MC-22213: Implementation - Merge cart

- Added resolver for merge cart

Author: Prabhu Ram

app/code/Magento/QuoteGraphQl/Model/Resolver/MergeCarts.php

@@ -0,0 +1,62 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\QuoteGraphQl\Model\Resolver;
+
+use Magento\Framework\GraphQl\Config\Element\Field;
+use Magento\Framework\GraphQl\Exception\GraphQlInputException;
+use Magento\Framework\GraphQl\Query\ResolverInterface;
+use Magento\Framework\GraphQl\Schema\Type\ResolveInfo;
+use Magento\QuoteGraphQl\Model\Cart\GetCartForUser;
+
+/**
+ * Merge Carts Resolver
+ */
+class MergeCarts implements ResolverInterface
+{
+    /**
+     * @var GetCartForUser
+     */
+    private $getCartForUser;
+
+    /**
+     * @param GetCartForUser $getCartForUser
+     */
+    public function __construct(
+        GetCartForUser $getCartForUser
+    ) {
+        $this->getCartForUser = $getCartForUser;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function resolve(Field $field, $context, ResolveInfo $info, array $value = null, array $args = null)
+    {
+        if (empty($args['source_cart_id'])) {
+            throw new GraphQlInputException(__('Required parameter "cart_id" is missing'));
+        }
+
+        if (empty($args['destination_cart_id'])) {
+            throw new GraphQlInputException(__('Required parameter "destination_cart_id" is missing'));
+        }
+
+        $guestMaskedCartId = $args['source_cart_id'];
+        $customerMaskedCartId = $args['destination_cart_id'];
+
+        $currentUserId = $context->getUserId();
+        $storeId = $storeId = (int)$context->getExtensionAttributes()->getStore()->getId();
+        // passing customerId as null enforces source cart should always be a guestcart
+        $guestCart = $this->getCartForUser->execute($guestMaskedCartId, null, $storeId);
+        $customerCart = $this->getCartForUser->execute($customerMaskedCartId, $currentUserId, $storeId);
+        $customerCart->merge($guestCart);
+
+        return [
+            'model' => $customerCart,
+        ];
+    }
+}

app/code/Magento/QuoteGraphQl/etc/schema.graphqls

@@ -19,6 +19,7 @@ type Mutation {
     setPaymentMethodOnCart(input: SetPaymentMethodOnCartInput): SetPaymentMethodOnCartOutput @resolver(class: "Magento\\QuoteGraphQl\\Model\\Resolver\\SetPaymentMethodOnCart")
     setGuestEmailOnCart(input: SetGuestEmailOnCartInput): SetGuestEmailOnCartOutput @resolver(class: "Magento\\QuoteGraphQl\\Model\\Resolver\\SetGuestEmailOnCart")
     setPaymentMethodAndPlaceOrder(input: SetPaymentMethodAndPlaceOrderInput): PlaceOrderOutput @deprecated(reason: "Should use setPaymentMethodOnCart and placeOrder mutations in single request.") @resolver(class: "\\Magento\\QuoteGraphQl\\Model\\Resolver\\SetPaymentAndPlaceOrder")
+    mergeCarts(source_cart_id: String, destination_cart_id: String): Cart! @doc(description:"Merges source cart into the destination cart") @resolver(class: "Magento\\QuoteGraphQl\\Model\\Resolver\\MergeCarts")
     placeOrder(input: PlaceOrderInput): PlaceOrderOutput @resolver(class: "\\Magento\\QuoteGraphQl\\Model\\Resolver\\PlaceOrder")
 }