Add source kinds and the Learn tab with Learning sources (#2)

Every Source now has a kind: News, Learning or Fun. Curated Sources default
to News, and custom Sources persist their kind (ones saved before default
to News). Each kind has its own time window: News follows the 12/24/48 h
setting, Learning reaches back 14 days, Fun 3 days.

A new Learn tab between Briefing and Sources lists Learning articles with
the same paid/sponsored filters and reader view as Today. It is built from
a list of kinds so a Fun section can follow. Today and the Briefing only
use News. ByteByteGo is the first Learning source, on by default.

The home shell names its tabs instead of using hard-coded indexes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/data/default_sources.dart

@@ -184,6 +184,18 @@ const defaultSources = <NewsSource>[
     language: SourceLanguage.en,
     description: 'Security and malware news',
   ),
+
+  // --- Learning -----------------------------------------------------------
+  NewsSource(
+    id: 'bytebytego',
+    name: 'ByteByteGo',
+    feedUrl: 'https://blog.bytebytego.com/feed',
+    homepage: 'https://blog.bytebytego.com',
+    language: SourceLanguage.en,
+    kind: SourceKind.learning,
+    description: 'System design explained with diagrams',
+    enabledByDefault: true,
+  ),
 ];
 
 /// The curated sources before the app remembered which ones it had seen.

lib/models/news_source.dart

@@ -8,6 +8,19 @@ enum SourceLanguage {
   final String flag;
 }
 
+/// What a Source's articles are for; see GLOSSARY.md. Each kind has its own
+/// section in the app and its own time window.
+enum SourceKind {
+  news('News'),
+  learning('Learning'),
+  fun('Fun');
+
+  const SourceKind(this.label);
+
+  final String label;
+}
+
+/// A Source of any [kind]; the class name predates the kinds.
 class NewsSource {
   const NewsSource({
     required this.id,
@@ -15,6 +28,7 @@ class NewsSource {
     required this.feedUrl,
     required this.homepage,
     required this.language,
+    this.kind = SourceKind.news,
     this.description = '',
     this.enabledByDefault = false,
     this.isCustom = false,
@@ -26,6 +40,7 @@ class NewsSource {
   final String feedUrl;
   final String homepage;
   final SourceLanguage language;
+  final SourceKind kind;
   final String description;
   final bool enabledByDefault;
   final bool isCustom;
@@ -40,6 +55,7 @@ class NewsSource {
         'feedUrl': feedUrl,
         'homepage': homepage,
         'language': language.name,
+        'kind': kind.name,
         'description': description,
       };
 
@@ -49,6 +65,8 @@ class NewsSource {
         feedUrl: json['feedUrl'] as String,
         homepage: json['homepage'] as String? ?? '',
         language: SourceLanguage.values.byName(json['language'] as String? ?? 'en'),
+        // Custom sources saved before kinds existed are News sources.
+        kind: SourceKind.values.asNameMap()[json['kind']] ?? SourceKind.news,
         description: json['description'] as String? ?? '',
         isCustom: true,
       );

lib/services/feed_service.dart

@@ -23,14 +23,15 @@ class FeedService {
 
   static const _timeout = Duration(seconds: 20);
 
-  /// Fetches all [sources] in parallel. Failing feeds are reported in
+  /// Fetches all [sources] in parallel and drops articles older than the age
+  /// [maxAgeOf] gives for their Source. Failing feeds are reported in
   /// [FeedResult.errors] instead of failing the whole refresh.
   ///
   /// [corsProxy] is only used on web, where browsers block cross-origin feed
   /// requests. It is prepended to the feed URL, e.g. `https://proxy/?url=`.
   Future<FeedResult> fetchAll(
     List<NewsSource> sources, {
-    required Duration maxAge,
+    required Duration Function(NewsSource source) maxAgeOf,
     String corsProxy = '',
   }) async {
     final errors = <String, String>{};
@@ -43,12 +44,15 @@ class FeedService {
       }
     }));
 
