FEATURE: Allow admin to change timestamp of topic.

app/services/post_timestamp_changer.rb

@@ -0,0 +1,43 @@
+class PostTimestampChanger
+  def initialize(params)
+    @topic = Topic.with_deleted.find(params[:topic_id])
+    @posts = @topic.posts
+    @timestamp = Time.at(params[:timestamp])
+    @time_difference = calculate_time_difference
+  end
+
+  def change!
+    ActiveRecord::Base.transaction do
+      update_topic
+
+      @posts.each do |post|
+        if post.is_first_post?
+          update_post(post, @timestamp)
+        else
+          update_post(post, Time.at(post.created_at.to_f + @time_difference))
+        end
+      end
+    end
+
+    # Burst the cache for stats
+    [AdminDashboardData, About].each { |klass| $redis.del klass.stats_cache_key }
+  end
+
+  private
+
+  def calculate_time_difference
+    @timestamp - @topic.created_at
+  end
+
+  def update_topic
+    @topic.update_attributes(
+      created_at: @timestamp,
+      updated_at: @timestamp,
+      bumped_at: @timestamp
+    )
+  end
+
+  def update_post(post, timestamp)
+    post.update_attributes(created_at: timestamp, updated_at: timestamp)
+  end
+end