kdb_brugbyen.module

<?php

use Drupal\Core\Form\FormStateInterface;

/**
 * @file
 * Integration with brugbyen.kk.dk
 */

/**
 * Implements hook_form_alter().
 */
function kdb_brugbyen_form_alter(array &$form, FormStateInterface $form_state, $form_id) {
  if (!in_array($form_id, ['eventseries_default_add_form', 'eventseries_default_edit_form'])) {
    return;
  }

  $form['#attached']['library'][] = 'kdb_brugbyen/fieldset';

  $form['#validate'][] = 'kdb_brugbyen_eventseries_default_validate';

  $form['field_bb_district']['widget']['#description'] = t('Selected "district" is used for filtering events on brugbyen.');

  // Only activate the secondary categories, target groups and tags elements
  // when district is non-empty.
  $districtIsEmpty = [':input[name="field_bb_district"]' => ['value' => '']];

  $form['field_bb_categories']['widget']['#description'] = t('Selected "category" is used for filtering events on brugbyen.');

  $form['field_bb_categories']['#states'] = [
    // We go with both invisible and disabled. Adding in disabled has the
    // sideeffect of not submitting any value, so the fields is automatically
    // cleared when district is unset.
    '!visible' => $districtIsEmpty,
    'disabled' => $districtIsEmpty,
  ];

  // Mark the required fields as such. Setting #required would cause the Form
  // API to require the fields unconditionally, but we only require them if
  // district is non empty. So we have our own validation and just add the
  // required classes to the label. As the fields are hidden when not required,
  // we don't need to do this in states (which doesn't work with Select2 and/or
  // field widgets for some reason).
  $form['field_bb_categories']['widget']['#label_attributes'] = ['class' => ['form-required', 'js-form-required']];

  $form['field_bb_target_groups']['widget']['#description'] = t('Selected "target group" is used for filtering events on brugbyen.');

  $form['field_bb_target_groups']['#states'] = [
    '!visible' => $districtIsEmpty,
    'disabled' => $districtIsEmpty,
  ];

  $form['field_bb_target_groups']['widget']['#label_attributes'] = ['class' => ['form-required', 'js-form-required']];

  $form['field_bb_tags']['widget']['#description'] = t('Selected "tag" is used for filtering events on brugbyen.');

  $form['field_bb_tags']['#states'] = [
    '!visible' => $districtIsEmpty,
    'disabled' => $districtIsEmpty,
  ];
}

/**
 * Validate handler for brugbyen data.
 *
 * Validates that categories and target_groups are provided when a district is
 * selected.
 */
function kdb_brugbyen_eventseries_default_validate(array &$form, FormStateInterface $form_state) {
  if (!empty($form_state->getValue('field_bb_district'))) {
    if (empty($form_state->getValue('field_bb_categories'))) {
      $form_state->setError(
        $form['field_bb_categories']['widget'],
        t('@name field is required.', [
          '@name' => $form['field_bb_categories']['widget']['#title'],
        ]),
      );
    }

    if (empty($form_state->getValue('field_bb_target_groups'))) {
      $form_state->setError(
        $form['field_bb_target_groups']['widget'],
        t('@name field is required.', [
          '@name' => $form['field_bb_target_groups']['widget']['#title'],
        ]),
      );
    }
  }
}