class TableDragTestForm

class TableDragTestForm extends FormBase {
    
    /**
     * The state service.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Constructs a TableDragTestForm object.
     *
     * @param \Drupal\Core\State\StateInterface $state
     *   The state service.
     */
    public function __construct(StateInterface $state) {
        $this->state = $state;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('state'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'tabledrag_test_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['table'] = [
            '#type' => 'table',
            '#header' => [
                [
                    'data' => $this->t('Text'),
                    'colspan' => 4,
                ],
                $this->t('Weight'),
            ],
            '#tabledrag' => [
                [
                    'action' => 'order',
                    'relationship' => 'sibling',
                    'group' => 'tabledrag-test-weight',
                ],
                [
                    'action' => 'match',
                    'relationship' => 'parent',
                    'group' => 'tabledrag-test-parent',
                    'subgroup' => 'tabledrag-test-parent',
                    'source' => 'tabledrag-test-id',
                    'hidden' => TRUE,
                    'limit' => 2,
                ],
                [
                    'action' => 'depth',
                    'relationship' => 'group',
                    'group' => 'tabledrag-test-depth',
                    'hidden' => TRUE,
                ],
            ],
            '#attributes' => [
                'id' => 'tabledrag-test-table',
            ],
            '#attached' => [
                'library' => [
                    'tabledrag_test/tabledrag',
                ],
            ],
        ];
        // Provide a default set of five rows.
        $rows = $this->state
            ->get('tabledrag_test_table', array_flip(range(1, 5)));
        foreach ($rows as $id => $row) {
            if (!is_array($row)) {
                $row = [];
            }
            $row += [
                'parent' => '',
                'weight' => 0,
                'depth' => 0,
                'classes' => [],
                'draggable' => TRUE,
            ];
            if (!empty($row['draggable'])) {
                $row['classes'][] = 'draggable';
            }
            $form['table'][$id] = [
                'title' => [
                    'indentation' => [
                        '#theme' => 'indentation',
                        '#size' => $row['depth'],
                    ],
                    '#plain_text' => "Row with id {$id}",
                ],
                'id' => [
                    '#type' => 'hidden',
                    '#value' => $id,
                    '#attributes' => [
                        'class' => [
                            'tabledrag-test-id',
                        ],
                    ],
                ],
                'parent' => [
                    '#type' => 'hidden',
                    '#default_value' => $row['parent'],
                    '#parents' => [
                        'table',
                        $id,
                        'parent',
                    ],
                    '#attributes' => [
                        'class' => [
                            'tabledrag-test-parent',
                        ],
                    ],
                ],
                'depth' => [
                    '#type' => 'hidden',
                    '#default_value' => $row['depth'],
                    '#attributes' => [
                        'class' => [
                            'tabledrag-test-depth',
                        ],
                    ],
                ],
                'weight' => [
                    '#type' => 'weight',
                    '#default_value' => $row['weight'],
                    '#attributes' => [
                        'class' => [
                            'tabledrag-test-weight',
                        ],
                    ],
                ],
                '#attributes' => [
                    'class' => $row['classes'],
                ],
            ];
        }
        $form['save'] = [
            '#type' => 'submit',
            '#value' => $this->t('Save'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $test_table = [];
        foreach ($form_state->getValue('table') as $row) {
            $test_table[$row['id']] = $row;
        }
        $this->state
            ->set('tabledrag_test_table', $test_table);
    }

}