feat: add Gemini and Spartan protocol support

app/lib/mews/gemtext.dart

@@ -0,0 +1,154 @@
+/// Converts gemtext, the format Gemini and Spartan pages are written in, into
+/// the document model (document.dart), so protocol pages render through the
+/// same reader presentation as Mews pages. Gemtext declares neither structure
+/// nor metadata: there is no inline markup, no head, no title, so the first
+/// level-1 heading stands in for a title and the reader presentation decides
+/// everything else.
+///
+/// A link line whose label begins with a date is a dated entry (mews-spec
+/// 6.1), which keeps subscriptions working on protocol sites.
+library;
+
+import 'dart:convert';
+
+import 'document.dart';
+
+/// The conformance marker gemtext pages carry in place of the Mews one, so the
+/// renderer applies the reader presentation instead of falling back to plain.
+const gemtextSpecVersion = 'gemtext';
+
+final _entryDatePattern = RegExp(r'^(\d{4}-\d{2}-\d{2}) (.+)$');
+
+MewsPage parseGemtextPage({required String source, required String url}) {
+  final blocks = <MewsBlock>[];
+  final entries = <MewsEntry>[];
+  String? title;
+
+  var inPre = false;
+  final pre = StringBuffer();
+  final quote = StringBuffer();
+  final linkItems = <MewsListItem>[];
+
+  void closePre() {
+    // One trailing newline rides with the last line; the fence is not content.
+    blocks.add(PreBlock(pre.toString().replaceFirst(RegExp(r'\n$'), '')));
+    pre.clear();
+  }
+
+  // Consecutive lines of one kind are gathered until a line of another kind
+  // ends them.
+  void closeQuote() {
+    if (quote.isEmpty) return;
+    final lines = quote.toString().split('\n');
+    blocks.add(QuoteBlock([
+      for (final line in lines)
+        if (line.trim().isNotEmpty) ParagraphBlock([MewsText(line.trim())]),
+    ]));
+    quote.clear();
+  }
+
+  void closeLinks() {
+    if (linkItems.isEmpty) return;
+    blocks.add(ListBlock(ordered: false, start: 1, items: List.of(linkItems)));
+    linkItems.clear();
+  }
+
+  for (final line in const LineSplitter().convert(source)) {
+    if (inPre) {
+      if (line.startsWith('```')) {
+        closePre();
+        inPre = false;
+      } else {
+        pre.writeln(line);
+      }
+      continue;
+    }
+    if (line.startsWith('```')) {
+      closeQuote();
+      closeLinks();
+      inPre = true;
+      continue;
+    }
+    if (line.startsWith('=>')) {
+      closeQuote();
+      final parts = line.substring(2).trim().split(RegExp(r'\s+'));
+      if (parts.isEmpty || parts.first.isEmpty) continue;
+      final href = Uri.parse(url).resolve(parts.first).toString();
+      final label = parts.skip(1).join(' ').trim();
+      final text = label.isEmpty ? parts.first : label;
+      final match = _entryDatePattern.firstMatch(text);
+      if (match != null) {
+        final date = DateTime.tryParse(match.group(1)!);
+        if (date != null) {
+          entries.add(MewsEntry(url: href, date: date, title: match.group(2)!.trim()));
+        }
+      }
+      linkItems.add(MewsListItem([ParagraphBlock([MewsLink(href, [MewsText(text)])])]));
+      continue;
+    }
+    closeLinks();
+    if (line.startsWith('###') && !line.startsWith('####')) {
+      closeQuote();
+      final text = line.substring(3).trim();
+      blocks.add(HeadingBlock(3, [MewsText(text)]));
+    } else if (line.startsWith('##') && !line.startsWith('###')) {
+      closeQuote();
+      final text = line.substring(2).trim();
+      blocks.add(HeadingBlock(2, [MewsText(text)]));
+    } else if (line.startsWith('#') && !line.startsWith('##')) {
+      closeQuote();
+      final text = line.substring(1).trim();
+      final heading = HeadingBlock(1, [MewsText(text)]);
+      title ??= text;
+      blocks.add(heading);
+    } else if (line.startsWith('* ')) {
+      closeQuote();
+      _listOf(blocks).items.add(MewsListItem([ParagraphBlock([MewsText(line.substring(2).trim())])]));
+    } else if (line.startsWith('>')) {
+      quote.writeln(line.substring(1).trim());
+    } else if (line.trim().isNotEmpty) {
+      closeQuote();
+      blocks.add(ParagraphBlock([MewsText(line.trim())]));
+    } else {
+      closeQuote();
+    }
+  }
+  if (inPre) closePre();
+  closeQuote();
+  closeLinks();
+
+  entries.sort((a, b) => b.date.compareTo(a.date));
+
+  final text = source;
+  return MewsPage(
+    url: url,
+    specVersion: gemtextSpecVersion,
+    title: title,
+    lang: _langOf(text),
+    direction: _isRtl(text) ? TextDirection.rtl : TextDirection.ltr,
+    variant: MewsVariant.plain,
+    entries: entries,
+    body: blocks,
+  );
+}
+
+/// Appends a list block to build on, reusing the last one while consecutive
+/// items keep coming.
+ListBlock _listOf(List<MewsBlock> blocks) {
+  if (blocks.isNotEmpty && blocks.last is ListBlock && !(blocks.last as ListBlock).ordered) {
+    return blocks.last as ListBlock;
+  }
+  final fresh = ListBlock(ordered: false, start: 1, items: []);
+  blocks.add(fresh);
+  return fresh;
+}
+
+final _rtlPattern = RegExp(r'[\u0590-\u08FF]');
+
+bool _isRtl(String text) => _rtlPattern.hasMatch(text);
+
+String _langOf(String text) {
+  if (RegExp(r'[\u0590-\u05FF]').hasMatch(text)) return 'he';
+  if (RegExp(r'[\u0600-\u06FF]').hasMatch(text)) return 'ar';
+  return 'en';
+}