<?php

namespace Drupal\ukkb_commerce\Resolver;

use Drupal\commerce_product\Entity\ProductInterface;
use Drupal\commerce_product\Entity\ProductVariationInterface;
use Drupal\commerce_order\Entity\OrderItemInterface;
use Drupal\commerce_tax\Resolver\TaxRateResolverInterface;
use Drupal\commerce_tax\TaxZone;
use Drupal\profile\Entity\ProfileInterface;

/**
 * Returns the tax zone's default tax rate.
 */
class ProductTaxRateResolver implements TaxRateResolverInterface {

  /**
   * {@inheritdoc}
   */
  public function resolve(TaxZone $zone, OrderItemInterface $order_item, ProfileInterface $customer_profile) {
    $rates = $zone->getRates();

    // Get ordered entity.
    $item = $order_item->getPurchasedEntity();
    if (!($item instanceof ProductVariationInterface)) {
      // Item is not a product variation. Abort.
      return;
    }

    // Get ordered product.
    $product = $item->getProduct();
    if (!($product instanceof ProductInterface)) {
      // No product.
      return;
    }

    // Get product type.
    $product_type = $product->bundle();

    // Take a rate depending on product type.
    switch ($product_type) {
      case 'book':
        $rate_id = 'reduced';
        break;

      default:
        // The rate for this product type can be resolved using the default tax
        // rate resolver.
        return;
    }

    // Find a rate with this ID.
    foreach ($rates as $rate) {
      if ($rate->getId() == $rate_id) {
        return $rate;
      }
    }

    // If no rate has been found, resolving the right rate will be done by the
    // next rate resolver in line.
    return NULL;
  }

}