Drupal: Form mode switcher for imported content

mymodule.info.yml

name: 'mymodule'
type: module
description: 'Demo module to show how to switch form modes for imported/migrated content'
package: Custom
core_version_requirement: ^10

dependencies:
  - drupal:migrate

mymodule.module

<?php

use \Drupal\Core\Entity\EntityInterface;

/**
 * @file
 * Primary module hooks for mymodule module.
 */

/**
 * Implements hook_entity_form_mode_alter().
 */
function mymodule_entity_form_mode_alter(&$form_mode, EntityInterface $entity) {
  // Switches imported events to the "imported" form mode,
  // which restricts someone from editing imported fields (because their changes
  // would be overwritten if source data gets updated).
  if ($entity->getEntityTypeId() === 'node' && $entity->bundle() === 'event') {
    if (!$entity->isNew()) {
      // Provides an "escape hatch" in case you want to disable this form mode
      // switcher.
      if (!_mymodule_event_can_switch_mode_form()) {
        return;
      }

      if (_mymodule_event_has_been_imported($entity->id())) {
        // See mymodule_entity_extra_field_info() and
        // mymodule_form_node_event_edit_form_alter() for a visual indicator
        // that this view mode has been switched.
        $form_mode = 'imported';
      }
    }
  }
}

/**
 * Determines whether the events form mode switcher is enabled.
 *
 * It is enabled by default, but someone can disable it without a code change:
 * @code
 * drush state:set mymodule.events_form_mode_switcher_enabled 0 --input-format=boolean
 * @endcode
 *
 * @return bool
 *   Returns true if this feature is enabled (default is enabled).
 *
 * @see https://www.drupal.org/docs/develop/drupal-apis/state-api/state-api-overview
 */
function _mymodule_event_can_switch_mode_form(): bool {
  return (bool) \Drupal::state()->get('mymodule.events_form_mode_switcher_enabled', TRUE);
}

/**
 * Determines whether a node was imported by the events migration.
 *
 * @param string $node_id
 *   The node's ID.
 *
 * @return bool
 *   Returns true if this node was migrated as part of migration
 *   `mymodule_events`.
 *
 * @throws \Drupal\Component\Plugin\Exception\PluginException
 */
function _mymodule_event_has_been_imported(string $node_id): bool {
  $migration_id = 'mymodule_events';

  /** @var \Drupal\migrate\Plugin\MigrationPluginManagerInterface $service */
  $service = \Drupal::service('plugin.manager.migration');
  /** @var \Drupal\migrate\Plugin\MigrationInterface $migration */
  $migration = $service->createInstance($migration_id);

  if ($migration) {
    $migration->getIdMap()->getQualifiedMapTableName();
    $source_values = $migration->getIdMap()->lookupSourceId(['nid' => $node_id]);
    return count($source_values) > 0;
  }

  return FALSE;
}

/**
 * Implements hook_entity_extra_field_info().
 */
function mymodule_entity_extra_field_info() {
  $extra = [];

  $extra['node']['event']['form']['mymodule_form_mode_override_notice'] = [
    'label' => t('MyModule: Form mode override notice'),
    'description' => t('Alerts the user that this node has been imported, so certain fields may be read-only.'),
    'visible' => TRUE,
    'weight' => 0,
  ];

  return $extra;
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function mymodule_form_node_event_edit_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  // Bail early if our notice is not even configured to display in this form
  // mode.
  if (!$form_state->get('form_display')->getComponent('mymodule_form_mode_override_notice')) {
    return;
  }

  // We only care about imported nodes.
  $form_object = $form_state->getFormObject();
  /** @var \Drupal\node\NodeInterface $node */
  $node = $form_object->getEntity();
  if (!_mymodule_event_has_been_imported($node->id())) {
    return;
  }

  // Is the form mode switcher activated?
  if (_mymodule_event_can_switch_mode_form()) {
    $message = t('This item has been imported, so some fields cannot be edited.');
  }
  else {
    $message = t('Although this item has been imported, you can edit all fields. Use caution, because your edits could be overwritten by a future import.');
  }
  $form['mymodule_form_mode_override_notice'] = [
    '#markup' => '<p><em><strong>Notice: </strong> ' . $message . '</em></p>',
  ];
}