Dart 3.0 (#2)

* flutter 3.10.0, deps

* either, dart 3.0

* cancel op

* cancel op

* better

* better

lib/main.dart

@@ -1,5 +1,5 @@
-import 'package:batch_api_demo/main/bloc.dart';
 import 'package:batch_api_demo/main/home_page.dart';
+import 'package:batch_api_demo/main/main_bloc.dart';
 import 'package:batch_api_demo/users_repo.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc_pattern/flutter_bloc_pattern.dart';
@@ -25,6 +25,7 @@ class MyApp extends StatelessWidget {
         useMaterial3: true,
         colorSchemeSeed: Colors.purple,
       ),
+      debugShowCheckedModeBanner: false,
       home: BlocProvider(
         initBloc: (context) => MainBloc(usersRepo: context.get()),
         child: const MyHomePage(),

lib/main/home_page.dart

@@ -1,6 +1,8 @@
-import 'package:batch_api_demo/main/bloc.dart';
-import 'package:batch_api_demo/main/state.dart';
+import 'package:batch_api_demo/main/main_bloc.dart';
+import 'package:batch_api_demo/main/main_state.dart';
 import 'package:batch_api_demo/optional.dart';
+import 'package:batch_api_demo/users_repo.dart';
+import 'package:built_collection/built_collection.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc_pattern/flutter_bloc_pattern.dart';
 
@@ -23,14 +25,40 @@ class _MyHomePageState extends State<MyHomePage> {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Batch API demo'),
+        actions: [
+          IconButton(
+            onPressed: () => context.bloc<MainBloc>().fetch(),
+            icon: const Icon(Icons.refresh),
+          ),
+          IconButton(
+            onPressed: () => context.bloc<MainBloc>().cancel(),
+            icon: const Icon(Icons.cancel),
+          ),
+          RxStreamBuilder<bool>(
+            stream: UsersRepo.failed$,
+            builder: (context, state) => TextButton(
+              onPressed: UsersRepo.toggleFailed,
+              child: Text(
+                state ? 'failed' : 'succeed',
+                style: TextStyle(color: state ? Colors.red : Colors.green),
+              ),
+            ),
+          ),
+        ],
       ),
       body: SizedBox.expand(
         child: RxStreamBuilder<MainState>(
           stream: context.bloc<MainBloc>().state$,
           builder: (context, state) {
+            if (state.cancelled) {
+              return const Center(
+                child: Text('Cancelled'),
+              );
+            }
+
             if (state.error.isNotEmpty) {
               return Center(
-                child: Text('Error: ${state.error.valueOrNull()}'),
+                child: Text('Error: ${state.error.valueOrNull()!.message}'),
               );
             }
 
@@ -49,7 +77,7 @@ class _MyHomePageState extends State<MyHomePage> {
 }
 
 class UsersListView extends StatelessWidget {
-  final List<UserItem> items;
+  final BuiltList<UserItem> items;
 
   const UsersListView({Key? key, required this.items}) : super(key: key);
 
@@ -59,7 +87,10 @@ class UsersListView extends StatelessWidget {
       itemCount: items.length,
       itemBuilder: (context, index) {
         final item = items[index];
-        return UserItemRow(item: item);
+        return UserItemRow(
+          key: ValueKey(item.user.id),
+          item: item,
+        );
       },
     );
   }
@@ -74,17 +105,19 @@ class UserItemRow extends StatelessWidget {
   Widget build(BuildContext context) {
     return ListTile(
       title: Text(item.user.name),
-      subtitle: item.isLoading
-          ? Text(
-              'Loading...',
-              style: Theme.of(context)
-                  .textTheme
-                  .bodyMedium!
-                  .copyWith(color: Colors.red),
-            )
-          : item.user.avatarUrl != null
-              ? Text('Avatar: ${item.user.avatarUrl}')
-              : const Text('No avatar'),
+      subtitle: switch ((item.isLoading, item.error)) {
+        (true, _) => Text(
+            'Loading...',
+            style: Theme.of(context)
+                .textTheme
+                .bodyMedium!
+                .copyWith(color: Colors.red),
+          ),
+        (_, Some(value: final error)) => Text('Error: ${error.message}'),
+        _ => item.user.avatarUrl != null
+            ? Text('Avatar: ${item.user.avatarUrl}')
+            : const Text('No avatar'),
+      },
       leading: const CircleAvatar(
         child: Icon(Icons.person),
       ),

