Use WindowInsetsController on API 30+ for fullscreen

Replace deprecated setSystemUiVisibility() and SYSTEM_UI_FLAG_*
constants with WindowInsetsController on Android 11+, falling back
to the deprecated methods on older devices.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rtibbles

app/src/main/java/org/learningequality/Kolibri/KolibriWebChromeClient.java

@@ -1,7 +1,11 @@
 package org.learningequality.Kolibri;
 
 import android.app.Activity;
+import android.os.Build;
 import android.view.View;
+import android.view.Window;
+import android.view.WindowInsets;
+import android.view.WindowInsetsController;
 import android.webkit.WebChromeClient;
 import android.widget.FrameLayout;
 
@@ -32,15 +36,7 @@ public void onShowCustomView(View view, CustomViewCallback callback) {
     customViewCallback = callback;
 
     // Hide system UI for immersive fullscreen
-    activity
-        .getWindow()
-        .getDecorView()
-        .setSystemUiVisibility(
-            View.SYSTEM_UI_FLAG_FULLSCREEN
-                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
-                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
-                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
-                | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
+    hideSystemUI();
 
     // Add the custom view to the fullscreen container
     fullscreenContainer.addView(customView);
@@ -59,12 +55,47 @@ public void onHideCustomView() {
     fullscreenContainer.setVisibility(View.GONE);
 
     // Restore system UI
-    activity.getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_VISIBLE);
+    showSystemUI();
 
     // Notify the callback
     if (customViewCallback != null) {
       customViewCallback.onCustomViewHidden();
       customViewCallback = null;
     }
   }
+
+  private void hideSystemUI() {
+    Window window = activity.getWindow();
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+      WindowInsetsController controller = window.getInsetsController();
+      if (controller != null) {
+        controller.hide(WindowInsets.Type.statusBars() | WindowInsets.Type.navigationBars());
+        controller.setSystemBarsBehavior(
+            WindowInsetsController.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE);
+      }
+    } else {
+      @SuppressWarnings("deprecation")
+      int flags =
+          View.SYSTEM_UI_FLAG_FULLSCREEN
+              | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
+              | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
+              | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
+              | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN;
+      window.getDecorView().setSystemUiVisibility(flags);
+    }
+  }
+
+  private void showSystemUI() {
+    Window window = activity.getWindow();
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+      WindowInsetsController controller = window.getInsetsController();
+      if (controller != null) {
+        controller.show(WindowInsets.Type.statusBars() | WindowInsets.Type.navigationBars());
+      }
+    } else {
+      @SuppressWarnings("deprecation")
+      int flags = View.SYSTEM_UI_FLAG_VISIBLE;
+      window.getDecorView().setSystemUiVisibility(flags);
+    }
+  }
 }