add logging of avg module duration for course pace

Closes LS-3333

Test Plan: passes jenkins

Change-Id: I9ebe359daa7b5c8426a47fa2a7836eeda3889f73
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/298568
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jackson Howe <jackson.howe@instructure.com>
QA-Review: Jackson Howe <jackson.howe@instructure.com>
Product-Review: Robin Kuss <rkuss@instructure.com>

app/models/course_pace.rb

@@ -41,6 +41,7 @@ class CoursePace < ActiveRecord::Base
 
   after_create :log_pace_counts
   after_save :log_exclude_weekends_counts, if: :logging_for_weekends_required?
+  after_save :log_average_item_duration
 
   validates :course_id, presence: true
   validate :valid_secondary_context
@@ -302,4 +303,11 @@ class CoursePace < ActiveRecord::Base
       InstStatsd::Statsd.decrement("course_pacing.weekends_excluded") unless saved_change_to_id?
     end
   end
+
+  def log_average_item_duration
+    return if course_pace_module_items.empty?
+
+    average_duration = course_pace_module_items.pluck(:duration).sum / course_pace_module_items.length
+    InstStatsd::Statsd.count("course_pacing.average_assignment_duration", average_duration)
+  end
 end

spec/models/course_pace_spec.rb

@@ -547,7 +547,7 @@ describe CoursePace do
     end
   end
 
-  context "course pace publish logs statsd for exclude weekends" do
+  context "course pace publish logs statsd for various values" do
     before :once do
       course_with_student active_all: true
       @course.root_account.enable_feature!(:course_paces)
@@ -597,5 +597,54 @@ describe CoursePace do
       expect(InstStatsd::Statsd).to have_received(:increment).with("course_pacing.weekends_excluded")
       expect(InstStatsd::Statsd).to have_received(:decrement).with("course_pacing.weekends_excluded")
     end
+
+    it "logs the average module item duration as a count" do
+      allow(InstStatsd::Statsd).to receive(:count)
+
+      course_pace = @course.course_paces.create!(workflow_state: "active")
+      course_pace_module_item = course_pace.course_pace_module_items.create! module_item: @tag
+      course_pace_module_item.update duration: 2
+      course_pace.publish
+
+      expect(InstStatsd::Statsd).to have_received(:count).with("course_pacing.average_assignment_duration", 2)
+    end
+
+    it "logs updated average module item duration as a count when new assignment added" do
+      allow(InstStatsd::Statsd).to receive(:count)
+
+      course_pace = @course.course_paces.create!(workflow_state: "active")
+      course_pace_module_item = course_pace.course_pace_module_items.create! module_item: @tag
+      course_pace_module_item.update duration: 2
+      course_pace.publish
+
+      assignment = @course.assignments.create!
+      new_tag = assignment.context_module_tags.create! context_module: @module, context: @course, tag_type: "context_module"
+
+      new_course_pace_module_item = course_pace.course_pace_module_items.create! module_item: new_tag
+      new_course_pace_module_item.update duration: 4
+      course_pace.publish
+
+      expect(InstStatsd::Statsd).to have_received(:count).with("course_pacing.average_assignment_duration", 3)
+    end
+
+    it "doesn't log when no context modules exist" do
+      allow(InstStatsd::Statsd).to receive(:count)
+
+      course_pace = @course.course_paces.create!(workflow_state: "active")
+      course_pace.publish
+
+      expect(InstStatsd::Statsd).not_to have_received(:count).with("course_pacing.average_assignment_duration", 0)
+    end
+
+    it "logs when no context modules item duration is o" do
+      allow(InstStatsd::Statsd).to receive(:count)
+
+      course_pace = @course.course_paces.create!(workflow_state: "active")
+      course_pace_module_item = course_pace.course_pace_module_items.create! module_item: @tag
+      course_pace_module_item.update duration: 0
+      course_pace.publish
+
+      expect(InstStatsd::Statsd).to have_received(:count).with("course_pacing.average_assignment_duration", 0)
+    end
   end
 end