lib/main/main_bloc.dart

@@ -0,0 +1,96 @@
+import 'dart:async';
+
+import 'package:batch_api_demo/main/main_state.dart';
+import 'package:batch_api_demo/main/partial_state_change.dart';
+import 'package:batch_api_demo/users_repo.dart';
+import 'package:batch_api_demo/utils.dart';
+import 'package:built_collection/built_collection.dart';
+import 'package:disposebag/disposebag.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter_bloc_pattern/flutter_bloc_pattern.dart';
+import 'package:rxdart_ext/rxdart_ext.dart';
+
+const _batchSize = 4;
+const _maxRetries = 3;
+
+class MainBloc extends DisposeCallbackBaseBloc {
+  final Func0<void> fetch;
+  final Func0<void> cancel;
+
+  final StateStream<MainState> state$;
+
+  MainBloc._({
+    required Func0<void> dispose,
+    required this.fetch,
+    required this.cancel,
+    required this.state$,
+  }) : super(dispose);
+
+  factory MainBloc({
+    required UsersRepo usersRepo,
+  }) {
+    final fetchS = StreamController<void>();
+    final cancelS = PublishSubject<void>(sync: true);
+
+    final state$ = Rx.merge([
+      fetchS.stream.switchMap(
+        (_) => _fetchUsersAndAvatars(usersRepo)
+            .doOnCancel(
+                () => debugPrint('MainBloc._fetchUsersAndAvatars() cancelled!'))
+            .takeUntil(cancelS.stream),
+      ),
+      cancelS.stream.asyncMap((event) => Future.value(UsersCancelledChange())),
+    ])
+        .scan((state, change, _) => change.reduce(state), MainState.initial)
+        .publishState(MainState.initial);
+
+    return MainBloc._(
+      dispose: DisposeBag([
+        fetchS,
+        cancelS,
+        state$.connect(),
+      ]).dispose,
+      fetch: fetchS.addNull,
+      cancel: cancelS.addNull,
+      state$: state$,
+    );
+  }
+}
+
+Stream<MainPartialStateChange> _fetchUsersAndAvatars(UsersRepo usersRepo) =>
+    usersRepo
+        .fetchUsers()
+        .exhaustMap(
+          (either) => either.fold(
+            ifLeft: (e) => Stream.value(UsersErrorChange(e)),
+            ifRight: (users) {
+              final items = users.map(UserItem.loading).toBuiltList();
+
+              return Rx.concat<MainPartialStateChange>([
+                Stream.value(UsersListChange(items)),
+                Stream.fromIterable(items)
+                    .flatMapBatches(
+                        (e) => _fetchAvatars(usersRepo, e.user), _batchSize)
+                    .expand(identity),
+              ]);
+            },
+          ),
+        )
+        .startWith(UsersLoadingChange());
+
+Stream<MainPartialStateChange> _fetchAvatars(
+  UsersRepo usersRepo,
+  User user,
+) =>
+    retryEitherSingle<UserError, String>(
+      () => usersRepo.fetchUserAvatarUrl(user),
+      _maxRetries,
+    )
+        .map(
+          (either) => either.fold(
+            ifLeft: (e) => UserItem.failed(user, e),
+            ifRight: (avatarUrl) =>
+                UserItem.loaded(user.copyWithNewAvatarUrl(avatarUrl)),
+          ),
+        )
+        .map(UserItemUpdatedChange.new);