'data' => $region['title'],
                            'colspan' => $columns_count,
                        ],
                    ],
                ];
            }
            if (isset($region['message'])) {
                $class = empty($region['rows_order']) ? 'region-empty' : 'region-populated';
                $elements['#rows'][] = [
                    'class' => [
                        'region-message',
                        'region-' . $region_name_class . '-message',
                        $class,
                    ],
                    'no_striping' => TRUE,
                    'data' => [
                        [
                            'data' => $region['message'],
                            'colspan' => $columns_count,
                        ],
                    ],
                ];
            }
            // Add form rows, in the order determined at pre-render time.
            foreach ($region['rows_order'] as $name) {
                $element = $rows[$name];
                $row = [
                    'data' => [],
                ];
                if (isset($element['#attributes'])) {
                    $row += $element['#attributes'];
                }
                // Render children as table cells.
                foreach (Element::children($element) as $cell_key) {
                    $child = $element[$cell_key];
                    // Do not render a cell for children of #type 'value'.
                    if (!(isset($child['#type']) && $child['#type'] == 'value')) {
                        $cell = [
                            'data' => $child,
                        ];
                        if (isset($child['#cell_attributes'])) {
                            $cell += $child['#cell_attributes'];
                        }
                        $row['data'][] = $cell;
                    }
                }
                $elements['#rows'][] = $row;
            }
        }
        return $elements;
    }
    
    /**
     * Determines the rendering order of an array representing a tree.
     *
     * Callback for array_reduce() within ::tablePreRender().
     *
     * @param mixed $array
     *   Holds the return value of the previous iteration; in the case of the
     *   first iteration it instead holds the value of the initial array.
     * @param mixed $a
     *   Holds the value of the current iteration.
     *
     * @return array
     *   Array where rendering order has been determined.
     */
    public static function reduceOrder($array, $a) {
        $array = !$array ? [] : $array;
        if ($a['name']) {
            $array[] = $a['name'];
        }
        if (!empty($a['children'])) {
            uasort($a['children'], [
                'Drupal\\Component\\Utility\\SortArray',
                'sortByWeightElement',
            ]);
            $array = array_merge($array, array_reduce($a['children'], [
                static::class,
                'reduceOrder',
            ]));
        }
        return $array;
    }

}