Allow customer to specify associated product qtys when adding grouped product to cart via RESTful API

app/code/Magento/GroupedProduct/Api/Data/GroupedOptionsInterface.php

@@ -0,0 +1,45 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\GroupedProduct\Api\Data;
+
+use Magento\Framework\Api\ExtensibleDataInterface;
+
+/**
+ * Represents `product item id with qty` of a grouped product.
+ */
+interface GroupedOptionsInterface extends ExtensibleDataInterface
+{
+    /**
+     * Get associated product id
+     *
+     * @return int|null
+     */
+    public function getId(): ?int;
+
+    /**
+     * Get associated product qty
+     *
+     * @return int|null
+     */
+    public function getQty(): ?int;
+
+    /**
+     * Set extension attributes
+     *
+     * @param \Magento\GroupedProduct\Api\Data\GroupedOptionsExtensionInterface $extensionAttributes
+     * @return void
+     */
+    public function setExtensionAttributes(GroupedOptionsExtensionInterface $extensionAttributes): void;
+
+    /**
+     * Get extension attributes
+     *
+     * @return \Magento\GroupedProduct\Api\Data\GroupedOptionsExtensionInterface|null
+     */
+    public function getExtensionAttributes(): ?GroupedOptionsExtensionInterface;
+}

app/code/Magento/GroupedProduct/Model/Quote/Item/CartItemProcessor.php

@@ -0,0 +1,124 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\GroupedProduct\Model\Quote\Item;
+
+use Magento\Framework\DataObject;
+use Magento\Framework\DataObject\Factory as ObjectFactory;
+use Magento\Framework\Exception\LocalizedException;
+use Magento\GroupedProduct\Api\Data\GroupedOptionsInterface;
+use Magento\GroupedProduct\Model\Product\Type\Grouped;
+use Magento\Quote\Api\Data as QuoteApi;
+use Magento\Quote\Api\Data\CartItemInterface;
+use Magento\Quote\Model\Quote\Item\CartItemProcessorInterface;
+
+/**
+ * Converts grouped_options to super_group for the grouped product.
+ */
+class CartItemProcessor implements CartItemProcessorInterface
+{
+    private const SUPER_GROUP_CODE = 'super_group';
+
+    /**
+     * @var ObjectFactory
+     */
+    private $objectFactory;
+
+    /**
+     * @var QuoteApi\ProductOptionExtensionFactory
+     */
+    private $productOptionExtensionFactory;
+
+    /**
+     * @var QuoteApi\ProductOptionInterfaceFactory
+     */
+    private $productOptionFactory;
+
+    /**
+     * @var array|null
+     */
+    private $groupedOptions;
+
+    /**
+     * @param ObjectFactory $objectFactory
+     * @param QuoteApi\ProductOptionExtensionFactory $productOptionExtensionFactory
+     * @param QuoteApi\ProductOptionInterfaceFactory $productOptionFactory
+     */
+    public function __construct(
+        ObjectFactory $objectFactory,
+        QuoteApi\ProductOptionExtensionFactory $productOptionExtensionFactory,
+        QuoteApi\ProductOptionInterfaceFactory $productOptionFactory
+    ) {
+        $this->objectFactory = $objectFactory;
+        $this->productOptionExtensionFactory = $productOptionExtensionFactory;
+        $this->productOptionFactory = $productOptionFactory;
+    }
+
+    /**
+     * Converts the grouped_options request data into the same format as native frontend add-to-cart
+     *
+     * @param CartItemInterface $cartItem
+     * @return DataObject|null
+     */
+    public function convertToBuyRequest(CartItemInterface $cartItem): ?DataObject
+    {
+        if ($cartItem->getProductOption()
+            && $cartItem->getProductOption()->getExtensionAttributes()
+            && $cartItem->getProductOption()->getExtensionAttributes()->getGroupedOptions()
+        ) {
+            $groupedOptions = $cartItem->getProductOption()->getExtensionAttributes()->getGroupedOptions();
+            $this->groupedOptions = $groupedOptions;
+
+            return $this->objectFactory->create($this->getConvertedData($groupedOptions));
+        }
+
+        return null;
+    }
+
+    /**
+     * Returns grouped_options converted to super_group data
+     *
+     * @param GroupedOptionsInterface[] $groupedOptions
+     * @return array
+     * @throws LocalizedException
+     */
+    private function getConvertedData(array $groupedOptions): array
+    {
+        $requestData = [];
+        foreach ($groupedOptions as $item) {
+            /** @var GroupedOptionsInterface $item */
+            if ($item->getQty() === null || $item->getId() === null) {
+                throw new LocalizedException(__('Please specify id and qty for grouped options.'));
+            }
+            $requestData[self::SUPER_GROUP_CODE][$item->getId()] = $item->getQty();
+        }
+
+        return $requestData;
+    }
+
+    /**
+     * Option processor
+     *
+     * @param CartItemInterface $cartItem
+     * @return CartItemInterface
+     */
+    public function processOptions(CartItemInterface $cartItem): CartItemInterface
+    {
+        if (empty($this->groupedOptions) || $cartItem->getProductType() !== Grouped::TYPE_CODE) {
+            return $cartItem;
+        }
+
+        $extension = $this->productOptionExtensionFactory->create()
+            ->setGroupedOptions($this->groupedOptions);
+        if (!$cartItem->getProductOption()) {
+            $cartItem->setProductOption($this->productOptionFactory->create());
+        }
+        $cartItem->getProductOption()->setExtensionAttributes($extension);
+
+        return $cartItem;
+    }
+}

