class EntityForm

class EntityForm extends FormBase implements EntityFormInterface {

  /**
   * The name of the current operation.
   *
   * Subclasses may use this to implement different behaviors depending on its
   * value.
   *
   * @var string
   */
  protected $operation;

  /**
   * The module handler service.
   *
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected $moduleHandler;

  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * The entity being used by this form.
   *
   * @var \Drupal\Core\Entity\EntityInterface
   */
  protected $entity;

  /**
   * {@inheritdoc}
   */
  public function setOperation($operation) {

    // If NULL is passed, do not overwrite the operation.
    if ($operation) {
      $this->operation = $operation;
    }
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public function getBaseFormId() {

    // Assign ENTITY_TYPE_form as base form ID to invoke corresponding
    // hook_form_alter(), #validate, #submit, and #theme callbacks, but only if
    // it is different from the actual form ID, since callbacks would be invoked
    // twice otherwise.
    $base_form_id = $this->entity
      ->getEntityTypeId() . '_form';
    if ($base_form_id == $this
      ->getFormId()) {
      $base_form_id = NULL;
    }
    return $base_form_id;
  }

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    $form_id = $this->entity
      ->getEntityTypeId();
    if ($this->entity
      ->getEntityType()
      ->hasKey('bundle')) {
      $form_id .= '_' . $this->entity
        ->bundle();
    }
    if ($this->operation != 'default') {
      $form_id = $form_id . '_' . $this->operation;
    }
    return $form_id . '_form';
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {

    // During the initial form build, add this form object to the form state and
    // allow for initial preparation before form building and processing.
    if (!$form_state
      ->has('entity_form_initialized')) {
      $this
        ->init($form_state);
    }

    // Ensure that edit forms have the correct cacheability metadata so they can
    // be cached.
    if (!$this->entity
      ->isNew()) {
      \Drupal::service('renderer')
        ->addCacheableDependency($form, $this->entity);
    }

    // Retrieve the form array using the possibly updated entity in form state.
    $form = $this
      ->form($form, $form_state);

    // Retrieve and add the form actions array.
    $actions = $this
      ->actionsElement($form, $form_state);
    if (!empty($actions)) {
      $form['actions'] = $actions;
    }
    return $form;
  }

  /**
   * Initialize the form state and the entity before the first form build.
   */
  protected function init(FormStateInterface $form_state) {

    // Flag that this form has been initialized.
    $form_state
      ->set('entity_form_initialized', TRUE);

    // Prepare the entity to be presented in the entity form.
    $this
      ->prepareEntity();

    // Invoke the prepare form hooks.
    $this
      ->prepareInvokeAll('entity_prepare_form', $form_state);
    $this
      ->prepareInvokeAll($this->entity
      ->getEntityTypeId() . '_prepare_form', $form_state);
  }

  /**
   * Gets the actual form array to be built.
   *
   * @see \Drupal\Core\Entity\EntityForm::processForm()
   * @see \Drupal\Core\Entity\EntityForm::afterBuild()
   */
  public function form(array $form, FormStateInterface $form_state) {

    // Add #process and #after_build callbacks.
    $form['#process'][] = '::processForm';
    $form['#after_build'][] = '::afterBuild';
    return $form;
  }

  /**
   * Process callback: assigns weights and hides extra fields.
   *
   * @see \Drupal\Core\Entity\EntityForm::form()
   */
  public function processForm($element, FormStateInterface $form_state, $form) {

    // If the form is cached, process callbacks may not have a valid reference
    // to the entity object, hence we must restore it.
    $this->entity = $form_state
      ->getFormObject()
      ->getEntity();
    return $element;
  }

  /**
   * Form element #after_build callback: Updates the entity with submitted data.
   *
   * Updates the internal $this->entity object with submitted values when the
   * form is being rebuilt (e.g. submitted via AJAX), so that subsequent
   * processing (e.g. AJAX callbacks) can rely on it.
   */
  public function afterBuild(array $element, FormStateInterface $form_state) {

    // Rebuild the entity if #after_build is being called as part of a form
    // rebuild, i.e. if we are processing input.
    if ($form_state
      ->isProcessingInput()) {
      $this->entity = $this
        ->buildEntity($element, $form_state);
    }
    return $element;
  }

  /**
   * Returns the action form element for the current entity form.
   */
  protected function actionsElement(array $form, FormStateInterface $form_state) {
    $element = $this
      ->actions($form, $form_state);
    if (isset($element['delete'])) {

      // Move the delete action as last one, unless weights are explicitly
      // provided.
      $delete = $element['delete'];
      unset($element['delete']);
      $element['delete'] = $delete;
      $element['delete']['#button_type'] = 'danger';
    }
    if (isset($element['submit'])) {

      // Give the primary submit button a #button_type of primary.
      $element['submit']['#button_type'] = 'primary';
    }
    $count = 0;
    foreach (Element::children($element) as $action) {
      $element[$action] += [
        '#weight' => ++$count * 5,
      ];
    }
    if (!empty($element)) {
      $element['#type'] = 'actions';
    }
    return $element;
  }

  /**
   * Returns an array of supported actions for the current entity form.
   *
   * This function generates a list of Form API elements which represent
   * actions supported by the current entity form.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @return array
   *   An array of supported Form API action elements keyed by name.
   *
   * @todo Consider introducing a 'preview' action here, since it is used by
   *   many entity types.
   */
  protected function actions(array $form, FormStateInterface $form_state) {

