FEATURE: Allow admin to auto reopen at topic.

* This commit also introduces a `TopicStatusUpdate`
  model to support other forms of deferred topic
  status update in the future.

spec/services/topic_status_updater_spec.rb

@@ -0,0 +1,59 @@
+# encoding: UTF-8
+
+require 'rails_helper'
+require_dependency 'post_destroyer'
+
+# TODO - test pinning, create_moderator_post
+
+describe TopicStatusUpdater do
+
+  let(:user) { Fabricate(:user) }
+  let(:admin) { Fabricate(:admin) }
+
+  it "avoids notifying on automatically closed topics" do
+    # TODO: TopicStatusUpdater should suppress message bus updates from the users it "pretends to read"
+    post = PostCreator.create(user,
+      raw: "this is a test post 123 this is a test post",
+      title: "hello world title",
+    )
+    # TODO needed so counts sync up, PostCreator really should not give back out-of-date Topic
+    post.topic.set_or_create_status_update(TopicStatusUpdate.types[:close], '10')
+    post.topic.reload
+
+    TopicStatusUpdater.new(post.topic, admin).update!("autoclosed", true)
+
+    expect(post.topic.posts.count).to eq(2)
+
+    tu = TopicUser.find_by(user_id: user.id)
+    expect(tu.last_read_post_number).to eq(2)
+  end
+
+  it "adds an autoclosed message" do
+    topic = create_topic
+    topic.set_or_create_status_update(TopicStatusUpdate.types[:close], '10')
+
+    TopicStatusUpdater.new(topic, admin).update!("autoclosed", true)
+
+    last_post = topic.posts.last
+    expect(last_post.post_type).to eq(Post.types[:small_action])
+    expect(last_post.action_code).to eq('autoclosed.enabled')
+    expect(last_post.raw).to eq(I18n.t("topic_statuses.autoclosed_enabled_minutes", count: 0))
+  end
+
+  it "adds an autoclosed message based on last post" do
+    topic = create_topic
+    Fabricate(:post, topic: topic)
+
+    topic.set_or_create_status_update(
+      TopicStatusUpdate.types[:close], '10', based_on_last_post: true
+    )
+
+    TopicStatusUpdater.new(topic, admin).update!("autoclosed", true)
+
+    last_post = topic.posts.last
+    expect(last_post.post_type).to eq(Post.types[:small_action])
+    expect(last_post.action_code).to eq('autoclosed.enabled')
+    expect(last_post.raw).to eq(I18n.t("topic_statuses.autoclosed_enabled_lastpost_hours", count: 10))
+  end
+
+end