content: Add UserGroupMentionNode and update parseMention

Author: Ruhdee

lib/model/content.dart

@@ -1097,7 +1097,7 @@ class UserMentionNode extends MentionNode {
 
   /// The ID of the user being mentioned.
   ///
-  /// This is null for wildcard mentions, user group mentions,
+  /// This is null for wildcard mentions
   /// or when the user ID is unavailable in the HTML (e.g., legacy mentions).
   final int? userId;
 
@@ -1108,6 +1108,27 @@ class UserMentionNode extends MentionNode {
   }
 }
 
+class UserGroupMentionNode extends MentionNode {
+  const UserGroupMentionNode({
+    super.debugHtmlNode,
+    required super.nodes,
+    required super.isSilent,
+    required this.userGroupId,
+  });
+
+  /// The ID of the user group being mentioned.
+  ///
+  /// This is non-nullable because user group mentions
+  /// always have data-user-group-id.
+  final int userGroupId;
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(IntProperty('userGroupId', userGroupId));
+  }
+}
+
 // TODO(#646) add WildcardMentionNode
 
 sealed class EmojiNode extends InlineContentNode {
@@ -1325,15 +1346,16 @@ class _ZulipInlineContentParser {
       i++;
     }
 
+    String? mentionType;
     if (i >= classes.length) return null;
     if ((classes[i] == 'topic-mention' && !hasChannelWildcardClass)
         || classes[i] == 'user-mention'
         || (classes[i] == 'user-group-mention' && !hasChannelWildcardClass)) {
       // The class we already knew we'd find before we called this function.
-      // We ignore the distinction between these; see [UserMentionNode].
-      // Also, we don't expect "user-group-mention" and "channel-wildcard-mention"
+      // We don't expect "user-group-mention" and "channel-wildcard-mention"
       // to be in the list at the same time and neither we expect "topic-mention"
       // and "channel-wildcard-mention" to be in the list at the same time.
+      mentionType = classes[i];
       i++;
     }
 
@@ -1342,21 +1364,35 @@ class _ZulipInlineContentParser {
       return null;
     }
 
-    final userId = switch (element.attributes['data-user-id']) {
-      // For legacy, user group or wildcard mentions.
-      null || '*' => null,
-      final userIdString => int.tryParse(userIdString, radix: 10),
-    };
-
     // TODO assert MentionNode can't contain LinkNode;
     //   either a debug-mode check, or perhaps we can make expectations much
     //   tighter on a MentionNode's contents overall.
     final nodes = parseInlineContentList(element.nodes);
-    return UserMentionNode(
-      nodes: nodes,
-      userId: userId,
-      isSilent: isSilent,
-      debugHtmlNode: debugHtmlNode);
+
+    if (mentionType case 'user-group-mention') {
+      final userGroupId = int.tryParse(
+        element.attributes['data-user-group-id'] ?? '',
+        radix: 10);
+      if (userGroupId == null) {
+        return null;
+      }
+      return UserGroupMentionNode(
+        nodes: nodes,
+        isSilent: isSilent,
+        userGroupId: userGroupId,
+        debugHtmlNode: debugHtmlNode);
+    } else {
+      final userId = switch (element.attributes['data-user-id']) {
+        // For legacy or wildcard mentions.
+        null || '*' => null,
+        final userIdString => int.tryParse(userIdString, radix: 10),
+      };
+      return UserMentionNode(
+        nodes: nodes,
+        isSilent: isSilent,
+        userId: userId,
+        debugHtmlNode: debugHtmlNode);
+    }
   }
 
   /// The links found so far in the current block inline container.

test/model/content_test.dart

@@ -132,21 +132,21 @@ class ContentExample {
     "@*test-empty*",
     expectedText: '@test-empty',
     '<p><span class="user-group-mention" data-user-group-id="186">@test-empty</span></p>',
-    const UserMentionNode(nodes: [TextNode('@test-empty')], isSilent: false, userId: null));
+    const UserGroupMentionNode(nodes: [TextNode('@test-empty')], isSilent: false, userGroupId: 186));
 
   static final groupMentionSilent = ContentExample.inline(
     'silent group @-mention',
     "@_*test-empty*",
     expectedText: 'test-empty',
     '<p><span class="user-group-mention silent" data-user-group-id="186">test-empty</span></p>',
-    const UserMentionNode(nodes: [TextNode('test-empty')], isSilent: true, userId: null));
+    const UserGroupMentionNode(nodes: [TextNode('test-empty')], isSilent: true, userGroupId: 186));
 
   static final groupMentionSilentClassOrderReversed = ContentExample.inline(
     'silent group @-mention, class order reversed',
     "@_*test-empty*", // (hypothetical server variation)
     expectedText: 'test-empty',
     '<p><span class="silent user-group-mention" data-user-group-id="186">test-empty</span></p>',
-    const UserMentionNode(nodes: [TextNode('test-empty')], isSilent: true, userId: null));
+    const UserGroupMentionNode(nodes: [TextNode('test-empty')], isSilent: true, userGroupId: 186));
 
   static final channelWildcardMentionPlain = ContentExample.inline(
     'plain channel wildcard @-mention',