content [nfc]: Extract a superclass for ZulipContent

This prepares for later changes that introduce new content types
like polls and todos.

There is no user visible change here yet.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/model/content.dart

@@ -72,13 +72,16 @@ mixin UnimplementedNode on ContentNode {
   }
 }
 
+/// A parsed, ready-to-render representation of Zulip message content.
+sealed class ZulipMessageContent {}
+
 /// A complete parse tree for a Zulip message's content,
 /// or other complete piece of Zulip HTML content.
 ///
 /// This is a parsed representation for an entire value of [Message.content],
 /// [Stream.renderedDescription], or other text from a Zulip server that comes
 /// in the same Zulip HTML format.
-class ZulipContent extends ContentNode {
+class ZulipContent extends ContentNode implements ZulipMessageContent {
   const ZulipContent({super.debugHtmlNode, required this.nodes});
 
   final List<BlockContentNode> nodes;

lib/model/message_list.dart

@@ -35,7 +35,7 @@ class MessageListDateSeparatorItem extends MessageListItem {
 /// A message to show in the message list.
 class MessageListMessageItem extends MessageListItem {
   final Message message;
-  ZulipContent content;
+  ZulipMessageContent content;
   bool showSender;
   bool isLastInBlock;
 
@@ -98,7 +98,7 @@ mixin _MessageSequence {
   ///
   /// This information is completely derived from [messages].
   /// It exists as an optimization, to memoize the work of parsing.
-  final List<ZulipContent> contents = [];
+  final List<ZulipMessageContent> contents = [];
 
   /// The messages and their siblings in the UI, in order.
   ///
@@ -134,10 +134,14 @@ mixin _MessageSequence {
     }
   }
 
+  ZulipMessageContent _parseMessageContent(Message message) {
+    return parseContent(message.content);
+  }
+
   /// Update data derived from the content of the index-th message.
   void _reparseContent(int index) {
     final message = messages[index];
-    final content = parseContent(message.content);
+    final content = _parseMessageContent(message);
     contents[index] = content;
 
     final itemIndex = findItemWithMessageId(message.id);
@@ -154,7 +158,7 @@ mixin _MessageSequence {
   void _addMessage(Message message) {
     assert(contents.length == messages.length);
     messages.add(message);
-    contents.add(parseContent(message.content));
+    contents.add(_parseMessageContent(message));
     assert(contents.length == messages.length);
     _processMessage(messages.length - 1);
   }
@@ -197,7 +201,7 @@ mixin _MessageSequence {
   /// If none of [messageIds] are found, this is a no-op.
   bool _removeMessagesById(Iterable<int> messageIds) {
     final messagesToRemoveById = <int>{};
-    final contentToRemove = Set<ZulipContent>.identity();
+    final contentToRemove = Set<ZulipMessageContent>.identity();
     for (final messageId in messageIds) {
       final index = _findMessageWithId(messageId);
       if (index == -1) continue;
@@ -223,7 +227,7 @@ mixin _MessageSequence {
     assert(contents.length == messages.length);
     messages.insertAll(index, toInsert);
     contents.insertAll(index, toInsert.map(
-      (message) => parseContent(message.content)));
+      (message) => _parseMessageContent(message)));
     assert(contents.length == messages.length);
     _reprocessAll();
   }
@@ -243,7 +247,7 @@ mixin _MessageSequence {
   void _recompute() {
     assert(contents.length == messages.length);
     contents.clear();
-    contents.addAll(messages.map((message) => parseContent(message.content)));
+    contents.addAll(messages.map((message) => _parseMessageContent(message)));
     assert(contents.length == messages.length);
     _reprocessAll();
   }

lib/widgets/content.dart

@@ -225,14 +225,17 @@ class MessageContent extends StatelessWidget {
   const MessageContent({super.key, required this.message, required this.content});
 
   final Message message;
-  final ZulipContent content;
+  final ZulipMessageContent content;
 
   @override
   Widget build(BuildContext context) {
+    final content = this.content;
     return InheritedMessage(message: message,
       child: DefaultTextStyle(
         style: ContentTheme.of(context).textStylePlainParagraph,
-        child: BlockContentList(nodes: content.nodes)));
+        child: switch (content) {
+          ZulipContent() => BlockContentList(nodes: content.nodes),
+        }));
   }
 }
 

test/model/message_list_checks.dart

@@ -15,7 +15,7 @@ extension MessageListDateSeparatorItemChecks on Subject<MessageListDateSeparator
 
 extension MessageListMessageItemChecks on Subject<MessageListMessageItem> {
   Subject<Message> get message => has((x) => x.message, 'message');
-  Subject<ZulipContent> get content => has((x) => x.content, 'content');
+  Subject<ZulipMessageContent> get content => has((x) => x.content, 'content');
   Subject<bool> get showSender => has((x) => x.showSender, 'showSender');
   Subject<bool> get isLastInBlock => has((x) => x.isLastInBlock, 'isLastInBlock');
 }
@@ -24,7 +24,7 @@ extension MessageListViewChecks on Subject<MessageListView> {
   Subject<PerAccountStore> get store => has((x) => x.store, 'store');
   Subject<Narrow> get narrow => has((x) => x.narrow, 'narrow');
   Subject<List<Message>> get messages => has((x) => x.messages, 'messages');
-  Subject<List<ZulipContent>> get contents => has((x) => x.contents, 'contents');
+  Subject<List<ZulipMessageContent>> get contents => has((x) => x.contents, 'contents');
   Subject<List<MessageListItem>> get items => has((x) => x.items, 'items');
   Subject<bool> get fetched => has((x) => x.fetched, 'fetched');
   Subject<bool> get haveOldest => has((x) => x.haveOldest, 'haveOldest');

test/model/message_list_test.dart

@@ -1260,12 +1260,13 @@ void main() {
     model.contents[0] = const ZulipContent(nodes: [
       ParagraphNode(links: null, nodes: [TextNode('something outdated')])
     ]);
-    check(model.contents[0]).not((it) => it.equalsNode(correctContent));
+    check(model.contents[0]).isA<ZulipContent>()
+      .not((it) => it.equalsNode(correctContent));
 
     model.reassemble();
     checkNotifiedOnce();
     check(model).messages.length.equals(31);
-    check(model.contents[0]).equalsNode(correctContent);
+    check(model.contents[0]).isA<ZulipContent>().equalsNode(correctContent);
   });
 
   group('stream/topic muting', () {
@@ -1743,7 +1744,7 @@ void checkInvariants(MessageListView model) {
 
   check(model).contents.length.equals(model.messages.length);
   for (int i = 0; i < model.contents.length; i++) {
-    check(model.contents[i])
+    check(model.contents[i]).isA<ZulipContent>()
       .equalsNode(parseContent(model.messages[i].content));
   }