Add error notification for failed wallpaper downloads

src/notifications.ts

@@ -16,6 +16,20 @@ class Notification {
         const message = `A new wallpaper was set!\n${infoString}`;
         notify('New Wallpaper', message);
     }
+
+    /**
+     * Show an error notification for failed wallpaper downloads.
+     *
+     * @param {unknown} error The error that was thrown when fetching a new wallpaper
+     */
+    static fetchWallpaperFailed(error: unknown): void {
+        let errorMessage = String(error);
+
+        if (error instanceof Error)
+            errorMessage = error.message;
+
+        notify('RandomWallpaperGnome3: Wallpaper Download Failed!', errorMessage);
+    }
 }
 
 export {Notification};

src/wallpaperController.ts

@@ -562,6 +562,8 @@ class WallpaperController {
                 Notification.newWallpaper(newImageEntries.reverse());
         } catch (error) {
             Logger.error(error, this);
+            if (this._settings.getBoolean('show-notifications'))
+                Notification.fetchWallpaperFailed(error);
         } finally {
             this._stopLoadingHooks.forEach(element => element());
         }