app/code/Magento/GroupedProduct/Model/Quote/Item/GroupedOptions.php

@@ -0,0 +1,79 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\GroupedProduct\Model\Quote\Item;
+
+use Magento\GroupedProduct\Api\Data\GroupedOptionsInterface;
+use Magento\GroupedProduct\Api\Data\GroupedOptionsExtensionInterface;
+
+/**
+ * @inheritDoc
+ */
+class GroupedOptions implements GroupedOptionsInterface
+{
+    /**
+     * @var int|null
+     */
+    private $qty;
+
+    /**
+     * @var int|null
+     */
+    private $id;
+
+    /**
+     * @var GroupedOptionsExtensionInterface|null
+     */
+    private $extensionAttributes;
+
+    /**
+     * @param int|null $id
+     * @param int|null $qty
+     * @param GroupedOptionsExtensionInterface|null $extensionAttributes
+     */
+    public function __construct(
+        ?int $id = null,
+        ?int $qty = null,
+        ?GroupedOptionsExtensionInterface $extensionAttributes = null
+    ) {
+        $this->id = $id;
+        $this->qty = $qty;
+        $this->extensionAttributes = $extensionAttributes;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getId(): ?int
+    {
+        return $this->id;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getQty(): ?int
+    {
+        return $this->qty;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function setExtensionAttributes(GroupedOptionsExtensionInterface $extensionAttributes): void
+    {
+        $this->extensionAttributes = $extensionAttributes;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getExtensionAttributes(): ?GroupedOptionsExtensionInterface
+    {
+        return $this->extensionAttributes;
+    }
+}

app/code/Magento/GroupedProduct/etc/di.xml

@@ -6,6 +6,8 @@
  */
 -->
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
+    <preference for="Magento\GroupedProduct\Api\Data\GroupedOptionsInterface" type="Magento\GroupedProduct\Model\Quote\Item\GroupedOptions" />
+
     <type name="Magento\Quote\Model\Quote\Item\RelatedProducts">
         <arguments>
             <argument name="relatedProductTypes" xsi:type="array">
@@ -105,6 +107,13 @@
             </argument>
         </arguments>
     </type>
+    <type name="Magento\Quote\Model\Quote\Item\Repository">
+        <arguments>
+            <argument name="cartItemProcessors" xsi:type="array">
+                <item name="grouped" xsi:type="object">Magento\GroupedProduct\Model\Quote\Item\CartItemProcessor\Proxy</item>
+            </argument>
+        </arguments>
+    </type>
     <type name="Magento\CatalogInventory\Observer\SaveInventoryDataObserver">
         <arguments>
             <argument name="parentItemProcessorPool" xsi:type="array">

app/code/Magento/GroupedProduct/etc/extension_attributes.xml

@@ -9,4 +9,8 @@
     <extension_attributes for="Magento\Catalog\Api\Data\ProductLinkInterface">
         <attribute code="qty" type="float" />
     </extension_attributes>
+
+    <extension_attributes for="Magento\Quote\Api\Data\ProductOptionInterface">
+        <attribute code="grouped_options" type="Magento\GroupedProduct\Api\Data\GroupedOptionsInterface[]" />
+    </extension_attributes>
 </config>