feat(thread_publish): Logic of thread publishing

lib/exceptions/exceptions.dart

@@ -314,3 +314,22 @@ class ReplyPersonalMessageFailedException extends AppException
   /// Constructor.
   ReplyPersonalMessageFailedException(String message) : super(message: message);
 }
+
+/// Failed to publish a thread.
+///
+/// Server returned unexpected status code.
+@MappableClass()
+final class ThreadPublishFailedException extends AppException
+    with ThreadPublishFailedExceptionMappable {
+  /// Constructor.
+  ThreadPublishFailedException(this.code);
+
+  /// Unexpected http status code.
+  final int code;
+}
+
+/// Thread published, but the redirect location of published thread page
+/// is not found in the response header.
+@MappableClass()
+final class ThreadPublishLocationNotFoundException extends AppException
+    with ThreadPublishLocationNotFoundExceptionMappable {}

lib/features/thread_publish/bloc/thread_publish_bloc.dart

@@ -0,0 +1,84 @@
+import 'package:bloc/bloc.dart';
+import 'package:dart_mappable/dart_mappable.dart';
+import 'package:tsdm_client/extensions/fp.dart';
+import 'package:tsdm_client/features/thread_publish/models/models.dart';
+import 'package:tsdm_client/features/thread_publish/repository/thread_pub_repository.dart';
+import 'package:tsdm_client/utils/logger.dart';
+
+part 'thread_publish_bloc.mapper.dart';
+part 'thread_publish_event.dart';
+part 'thread_publish_state.dart';
+
+typedef _Emit = Emitter<ThreadPubState>;
+
+/// Bloc of thread publish.
+///
+/// * Fetch thread info.
+/// * Post thread data.
+/// * Save thread data.
+final class ThreadPubBloc extends Bloc<ThreadPubEvent, ThreadPubState>
+    with LoggerMixin {
+  /// Constructor.
+  ThreadPubBloc(this._repo)
+      : super(const ThreadPubState(status: ThreadPubStatus.initial)) {
+    on<ThreadPubEvent>(
+      (event, emit) => switch (event) {
+        ThreadPubFetchInfoRequested(:final fid) => _onFetchInfo(fid, emit),
+        ThreadPubPostThread(:final info) => _onPostThread(info, emit),
+      },
+    );
+  }
+
+  final ThreadPubRepository _repo;
+
+  Future<void> _onFetchInfo(String fid, _Emit emit) async {
+    emit(state.copyWith(status: ThreadPubStatus.loadingInfo));
+
+    final docEither = await _repo.prepareInfo(fid).run();
+    if (docEither.isLeft()) {
+      handle(docEither.unwrapErr());
+      emit(state.copyWith(status: ThreadPubStatus.failure));
+      return;
+    }
+
+    final doc = docEither.unwrap();
+    final formHash = doc.querySelector('input#formhash')?.attributes['value'];
+    final postTime = doc.querySelector('input#posttime')?.attributes['value'];
+
+    if (formHash == null || postTime == null) {
+      error('failed to fetch info: form hash or post time not found: '
+          'formHash=$formHash, postTime=$postTime');
+      emit(state.copyWith(status: ThreadPubStatus.failure));
+      return;
+    }
+
+    emit(
+      state.copyWith(
+        status: ThreadPubStatus.readyToPost,
+        forumHash: formHash,
+        postTime: postTime,
+      ),
+    );
+  }
+
+  Future<void> _onPostThread(
+    ThreadPublishInfo info,
+    _Emit emit,
+  ) async {
+    emit(state.copyWith(status: ThreadPubStatus.posting));
+
+    final urlEither = await _repo.postThread(info).run();
+    if (urlEither.isLeft()) {
+      handle(urlEither.unwrapErr());
+      emit(state.copyWith(status: ThreadPubStatus.failure));
+      return;
+    }
+
+    emit(
+      state.copyWith(
+        status: ThreadPubStatus.success,
+        redirectUrl: urlEither.unwrap(),
+      ),
+    );
+  }
+}

lib/features/thread_publish/bloc/thread_publish_event.dart

@@ -0,0 +1,30 @@
+part of 'thread_publish_bloc.dart';
+
+/// Base event.
+@MappableClass()
+sealed class ThreadPubEvent with ThreadPubEventMappable {
+  /// Constructor.
+  const ThreadPubEvent();
+}
+
+/// Fetch required info for publishing, including form hash, post time and more.
+@MappableClass()
+final class ThreadPubFetchInfoRequested extends ThreadPubEvent
+    with ThreadPubFetchInfoRequestedMappable {
+  /// Constructor.
+  const ThreadPubFetchInfoRequested({required this.fid});
+
+  /// Forum id.
+  final String fid;
+}
+
+/// Post a new thread to forum.
+@MappableClass()
+final class ThreadPubPostThread extends ThreadPubEvent
+    with ThreadPubPostThreadMappable {
+  /// Constructor.
+  const ThreadPubPostThread(this.info);
+
+  /// All info to post in body.
+  final ThreadPublishInfo info;
+}

