feat: offer a non-Mews web page as a simplified view or in the browser

app/lib/presentation/reader/reader_screen.dart

@@ -22,7 +22,6 @@ import '../../application/controllers/browser_controller.dart'
 import '../../database/database.dart' show ClientCertificate;
 import '../../application/pages/mews_urls.dart';
 import '../../mews/document.dart';
-import '../../mews/parser.dart' show mewsPlainText;
 import '../app.dart';
 import 'address_bar.dart';
 import 'mews_page_view.dart';
@@ -46,7 +45,11 @@ class _ReaderScreenState extends State<ReaderScreen> {
   /// scrolls down, back on any upward scroll. A pointer host with a keyboard
   /// has room to spare and keys to reach the bar, so it never hides.
   bool _chromeVisible = true;
-  bool _showBrokenText = false;
+
+  /// The address whose simplified view the reader asked for. Keyed by address
+  /// so the choice applies to that page alone: a link from it that also fails
+  /// explains itself rather than silently simplifying too.
+  String? _simplifiedFor;
   final _checkedSubscriptions = <String>{};
 
   // The finger behind a possible tap on the page, tracked outside the
@@ -274,7 +277,7 @@ class _ReaderScreenState extends State<ReaderScreen> {
       return SignalBuilder(builder: (context) {
         final error = deps.browser.error.value;
         return switch (error) {
-          BrokenPage(:final source) => _errorPage(context, source),
+          final BrokenPage broken => _errorPage(context, broken),
           LoadFailed() => _errorPage(context, null),
           // A protocol status carries the site's own words for what went
           // wrong.
@@ -300,7 +303,15 @@ class _ReaderScreenState extends State<ReaderScreen> {
     }
 
     _checkSubscription(context, page);
-    _showBrokenText = false;
+
+    return _pageView(context, page);
+  }
+
+  /// A page as the reader sees it. Both the fetched page and the simplified
+  /// view of a web page come through here, so they share the palette, the
+  /// fonts, the link handling and the choice to keep a quotation.
+  Widget _pageView(BuildContext context, MewsPage page) {
+    final deps = AppScope.of(context).deps;
 
     return SignalBuilder(builder: (context) {
       final settings = deps.settings;
@@ -536,20 +547,28 @@ class _ReaderScreenState extends State<ReaderScreen> {
     }
   }
 
-  Widget _errorPage(BuildContext context, String? brokenSource) {
+  /// The page that stands in for one the reader cannot have: [broken] is a
+  /// page the Mews parse refused, and null is a page that would not load.
+  Widget _errorPage(BuildContext context, BrokenPage? broken) {
     final strings = AppScope.of(context).strings;
     final deps = AppScope.of(context).deps;
 
     // A web address can be shown by the system's browser, so a page that
-    // will not load here can leave; a protocol page has nowhere else to go,
-    // so only trying again is offered there.
+    // will not load here, or that this client cannot read, can leave; a
+    // protocol page has nowhere else to go, so only trying again is offered
+    // there.
     final failed = deps.browser.currentAddress;
     final failedScheme = Uri.tryParse(failed)?.scheme;
-    final canOpenOutside =
-        brokenSource == null && (failedScheme == 'http' || failedScheme == 'https');
+    final canOpenOutside = failedScheme == 'http' || failedScheme == 'https';
+
+    // The simplified view is a page, not a notice, so it fills the screen
+    // rather than sitting in the centered column below.
+    if (broken?.simplified != null && _simplifiedFor == failed) {
+      return _pageView(context, broken!.simplified!);
+    }
 
     Widget content;
-    if (brokenSource == null) {
+    if (broken == null) {
       content = Column(
         mainAxisSize: MainAxisSize.min,
         children: [
@@ -568,25 +587,33 @@ class _ReaderScreenState extends State<ReaderScreen> {
           ],
         ],
       );
-    } else if (_showBrokenText) {
-      content = Column(
-        children: [
-          Text(strings.t('error-broken-page-text-title'),
-              style: Theme.of(context).textTheme.titleMedium),
-          const SizedBox(height: 8),
-          Expanded(child: SingleChildScrollView(child: Text(mewsPlainText(brokenSource)))),
-        ],
-      );
     } else {
+      // A page claiming the Mews marker that still will not parse has a real
+      // markup error. One that never claimed it is an ordinary web page, and
+      // saying so is the honest answer; the MIME type cannot tell them apart,
+      // since Mews pages are served as text/html (spec 7.1).
       content = Column(
         mainAxisSize: MainAxisSize.min,
         children: [
-          Text(strings.t('error-broken-page'), textAlign: TextAlign.center),
-          const SizedBox(height: 16),
-          FilledButton(
-            onPressed: _press(() => setState(() => _showBrokenText = true)),
-            child: Text(strings.t('error-broken-page-show-text')),
+          Text(
+            strings.t(broken.declaresMews
+                ? 'error-broken-page'
+                : 'error-not-mews-page'),
+            textAlign: TextAlign.center,
           ),
+          const SizedBox(height: 16),
+          if (broken.simplified != null)
+            FilledButton(
+              onPressed: _press(() => setState(() => _simplifiedFor = failed)),
+              child: Text(strings.t('error-show-simplified')),
+            ),
+          if (canOpenOutside) ...[
+            const SizedBox(height: 8),
+            OutlinedButton(
+              onPressed: _press(() => _openOutside(failed)),
+              child: Text(strings.t('error-open-in-browser')),
+            ),
+          ],
         ],
       );
     }