-    final cutoff = DateTime.now().toUtc().subtract(maxAge);
+    final now = DateTime.now().toUtc();
     final seen = <String>{};
     final articles = <Article>[
-      for (final list in results)
+      for (final (i, list) in results.indexed)
         for (final a in list)
-          if ((a.published == null || a.published!.isAfter(cutoff)) && seen.add(a.id)) a,
+          if ((a.published == null ||
+                  a.published!.isAfter(now.subtract(maxAgeOf(sources[i])))) &&
+              seen.add(a.id))
+            a,
     ];
     articles.sort((a, b) {
       final pa = a.published, pb = b.published;

lib/state/app_state.dart

@@ -34,8 +34,10 @@ class AppState extends ChangeNotifier {
     FeedService? feedService,
     ArticleExtractor? extractor,
     List<NewsSource> curatedSources = defaultSources,
+    Summarizer? summarizer,
   })  : _feeds = feedService ?? FeedService(),
         _curated = curatedSources,
+        _summarizerOverride = summarizer,
         consent = ConsentService(),
         paywall = PaywallService(_storage) {
     _extractor = extractor ?? ArticleExtractor(consent: consent);
@@ -46,6 +48,9 @@ class AppState extends ChangeNotifier {
 
   /// The curated catalog; [defaultSources] outside of tests.
   final List<NewsSource> _curated;
+
+  /// Used instead of the AI set up in [settings]; for tests.
+  final Summarizer? _summarizerOverride;
   late final ArticleExtractor _extractor;
   final PaywallService paywall;
 
@@ -56,7 +61,7 @@ class AppState extends ChangeNotifier {
   List<NewsSource> customSources = [];
   Set<String> enabledSourceIds = {};
 
-  /// Everything the feeds returned; see [visibleArticles] for what is shown.
+  /// Everything the feeds returned; see [articlesOf] for what is shown.
   List<Article> articles = [];
   Map<String, String> feedErrors = {};
   bool loading = false;
@@ -77,10 +82,22 @@ class AppState extends ChangeNotifier {
       (settings.hidePaid && paywall.isPaid(a)) ||
       (settings.hideSponsored && paywall.isSponsored(a));
 
-  /// Articles after the paid/sponsored filters. The feed and the briefing use these.
-  List<Article> get visibleArticles => articles.where((a) => !_isHidden(a)).toList();
+  /// Articles from Sources of [kind] after the paid/sponsored filters. Today
+  /// and the Briefing use News, the Learn tab the other kinds.
+  List<Article> articlesOf(SourceKind kind) =>
+      articles.where((a) => a.source.kind == kind && !_isHidden(a)).toList();
 
-  int get hiddenCount => articles.where(_isHidden).length;
+  /// Articles from Sources of [kind] that the paid/sponsored filters hide.
+  int hiddenCountOf(SourceKind kind) =>
+      articles.where((a) => a.source.kind == kind && _isHidden(a)).length;
+
+  /// How far back articles from Sources of [kind] reach. News follows the
+  /// user's setting; the other kinds age slower.
+  Duration windowOf(SourceKind kind) => switch (kind) {
+        SourceKind.news => Duration(hours: settings.maxAgeHours),
+        SourceKind.learning => const Duration(days: 14),
+        SourceKind.fun => const Duration(days: 3),
+      };
 
   List<NewsSource> get allSources => [..._curated, ...customSources];
 
@@ -102,7 +119,7 @@ class AppState extends ChangeNotifier {
     notifyListeners();
     final result = await _feeds.fetchAll(
       enabledSources,
-      maxAge: Duration(hours: settings.maxAgeHours),
+      maxAgeOf: (source) => windowOf(source.kind),
       corsProxy: settings.corsProxy,
     );
     articles = result.articles;
@@ -148,6 +165,7 @@ class AppState extends ChangeNotifier {
     required String name,
     required String feedUrl,
     required SourceLanguage language,
+    SourceKind kind = SourceKind.news,
   }) async {
     final uri = Uri.tryParse(feedUrl);
     final source = NewsSource(
@@ -156,6 +174,7 @@ class AppState extends ChangeNotifier {
       feedUrl: feedUrl,
       homepage: uri == null ? '' : '${uri.scheme}://${uri.host}',
       language: language,
+      kind: kind,
       isCustom: true,
     );
     try {
@@ -226,7 +245,7 @@ class AppState extends ChangeNotifier {
 
