markdown support for talk messages

2026-08-16 21:35:41 +02:00
parent bd83a88e70
commit 02a7b87b5b
14 changed files with 379 additions and 19 deletions
@@ -0,0 +1,76 @@
+import 'package:markdown/markdown.dart' as md;
+
+/// The Markdown feature set the app renders for Talk messages — CommonMark plus
+/// the GFM extensions the official Talk clients enable.
+///
+/// It deliberately omits `InlineHtmlSyntax` (raw HTML stays literal), footnotes,
+/// alert blocks, color swatches and `:shortcode:` emoji — matching Talk's
+/// restrictions. Shared by the renderer ([MessageMarkdown]) and the plain-text
+/// stripper below so both agree on what counts as Markdown.
+final md.ExtensionSet talkMarkdownExtensionSet = md.ExtensionSet(
+  <md.BlockSyntax>[
+    const md.FencedCodeBlockSyntax(),
+    const md.TableSyntax(),
+    const md.UnorderedListWithCheckboxSyntax(),
+    const md.OrderedListWithCheckboxSyntax(),
+  ],
+  <md.InlineSyntax>[
+    md.StrikethroughSyntax(),
+    md.AutolinkExtensionSyntax(),
+  ],
+);
+
+/// Block-level tags after which running text would otherwise glue together;
+/// their boundaries become a single space in the flattened preview.
+const Set<String> _blockTags = {
+  'p',
+  'li',
+  'blockquote',
+  'pre',
+  'h1',
+  'h2',
+  'h3',
+  'h4',
+  'h5',
+  'h6',
+  'br',
+  'hr',
+  'tr',
+  'th',
+  'td',
+};
+
+/// Flattens a Markdown [source] into a single line of readable plain text —
+/// markers (`**`, `#`, `` ` ``, list bullets, link/image syntax …) removed,
+/// links reduced to their label and images to their alt text. Used for the
+/// one-line previews (reply quote, conversation list) where Talk also strips
+/// formatting rather than rendering it.
+String markdownToPlainText(String source) {
+  final nodes = md.Document(
+    extensionSet: talkMarkdownExtensionSet,
+    encodeHtml: false,
+  ).parse(source);
+
+  final buffer = StringBuffer();
+  _collect(nodes, buffer);
+  return buffer.toString().replaceAll(RegExp(r'\s+'), ' ').trim();
+}
+
+void _collect(List<md.Node> nodes, StringBuffer buffer) {
+  for (final node in nodes) {
+    if (node is md.Text) {
+      buffer.write(node.text);
+    } else if (node is md.Element) {
+      // Images carry their text in the `alt` attribute, not in child nodes.
+      if (node.tag == 'img') {
+        buffer.write(node.attributes['alt'] ?? '');
+        continue;
+      }
+      final isBlock = _blockTags.contains(node.tag);
+      if (isBlock) buffer.write(' ');
+      final children = node.children;
+      if (children != null) _collect(children, buffer);
+      if (isBlock) buffer.write(' ');
+    }
+  }
+}