<?php
/**
 *
 * Copyright © 2016 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Magento\CatalogInventory\Model\Plugin;

class AfterProductLoad
{
    /**
     * @var \Magento\CatalogInventory\Api\StockRegistryInterface
     */
    protected $stockRegistry;

    /**
     * @var \Magento\Catalog\Api\Data\ProductExtensionFactory
     */
    protected $productExtensionFactory;

    /**
     * @param \Magento\CatalogInventory\Api\StockRegistryInterface $stockRegistry
     * @param \Magento\Catalog\Api\Data\ProductExtensionFactory $productExtensionFactory
     */
    public function __construct(
        \Magento\CatalogInventory\Api\StockRegistryInterface $stockRegistry,
        \Magento\Catalog\Api\Data\ProductExtensionFactory $productExtensionFactory
    ) {
        $this->stockRegistry = $stockRegistry;
        $this->productExtensionFactory = $productExtensionFactory;
    }

    /**
     * Add stock item information to the product's extension attributes
     *
     * @param \Magento\Catalog\Model\Product $product
     * @return \Magento\Catalog\Model\Product
     */
    public function afterLoad(\Magento\Catalog\Model\Product $product)
    {
        $productExtension = $product->getExtensionAttributes();
        if ($productExtension === null) {
            $productExtension = $this->productExtensionFactory->create();
        }
        // stockItem := \Magento\CatalogInventory\Api\Data\StockItemInterface
        $productExtension->setStockItem($this->stockRegistry->getStockItem($product->getId()));
        $product->setExtensionAttributes($productExtension);
        return $product;
    }
}