Introduce Stock quantity calculation

app/code/Magento/Inventory/Indexer/StockItem/StockItem.php

@@ -146,11 +146,17 @@ public function executeList(array $sourceItemIds)
                 ->setAlias(Alias::ALIAS_MAIN)
                 ->build();
 
-            $this->indexHandler->cleanIndex(
-                $mainIndexName,
-                new \ArrayIterator($skuList),
-                ResourceConnection::DEFAULT_CONNECTION
-            );
+            if ($this->indexStructure->isExist($mainIndexName, ResourceConnection::DEFAULT_CONNECTION)) {
+                $this->indexHandler->cleanIndex(
+                    $mainIndexName,
+                    new \ArrayIterator($skuList),
+                    ResourceConnection::DEFAULT_CONNECTION
+                );
+            } else {
+                // TODO: need to remove after creating separate indexes
+                $this->indexStructure->create($mainIndexName, ResourceConnection::DEFAULT_CONNECTION);
+            }
+
             $this->indexHandler->saveIndex(
                 $mainIndexName,
                 $this->indexDataProvider->getData($stockId, $skuList),

app/code/Magento/Inventory/Model/GetProductQuantityInStock.php

@@ -0,0 +1,53 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Inventory\Model;
+
+use Magento\Inventory\Model\ResourceModel\Reservation\ReservationQuantity;
+use Magento\Inventory\Model\ResourceModel\Stock\StockItemQuantity;
+use Magento\InventoryApi\Api\GetProductQuantityInStockInterface;
+
+/**
+ * Return Quantity of product available to be sold by Product SKU and Stock Id
+ *
+ * @see \Magento\InventoryApi\Api\GetProductQuantityInStockInterface
+ * @api
+ */
+class GetProductQuantityInStock implements GetProductQuantityInStockInterface
+{
+    /**
+     * @var StockItemQuantity
+     */
+    private $stockItemQty;
+
+    /**
+     * @var ReservationQuantity
+     */
+    private $reservationQty;
+
+    /**
+     * @param StockItemQuantity $stockItemQty
+     * @param ReservationQuantity $reservationQty
+     */
+    public function __construct(
+        StockItemQuantity $stockItemQty,
+        ReservationQuantity $reservationQty
+    ) {
+        $this->stockItemQty = $stockItemQty;
+        $this->reservationQty = $reservationQty;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function execute(string $sku, int $stockId): float
+    {
+        $productQtyInStock = $this->stockItemQty->execute($sku, $stockId) +
+            $this->reservationQty->execute($sku, $stockId);
+        return $productQtyInStock;
+    }
+}

app/code/Magento/Inventory/Model/IsProductInStock.php

@@ -0,0 +1,54 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Inventory\Model;
+
+use Magento\Inventory\Model\ResourceModel\Reservation\ReservationQuantity;
+use Magento\Inventory\Model\ResourceModel\Stock\StockItemQuantity;
+use Magento\InventoryApi\Api\IsProductInStockInterface;
+
+/**
+ * Return product availability by Product SKU and Stock Id.
+ *
+ * @see \Magento\InventoryApi\Api\GetProductQuantityInStockInterface
+ * @see \Magento\Inventory\Model\Stock\Command\IsInStockInterface
+ * @api
+ */
+class IsProductInStock implements IsProductInStockInterface
+{
+    /**
+     * @var StockItemQuantity
+     */
+    private $stockItemQty;
+
+    /**
+     * @var ReservationQuantity
+     */
+    private $reservationQty;
+
+    /**
+     * @param StockItemQuantity $stockItemQty
+     * @param ReservationQuantity $reservationQty
+     */
+    public function __construct(
+        StockItemQuantity $stockItemQty,
+        ReservationQuantity $reservationQty
+    ) {
+        $this->stockItemQty = $stockItemQty;
+        $this->reservationQty = $reservationQty;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function execute(string $sku, int $stockId): bool
+    {
+        $productQtyInStock = $this->stockItemQty->execute($sku, $stockId) +
+            $this->reservationQty->execute($sku, $stockId);
+        return $productQtyInStock > 0;
+    }
+}

app/code/Magento/Inventory/Model/Reservation.php

@@ -3,6 +3,8 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+declare(strict_types=1);
+
 namespace Magento\Inventory\Model;
 
 use Magento\InventoryApi\Api\Data\ReservationInterface;
@@ -39,6 +41,13 @@ class Reservation implements ReservationInterface
      */
     private $metadata;
 
