Fix double sorting for some attribute, fix configurable products issue

Model/Indexer/Stock/Configurable.php

@@ -0,0 +1,38 @@
+<?php
+declare(strict_types=1);
+
+namespace GhoSter\OutOfStockAtLast\Model\Indexer\Stock;
+
+use Magento\ConfigurableProduct\Model\ResourceModel\Indexer\Stock\Configurable as DefaultIndexer;
+use Magento\Framework\DB\Select;
+
+class Configurable extends DefaultIndexer
+{
+    /**
+     * @inheritdoc
+     */
+    protected function _getStockStatusSelect($entityIds = null, $usePrimaryTable = false)
+    {
+        $select = parent::_getStockStatusSelect($entityIds, $usePrimaryTable);
+        $this->_autoCalculate($select);
+
+        return $select;
+    }
+
+    /**
+     * Calculate depends on simple products
+     *
+     * @param Select $select
+     * @throws \Zend_Db_Select_Exception
+     */
+    private function _autoCalculate($select)
+    {
+        $columns = $select->getPart(Select::COLUMNS);
+        foreach ($columns as &$column) {
+            if (isset($column[2]) && $column[2] == 'qty') {
+                $column[1] = new \Zend_Db_Expr('SUM(IF(i.stock_status > 0, i.qty, 0))');
+            }
+        }
+        $select->setPart(Select::COLUMNS, $columns);
+    }
+}

Plugin/Model/ResourceModel/Product/CollectionPlugin.php

@@ -85,8 +85,8 @@ public function aroundSetOrder(
      */
     private function applyOutOfStockAtLastOrders(Collection $collection)
     {
-        if (!$collection->getFlag('is_sorted_by_oos')) {
-            $collection->setFlag('is_sorted_by_oos', true);
+        if (!$collection->getFlag('sorted_by_oos_flag')) {
+            $collection->setFlag('sorted_by_oos_flag', true);
             $collection->setOrder('out_of_stock_at_last', Select::SQL_DESC);
         }
     }
@@ -110,4 +110,27 @@ public function beforeAddOrder(
 
         return $result ?? [$attribute, $dir];
     }
+
+    /**
+     * Prevent double sorting by some attribute.
+     *
+     * @param Collection $collection
+     * @param callable $proceed
+     * @param string $attribute
+     * @param string $dir
+     * @return Collection
+     */
+    public function aroundAddAttributeToSort(
+        Collection $collection,
+        callable $proceed,
+        string $attribute,
+        string $dir = Collection::SORT_ORDER_ASC
+    ): Collection {
+        if (!$collection->getFlag(sprintf('sorted_by_%s_attribute', $attribute))) {
+            $collection->setFlag(sprintf('sorted_by_%s_attribute', $attribute), true);
+            $proceed($attribute, $dir);
+        }
+
+        return $collection;
+    }
 }

etc/di.xml

@@ -28,4 +28,12 @@
         <plugin sortOrder="10" name="GhoSter_OutOfStockAtLast::mark_apply_flag"
                 type="GhoSter\OutOfStockAtLast\Plugin\Model\ResourceModel\Fulltext\Collection\SearchResultApplierPlugin"/>
     </type>
+
+    <type name="Magento\Catalog\Model\ProductTypes\Config\Reader">
+        <arguments>
+            <argument name="idAttributes" xsi:type="array">
+                <item name="/config/type/stockIndexerModel" xsi:type="string"/>
+            </argument>
+        </arguments>
+    </type>
 </config>

etc/product_types.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0"?>
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Catalog:etc/product_types.xsd">
+    <type name="configurable" label="Configurable Product" modelInstance="Magento\ConfigurableProduct\Model\Product\Type\Configurable">
+        <stockIndexerModel instance="GhoSter\OutOfStockAtLast\Model\Indexer\Stock\Configurable" />
+    </type>
+</config>