   // --- AI ------------------------------------------------------------------
 
-  Summarizer? get _summarizer => switch (settings.aiProvider) {
+  Summarizer? get _summarizer => _summarizerOverride ?? switch (settings.aiProvider) {
         _ when !settings.aiConfigured => null,
         AiProvider.claude => ClaudeSummarizer(
             apiKey: settings.claudeApiKey, model: settings.claudeModel),
@@ -270,7 +289,7 @@ class AppState extends ChangeNotifier {
   Future<void> generateBriefing() async {
     final summarizer = _summarizer;
     if (summarizer == null || briefingLoading) return;
-    final articles = visibleArticles;
+    final articles = articlesOf(SourceKind.news);
     if (articles.isEmpty) {
       briefingError = 'No articles loaded yet. Pull to refresh the feed first.';
       notifyListeners();

lib/ui/briefing_screen.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import '../models/briefing.dart';
+import '../models/news_source.dart';
 import '../state/app_state.dart';
 import 'article_screen.dart';
 import 'briefing_history_screen.dart';
@@ -59,7 +60,7 @@ class BriefingScreen extends StatelessWidget {
     if (state.briefingLoading) {
       return EmptyState(
         icon: Icons.hourglass_top,
-        title: 'Reading ${state.visibleArticles.length} headlines…',
+        title: 'Reading ${state.articlesOf(SourceKind.news).length} headlines…',
         message: 'This usually takes 10-60 seconds.',
         action: const SizedBox(width: 160, child: LinearProgressIndicator()),
       );
@@ -69,7 +70,7 @@ class BriefingScreen extends StatelessWidget {
       icon: const Icon(Icons.auto_awesome),
       label: Text(state.loading
           ? 'Waiting for feeds…'
-          : 'Generate from ${state.visibleArticles.length} articles'),
+          : 'Generate from ${state.articlesOf(SourceKind.news).length} articles'),
     );
     if (briefing == null) {
       return EmptyState(

lib/ui/feed_screen.dart

@@ -25,13 +25,13 @@ class _FeedScreenState extends State<FeedScreen> {
       listenable: widget.state,
       builder: (context, _) {
         final state = widget.state;
-        final all = state.visibleArticles;
+        final all = state.articlesOf(SourceKind.news);
         final visible = all
             .where((a) => _language == null || a.source.language == _language)
             .where((a) => _sourceId == null || a.source.id == _sourceId)
             .toList();
         final sourcesInFeed = {for (final a in all) a.source.id: a.source};
-        final hidden = state.hiddenCount;
+        final hidden = state.hiddenCountOf(SourceKind.news);
 
         return Scaffold(
           appBar: AppBar(

lib/ui/home_shell.dart

@@ -3,9 +3,13 @@ import 'package:flutter/material.dart';
 import '../state/app_state.dart';
 import 'briefing_screen.dart';
 import 'feed_screen.dart';
+import 'learn_screen.dart';
 import 'settings_screen.dart';
 import 'sources_screen.dart';
 
+/// The tabs in the order they appear in the navigation bar.
+enum _Tab { today, briefing, learn, sources, settings }
+
 class HomeShell extends StatefulWidget {
   const HomeShell({super.key, required this.state});
 
@@ -16,20 +20,20 @@ class HomeShell extends StatefulWidget {
 }
 
 class _HomeShellState extends State<HomeShell> {
-  int _index = 0;
+  _Tab _tab = _Tab.today;
   bool _sourcesChanged = false;
 
-  void _select(int index) {
+  void _select(_Tab tab) {
     // A text field left focused in Settings would otherwise get focus back
     // (and open the keyboard) when returning from an article.
     FocusManager.instance.primaryFocus?.unfocus();
     // Source toggles only take effect on the next refresh; do it when the
     // user leaves the Sources tab.
-    if (_index == 2 && index != 2 && _sourcesChanged) {
+    if (_tab == _Tab.sources && tab != _Tab.sources && _sourcesChanged) {
       _sourcesChanged = false;
       widget.state.refresh();
     }
-    setState(() => _index = index);
+    setState(() => _tab = tab);
   }
 
