feat: store subscription posts with a read mark and split the library controller

app/lib/application/controllers/subscriptions_controller.dart

@@ -0,0 +1,50 @@
+import 'package:signals/signals.dart';
+
+import '../../database/database.dart';
+import '../../mews/document.dart';
+
+/// Which sites the reader subscribes to (spec 6). The posts themselves live in
+/// the database, so an unread post survives a restart; only the set of
+/// addresses is held here, because that is what the chrome watches.
+class SubscriptionsController {
+  SubscriptionsController(this._db);
+
+  final MewsDatabase _db;
+
+  final subscribedUrls = signal(<String>{});
+
+  Future<void> load() async {
+    final rows = await _db.allSubscriptions();
+    subscribedUrls.value = rows.map((row) => row.url).toSet();
+  }
+
+  bool isSubscribed(String url) => subscribedUrls.value.contains(url);
+
+  Future<void> toggle(MewsPage page) async {
+    if (isSubscribed(page.url)) {
+      await remove(page.url);
+      return;
+    }
+    await _db.addSubscription(page.url, page.title, page.atomFeedHref);
+    subscribedUrls.value = {...subscribedUrls.value, page.url};
+    // The posts already on the page are the site's back catalogue, not news,
+    // so they are stored read and only later posts are flagged.
+    await _db.addEntries(page.url, page.entries, read: true);
+  }
+
+  Future<void> remove(String siteUrl) async {
+    await _db.removeSubscription(siteUrl);
+    subscribedUrls.value = {...subscribedUrls.value}..remove(siteUrl);
+  }
+
+  /// Records the posts on a subscribed page the reader just opened, and
+  /// returns the ones that are new. Does nothing for a site not subscribed to.
+  Future<List<MewsEntry>> refreshSite(MewsPage page) async {
+    if (!isSubscribed(page.url)) return const [];
+    await _db.describeSubscription(page.url,
+        title: page.title, atomHref: page.atomFeedHref);
+    final fresh = await _db.addEntries(page.url, page.entries);
+    await _db.touchSubscription(page.url, DateTime.now());
+    return fresh;
+  }
+}