+    /**
+     * @param int|null $reservationId
+     * @param int $stockId
+     * @param string $sku
+     * @param float $quantity
+     * @param null $metadata
+     */
     public function __construct(
         $reservationId,
         int $stockId,

app/code/Magento/Inventory/Model/Reservation/Command/ReservationsAppend.php

@@ -3,6 +3,8 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+declare(strict_types=1);
+
 namespace Magento\Inventory\Model\Reservation\Command;
 
 use Magento\Framework\Exception\CouldNotSaveException;

app/code/Magento/Inventory/Model/Reservation/ReservationBuilder.php

@@ -3,6 +3,8 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+declare(strict_types=1);
+
 namespace Magento\Inventory\Model\Reservation;
 
 use Magento\Framework\ObjectManagerInterface;

app/code/Magento/Inventory/Model/ReservationCleanupInterface.php

@@ -0,0 +1,24 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Inventory\Model;
+
+/**
+ * Extension point for reservation cleanup (Service Provider Interface - SPI).
+ * Provide own implementation of this interface if you would like to replace cleanup strategy.
+ *
+ * @api
+ */
+interface ReservationCleanupInterface
+{
+    /**
+     * Clean reservation table to prevent overloading.
+     *
+     * @return void
+     */
+    public function execute();
+}

app/code/Magento/Inventory/Model/ResourceModel/Reservation/ReservationCleanup.php

@@ -0,0 +1,54 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Inventory\Model\ResourceModel\Reservation;
+
+use Magento\Framework\App\ResourceConnection;
+use Magento\Inventory\Model\ReservationCleanupInterface;
+use Magento\Inventory\Setup\Operation\CreateReservationTable;
+use Magento\InventoryApi\Api\Data\ReservationInterface;
+
+/**
+ * @inheritdoc
+ */
+class ReservationCleanup implements ReservationCleanupInterface
+{
+    /**
+     * @var ResourceConnection
+     */
+    private $resource;
+
+    /**
+     * @param ResourceConnection $resource
+     */
+    public function __construct(
+        ResourceConnection $resource
+    ) {
+        $this->resource = $resource;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function execute()
+    {
+        $connection = $this->resource->getConnection();
+        $reservationTable = $this->resource->getTableName(CreateReservationTable::TABLE_NAME_RESERVATION);
+
+        $select = $connection->select()
+            ->from(
+                $reservationTable,
+                ['GROUP_CONCAT(' . ReservationInterface::RESERVATION_ID . ')']
+            )
+            ->group([ReservationInterface::STOCK_ID, ReservationInterface::SKU])
+            ->having('SUM(' . ReservationInterface::QUANTITY . ') = 0');
+        $groupedReservationIds = implode(',', $connection->fetchCol($select));
+
+        $condition = [ReservationInterface::RESERVATION_ID . ' IN (?)' => explode(',', $groupedReservationIds)];
+        $connection->delete($reservationTable, $condition);
+    }
+}

app/code/Magento/Inventory/Model/ResourceModel/Reservation/ReservationQuantity.php

@@ -0,0 +1,58 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Inventory\Model\ResourceModel\Reservation;
+
+use Magento\Framework\App\ResourceConnection;
+use Magento\Inventory\Setup\Operation\CreateReservationTable;
+use Magento\InventoryApi\Api\Data\ReservationInterface;
+
+/**
+ * The resource model responsible for retrieving Reservation Quantity.
+ * Used by Service Contracts that are agnostic to the Data Access Layer.
+ */
+class ReservationQuantity
+{
+    /**
+     * @var ResourceConnection
+     */
+    private $resource;
+
+    /**
+     * @param ResourceConnection $resource
+     */
+    public function __construct(
+        ResourceConnection $resource
+    ) {
+        $this->resource = $resource;
+    }
+
+    /**
+     * Given a product sku and a stock id, return reservation quantity.
+     *
+     * @param string $sku
+     * @param int $stockId
+     * @return float
+     */
+    public function execute(string $sku, int $stockId): float
+    {
+        $connection = $this->resource->getConnection();
+        $reservationTable = $this->resource->getTableName(CreateReservationTable::TABLE_NAME_RESERVATION);
+
+        $select = $connection->select()
+            ->from($reservationTable, [ReservationInterface::QUANTITY => 'SUM(' . ReservationInterface::QUANTITY . ')'])
+            ->where(ReservationInterface::SKU . ' = ?', $sku)
+            ->where(ReservationInterface::STOCK_ID . ' = ?', $stockId)
+            ->limit(1);
+
+        $reservationQty = $connection->fetchOne($select);
+        if (false === $reservationQty) {
+            $reservationQty = 0;
+        }
+        return (float)$reservationQty;
+    }
+}

app/code/Magento/Inventory/Model/ResourceModel/Reservation/SaveMultiple.php

@@ -3,6 +3,8 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+declare(strict_types=1);
+
 namespace Magento\Inventory\Model\ResourceModel\Reservation;
 
 use Magento\Framework\App\ResourceConnection;