publish selected provisional grades

test plan:
 - have a moderated assignment and add some users to moderation
   (leave some users out of the moderation set)
 - as two separate TAs, create provisional grades
   for the students in the moderation set
 - also create one provisional grade for each student that
   is not in the moderation set (eventually speedgrader will
   prevent you from creating more than one)
 - as a moderator, select provisional grades on the moderation
   page
 - ensure that the correct provisional grades are published:
   - for students in the moderation set, the grade selected
     by radio button
   - for students not in the moderation set, the one and only
     provisional grade

fixes CNVS-23036

Change-Id: Icf0919d65648e48e31322e09318bff00a1e98949
Reviewed-on: https://gerrit.instructure.com/63313
Tested-by: Jenkins
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>

app/controllers/submissions_api_controller.rb

@@ -671,9 +671,7 @@ class SubmissionsApiController < ApplicationController
   # Use the "Select provisional grade" endpoint to choose which provisional grade to publish
   # for a particular submission.
   #
-  # NOTE: The preceding paragraph is a lie, because provisional grade selection is not yet implemented.
-  # What will _actually_ happen is, we'll publish the first provisional grade for the submission
-  # (by graded_at date).
+  # Students not in the moderation set will have their one and only provisional grade published.
   #
   # WARNING: This is irreversible. This will overwrite any existing grades in the gradebook.
   #
@@ -694,12 +692,20 @@ class SubmissionsApiController < ApplicationController
 
       submissions = @assignment.submissions.preload(:all_submission_comments,
                                                      { :provisional_grades => :rubric_assessments })
+      selections = @assignment.moderated_grading_selections.index_by(&:student_id)
       submissions.each do |submission|
-        # TODO M2 use an actual selection instead of just picking the first one
-        selected_provisional_grade = submission.provisional_grades
-          .select { |pg| pg.graded_at.present? }
-          .sort_by { |pg| pg.graded_at }
-          .first
+        if (selection = selections[submission.user_id])
+          # student in moderation: choose the selected provisional grade
+          selected_provisional_grade = submission.provisional_grades
+            .detect { |pg| pg.id == selection.selected_provisional_grade_id }
+        else
+          # student not in moderation: choose the first one with a grade (there should only be one)
+          selected_provisional_grade = submission.provisional_grades
+            .select { |pg| pg.graded_at.present? }
+            .sort_by { |pg| pg.created_at }
+            .first
+        end
+
         if selected_provisional_grade
           selected_provisional_grade.publish!
         end

spec/apis/v1/submissions_api_spec.rb

@@ -3294,6 +3294,24 @@ describe 'Submissions API', type: :request do
           @student.reload
           expect(@student.messages.map(&:notification_name)).to be_include 'Submission Graded'
         end
+
+        it "publishes the selected provisional grade when the student is in the moderation set" do
+          @submission.provisional_grade(@ta).update_attribute(:graded_at, 1.minute.ago)
+
+          @other_ta = user :active_user => true
+          @course.enroll_ta @other_ta, :enrollment_state => 'active'
+          @assignment.grade_student(@student, { :grader => @other_ta, :score => 90, :provisional => true })
+          sel = @assignment.moderated_grading_selections.build
+          sel.student_id = @student.id
+          sel.selected_provisional_grade_id = @submission.provisional_grade(@other_ta).id
+          sel.save!
+
+          api_call_as_user(@teacher, :post, @path, @params)
+
+          expect(@submission.reload.workflow_state).to eq 'graded'
+          expect(@submission.grader).to eq @other_ta
+          expect(@submission.score).to eq 90
+        end
       end
     end
   end