   @override
@@ -37,20 +41,27 @@ class _HomeShellState extends State<HomeShell> {
     final state = widget.state;
     return Scaffold(
       body: IndexedStack(
-        index: _index,
+        index: _tab.index,
         children: [
-          FeedScreen(state: state),
-          BriefingScreen(state: state, openSettings: () => _select(3)),
-          SourcesScreen(state: state, onChanged: () => _sourcesChanged = true),
-          SettingsScreen(state: state),
-        ].indexed
+          for (final tab in _Tab.values)
             // Hidden tabs stay alive but must not hold or regain focus.
-            .map((e) => ExcludeFocus(excluding: e.$1 != _index, child: e.$2))
-            .toList(),
+            ExcludeFocus(
+              excluding: tab != _tab,
+              child: switch (tab) {
+                _Tab.today => FeedScreen(state: state),
+                _Tab.briefing => BriefingScreen(
+                    state: state, openSettings: () => _select(_Tab.settings)),
+                _Tab.learn => LearnScreen(state: state),
+                _Tab.sources =>
+                  SourcesScreen(state: state, onChanged: () => _sourcesChanged = true),
+                _Tab.settings => SettingsScreen(state: state),
+              },
+            ),
+        ],
       ),
       bottomNavigationBar: NavigationBar(
-        selectedIndex: _index,
-        onDestinationSelected: _select,
+        selectedIndex: _tab.index,
+        onDestinationSelected: (i) => _select(_Tab.values[i]),
         destinations: const [
           NavigationDestination(
               icon: Icon(Icons.newspaper_outlined),
@@ -60,6 +71,10 @@ class _HomeShellState extends State<HomeShell> {
               icon: Icon(Icons.auto_awesome_outlined),
               selectedIcon: Icon(Icons.auto_awesome),
               label: 'Briefing'),
+          NavigationDestination(
+              icon: Icon(Icons.school_outlined),
+              selectedIcon: Icon(Icons.school),
+              label: 'Learn'),
           NavigationDestination(
               icon: Icon(Icons.rss_feed_outlined),
               selectedIcon: Icon(Icons.rss_feed),

lib/ui/learn_screen.dart

@@ -0,0 +1,98 @@
+import 'package:flutter/material.dart';
+
+import '../models/news_source.dart';
+import '../state/app_state.dart';
+import 'article_screen.dart';
+import 'feed_screen.dart';
+
+/// Reading that keeps for days, from the Sources that aren't News: one
+/// section per kind, each with its own time window.
+class LearnScreen extends StatelessWidget {
+  const LearnScreen({super.key, required this.state});
+
+  final AppState state;
+
+  /// The sections, top to bottom.
+  static const kinds = [SourceKind.learning];
+
+  @override
+  Widget build(BuildContext context) {
+    return ListenableBuilder(
+      listenable: state,
+      builder: (context, _) => Scaffold(
+        appBar: AppBar(
+          title: const Text('Learn'),
+          actions: [
+            IconButton(
+              tooltip: 'Refresh',
+              onPressed: state.loading ? null : state.refresh,
+              icon: const Icon(Icons.refresh),
+            ),
+          ],
+        ),
+        body: Column(
+          children: [
+            if (state.loading) const LinearProgressIndicator(),
+            Expanded(
+              child: RefreshIndicator(
+                onRefresh: state.refresh,
+                child: ListView(
+                  padding: const EdgeInsets.fromLTRB(12, 0, 12, 24),
+                  children: [for (final kind in kinds) ..._section(context, kind)],
+                ),
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+
+  List<Widget> _section(BuildContext context, SourceKind kind) {
+    final theme = Theme.of(context);
+    final muted = theme.colorScheme.onSurfaceVariant;
+    final articles = state.articlesOf(kind);
+    final hidden = state.hiddenCountOf(kind);
+    final hasSources = state.enabledSources.any((s) => s.kind == kind);
+    return [
+      Padding(
+        padding: const EdgeInsets.fromLTRB(4, 16, 4, 8),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Text(kind.label,
+                style: theme.textTheme.titleMedium?.copyWith(color: theme.colorScheme.primary)),
+            Text(
+              '${articles.length} articles · last ${_describe(state.windowOf(kind))}'
+              '${hidden > 0 ? ' · $hidden paid/ads hidden' : ''}',
+              style: theme.textTheme.bodySmall?.copyWith(color: muted),
+            ),
+          ],
+        ),
+      ),
+      if (articles.isEmpty && !state.loading)
+        Padding(
+          padding: const EdgeInsets.fromLTRB(4, 8, 4, 16),
+          child: Text(
+            hasSources
+                ? 'Nothing new in this window. Pull down to refresh.'
+                : 'No ${kind.label} sources enabled. Turn some on in the Sources tab.',
+            style: theme.textTheme.bodyMedium?.copyWith(color: muted),
+          ),
+        ),
+      for (final article in articles)
+        Padding(
+          padding: const EdgeInsets.only(bottom: 8),
+          child: ArticleCard(
+            article: article,
+            hasSummary: state.summaries[article.id]?.text != null,
+            isPaid: state.paywall.isPaid(article),
+            onTap: () => openArticle(context, state, article),
+          ),
+        ),
+    ];
+  }
+
+  static String _describe(Duration window) =>
+      window.inHours < 72 ? '${window.inHours} h' : '${window.inDays} days';
+}