trait CustomerFormTrait in Commerce Core 8.2

trait CustomerFormTrait {

  /**
   * Builds the customer form.
   *
   * @param array $form
   *   The parent form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   * @param \Drupal\commerce_order\Entity\OrderInterface $order
   *   The current order, if known.
   *
   * @return array
   *   The parent form with the customer form elements added.
   */
  public function buildCustomerForm(array $form, FormStateInterface $form_state, OrderInterface $order = NULL) {
    $selected_customer_type = $form_state
      ->getValue([
      'customer_type',
    ], 'existing');
    $wrapper_id = Html::getUniqueId('customer-fieldset-wrapper');
    $form['customer'] = [
      '#type' => 'fieldset',
      '#title' => t('Customer'),
      '#prefix' => '<div id="' . $wrapper_id . '">',
      '#suffix' => '</div>',
    ];
    $form['customer']['customer_type'] = [
      '#type' => 'radios',
      '#title' => t('Order for'),
      '#title_display' => 'invisible',
      '#attributes' => [
        'class' => [
          'container-inline',
        ],
      ],
      '#required' => TRUE,
      '#options' => [
        'existing' => t('Existing customer'),
        'new' => t('New customer'),
      ],
      '#default_value' => $selected_customer_type,
      '#ajax' => [
        'callback' => [
          $this,
          'customerFormAjax',
        ],
        'wrapper' => $wrapper_id,
      ],
    ];
    if ($selected_customer_type == 'existing') {
      $form['customer']['uid'] = [
        '#type' => 'entity_autocomplete',
        '#title' => t('Search'),
        '#attributes' => [
          'class' => [
            'container-inline',
          ],
        ],
        '#placeholder' => t('Search by username or email address'),
        '#target_type' => 'user',
        '#required' => TRUE,
        '#selection_settings' => [
          'match_operator' => 'CONTAINS',
          'include_anonymous' => FALSE,
        ],
      ];
    }
    else {

      // New customer.
      $form['customer']['uid'] = [
        '#type' => 'value',
        '#value' => 0,
      ];
      $form['customer']['mail'] = [
        '#type' => 'email',
        '#title' => t('Email'),
        '#required' => TRUE,
      ];
      $form['customer']['password'] = [
        '#type' => 'container',
      ];
      $form['customer']['password']['generate'] = [
        '#type' => 'checkbox',
        '#title' => t('Generate password'),
        '#default_value' => 1,
      ];

      // The password_confirm element needs to be wrapped in order for #states
      // to work properly. See https://www.drupal.org/node/1427838.
      $form['customer']['password']['password_confirm_wrapper'] = [
        '#type' => 'container',
        '#states' => [
          'visible' => [
            ':input[name="generate"]' => [
              'checked' => FALSE,
            ],
          ],
        ],
      ];

      // We cannot make this required due to HTML5 validation.
      $form['customer']['password']['password_confirm_wrapper']['pass'] = [
        '#type' => 'password_confirm',
        '#size' => 25,
      ];
      $form['customer']['notify'] = [
        '#type' => 'checkbox',
        '#title' => t('Notify user of new account'),
      ];
    }
    return $form;
  }

  /**
   * Ajax callback.
   */
  public function customerFormAjax(array $form, FormStateInterface $form_state) {
    return $form['customer'];
  }

  /**
   * Submit handler for the customer select form.
   *
   * @param array $form
   *   The parent form.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The current state of the form.
   */
  public function submitCustomerForm(array &$form, FormStateInterface $form_state) {
    $values = $form_state
      ->getValues();
    if ($values['customer_type'] == 'existing') {
      $values['mail'] = User::load($values['uid'])
        ->getEmail();
    }
    else {
      $user = User::create([
        'name' => $values['mail'],
        'mail' => $values['mail'],
        'pass' => $values['generate'] ? user_password() : $values['pass'],
        'status' => TRUE,
      ]);
      $user
        ->save();
      $values['uid'] = $user
        ->id();
      if ($values['notify']) {
        _user_mail_notify('register_admin_created', $user);
      }
    }
    $form_state
      ->setValues($values);
  }

}