Limit by product commerce condition plugin with add another

GaltOrderItemProduct.php

<?php

namespace Drupal\galt\Plugin\Commerce\Condition;

use Drupal\commerce\Plugin\Commerce\Condition\ConditionBase;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Provides the product condition for order items, with add another.
 *
 * @CommerceCondition(
 *   id = "galt_order_item_product",
 *   label = @Translation("Product (add another)"),
 *   display_label = @Translation("Limit by product (add another)"),
 *   category = @Translation("Product"),
 *   entity_type = "commerce_order_item",
 * )
 */
class GaltOrderItemProduct extends ConditionBase implements ContainerFactoryPluginInterface {

  /**
   * The product storage.
   *
   * @var \Drupal\Core\Entity\EntityStorageInterface
   */
  protected $productStorage;

  /**
   * Constructs a new GaltOrderItemProduct object.
   *
   * @param array $configuration
   *   The plugin configuration, i.e. an array with configuration values keyed
   *   by configuration option name.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);

    $this->productStorage = $entity_type_manager->getStorage('commerce_product');
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('entity_type.manager')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'products' => [],
    ] + parent::defaultConfiguration();
  }

  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $form = parent::buildConfigurationForm($form, $form_state);

    $form['products'] = [
      '#prefix' => '<div id="products-wrapper">',
      '#suffix' => '</div>',
      '#type' => 'fieldset',
      '#tree' => TRUE,
      '#title' => $this->t('Products'),
    ];
    $products = [];
    $product_ids = array_column($this->configuration['products'], 'product_id');
    if (!empty($product_ids)) {
      $products = $this->productStorage->loadMultiple($product_ids);
    }
    $productCount = $form_state->get('product_count');
    if (empty($productCount)) {
      $productCount = (empty($products) ? 1 : count($products));
      $form_state->set('product_count', $productCount);
    }

    for ($delta = 0; $delta < $productCount; $delta++) {
      $form['products'][$delta] = [
        '#type' => 'entity_autocomplete',
        '#title' => $this->t('Product'),
        '#default_value' => array_shift($products),
        '#target_type' => 'commerce_product',
        '#required' => ($delta === 0) ? TRUE : FALSE,
      ];
    }

    $form['products']['add_item'] = [
      '#type' => 'submit',
      '#value' => $this->t('Add another item'),
      '#limit_validation_errors' => [],
      '#submit' => [[get_class($this), 'product_add_item']],
      '#ajax' => [
        'callback' => [get_class($this), 'product_ajax_callback'],
        'wrapper' => 'products-wrapper',
      ],
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
    parent::submitConfigurationForm($form, $form_state);
    $values = $form_state->getValue($form['#parents']);
    $this->configuration['products'] = [];
    foreach ($values['products'] as $key => $value) {
      if ($key === 'add_item') {
        continue;
      }
      if ($value) {
        $this->configuration['products'][] = [
          'product_id' => $value,
        ];
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public function evaluate(EntityInterface $entity) {
    $this->assertEntity($entity);
    /** @var \Drupal\commerce_order\Entity\OrderItemInterface $order_item */
    $order_item = $entity;
    /** @var \Drupal\commerce_product\Entity\ProductVariationInterface $purchasable_entity */
    $purchasable_entity = $order_item->getPurchasedEntity();
    if (!$purchasable_entity || $purchasable_entity->getEntityTypeId() != 'commerce_product_variation') {
      return FALSE;
    }
    $product_ids = array_column($this->configuration['products'], 'product_id');
    return in_array($purchasable_entity->getProductId(), $product_ids);
  }

  /**
   * Ajax callback.
   */
  public static function product_ajax_callback(&$form, FormStateInterface $form_state) {
    $triggering_element = $form_state->getTriggeringElement();
    $parents = array_slice($triggering_element['#array_parents'], 0, -1);
    return NestedArray::getValue($form, $parents);
  }

  /**
   * #ajax callback: Increases product text field count by one.
   *
   * Assumes the existence of a 'product_count' in $form_state.
   */
  public static function product_add_item(&$form, FormStateInterface $form_state) {
    $productCount = $form_state->get('product_count');
    $form_state->set('product_count', ($productCount+1));
    $form_state->setRebuild();
  }

}