FIX: when a topic is deleted, update the post count stats of all user who replied

app/models/user_stat.rb

@@ -52,6 +52,7 @@ class UserStat < ActiveRecord::Base
     ", seen_at: last_seen
   end
 
+  # topic_reply_count is a count of posts in other users' topics
   def update_topic_reply_count
     self.topic_reply_count =
         Topic

lib/post_destroyer.rb

@@ -245,6 +245,16 @@ class PostDestroyer
       author.last_posted_at = author.posts.order('created_at DESC').first.try(:created_at)
       author.save!
     end
+
+    if @post.is_first_post? && @post.topic && !@post.topic.private_message?
+      # Update stats of all people who replied
+      counts = Post.where(post_type: Post.types[:regular]).where(topic_id: @post.topic_id).group(:user_id).count
+      counts.each do |user_id, count|
+        if user_stat = UserStat.where(user_id: user_id).first
+          user_stat.update_attributes(post_count: user_stat.post_count - count)
+        end
+      end
+    end
   end
 
 end

spec/components/post_destroyer_spec.rb

@@ -207,6 +207,7 @@ describe PostDestroyer do
         DiscourseEvent.on(:topic_destroyed, &topic_destroyed)
 
         @orig = post2.cooked
+        # Guardian.new(post2.user).can_delete_post?(post2) == false
         PostDestroyer.new(post2.user, post2).destroy
         post2.reload
 
@@ -239,6 +240,26 @@ describe PostDestroyer do
       end
     end
 
+    it "when topic is destroyed, it updates user_stats correctly" do
+      post
+      user1 = post.user
+      user1.reload
+      user2 = Fabricate(:user)
+      reply = create_post(topic_id: post.topic_id, user: user2)
+      reply2 = create_post(topic_id: post.topic_id, user: user1)
+      expect(user1.user_stat.topic_count).to eq(1)
+      expect(user1.user_stat.post_count).to eq(2)
+      expect(user2.user_stat.topic_count).to eq(0)
+      expect(user2.user_stat.post_count).to eq(1)
+      PostDestroyer.new(Fabricate(:admin), post).destroy
+      user1.reload
+      user2.reload
+      expect(user1.user_stat.topic_count).to eq(0)
+      expect(user1.user_stat.post_count).to eq(0)
+      expect(user2.user_stat.topic_count).to eq(0)
+      expect(user2.user_stat.post_count).to eq(0)
+    end
+
     it "accepts a delete_removed_posts_after option" do
       SiteSetting.delete_removed_posts_after = 0