Add conversation model, <ostatus:conversation /> (#3016)

* Add <ostatus:conversation /> tag to Atom input/output

Only uses ref attribute (not href) because href would be
the alternate link that's always included also.

Creates new conversation for every non-reply status. Carries
over conversation for every reply. Keeps remote URIs verbatim,
generates local URIs on the fly like the rest of them.

* Fix conversation migration

* More spec coverage for status before_create

* Prevent n+1 query when generating Atom with the new conversations

* Improve code style

* Remove redundant local variable

1 files changed, 14 insertions, 1 deletions

diff --git a/app/services/process_feed_service.rb b/app/services/process_feed_service.rb
index 1558f8790..afd44aafe 100644
--- a/app/services/process_feed_service.rb
+++ b/app/services/process_feed_service.rb
@@ -141,7 +141,8 @@ class ProcessFeedService < BaseService
         created_at: published(entry),
         reply: thread?(entry),
         language: content_language(entry),
-        visibility: visibility_scope(entry)
+        visibility: visibility_scope(entry),
+        conversation: find_or_create_conversation(entry)
       )
 
       if thread?(entry)
@@ -164,6 +165,18 @@ class ProcessFeedService < BaseService
       status
     end
 
+    def find_or_create_conversation(xml)
+      uri = xml.at_xpath('./ostatus:conversation', ostatus: TagManager::OS_XMLNS)&.attribute('ref')&.content
+      return if uri.nil?
+
+      if TagManager.instance.local_id?(uri)
+        local_id = TagManager.instance.unique_tag_to_local_id(uri, 'Conversation')
+        return Conversation.find_by(id: local_id)
+      end
+
+      Conversation.find_by(uri: uri)
+    end
+
     def find_status(uri)
       if TagManager.instance.local_id?(uri)
         local_id = TagManager.instance.unique_tag_to_local_id(uri, 'Status')