add UnifiedPushAllowedController

lib/controllers/settings_sections.dart

@@ -11,6 +11,7 @@ import "package:nexus/controllers/client_state.dart";
 import "package:nexus/controllers/settings.dart";
 import "package:nexus/controllers/unified_push.dart";
 import "package:nexus/controllers/spec_versions.dart";
+import "package:nexus/controllers/unified_push_allowed.dart";
 import "package:nexus/models/account_data.dart";
 import "package:nexus/models/settings_category.dart";
 import "package:nexus/main.dart";
@@ -100,7 +101,6 @@ class SettingsSectionsController
             title: "Notifications",
             icon: Icons.notifications,
             settings: .new([
-              // TODO: Disable if not supported
               .new(
                 title: "Push notifications",
                 description: "Enable push notifications using Web Push",
@@ -109,26 +109,43 @@ class SettingsSectionsController
                     final pusherRegistered = ref.watch(
                       UnifiedPushController.provider,
                     );
+                    final unifiedPushAllowed = ref.watch(
+                      UnifiedPushAllowedController.provider,
+                    );
                     return SwitchListTile(
                       title: Text(title),
-                      subtitle: Text(description),
+                      subtitle: Text(
+                        unifiedPushAllowed.maybeWhen(
+                              data: (data) => data,
+                              orElse: () => null,
+                            ) ??
+                            description,
+                      ),
                       secondary: Icon(icon),
                       value: pusherRegistered.maybeWhen(
                         data: (value) => value,
                         orElse: () => false,
                       ),
-                      onChanged: pusherRegistered.maybeWhen(
-                        data: (_) =>
-                            (value) => value
-                            ? ref
-                                  .watch(
-                                    UnifiedPushController.provider.notifier,
-                                  )
-                                  .register()
-                                  .onError(showError)
-                            : /*deregeister*/ null,
-                        orElse: () => null,
-                      ),
+                      onChanged:
+                          unifiedPushAllowed.maybeWhen(
+                            data: (data) => data == null,
+                            orElse: () => false,
+                          )
+                          ? pusherRegistered.maybeWhen(
+                              data: (_) =>
+                                  (value) => value
+                                  ? ref
+                                        .watch(
+                                          UnifiedPushController
+                                              .provider
+                                              .notifier,
+                                        )
+                                        .register()
+                                        .onError(showError)
+                                  : /*deregeister*/ null,
+                              orElse: () => null,
+                            )
+                          : null,
                     );
                   },
                 ),

lib/controllers/unified_push.dart

@@ -78,8 +78,9 @@ class UnifiedPushController extends AsyncNotifier<bool> {
     if (clientState?.deviceId == null) ref.invalidateSelf();
 
     final alreadyRegistered = early ? true : await future;
-    final client = ref.watch(ClientController.provider.notifier);
-    final capabilities = await client.getCapabilities();
+    final capabilities = await ref
+        .watch(ClientController.provider.notifier)
+        .getCapabilities();
 
     if (capabilities.webpush?.vapid == null) {
       throw UnsupportedError(

lib/controllers/unified_push_allowed.dart

@@ -0,0 +1,33 @@
+import "dart:io";
+
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/controllers/client.dart";
+import "package:unifiedpush/unifiedpush.dart";
+
+class UnifiedPushAllowedController extends AsyncNotifier<String?> {
+  @override
+  Future<String?> build() async {
+    if (!await UnifiedPush.tryUseCurrentOrDefaultDistributor()) {
+      return "No valid distributors found. Try installing ${Platform.isLinux
+          ? "KUnifiedPush"
+          : Platform.isAndroid
+          ? "FCM or NTFY"
+          : "NTFY"}.";
+    }
+
+    final capabilities = await ref
+        .watch(ClientController.provider.notifier)
+        .getCapabilities();
+
+    if (capabilities.webpush?.vapid == null) {
+      return "Your homeserver does not support MSC4174 (Web Push), and therefore cannot send notifications to Nexus.";
+    }
+
+    return null;
+  }
+
+  static final provider =
+      AsyncNotifierProvider.autoDispose<UnifiedPushAllowedController, String?>(
+        UnifiedPushAllowedController.new,
+      );
+}