feat: add quotations from marked text, with citations and sharing

app/lib/database/database.dart

@@ -148,6 +148,21 @@ class SiteCertificates extends Table {
   Set<Column> get primaryKey => {host, port};
 }
 
+/// A stretch of text the reader marked on a page and kept, together with the
+/// page it came from. The author is carried only when the page's metadata
+/// said one, and the site's title when the reader's subscriptions know the
+/// site the page belongs to. The column is named [Quotations.quote] because
+/// `text` is the drift builder the declaration would otherwise call.
+class Quotations extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get pageUrl => text()();
+  TextColumn get pageTitle => text().nullable()();
+  TextColumn get author => text().nullable()();
+  TextColumn get siteTitle => text().nullable()();
+  TextColumn get quote => text()();
+  DateTimeColumn get createdAt => dateTime().withDefault(currentDateAndTime)();
+}
+
 @DriftDatabase(tables: [
   HistoryItems,
   Bookmarks,
@@ -160,6 +175,7 @@ class SiteCertificates extends Table {
   ClientCertificates,
   SiteCertificates,
   FirstStart,
+  Quotations,
 ])
 class MewsDatabase extends _$MewsDatabase {
   MewsDatabase() : super(_open());
@@ -168,7 +184,7 @@ class MewsDatabase extends _$MewsDatabase {
   MewsDatabase.test(super.executor);
 
   @override
-  int get schemaVersion => 6;
+  int get schemaVersion => 8;
 
   @override
   MigrationStrategy get migration => MigrationStrategy(
@@ -197,6 +213,12 @@ class MewsDatabase extends _$MewsDatabase {
           if (from < 6) {
             await m.createTable(firstStart);
           }
+          if (from < 7) {
+            await m.createTable(quotations);
+          }
+          if (from < 8) {
+            await m.addColumn(quotations, quotations.siteTitle);
+          }
         },
       );
 
@@ -717,6 +739,87 @@ class MewsDatabase extends _$MewsDatabase {
     return [for (final row in rows) '${row.host}:${row.port}'];
   }
 
+  // Quotations --------------------------------------------------------------
+
+  /// Keeps a marked stretch of text together with the page it came from,
+  /// and with the site's title when the reader's subscriptions know the site
+  /// the page belongs to: the site whose posts listed the page, or the page
+  /// itself when it is the subscribed one.
+  Future<void> addQuotation({
+    required String quote,
+    required String pageUrl,
+    String? pageTitle,
+    String? author,
+  }) async {
+    into(quotations).insert(QuotationsCompanion.insert(
+      quote: quote,
+      pageUrl: pageUrl,
+      pageTitle: Value(pageTitle),
+      author: Value(author),
+      siteTitle: Value(await siteTitleOf(pageUrl)),
+    ));
+  }
+
+  /// The title of the site [pageUrl] belongs to, or null when the reader's
+  /// subscriptions do not know it. A page the site lists as a post takes the
+  /// subscribing site's title; a subscribed page is its own site.
+  Future<String?> siteTitleOf(String pageUrl) async {
+    final site = alias(subscriptions, 'site');
+    final throughPosts = await ((select(feedEntries).join([
+      leftOuterJoin(site, site.url.equalsExp(feedEntries.siteUrl)),
+    ]))
+          ..where(feedEntries.url.equals(pageUrl)))
+        .get();
+    if (throughPosts.isNotEmpty) {
+      return throughPosts.first.readTableOrNull(site)?.title;
+    }
+    final own =
+        await (select(subscriptions)..where((r) => r.url.equals(pageUrl)))
+            .getSingleOrNull();
+    return own?.title;
+  }
+
+  Future<void> removeQuotation(int id) =>
+      (delete(quotations)..where((q) => q.id.equals(id))).go();
+
+  /// One quotation, so an action address can act on it.
+  Future<Quotation?> quotationById(int id) =>
+      (select(quotations)..where((q) => q.id.equals(id))).getSingleOrNull();
+
+  /// Every kept quotation, for the quotations page. [query] narrows by the
+  /// quoted text, the page's title, its author or its address.
+  Future<List<Quotation>> quotationsList({
+    QuotationSort sort = QuotationSort.date,
+    String? query,
+  }) async {
+    final statement = select(quotations)
+      ..orderBy(switch (sort) {
+        QuotationSort.date => [
+            // Tiebreak quotations saved within the same clock tick.
+            (r) => OrderingTerm.desc(r.createdAt),
+            (r) => OrderingTerm.asc(r.id),
+          ],
+        QuotationSort.page => [
+            // A page without a title sorts under its address, so the order
+            // never depends on a null.
+            (r) => OrderingTerm.asc(coalesce([r.pageTitle, r.pageUrl])),
+            (r) => OrderingTerm.desc(r.createdAt),
+          ],
+      });
+    final filter = _search(
+        [quotations.quote, quotations.pageTitle, quotations.author, quotations.pageUrl],
+        query);
+    if (filter != null) statement.where((_) => filter);
+    return statement.get();
+  }
+
+  /// How many quotations are held, for the hub.
+  Future<int> countQuotations() async {
+    final total = quotations.id.count();
+    final query = selectOnly(quotations)..addColumns([total]);
+    return (await query.getSingle()).read(total) ?? 0;
+  }
+
   /// Binds a certificate to a host, replacing whatever was bound before.
   Future<void> bindCertificate(String host, int port, int certificateId) =>
       into(siteCertificates).insert(
@@ -743,6 +846,17 @@ enum EntrySort {
   };
 }
 
+/// How the quotations page is ordered.
+enum QuotationSort {
+  date,
+  page;
+
+  /// Reads the order from an address, falling back to the default rather than
+  /// refusing a value the reader may have typed.
+  static QuotationSort parse(String? name) =>
+      name == 'page' ? QuotationSort.page : QuotationSort.date;
+}
+
 /// How widely one tag is used.
 class TagUse {
   const TagUse({required this.bookmarks, required this.sites});