don't set last_reply_at for imported discussions

test plan:
* create a discussion
* note the "last post" date on the discussions index
* copy the course
* the new discussion should not have a "last post"

closes #CNVS-14623

Change-Id: I1ac54a9023a5e9a574e886b2b37bc945c74fe30f
Reviewed-on: https://gerrit.instructure.com/51212
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>

Author: maneframe

app/coffeescripts/views/DiscussionTopics/DiscussionView.coffee

@@ -152,7 +152,8 @@ define [
       if @model.get('locked') and !_.intersection(ENV.current_user_roles, ['teacher', 'ta', 'admin']).length
         base.permissions.delete = false
 
-      base.display_last_reply_at = I18n.l "#date.formats.medium", base.last_reply_at
+      if base.last_reply_at
+        base.display_last_reply_at = I18n.l "#date.formats.medium", base.last_reply_at
       base.ENV = ENV
       base.discussion_topic_menu_tools = ENV.discussion_topic_menu_tools
       _.each base.discussion_topic_menu_tools, (tool) =>

app/models/discussion_entry.rb

@@ -260,7 +260,7 @@ def infer_root_entry_id
 
   def update_topic
     if self.discussion_topic
-      last_reply_at = [self.discussion_topic.last_reply_at, self.created_at].max
+      last_reply_at = [self.discussion_topic.last_reply_at, self.created_at].compact.max
       DiscussionTopic.where(:id => self.discussion_topic_id).update_all(:last_reply_at => last_reply_at, :updated_at => Time.now.utc)
     end
   end

app/models/discussion_topic.rb

@@ -32,7 +32,7 @@ class DiscussionTopic < ActiveRecord::Base
     :plaintext_message, :podcast_enabled, :podcast_has_student_posts,
     :require_initial_post, :threaded, :discussion_type, :context, :pinned, :locked,
     :group_category
-  attr_accessor :user_has_posted
+  attr_accessor :user_has_posted, :saved_by
 
   module DiscussionTypes
     SIDE_COMMENT = 'side_comment'
@@ -750,7 +750,7 @@ def self.per_page
 
   def initialize_last_reply_at
     self.posted_at ||= Time.now.utc
-    self.last_reply_at ||= Time.now.utc
+    self.last_reply_at ||= Time.now.utc unless self.saved_by == :migration
   end
 
   set_policy do

app/models/importers/discussion_topic_importer.rb

@@ -67,6 +67,7 @@ def find_or_create_topic(topic = nil)
                 else
                   context.discussion_topics.scoped.new
                 end
+      topic.saved_by = :migration
       topic
     end
 
@@ -90,7 +91,7 @@ def run
       item.posted_at            = Canvas::Migration::MigratorHelper.get_utc_time_from_timestamp(options[:posted_at])
       item.delayed_post_at      = Canvas::Migration::MigratorHelper.get_utc_time_from_timestamp(options.delayed_post_at)
       item.lock_at              = Canvas::Migration::MigratorHelper.get_utc_time_from_timestamp(options[:lock_at])
-      item.last_reply_at        = item.posted_at if item.new_record?
+      item.last_reply_at        = nil if item.new_record?
 
       if options[:workflow_state].present?
         item.workflow_state = options[:workflow_state]
@@ -115,6 +116,7 @@ def run
       item.save_without_broadcasting!
       import_migration_item
       add_missing_content_links(missing_links)
+      item.saved_by = nil
       item
     end
 

app/views/jst/DiscussionTopics/discussion.handlebars

@@ -22,7 +22,9 @@
         {{/if}}
         <a href="{{html_url}}" class="title">{{title}}</a>
       </h3>
-      <small {{ contextSensitiveDatetimeTitle last_reply_at }}>{{#t "last_post_date"}}Last post {{display_last_reply_at}}{{/t}}</small>
+      {{#if display_last_reply_at}}
+        <small {{ contextSensitiveDatetimeTitle last_reply_at }}>{{#t "last_post_date"}}Last post {{display_last_reply_at}}{{/t}}</small>
+      {{/if}}
     </div>
 
     <div class="discussion-date-available">

spec/models/content_migration/course_copy_discussions_spec.rb

@@ -29,7 +29,7 @@ def graded_discussion_topic
       attrs = ["title", "message", "discussion_type", "type", "pinned", "position", "require_initial_post"]
       expect(topic.attributes.slice(*attrs)).to eq new_topic.attributes.slice(*attrs)
 
-      expect(new_topic.last_reply_at.to_i).to eq new_topic.posted_at.to_i
+      expect(new_topic.last_reply_at).to be_nil
       expect(topic.posted_at.to_i).to eq new_topic.posted_at.to_i
     end
 

spec/models/discussion_entry_spec.rb

@@ -241,6 +241,15 @@
       @topic.reload
       expect(@topic.last_reply_at).to eq @original_last_reply_at
     end
+
+    it "should still work with no last_reply_at" do
+      @topic.saved_by = :migration
+      @topic.last_reply_at = nil
+      @topic.save!
+
+      @entry.reload
+      @entry.update_topic
+    end
   end
 
   context "deleting entry" do