Compass App: Add "server" dart shelf-app and "shared" dart package (#2359)

This PR introduces two new subprojects:

- `compass_server` under `compass_app/server`.
- `compass_model` under `compass_app/model`.

**`compass_server`**

- Dart server implemented using `shelf`.
- Created with the `dart create -t server-shelf` template.
- Implements two REST endpoints:
  - `GET /continent`: Returns the list of `Continent` as JSON.
  - `GET /destination`: Returns the list of `Destination` as JSON.
- Generated Docker files have been removed.
- Implemented tests.
- TODO: Implement some basic auth.

**`compass_model`**

- Dart package to share data model classes between the `server` and
`app`.
- Contains the data model classes (`Continent`, `Destination`).
- Generated JSON from/To methods and data classes using `freezed`.
- The sole purpose of this package is to host the data model. Other
shared code should go in a different package.

**Other changes**

- Created an API Client to connect to the local dart server.
- Created "remote" repositories, which also implement a basic in-memory
caching strategy.
- Created two dependency configurations, one with local repositories and
one with remote repos.
- Created two application main targets to select configuration:
- `lib/main_development.dart` which starts the app with the "local" data
configuration.
- `lib/main_staging.dart` which starts the app with the "remove" (local
dart server) configuration.
  - `lib/main.dart` still works as default entry point.
- Implemented tests for remote repositories.

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].

<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

Author: miquelbeltran

compass_app/app/lib/config/dependencies.dart

@@ -3,12 +3,34 @@ import 'package:provider/provider.dart';
 
 import '../data/repositories/continent/continent_repository.dart';
 import '../data/repositories/continent/continent_repository_local.dart';
+import '../data/repositories/continent/continent_repository_remote.dart';
 import '../data/repositories/destination/destination_repository.dart';
 import '../data/repositories/destination/destination_repository_local.dart';
+import '../data/repositories/destination/destination_repository_remote.dart';
+import '../data/services/api_client.dart';
 
-/// Configure dependencies as a list of Providers
-List<SingleChildWidget> get providers {
-  // List of Providers
+/// Configure dependencies for remote data.
+/// This dependency list uses repositories that connect to a remote server.
+List<SingleChildWidget> get providersRemote {
+  final apiClient = ApiClient();
+
+  return [
+    Provider.value(
+      value: DestinationRepositoryRemote(
+        apiClient: apiClient,
+      ) as DestinationRepository,
+    ),
+    Provider.value(
+      value: ContinentRepositoryRemote(
+        apiClient: apiClient,
+      ) as ContinentRepository,
+    ),
+  ];
+}
+
+/// Configure dependencies for local data.
+/// This dependency list uses repositories that provide local data.
+List<SingleChildWidget> get providersLocal {
   return [
     Provider.value(
       value: DestinationRepositoryLocal() as DestinationRepository,

compass_app/app/lib/data/models/continent.dart

@@ -1,5 +1,6 @@
+import 'package:compass_model/model.dart';
+
 import '../../../utils/result.dart';
-import '../../models/continent.dart';
 
 /// Data source with all possible continents.
 abstract class ContinentRepository {

compass_app/app/lib/data/models/destination.dart

@@ -1,39 +1,40 @@
+import 'package:compass_model/model.dart';
+
 import '../../../utils/result.dart';
-import '../../models/continent.dart';
 import 'continent_repository.dart';
 
-/// Local data source with all possible regions.
+/// Local data source with all possible continents.
 class ContinentRepositoryLocal implements ContinentRepository {
   @override
   Future<Result<List<Continent>>> getContinents() {
     return Future.value(
       Result.ok(
         [
-          Continent(
+          const Continent(
             name: 'Europe',
             imageUrl: 'https://rstr.in/google/tripedia/TmR12QdlVTT',
           ),
-          Continent(
+          const Continent(
             name: 'Asia',
             imageUrl: 'https://rstr.in/google/tripedia/VJ8BXlQg8O1',
           ),
-          Continent(
+          const Continent(
             name: 'South America',
             imageUrl: 'https://rstr.in/google/tripedia/flm_-o1aI8e',
           ),
-          Continent(
+          const Continent(
             name: 'Africa',
             imageUrl: 'https://rstr.in/google/tripedia/-nzi8yFOBpF',
           ),
-          Continent(
+          const Continent(
             name: 'North America',
             imageUrl: 'https://rstr.in/google/tripedia/jlbgFDrSUVE',
           ),
-          Continent(
+          const Continent(
             name: 'Oceania',
             imageUrl: 'https://rstr.in/google/tripedia/vxyrDE-fZVL',
           ),
-          Continent(
+          const Continent(
             name: 'Australia',
             imageUrl: 'https://rstr.in/google/tripedia/z6vy6HeRyvZ',
           ),