lib/features/thread_publish/bloc/thread_publish_state.dart

@@ -0,0 +1,46 @@
+part of 'thread_publish_bloc.dart';
+
+/// Status of thread publish.
+enum ThreadPubStatus {
+  /// Initial state.
+  initial,
+
+  /// Loading form info required in posting thread.
+  loadingInfo,
+
+  /// Info fetched and waiting for post action.
+  readyToPost,
+
+  /// Posting data.
+  posting,
+
+  /// Post data success.
+  success,
+
+  /// Failed to load info or post thread.
+  failure,
+}
+
+/// State of thread publish
+@MappableClass()
+final class ThreadPubState with ThreadPubStateMappable {
+  /// Constructor.
+  const ThreadPubState({
+    required this.status,
+    this.forumHash,
+    this.postTime,
+    this.redirectUrl,
+  });
+
+  /// Status.
+  final ThreadPubStatus status;
+
+  /// Form hash.
+  final String? forumHash;
+
+  /// Thread post time.
+  final String? postTime;
+
+  /// Url of the published thread page when publish succeed.
+  final String? redirectUrl;
+}

lib/features/thread_publish/repository/thread_pub_repository.dart

@@ -0,0 +1,63 @@
+import 'dart:io' if (dart.library.js) 'package:web/web.dart';
+
+import 'package:fpdart/fpdart.dart';
+import 'package:tsdm_client/constants/url.dart';
+import 'package:tsdm_client/exceptions/exceptions.dart';
+import 'package:tsdm_client/features/thread_publish/models/models.dart';
+import 'package:tsdm_client/instance.dart';
+import 'package:tsdm_client/shared/providers/net_client_provider/net_client_provider.dart';
+import 'package:tsdm_client/utils/logger.dart';
+import 'package:universal_html/html.dart' as uh;
+import 'package:universal_html/parsing.dart';
+
+/// Repository for thread publish
+///
+/// * Fetch info when preparing page.
+/// * Post new thread content to server.
+final class ThreadPubRepository with LoggerMixin {
+  /// Constructor.
+  const ThreadPubRepository();
+
+  static String _buildInfoUrl(String fid) =>
+      '$homePage?mod=post&action=newthread&fid=$fid';
+
+  static String _buildPostUrl(String fid) =>
+      '$homePage?mod=post&action=newthread&fid=$fid&extra=&topicsubmit=yes';
+
+  /// Fetch required info that used in posting new thread.
+  ///
+  /// This step is far before posting final thread content to server.
+  AsyncEither<uh.Document> prepareInfo(String fid) => getIt
+      .get<NetClientProvider>()
+      .get(_buildInfoUrl(fid))
+      .mapHttp((v) => parseHtmlDocument(v.data as String));
+
+  /// Post new thread data to server.
+  ///
+  /// Generally the serer will response a status code of 301 with location in
+  /// header to redirect to published thread page.
+  AsyncEither<String> postThread(ThreadPublishInfo info) =>
+      AsyncEither(() async {
+        switch (await getIt
+            .get<NetClientProvider>()
+            .get(_buildPostUrl(info.fid))
+            .run()) {
+          case Left(:final value):
+            return left(value);
+          case Right(:final value)
+              when value.statusCode != HttpStatus.movedPermanently:
+            return left(ThreadPublishFailedException(value.statusCode!));
+          case Right(:final value):
+            if (value.headers.map.containsKey(HttpHeaders.locationHeader)) {
+              error('location header not found in response');
+              return left(ThreadPublishLocationNotFoundException());
+            }
+            final locations = value.headers.map[HttpHeaders.locationHeader];
+            if (locations?.isEmpty ?? true) {
+              error('empty location header');
+              return left(ThreadPublishLocationNotFoundException());
+            }
+            return right(locations!.first);
+        }
+      });
+}

lib/features/thread_publish/views/thread_publish_page.dart

@@ -1,9 +1,13 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:go_router/go_router.dart';
+import 'package:tsdm_client/features/thread_publish/bloc/thread_publish_bloc.dart';
+import 'package:tsdm_client/features/thread_publish/repository/thread_pub_repository.dart';
+import 'package:tsdm_client/i18n/strings.g.dart';
+import 'package:tsdm_client/routes/screen_paths.dart';
+import 'package:tsdm_client/utils/show_toast.dart';
 import 'package:tsdm_client/widgets/list_app_bar.dart';
 
-import '../../../routes/screen_paths.dart';
-
 /// Page to publish new thread.
 ///
 /// Similar to post edit page, especially when editing the first floor, but
@@ -31,17 +35,37 @@ class ThreadPublishPage extends StatefulWidget {
 class _ThreadPublishPageState extends State<ThreadPublishPage> {
   @override
   Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: ListAppBar(
-        title: 'publish new thread',
-        onSearch: () async {
-          await context.pushNamed(
-            ScreenPaths.search,
-            queryParameters: {'fid': widget.fid},
-          );
+    return MultiBlocProvider(
+      providers: [
+        RepositoryProvider(create: (_) => const ThreadPubRepository()),
+        BlocProvider(
+          create: (context) => ThreadPubBloc(RepositoryProvider.of(context)),
+        ),
+      ],
+      child: BlocListener<ThreadPubBloc, ThreadPubState>(
+        listener: (context, state) {
+          if (state.status == ThreadPubStatus.failure) {
+            showFailedToLoadSnackBar(context);
+          }
         },
+        child: BlocBuilder(
+          builder: (context, state) {
+            // TODO: Page body.
+            return Scaffold(
+              appBar: ListAppBar(
+                title: context.t.threadPublishPage.title,
+                onSearch: () async {
+                  await context.pushNamed(
+                    ScreenPaths.search,
+                    queryParameters: {'fid': widget.fid},
+                  );
+                },
+              ),
+              body: Center(child: Text('FID=${widget.fid}')),
+            );
+          },
+        ),
       ),
-      body: Center(child: Text('FID=${widget.fid}')),
     );
   }
 }