MAGETWO-36282: Refactor MySql search indexer to use indexer interface

 - MAGETWO-39532: Refactor Engine prepareData method

 - Reverted EngineProvider

Author: aohorodnyk

app/code/Magento/CatalogSearch/Model/Indexer/Fulltext/Action/Full.php

@@ -171,7 +171,7 @@ public function __construct(
         \Magento\Framework\Search\Request\Config $searchRequestConfig,
         \Magento\Catalog\Model\Product\Attribute\Source\Status $catalogProductStatus,
         \Magento\Catalog\Model\Resource\Product\Attribute\CollectionFactory $productAttributeCollectionFactory,
-        \Magento\CatalogSearch\Model\Resource\Engine $engine,
+        \Magento\CatalogSearch\Model\Resource\EngineProvider $engineProvider,
         \Magento\CatalogSearch\Model\Indexer\IndexerHandlerFactory $indexHandlerFactory,
         \Magento\Framework\Event\ManagerInterface $eventManager,
         \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig,
@@ -192,7 +192,7 @@ public function __construct(
         $this->eventManager = $eventManager;
         $this->scopeConfig = $scopeConfig;
         $this->storeManager = $storeManager;
-        $this->engine = $engine;
+        $this->engine = $engineProvider->get();
         $configData = $indexerConfig->getIndexer(Fulltext::INDEXER_ID);
         $this->indexHandler = $indexHandlerFactory->create(['data' => $configData]);
         $this->dateTime = $dateTime;

app/code/Magento/CatalogSearch/Model/Resource/EngineProvider.php

@@ -0,0 +1,88 @@
+<?php
+/**
+ * Copyright © 2015 Magento. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+/**
+ * Catalog Search engine provider
+ */
+namespace Magento\CatalogSearch\Model\Resource;
+
+use Magento\Store\Model\ScopeInterface;
+
+class EngineProvider
+{
+    const CONFIG_ENGINE_PATH = 'catalog/search/engine';
+
+    /**
+     * @var \Magento\CatalogSearch\Model\Resource\EngineInterface
+     */
+    protected $engine;
+
+    /**
+     * @var \Magento\Framework\App\Config\ScopeConfigInterface
+     */
+    protected $scopeConfig;
+
+    /**
+     * @var \Magento\Framework\ObjectManagerInterface
+     */
+    private $objectManager;
+
+    /**
+     * Pool of existing engines
+     *
+     * @var array
+     */
+    private $enginePool;
+
+    /**
+     * @param \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
+     * @param \Magento\Framework\ObjectManagerInterface $objectManager
+     * @param array $engines
+     */
+    public function __construct(
+        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig,
+        \Magento\Framework\ObjectManagerInterface $objectManager,
+        array $engines
+    ) {
+        $this->scopeConfig = $scopeConfig;
+        $this->objectManager = $objectManager;
+        $this->enginePool = $engines;
+    }
+
+    /**
+     * Get engine singleton
+     *
+     * @return EngineInterface
+     */
+    public function get()
+    {
+        if (!$this->engine) {
+            $currentEngine = $this->scopeConfig->getValue(self::CONFIG_ENGINE_PATH, ScopeInterface::SCOPE_STORE);
+            if (!isset($this->enginePool[$currentEngine])) {
+                throw new \LogicException(
+                    'There is no such engine: ' . $currentEngine
+                );
+            }
+            $engineClassName = $this->enginePool[$currentEngine];
+
+            $engine = $this->objectManager->create($engineClassName);
+            if (false === $engine instanceof \Magento\CatalogSearch\Model\Resource\EngineInterface) {
+                throw new \LogicException(
+                    $engineClassName . ' doesn\'t implement \Magento\CatalogSearch\Model\Resource\EngineInterface'
+                );
+            }
+
+            if ($engine && !$engine->isAvailable()) {
+                throw new \LogicException(
+                    'Engine is not available: ' . $currentEngine
+                );
+            }
+            $this->engine = $engine;
+        }
+
+        return $this->engine;
+    }
+}

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

@@ -219,6 +219,13 @@
             <argument name="attributePrefix" xsi:type="const">Magento\CatalogSearch\Model\Resource\Engine::ATTRIBUTE_PREFIX</argument>
         </arguments>
     </type>
+    <type name="Magento\CatalogSearch\Model\Resource\EngineProvider">
+        <arguments>
+            <argument name="engines" xsi:type="array">
+                <item name="mysql" xsi:type="string">Magento\CatalogSearch\Model\Resource\Engine</item>
+            </argument>
+        </arguments>
+    </type>
     <type name="Magento\Search\Model\AdapterFactory">
         <arguments>
             <argument name="path" xsi:type="const">Magento\CatalogSearch\Model\Resource\EngineInterface::CONFIG_ENGINE_PATH</argument>