compass_app/app/lib/data/repositories/continent/continent_repository.dart

@@ -0,0 +1,34 @@
+import 'package:compass_model/model.dart';
+
+import '../../../utils/result.dart';
+import '../../services/api_client.dart';
+import 'continent_repository.dart';
+
+/// Remote data source for [Continent].
+/// Implements basic local caching.
+/// See: https://docs.flutter.dev/get-started/fwe/local-caching
+class ContinentRepositoryRemote implements ContinentRepository {
+  ContinentRepositoryRemote({
+    required ApiClient apiClient,
+  }) : _apiClient = apiClient;
+
+  final ApiClient _apiClient;
+
+  List<Continent>? _cachedData;
+
+  @override
+  Future<Result<List<Continent>>> getContinents() async {
+    if (_cachedData == null) {
+      // No cached data, request continents
+      final result = await _apiClient.getContinents();
+      if (result is Ok) {
+        // Store value if result Ok
+        _cachedData = result.asOk.value;
+      }
+      return result;
+    } else {
+      // Return cached data if available
+      return Result.ok(_cachedData!);
+    }
+  }
+}

compass_app/app/lib/data/repositories/continent/continent_repository_local.dart

@@ -1,5 +1,6 @@
+import 'package:compass_model/model.dart';
+
 import '../../../utils/result.dart';
-import '../../models/destination.dart';
 
 /// Data source with all possible destinations
 abstract class DestinationRepository {

compass_app/app/lib/data/repositories/continent/continent_repository_remote.dart

@@ -1,11 +1,11 @@
 import 'dart:convert';
 
+import 'package:compass_model/model.dart';
+import 'package:flutter/services.dart' show rootBundle;
+
 import '../../../utils/result.dart';
-import '../../models/destination.dart';
 import 'destination_repository.dart';
 
-import 'package:flutter/services.dart' show rootBundle;
-
 /// Local implementation of DestinationRepository
 /// Uses data from assets folder
 class DestinationRepositoryLocal implements DestinationRepository {

compass_app/app/lib/data/repositories/destination/destination_repository.dart

@@ -0,0 +1,34 @@
+import 'package:compass_model/model.dart';
+
+import '../../../utils/result.dart';
+import '../../services/api_client.dart';
+import 'destination_repository.dart';
+
+/// Remote data source for [Destination].
+/// Implements basic local caching.
+/// See: https://docs.flutter.dev/get-started/fwe/local-caching
+class DestinationRepositoryRemote implements DestinationRepository {
+  DestinationRepositoryRemote({
+    required ApiClient apiClient,
+  }) : _apiClient = apiClient;
+
+  final ApiClient _apiClient;
+
+  List<Destination>? _cachedData;
+
+  @override
+  Future<Result<List<Destination>>> getDestinations() async {
+    if (_cachedData == null) {
+      // No cached data, request destinations
+      final result = await _apiClient.getDestinations();
+      if (result is Ok) {
+        // Store value if result Ok
+        _cachedData = result.asOk.value;
+      }
+      return result;
+    } else {
+      // Return cached data if available
+      return Result.ok(_cachedData!);
+    }
+  }
+}

compass_app/app/lib/data/repositories/destination/destination_repository_local.dart

