wip and finish selfHasContentAccess

Author: gnprice

lib/model/channel.dart

@@ -140,12 +140,19 @@ mixin ChannelStore on UserStore {
     }
   }
 
-  bool selfCanSubscribe(int channelId) {
-    // Compare web's stream_data.has_content_access_via_group_permissions.
+  bool selfHasContentAccess(ZulipStream channel) {
+    // Compare web's stream_data.has_content_access.
+    if (channel.isWebPublic) return true;
+    if (channel is Subscription) return true;
+    // Here web calls has_metadata_access... but that always returns true,
+    // as its comment says.
     if (selfUser.role == UserRole.guest) return false;
-    final channel = streams[channelId];
-    if (channel == null) return false;
     if (!channel.inviteOnly) return true;
+    return _selfHasContentAccessViaGroupPermissions(channel);
+  }
+
+  bool _selfHasContentAccessViaGroupPermissions(ZulipStream channel) {
+    // Compare web's stream_data.has_content_access_via_group_permissions.
     return selfHasPermissionForGroupSetting(channel.canAddSubscribersGroup,
         GroupSettingType.group, 'can_add_subscribers_group')
       || selfHasPermissionForGroupSetting(channel.canSubscribeGroup,