fix: add css and js as external files

assets/css/admin.css

+.wpdesk-notice-gutenberg { display: none; }
\ No newline at end of file

assets/js/notice.js

+jQuery( document ).ready(function() {
     jQuery(document).on('click', '.notice-dismiss', function () {
         const $notice_div= jQuery(this).closest('div.notice');
         const notice_name = $notice_div.data('notice-name');
@@ -23,3 +24,4 @@ jQuery( document ).on( 'click', '.notice-dismiss-link', function() {
         jQuery(this).closest('div.notice').data('source',jQuery(this).data('source'));
         jQuery(this).closest('div.notice').find('.notice-dismiss').click();
     });    
+} );

src/WPDesk/Notice/AjaxHandler.php

@@ -22,6 +22,7 @@ class AjaxHandler implements HookablePluginDependant {
 
     const SCRIPTS_VERSION = '4';
     const SCRIPT_HANDLE = 'wpdesk_notice';
+    const SCRIPT_HANDLE_GUTENBERG = 'wpdesk_notice_gutenberg';
 
     /**
      * @var string
@@ -34,21 +35,28 @@ class AjaxHandler implements HookablePluginDependant {
      * @param string|null $assetsURL Assets URL.
      */
     public function __construct( $assetsURL = null ) {
-        $this->assetsURL = $assetsURL;
+        $this->assetsURL = $assetsURL ?? dirname(__FILE__, 5) . '/assets/';
     }
 
     /**
      * Hooks.
      */
     public function hooks() {
-        if ( $this->assetsURL ) {
         add_action( 'admin_enqueue_scripts', [ $this, 'enqueueAdminScripts' ] );
-        } else {
-            add_action( 'admin_head', [ $this, 'addScriptToAdminHead' ] );
-        }
         add_action( 'wp_ajax_wpdesk_notice_dismiss', [ $this, 'processAjaxNoticeDismiss' ] );
     }
 
+    public function isBlockEditor():bool
+    {
+		if ( !function_exists( 'get_current_screen' ) ) {
+			return false;
+		}
+
+		$screen = \get_current_screen();
+
+		return is_object($screen) ? $screen->is_block_editor() : false;
+    }
+
     /**
      * Enqueue admin scripts.
      */
@@ -60,13 +68,24 @@ class AjaxHandler implements HookablePluginDependant {
             self::SCRIPTS_VERSION
         );
         wp_enqueue_script( self::SCRIPT_HANDLE );
-    }
 
-    /**
-     * Add Java Script to admin header.
-     */
-    public function addScriptToAdminHead() {
-        include __DIR__ . '/views/admin-head-js.php';
+        if($this->isBlockEditor()){
+            wp_register_script(
+                self::SCRIPT_HANDLE,
+                trailingslashit( $this->assetsURL ) . 'js/gutenberg.js',
+                [ 'jquery' ],
+                self::SCRIPTS_VERSION
+            );
+            wp_enqueue_script( self::SCRIPT_HANDLE );
+        }else{
+            wp_register_style(
+                self::SCRIPT_HANDLE,
+                trailingslashit( $this->assetsURL ) . 'css/admin.css',
+                [],
+                self::SCRIPTS_VERSION
+            );
+            wp_enqueue_style( self::SCRIPT_HANDLE );
+        }
     }
 
     /**

src/WPDesk/Notice/Notice.php

@@ -92,20 +92,6 @@ class Notice
         $this->addAction();
     }
 
-    /**
-     * @return bool
-     */
-    public function isBlockEditor()
-    {
-		if ( !function_exists( 'get_current_screen' ) ) {
-			require_once ABSPATH . '/wp-admin/includes/screen.php';
-		}
-
-		$screen = \get_current_screen();
-
-		return is_object($screen) ? $screen->is_block_editor() : false;
-    }
-
     /**
      * @return string
      */
@@ -186,7 +172,6 @@ class Notice
                 [$this, 'showNotice'],
                 self::ADMIN_FOOTER_BASE_PRIORITY + intval($this->priority)
             );
-			add_action('admin_head', [$this,'addGutenbergScript']);
             $this->actionAdded = true;
         }
     }
@@ -207,16 +192,6 @@ class Notice
         }
     }
 
-    /**
-     * Enqueue admin scripts.
-     */
-    public function addGutenbergScript()
-    {
-		if ($this->isBlockEditor()) {
-			include_once __DIR__ . '/views/admin-head-js-gutenberg.php';
-		}
-    }
-
     /**
      * Add attribute.
      *

tests/codeception/tests/integration/AjaxHandlerTest.php

@@ -48,10 +48,6 @@ class AjaxHandlerTest extends WPTestCase {
 		$ajaxHandler = new AjaxHandler();
 		$ajaxHandler->hooks();
 
-		$this->assertEquals(
-			self::WP_DEFAULT_PRIORITY,
-			has_action( 'admin_head', [ $ajaxHandler, 'addScriptToAdminHead' ] )
-		);
 		$this->assertEquals(
 			self::WP_DEFAULT_PRIORITY,
 			has_action( 'wp_ajax_wpdesk_notice_dismiss', [ $ajaxHandler, 'processAjaxNoticeDismiss' ] )
@@ -73,20 +69,6 @@ class AjaxHandlerTest extends WPTestCase {
 		);
 	}
 
-	public function testAddScriptToAdminHead() {
-		$ajaxHandler = new AjaxHandler();
-		$ajaxHandler->hooks();
-
-		$this->expectOutputString( '<script type="text/javascript">'
-                                   . "\n    "
-                                   . file_get_contents( __DIR__ . '/../../../../assets/js/notice.js' )
-                                   . '</script>
-'
-		);
-
-		$ajaxHandler->addScriptToAdminHead();
-	}
-
     public function testProcessAjaxNoticeDismiss() {
         $user_name = 'test_user';
         $random_password = wp_generate_password( $length = 12, $include_standard_special_chars = false );