@@ -0,0 +1,49 @@
+import 'dart:convert';
+import 'dart:io';
+import 'package:compass_model/model.dart';
+
+import '../../utils/result.dart';
+
+// TODO: Basic auth request
+// TODO: Configurable baseurl/host/port
+class ApiClient {
+  Future<Result<List<Continent>>> getContinents() async {
+    final client = HttpClient();
+    try {
+      final request = await client.get('localhost', 8080, '/continent');
+      final response = await request.close();
+      if (response.statusCode == 200) {
+        final stringData = await response.transform(utf8.decoder).join();
+        final json = jsonDecode(stringData) as List<dynamic>;
+        return Result.ok(
+            json.map((element) => Continent.fromJson(element)).toList());
+      } else {
+        return Result.error(const HttpException("Invalid response"));
+      }
+    } on Exception catch (error) {
+      return Result.error(error);
+    } finally {
+      client.close();
+    }
+  }
+
+  Future<Result<List<Destination>>> getDestinations() async {
+    final client = HttpClient();
+    try {
+      final request = await client.get('localhost', 8080, '/destination');
+      final response = await request.close();
+      if (response.statusCode == 200) {
+        final stringData = await response.transform(utf8.decoder).join();
+        final json = jsonDecode(stringData) as List<dynamic>;
+        return Result.ok(
+            json.map((element) => Destination.fromJson(element)).toList());
+      } else {
+        return Result.error(const HttpException("Invalid response"));
+      }
+    } on Exception catch (error) {
+      return Result.error(error);
+    } finally {
+      client.close();
+    }
+  }
+}

compass_app/app/lib/data/repositories/destination/destination_repository_remote.dart

@@ -1,20 +1,14 @@
-import 'config/dependencies.dart';
 import 'ui/core/themes/theme.dart';
 import 'routing/router.dart';
 import 'package:flutter/material.dart';
-import 'package:provider/provider.dart';
 
 import 'ui/core/ui/scroll_behavior.dart';
+import 'main_development.dart' as development;
 
+/// Default main method
 void main() {
-  runApp(
-    MultiProvider(
-      // Loading the default providers
-      // NOTE: We can load different configurations e.g. fakes
-      providers: providers,
-      child: const MainApp(),
-    ),
-  );
+  // Launch development config by default
+  development.main();
 }
 
 class MainApp extends StatelessWidget {

compass_app/app/lib/data/services/api_client.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import 'config/dependencies.dart';
+import 'main.dart';
+
+/// Development config entry point.
+/// Launch with `flutter run --target lib/main_development.dart`.
+/// Uses local data.
+void main() {
+  runApp(
+    MultiProvider(
+      providers: providersLocal,
+      child: const MainApp(),
+    ),
+  );
+}

compass_app/app/lib/main.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import 'config/dependencies.dart';
+import 'main.dart';
+
+/// Staging config entry point.
+/// Launch with `flutter run --target lib/main_staging.dart`.
+/// Uses remote data from a server.
+void main() {
+  runApp(
+    MultiProvider(
+      providers: providersRemote,
+      child: const MainApp(),
+    ),
+  );
+}

compass_app/app/lib/main_development.dart

@@ -13,7 +13,8 @@ final router = GoRouter(
     GoRoute(
       path: '/',
       builder: (context, state) {
-        final viewModel = SearchFormViewModel(continentRepository: context.read());
+        final viewModel =
+            SearchFormViewModel(continentRepository: context.read());
         return SearchFormScreen(viewModel: viewModel);
       },
       routes: [

compass_app/app/lib/main_staging.dart

@@ -8,8 +8,7 @@ class AppColors {
   static const grey3 = Color(0xFFA4A4A4);
   static const whiteTransparent =
       Color(0x4DFFFFFF); // Figma rgba(255, 255, 255, 0.3)
-  static const blackTransparent =
-      Color(0x4D000000);
+  static const blackTransparent = Color(0x4D000000);
 
   static const lightColorScheme = ColorScheme(
     brightness: Brightness.light,

compass_app/app/lib/routing/router.dart

@@ -6,8 +6,8 @@ import 'package:flutter/material.dart';
 class AppCustomScrollBehavior extends MaterialScrollBehavior {
   @override
   Set<PointerDeviceKind> get dragDevices => {
-    PointerDeviceKind.touch,
-    // Allow to drag with mouse on Regions carousel
-    PointerDeviceKind.mouse,
-  };
+        PointerDeviceKind.touch,
+        // Allow to drag with mouse on Regions carousel
+        PointerDeviceKind.mouse,
+      };
 }