autofill.module

<?php

use Drupal\Core\Routing\RouteMatchInterface;
use \Drupal\Core\Field\WidgetInterface;
use \Drupal\Core\Field\FieldDefinitionInterface;
use \Drupal\Core\Form\FormStateInterface;
use \Drupal\Core\Field\FieldStorageDefinitionInterface;

/**
 * @file
 * Contains autofill.module.
 */

/**
 * Implements hook_help().
 */
function autofill_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    // Main module help for the autofill module.
    case 'help.page.autofill':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('A field can automatically be autofilled while typing into another one.') . '</p>';
      return $output;

    default:
  }
}

/**
 * Implements hook_field_widget_third_party_settings_form().
 */
function autofill_field_widget_third_party_settings_form(WidgetInterface $plugin, FieldDefinitionInterface $field_definition, $form_mode, array $form, FormStateInterface $form_state) {
  $element = [];

  if ($field_definition->getType() === 'string') {
    $field_name = $field_definition->getName();
    $available_source_fields = _autofill_get_available_source_fields_as_options($form, $field_name);

    $element['enabled'] = [
      '#type' => 'checkbox',
      '#title' => t('Enable Autofill from another field'),
      '#disabled' => !empty($available_source_fields) ? FALSE : TRUE,
      '#default_value' => !empty($available_source_fields) ? $plugin->getThirdPartySetting('autofill', 'enabled') : NULL,
    ];

    // Check if there are available source fields.
    if (!empty($available_source_fields)) {
      $element['source_field'] = [
        '#type' => 'select',
        '#title' => t('Autofill source field'),
        '#default_value' => $plugin->getThirdPartySetting('autofill', 'source_field'),
        '#options' => $available_source_fields,
        '#states' => [
          'visible' => [
            ':input[name="fields[' . $field_name . '][settings_edit_form][third_party_settings][autofill][enabled]"]' => ['checked' => TRUE],
          ],
        ],
      ];
    }
    else {
      $element['source_field'] = ['#markup' => t('No source field available. Please create a text field from where this field should be autofilled.')];
    }
  }


  return $element;
}

/**
 * Build an option list of available autofill source fields.
 *
 * @param array $form
 *   The currently processed form.
 * @param string $current_field_name
 *   The currently process field name.
 *
 * @return array
 *   The field name and field label as a key/value pair.
 */
function _autofill_get_available_source_fields_as_options(array $form, $current_field_name) {
  $options = [];

  $entity_type = $form['#entity_type'];
  $bundle = $form['#bundle'];

  $field_storage_definitions = \Drupal::service('entity_field.manager')->getFieldStorageDefinitions($entity_type);
  // Filter the available fields by the support field type and make sure it is
  // not the currently processed field.
  $available_entity_fields = array_filter($field_storage_definitions, function(FieldStorageDefinitionInterface $field_storage) use ($current_field_name) {
    return $field_storage->getName() !== $current_field_name && $field_storage->getType() === 'string';
  });

  $form_fields = array_intersect_key($available_entity_fields, array_flip($form['#fields']));

  /** @var \Drupal\Core\Field\FieldStorageDefinitionInterface $field */
  foreach ($form_fields as $field) {
    $label = $field->getLabel();

    // Load labels from field_config for regular fields.
    $field_configs = \Drupal::entityTypeManager()
      ->getStorage('field_config')
      ->loadByProperties([
        'field_name' => $field->getName(),
        'entity_type' => $entity_type,
        'bundle' => $bundle,
      ]);
    /** @var \Drupal\field\FieldConfigInterface $field_config */
    if ($field_config = array_pop($field_configs)) {
      $label = $field_config->getLabel();
    }
    $options[$field->getName()] = $label;
  }

  return $options;
}

/**
 * Implements hook_field_widget_form_alter().
 */
function autofill_field_widget_form_alter(&$element, FormStateInterface $form_state, $context) {
  /** @var \Drupal\Core\Field\WidgetInterface $widget */
  $widget = $context['widget'];
  /** @var \Drupal\Core\Field\FieldDefinitionInterface $field_definition */
  $field_definition = $context['items']->getFieldDefinition();
  if ($widget->getThirdPartySetting('autofill', 'enabled') && $source_field = $widget->getThirdPartySetting('autofill', 'source_field')) {
    $element['#attached']['library'][] = 'autofill/autofill';
    $element['#attached']['drupalSettings']['autofill']['field_mapping'][$field_definition->getName()] = $source_field;
  }
}