    // @todo Consider renaming the action key from submit to save. The impacts
    //   are hard to predict. For example, see
    //   \Drupal\language\Element\LanguageConfiguration::processLanguageConfiguration().
    $actions['submit'] = [
      '#type' => 'submit',
      '#value' => $this
        ->t('Save'),
      '#submit' => [
        '::submitForm',
        '::save',
      ],
    ];
    if (!$this->entity
      ->isNew() && $this->entity
      ->hasLinkTemplate('delete-form')) {
      $route_info = $this->entity
        ->toUrl('delete-form');
      if ($this
        ->getRequest()->query
        ->has('destination')) {
        $query = $route_info
          ->getOption('query');
        $query['destination'] = $this
          ->getRequest()->query
          ->get('destination');
        $route_info
          ->setOption('query', $query);
      }
      $actions['delete'] = [
        '#type' => 'link',
        '#title' => $this
          ->t('Delete'),
        '#access' => $this->entity
          ->access('delete'),
        '#attributes' => [
          'class' => [
            'button',
            'button--danger',
            'use-ajax',
          ],
          'data-dialog-type' => 'modal',
          'data-dialog-options' => Json::encode([
            'width' => 880,
          ]),
        ],
        '#url' => $route_info,
        '#attached' => [
          'library' => [
            'core/drupal.dialog.ajax',
          ],
        ],
      ];
    }
    return $actions;
  }

  /**
   * {@inheritdoc}
   *
   * This is the default entity object builder function. It is called before any
   * other submit handler to build the new entity object to be used by the
   * following submit handlers. At this point of the form workflow the entity is
   * validated and the form state can be updated, this way the subsequently
   * invoked handlers can retrieve a regular entity object to act on. Generally
   * this method should not be overridden unless the entity requires the same
   * preparation for two actions, see \Drupal\comment\CommentForm for an example
   * with the save and preview actions.
   *
   * @param array $form
   *   An associative array containing the structure of the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {

    // Remove button and internal Form API values from submitted values.
    $form_state
      ->cleanValues();
    $this->entity = $this
      ->buildEntity($form, $form_state);
  }

  /**
   * {@inheritdoc}
   */
  public function save(array $form, FormStateInterface $form_state) {
    return $this->entity
      ->save();
  }

  /**
   * {@inheritdoc}
   */
  public function buildEntity(array $form, FormStateInterface $form_state) {
    $entity = clone $this->entity;
    $this
      ->copyFormValuesToEntity($entity, $form, $form_state);

    // Invoke all specified builders for copying form values to entity
    // properties.
    if (isset($form['#entity_builders'])) {
      foreach ($form['#entity_builders'] as $function) {
        call_user_func_array($form_state
          ->prepareCallback($function), [
          $entity
            ->getEntityTypeId(),
          $entity,
          &$form,
          &$form_state,
        ]);
      }
    }
    return $entity;
  }

  /**
   * Copies top-level form values to entity properties.
   *
   * This should not change existing entity properties that are not being edited
   * by this form.
   *
   * @param \Drupal\Core\Entity\EntityInterface $entity
   *   The entity the current form should operate upon.
   * @param array $form
   *   A nested array of form elements comprising the form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   *
   * @see \Drupal\Core\Form\ConfigFormBase::copyFormValuesToConfig()
   */
  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
    $values = $form_state
      ->getValues();
    if ($this->entity instanceof EntityWithPluginCollectionInterface) {

      // Do not manually update values represented by plugin collections.
      $values = array_diff_key($values, $this->entity
        ->getPluginCollections());
    }

    // @todo This relies on a method that only exists for config and content
    //   entities, in a different way. Consider moving this logic to a config
    //   entity specific implementation.
    foreach ($values as $key => $value) {
      $entity
        ->set($key, $value);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function getEntity() {
    return $this->entity;
  }

  /**
   * {@inheritdoc}
   */
  public function setEntity(EntityInterface $entity) {
    $this->entity = $entity;
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public function getEntityFromRouteMatch(RouteMatchInterface $route_match, $entity_type_id) {
    if ($route_match
      ->getRawParameter($entity_type_id) !== NULL) {
      $entity = $route_match
        ->getParameter($entity_type_id);
    }
    else {
      $values = [];

      // If the entity has bundles, fetch it from the route match.
      $entity_type = $this->entityTypeManager
        ->getDefinition($entity_type_id);
      if ($bundle_key = $entity_type
        ->getKey('bundle')) {
        if (($bundle_entity_type_id = $entity_type
          ->getBundleEntityType()) && $route_match
          ->getRawParameter($bundle_entity_type_id)) {
          $values[$bundle_key] = $route_match
            ->getParameter($bundle_entity_type_id)
            ->id();
        }
        elseif ($route_match
          ->getRawParameter($bundle_key)) {
          $values[$bundle_key] = $route_match
            ->getParameter($bundle_key);
        }
      }
      $entity = $this->entityTypeManager
        ->getStorage($entity_type_id)
        ->create($values);
    }
    return $entity;
  }

  /**
   * Prepares the entity object before the form is built first.
   */
  protected function prepareEntity() {
  }

  /**
   * Invokes the specified prepare hook variant.
   *
   * @param string $hook
   *   The hook variant name.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  protected function prepareInvokeAll($hook, FormStateInterface $form_state) {
    $this->moduleHandler
      ->invokeAllWith($hook, function (callable $hook, string $module) use ($form_state) {

      // Ensure we pass an updated translation object and form display at
      // each invocation, since they depend on form state which is alterable.
      $hook($this->entity, $this->operation, $form_state);
    });
  }

  /**
   * {@inheritdoc}
   */
  public function getOperation() {
    return $this->operation;
  }

  /**
   * {@inheritdoc}
   */
  public function setModuleHandler(ModuleHandlerInterface $module_handler) {
    $this->moduleHandler = $module_handler;
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public function setEntityTypeManager(EntityTypeManagerInterface $entity_type_manager) {
    $this->entityTypeManager = $entity_type_manager;
    return $this;
  }

}