fix phpcs

inc/Engine/Common/Cache/CacheInterface.php

@@ -33,4 +33,11 @@ public function get_root_path(): string;
 	 * @return string
 	 */
 	public function generate_path( string $url ): string;
+
+	/**
+	 * Wipes the whole cache directory .
+	 *
+	 * @return bool True on success and false on failure.
+	 */
+	public function full_clear(): bool;
 }

inc/Engine/Common/Cache/FilesystemCache.php

@@ -103,6 +103,20 @@ public function clear() {
 		return true;
 	}
 
+	/**
+	 * Clear the whole background-css directory.
+	 *
+	 * @return bool True on success and false on failure.
+	 */
+	public function full_clear(): bool {
+		$base_path = $this->get_base_path();
+		if ( ! $this->filesystem->exists( $base_path ) ) {
+			return false;
+		}
+		rocket_rrmdir( $base_path, [], $this->filesystem );
+		return true;
+	}
+
 	/**
 	 * Obtains multiple cache items by their unique keys.
 	 *
@@ -226,11 +240,20 @@ public function is_accessible(): bool {
 	}
 
 	/**
-	 * Get root path from the cache.
+	 * Get root path from the cache (including current blog ID) with trailing slash.
 	 *
 	 * @return string
 	 */
 	public function get_root_path(): string {
+		return $this->get_base_path() . get_current_blog_id() . '/';
+	}
+
+	/**
+	 * Get base path from the cache (/cache/background-css/) with trailing slash.
+	 *
+	 * @return string
+	 */
+	private function get_base_path(): string {
 		return rtrim( _rocket_normalize_path( rocket_get_constant( 'WP_ROCKET_CACHE_ROOT_PATH' ) ) . $this->root_folder, '/' ) . '/';
 	}
 }

inc/Engine/Common/ExtractCSS/ServiceProvider.php

@@ -41,7 +41,7 @@ public function register(): void {
 		 *
 		 * @param string $root Background CSS cache folder.
 		 */
-		$root = apply_filters( 'rocket_lazyload_css_cache_root', 'background-css/' . get_current_blog_id() );
+		$root = apply_filters( 'rocket_lazyload_css_cache_root', 'background-css/' );
 		$this->getContainer()->add( 'lazyload_css_cache', FilesystemCache::class )
 			->addArgument( $root );
 		$this->getContainer()->addShared( 'common_extractcss_subscriber', Subscriber::class );

inc/Engine/Media/Lazyload/CSS/Admin/Subscriber.php

@@ -34,6 +34,7 @@ public static function get_subscribed_events() {
 			'rocket_meta_boxes_fields'       => [ 'add_meta_box', 8 ],
 			'admin_notices'                  => 'maybe_add_error_notice',
 			'rocket_safe_mode_reset_options' => 'add_option_safemode',
+			'wp_rocket_upgrade'              => [ 'clear_background_css_with_upgrade', 10, 2 ],
 		];
 	}
 
@@ -79,4 +80,19 @@ public function add_option_safemode( array $options ) {
 		$options['lazyload_css_bg_img'] = 0;
 		return $options;
 	}
+
+	/**
+	 * Upgrade callback.
+	 *
+	 * @param string $new_version Plugin new version.
+	 * @param string $old_version Plugin old version.
+	 * @return void
+	 */
+	public function clear_background_css_with_upgrade( $new_version, $old_version ) {
+		if ( version_compare( $old_version, '3.18', '>' ) ) {
+			return;
+		}
+		// Completely clear background-css directory.
+		$this->cache->full_clear();
+	}
 }

inc/Engine/Media/Lazyload/CSS/ServiceProvider.php

@@ -24,7 +24,6 @@ class ServiceProvider extends AbstractServiceProvider {
 	 * @var array
 	 */
 	protected $provides = [
-		'lazyload_css_cache',
 		'lazyload_css_subscriber',
 	];