packages/go_router/lib/src/route_data.dart

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/widgets.dart';
import 'package:meta/meta.dart';
import 'package:meta/meta_meta.dart';

import 'route.dart';
import 'state.dart';

/// Baseclass for supporting
/// [typed routing](https://gorouter.dev/typed-routing).
///
/// Subclasses must override one of [build], [buildPage], or [redirect].
abstract class GoRouteData {
  /// Allows subclasses to have `const` constructors.
  ///
  /// [GoRouteData] is abstract and cannot be instantiated directly.
  const GoRouteData();

  /// Creates the [Widget] for `this` route.
  ///
  /// Subclasses must override one of [build], [buildPage], or [redirect].
  ///
  /// Corresponds to [GoRoute.builder].
  Widget build(BuildContext context) => throw UnimplementedError(
        'One of `build` or `buildPage` must be implemented.',
      );

  /// A page builder for this route.
  ///
  /// Subclasses can override this function to provide a custom [Page].
  ///
  /// Subclasses must override one of [build], [buildPage], or [redirect].
  ///
  /// Corresponds to [GoRoute.pageBuilder].
  ///
  /// By default, returns a [Page] instance that is ignored, causing a default
  /// [Page] implementation to be used with the results of [build].
  Page<void> buildPage(BuildContext context) => const NoOpPage();

  /// An optional redirect function for this route.
  ///
  /// Subclasses must override one of [build], [buildPage], or [redirect].
  ///
  /// Corresponds to [GoRoute.redirect].
  String? redirect() => null;

  /// A helper function used by generated code.
  ///
  /// Should not be used directly.
  static String $location(String path, {Map<String, String>? queryParams}) =>
      Uri.parse(path)
          .replace(
            queryParameters:
                // Avoid `?` in generated location if `queryParams` is empty
                queryParams?.isNotEmpty ?? false ? queryParams : null,
          )
          .toString();

  /// A helper function used by generated code.
  ///
  /// Should not be used directly.
  static GoRoute $route<T extends GoRouteData>({
    required String path,
    required T Function(GoRouterState) factory,
    List<GoRoute> routes = const <GoRoute>[],
  }) {
    T factoryImpl(GoRouterState state) {
      final Object? extra = state.extra;

      // If the "extra" value is of type `T` then we know it's the source
      // instance of `GoRouteData`, so it doesn't need to be recreated.
      if (extra is T) {
        return extra;
      }

      return (_stateObjectExpando[state] ??= factory(state)) as T;
    }

    Widget builder(BuildContext context, GoRouterState state) =>
        factoryImpl(state).build(context);

    Page<void> pageBuilder(BuildContext context, GoRouterState state) =>
        factoryImpl(state).buildPage(context);

    String? redirect(GoRouterState state) => factoryImpl(state).redirect();

    return GoRoute(
      path: path,
      builder: builder,
      pageBuilder: pageBuilder,
      redirect: redirect,
      routes: routes,
    );
  }

  /// Used to cache [GoRouteData] that corresponds to a given [GoRouterState]
  /// to minimize the number of times it has to be deserialized.
  static final Expando<GoRouteData> _stateObjectExpando = Expando<GoRouteData>(
    'GoRouteState to GoRouteData expando',
  );
}

/// Annotation for types that support typed routing.
@Target(<TargetKind>{TargetKind.library, TargetKind.classType})
class TypedGoRoute<T extends GoRouteData> {
  /// Instantiates a new instance of [TypedGoRoute].
  const TypedGoRoute({
    required this.path,
    this.routes = const <TypedGoRoute<GoRouteData>>[],
  });

  /// The path that corresponds to this rout.
  ///
  /// See [GoRoute.path].
  final String path;

  /// Child route definitions.
  ///
  /// See [GoRoute.routes].
  final List<TypedGoRoute<GoRouteData>> routes;
}

/// Internal class used to signal that the default page behavior should be used.
@internal
class NoOpPage extends Page<void> {
  /// Creates an instance of NoOpPage;
  const NoOpPage();

  @override
  Route<void> createRoute(BuildContext context) =>
      throw UnsupportedError('Should never be called');
}