From 67041d1c6dfa27872bbc713c7f79e3f57e1dbb23 Mon Sep 17 00:00:00 2001
From: Robin Ward <robin.ward@gmail.com>
Date: Thu, 14 Nov 2013 14:32:41 -0500
Subject: [PATCH] Support for tracking the count of unique participants in a
 topic

---
 app/models/topic_featured_users.rb            | 11 +++++--
 ...4185225_add_participant_count_to_topics.rb | 13 +++++++++
 spec/jobs/feature_topic_users_spec.rb         | 29 +++++++++++++++++++
 3 files changed, 50 insertions(+), 3 deletions(-)
 create mode 100644 db/migrate/20131114185225_add_participant_count_to_topics.rb

diff --git a/app/models/topic_featured_users.rb b/app/models/topic_featured_users.rb
index 6a0c0a491c8..fe6533a5580 100644
--- a/app/models/topic_featured_users.rb
+++ b/app/models/topic_featured_users.rb
@@ -14,13 +14,14 @@ class TopicFeaturedUsers
     topic.reload unless rails4?
     clear
     update keys(args)
+    update_participant_count
     topic.save
   end
 
   def user_ids
-    [topic.featured_user1_id, 
-     topic.featured_user2_id, 
-     topic.featured_user3_id, 
+    [topic.featured_user1_id,
+     topic.featured_user2_id,
+     topic.featured_user3_id,
      topic.featured_user4_id].uniq.compact
   end
 
@@ -48,4 +49,8 @@ class TopicFeaturedUsers
         topic.send("featured_user#{i+1}_id=", user_id)
       end
     end
+
+    def update_participant_count
+      topic.participant_count = topic.posts.count('distinct user_id')
+    end
 end
diff --git a/db/migrate/20131114185225_add_participant_count_to_topics.rb b/db/migrate/20131114185225_add_participant_count_to_topics.rb
new file mode 100644
index 00000000000..20983e64d93
--- /dev/null
+++ b/db/migrate/20131114185225_add_participant_count_to_topics.rb
@@ -0,0 +1,13 @@
+class AddParticipantCountToTopics < ActiveRecord::Migration
+  def up
+    add_column :topics, :participant_count, :integer, default: 1
+
+    execute "UPDATE topics SET participant_count =
+              (SELECT COUNT(DISTINCT p.user_id) FROM posts AS p WHERE p.topic_id = topics.id)"
+  end
+
+  def down
+    remove_column :topics, :participant_count
+  end
+
+end
diff --git a/spec/jobs/feature_topic_users_spec.rb b/spec/jobs/feature_topic_users_spec.rb
index cea64c128f6..36c7db9aa09 100644
--- a/spec/jobs/feature_topic_users_spec.rb
+++ b/spec/jobs/feature_topic_users_spec.rb
@@ -42,4 +42,33 @@ describe Jobs::FeatureTopicUsers do
 
   end
 
+  context "participant count" do
+
+    let!(:post) { create_post }
+    let(:topic) { post.topic }
+
+
+    it "it works as expected" do
+
+      # It has 1 participant after creation
+      topic.participant_count.should == 1
+
+      # It still has 1 after featuring
+      Jobs::FeatureTopicUsers.new.execute(topic_id: topic.id)
+      topic.reload.participant_count.should == 1
+
+      # If the OP makes another post, it's still 1.
+      create_post(topic: topic, user: post.user)
+      Jobs::FeatureTopicUsers.new.execute(topic_id: topic.id)
+      topic.reload.participant_count.should == 1
+
+      # If another users posts, it's 2.
+      create_post(topic: topic, user: Fabricate(:evil_trout))
+      Jobs::FeatureTopicUsers.new.execute(topic_id: topic.id)
+      topic.reload.participant_count.should == 2
+
+    end
+
+  end
+
 end