content: Start rendering poll content

We could also make Poll a subclass of ZulipMessageContent, but that
takes away our ability to seal ZulipMessageContent.  Making a wrapper
class around Poll is easy enough for keeping that benefit.

_reparseContent currently happens when there is content edit, which is
forbidden for poll messages, (and you can't turn an existing message
into a poll).  In most cases the same `PollContent` instance will be
used for each poll message, unlike `ZulipContent`, and a poll message
never needs to get reparsed.

Fixes: zulip#165

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

lib/model/content.dart

@@ -3,6 +3,7 @@ import 'package:flutter/foundation.dart';
 import 'package:html/dom.dart' as dom;
 import 'package:html/parser.dart';
 
+import '../api/model/submessage.dart';
 import 'code_block.dart';
 
 /// A node in a parse tree for Zulip message-style content.
@@ -75,6 +76,16 @@ mixin UnimplementedNode on ContentNode {
 /// A parsed, ready-to-render representation of Zulip message content.
 sealed class ZulipMessageContent {}
 
+/// A wrapper around a mutable representation of a Zulip poll message.
+///
+/// Consumers are expected to listen for [Poll]'s changes to receive
+/// live-updates.
+class PollContent implements ZulipMessageContent {
+  const PollContent(this.poll);
+
+  final Poll poll;
+}
+
 /// A complete parse tree for a Zulip message's content,
 /// or other complete piece of Zulip HTML content.
 ///

lib/model/message_list.dart

@@ -135,6 +135,8 @@ mixin _MessageSequence {
   }
 
   ZulipMessageContent _parseMessageContent(Message message) {
+    final poll = message.poll;
+    if (poll != null) return PollContent(poll);
     return parseContent(message.content);
   }
 

lib/widgets/content.dart

@@ -18,6 +18,7 @@ import 'dialog.dart';
 import 'icons.dart';
 import 'lightbox.dart';
 import 'message_list.dart';
+import 'poll.dart';
 import 'store.dart';
 import 'text.dart';
 
@@ -263,6 +264,7 @@ class MessageContent extends StatelessWidget {
         style: ContentTheme.of(context).textStylePlainParagraph,
         child: switch (content) {
           ZulipContent() => BlockContentList(nodes: content.nodes),
+          PollContent()  => PollWidget(poll: content.poll),
         }));
   }
 }

test/model/content_checks.dart

@@ -1,5 +1,7 @@
+import 'package:checks/checks.dart';
 import 'package:checks/context.dart';
 import 'package:flutter/foundation.dart';
+import 'package:zulip/api/model/submessage.dart';
 import 'package:zulip/model/content.dart';
 
 extension ContentNodeChecks on Subject<ContentNode> {
@@ -115,3 +117,7 @@ Iterable<LinkNode> _findLinkNodes(Iterable<InlineContentNode> nodes) {
     return _findLinkNodes(node.nodes);
   });
 }
+
+extension PollContentChecks on Subject<PollContent> {
+  Subject<Poll> get poll => has((x) => x.poll, 'poll');
+}

test/model/message_list_test.dart

@@ -1488,6 +1488,43 @@ void main() {
     });
   });
 
+  group('handle content parsing into subclasses of ZulipMessageContent', () {
+    test('ZulipContent', () async {
+      final stream = eg.stream();
+      await prepare(narrow: ChannelNarrow(stream.streamId));
+      await prepareMessages(foundOldest: true, messages: []);
+
+      await store.handleEvent(MessageEvent(id: 0,
+          message: eg.streamMessage(stream: stream)));
+      // Each [checkNotifiedOnce] call ensures there's been a [checkInvariants]
+      // call, where the [ContentNode] gets checked.  The additional checks to
+      // make this test explicit.
+      checkNotifiedOnce();
+      check(model).messages.single.poll.isNull();
+      check(model).contents.single.isA<ZulipContent>();
+    });
+
+    test('PollContent', () async {
+      final stream = eg.stream();
+      await prepare(narrow: ChannelNarrow(stream.streamId));
+      await prepareMessages(foundOldest: true, messages: []);
+
+      await store.handleEvent(MessageEvent(id: 0, message: eg.streamMessage(
+          stream: stream,
+          sender: eg.selfUser,
+          submessages: [
+            eg.submessage(senderId: eg.selfUser.userId,
+                content: eg.pollWidgetData(question: 'question', options: ['A'])),
+          ])));
+      // Each [checkNotifiedOnce] call ensures there's been a [checkInvariants]
+      // call, where the value of the [Poll] gets checked.  The additional
+      // checks make this test explicit.
+      checkNotifiedOnce();
+      check(model).messages.single.poll.isNotNull();
+      check(model).contents.single.isA<PollContent>();
+    });
+  });
+
   test('recipient headers are maintained consistently', () async {
     // TODO test date separators are maintained consistently too
     // This tests the code that maintains the invariant that recipient headers
@@ -1741,6 +1778,11 @@ void checkInvariants(MessageListView model) {
 
   check(model).contents.length.equals(model.messages.length);
   for (int i = 0; i < model.contents.length; i++) {
+    final poll = model.messages[i].poll;
+    if (poll != null) {
+      check(model).contents[i].isA<PollContent>().poll.identicalTo(poll);
+      continue;
+    }
     check(model.contents[i]).isA<ZulipContent>()
       .equalsNode(parseContent(model.messages[i].content));
   }