adjust discussion unread and total counts when deleting

fixes CNVS-5480

testing direction:
==================
using both threaded and unthreaded discussions:
* create a discussion using two different users
* create discussion replies (entries) and verify
  the "unread" count correctly changes
* delete an "unread" entry before the other
  user has seen it. verify the unread count is
  correctly updated.
* after deleting entries, verify the "total"
  count is correct on the index and show pages.
* verify that the discussion's list page counts
  match a specific discussion's show page counts

Change-Id: Id29ee1d03a60c6a78565661ee214bf9031fae69c
Reviewed-on: https://gerrit.instructure.com/20201
Product-Review: Marc LeGendre <marc@instructure.com>
QA-Review: Marc LeGendre <marc@instructure.com>
Reviewed-by: Mark Ericksen <marke@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>

Author: Mark Ericksen

app/models/discussion_entry.rb

@@ -174,6 +174,7 @@ def destroy
     self.deleted_at = Time.now
     save!
     update_topic_submission
+    decrement_unread_counts_for_this_entry
   end
 
   def update_discussion
@@ -207,6 +208,20 @@ def update_topic_submission
     end
   end
 
+  def decrement_unread_counts_for_this_entry
+    # decrement unread_entry_count for every participant that has not read the
+    transaction do
+      # get a list of users who have not read the entry yet
+      users = discussion_topic.discussion_topic_participants.
+          where(['user_id NOT IN (?)', discussion_entry_participants.read.pluck(:user_id)]).pluck(:user_id)
+      # decrement unread_entry_count for topic participants
+      if users.present?
+        DiscussionTopicParticipant.where(:discussion_topic_id => self.discussion_topic_id, :user_id => users).
+            update_all('unread_entry_count = unread_entry_count - 1')
+      end
+    end
+  end
+
   scope :active, where("discussion_entries.workflow_state<>'deleted'")
   scope :deleted, where(:workflow_state => 'deleted')
 

app/models/discussion_entry_participant.rb

@@ -33,4 +33,6 @@ def self.read_entry_ids(entry_ids, user)
     state :unread
     state :read
   end
+
+  scope :read, where(:workflow_state => 'read')
 end

app/models/discussion_topic.rb

@@ -280,7 +280,7 @@ def change_all_read_state(new_state, current_user = nil)
   end
 
   def default_unread_count
-    self.discussion_entries.count
+    self.discussion_entries.active.count
   end
 
   def unread_count(current_user = nil)

app/views/discussion_topics/show.html.erb

@@ -148,7 +148,7 @@
 
           <div class="discussion-header-right pull-right">
             <div class="discussion-pubdate"><%= friendly_datetime @topic.created_at %></div>
-            <%= render :partial => 'new_and_total_badge', :locals => { :unread_count => @topic.unread_count(@current_user), :reply_count => @topic.discussion_entries.size } %>
+            <%= render :partial => 'new_and_total_badge', :locals => { :unread_count => @topic.unread_count(@current_user), :reply_count => @topic.discussion_subentry_count } %>
           </div>
           <div class="discussion-title"><%= @topic.title %></div>
           <div class="discussion-subtitle">

spec/models/discussion_entry_spec.rb

@@ -224,6 +224,48 @@
     end
   end
 
+  context "deleting entry" do
+    before :each do
+      course_with_student(:active_all => true)
+      @author = @user
+      @reader = user()
+      @course.enroll_student(@author)
+      @course.enroll_student(@reader)
+
+      @topic = @course.discussion_topics.create!(:title => "title", :message => "message")
+
+      # Create 4 entries, first 2 are 'read' by reader.
+      @entry_1 = @topic.discussion_entries.create!(:message => "entry 1", :user => @author)
+      @entry_1.change_read_state('read', @reader)
+      @entry_2 = @topic.discussion_entries.create!(:message => "entry 2", :user => @author)
+      @entry_2.change_read_state('read', @reader)
+      @entry_3 = @topic.discussion_entries.create!(:message => "entry 3", :user => @author)
+      @entry_4 = @topic.discussion_entries.create!(:message => "entry 4", :user => @author)
+    end
+
+    describe "#destroy" do
+      it "should call decrement_unread_counts_for_this_entry" do
+        @entry_4.expects(:decrement_unread_counts_for_this_entry)
+        @entry_4.destroy
+      end
+    end
+
+    it "should decrement unread topic counts" do
+      @topic.unread_count(@reader).should == 2
+
+      # delete one read and one unread entry and check again
+      @entry_1.destroy
+      @entry_4.destroy
+      @topic.unread_count(@reader).should == 1
+      # delete remaining unread
+      @entry_3.destroy
+      @topic.unread_count(@reader).should == 0
+      # delete final 'read' entry
+      @entry_2.destroy
+      @topic.unread_count(@reader).should == 0
+    end
+  end
+
   it "should touch all parent discussion_topics through root_topic_id, on update" do
     course_with_student(:active_all => true)
     @topic = @course.discussion_topics.create!(:title => "title", :message => "message")

spec/selenium/discussions_spec.rb

@@ -389,6 +389,25 @@ def edit(title, message)
         f('.discussion-topic .icon-rss').should be_displayed
         DiscussionTopic.last.podcast_enabled.should be_true
       end
+
+      it "should exclude deleted entries from unread and total reply count" do
+        course_with_teacher_logged_in
+        discussion_topic_model(:user => @teacher)
+        @student = student_in_course(:active_all => true).user
+
+        @assignment = assignment_model(:course => @course)
+        @topic.assignment = @assignment
+        @topic.save
+
+        # Add two replies, delete one
+        @topic.reply_from(:user => @student, :text => "entry")
+        entry = @topic.reply_from(:user => @student, :text => "another entry")
+        entry.destroy
+
+        get "/courses/#{@course.id}/discussion_topics/#{@topic.id}"
+        f('.new-items').text.should == '1'
+        f('.total-items').text.should == '1'
+      end
     end
 
     context "editing" do