Add theme favicons to S3

Model/Theme/Design/Backend/Favicon/Plugin.php

@@ -0,0 +1,53 @@
+<?php
+namespace Thai\S3\Model\Theme\Design\Backend\Favicon;
+
+use Magento\MediaStorage\Helper\File\Storage\Database;
+use Magento\Theme\Model\Design\Backend\Favicon;
+use Thai\S3\Helper\Data;
+
+/**
+ * Plugin for Favicon.
+ *
+ * @see Favicon
+ */
+class Plugin
+{
+    /**
+     * @var Data
+     */
+    private $helper;
+
+    /**
+     * @var Database
+     */
+    private $database;
+
+    /**
+     * @param Data $helper
+     * @param Database $database
+     */
+    public function __construct(
+        Data $helper,
+        Database $database
+    )
+    {
+        $this->helper = $helper;
+        $this->database = $database;
+    }
+
+    /**
+     * @param Favicon $subject
+     * @param Favicon $result
+     * @return Favicon
+     */
+    public function afterBeforeSave(Favicon $subject, Favicon $result)
+    {
+        if ($this->helper->checkS3Usage()) {
+            $imgFile = $subject::UPLOAD_DIR . '/' . $subject->getValue();
+            $relativeImgFile = $this->database->getMediaRelativePath($imgFile);
+            $this->database->getStorageDatabaseModel()->saveFile($relativeImgFile);
+        }
+
+        return $result;
+    }
+}

etc/di.xml

@@ -63,4 +63,7 @@
     <type name="Magento\Theme\Model\Design\Backend\Logo">
         <plugin name="thai_s3_model_theme_design_backend_logo_plugin" type="Thai\S3\Model\Theme\Design\Backend\Logo\Plugin" />
     </type>
+    <type name="Magento\Theme\Model\Design\Backend\Favicon">
+        <plugin name="thai_s3_model_theme_design_backend_favicon_plugin" type="Thai\S3\Model\Theme\Design\Backend\Favicon\Plugin" />
+    </type>
 </config>