neon: enable apps to specify go_routes

packages/neon/neon/lib/src/models/app_implementation.dart

@@ -1,6 +1,7 @@
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_svg/flutter_svg.dart';
+import 'package:go_router/go_router.dart';
 import 'package:neon/l10n/localizations.dart';
 import 'package:neon/src/bloc/bloc.dart';
 import 'package:neon/src/blocs/accounts.dart';
@@ -68,6 +69,34 @@ abstract class AppImplementation<T extends Bloc, R extends NextcloudAppOptions>
     );
   }
 
+  /// Main branch displayed in the home page.
+  ///
+  /// There's usually no need to override this.
+  StatefulShellBranch get mainBranch => StatefulShellBranch(
+        routes: [
+          route,
+        ],
+      );
+
+  /// Route for the app.
+  ///
+  /// All pages of the app must be specified as subroutes.
+  /// If this is not [GoRoute] an inital route name must be specified by overriding [initialRouteName].
+  RouteBase get route => throw UnimplementedError();
+
+  /// Name of the initial route for this app.
+  ///
+  /// Subclasses that don't provide a [GoRoute] for [route] must override this.
+  String get initialRouteName {
+    final route = this.route;
+
+    if (route is GoRoute && route.name != null) {
+      return route.name!;
+    }
+
+    throw FlutterError('No name for the initial route provided.');
+  }
+
   Widget buildIcon({
     final Size size = const Size.square(32),
     final Color? color,

packages/neon/neon/lib/src/utils/app_route.dart

@@ -0,0 +1,16 @@
+import 'package:flutter/widgets.dart';
+import 'package:go_router/go_router.dart';
+
+/// [RouteData] for the initial page of an app.
+///
+/// Subclasses must override one of [build] or [redirect].
+abstract class NeonAppRoute extends GoRouteData {
+  const NeonAppRoute();
+
+  @override
+  Page<void> buildPage(final BuildContext context, final GoRouterState state) => NoTransitionPage(
+        child: build(context, state),
+      );
+}
+
+const appsRoutePrefix = '/apps/';

packages/neon/neon/lib/utils.dart

@@ -1,3 +1,4 @@
+export 'package:neon/src/utils/app_route.dart';
 export 'package:neon/src/utils/confirmation_dialog.dart';
 export 'package:neon/src/utils/exceptions.dart';
 export 'package:neon/src/utils/hex_color.dart';