feat: Implement basic general folder support (#2051)

- Related: #1748

src/view/item-classifier.ts

@@ -0,0 +1,31 @@
+import {
+  EventViewMedia,
+  RecordingViewMedia,
+  ViewFolder,
+  ViewItem,
+  ViewMedia,
+} from './item';
+
+export class ViewItemClassifier {
+  public static isMedia(item?: ViewItem | null): item is ViewMedia {
+    return item instanceof ViewMedia;
+  }
+  public static isFolder(item?: ViewItem | null): item is ViewFolder {
+    return item instanceof ViewFolder;
+  }
+  public static isEvent(item?: ViewItem | null): item is EventViewMedia {
+    return this.isMedia(item) && (this.isClip(item) || this.isSnapshot(item));
+  }
+  public static isRecording(item?: ViewItem | null): item is RecordingViewMedia {
+    return this.isMedia(item) && item.getMediaType() === 'recording';
+  }
+  public static isClip(item?: ViewItem | null): boolean {
+    return this.isMedia(item) && item.getMediaType() === 'clip';
+  }
+  public static isSnapshot(item?: ViewItem | null): boolean {
+    return this.isMedia(item) && item.getMediaType() === 'snapshot';
+  }
+  public static isVideo(item?: ViewItem | null): boolean {
+    return this.isMedia(item) && (this.isClip(item) || this.isRecording(item));
+  }
+}