From fc7abb2baf56f83a60134bb5d0069cbc1cf74e29 Mon Sep 17 00:00:00 2001
From: Andrew Gardener <andrew.e.gardener@gmail.com>
Date: Wed, 3 Jan 2018 11:52:13 -0800
Subject: [PATCH] Prevent students from performing extra comparisons

Closes #658
---
 compair/api/comparison.py             |  7 +++++--
 compair/tests/api/test_comparisons.py | 15 ++++++++++++---
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/compair/api/comparison.py b/compair/api/comparison.py
index ca1f2346a..3d6640981 100644
--- a/compair/api/comparison.py
+++ b/compair/api/comparison.py
@@ -52,12 +52,17 @@ def get(self, course_uuid, assignment_uuid):
             message="Comparisons can only be seen here by those enrolled in the course. Please double-check your enrollment in this course.")
         restrict_user = not allow(MANAGE, assignment)
 
+        comparison_count = assignment.completed_comparison_count_for_user(current_user.id)
+
         if not assignment.compare_grace:
             abort(403, title="Comparisons Unavailable",
                 message="Sorry, the comparison deadline has passed. No comparisons can be done after the deadline.")
         elif not restrict_user and not assignment.educators_can_compare:
             abort(403, title="Comparisons Unavailable",
                 message="Only students can currently compare answers for this assignment. To change these settings to include instructors and teaching assistants, edit the assignment.")
+        elif restrict_user and comparison_count >= assignment.total_comparisons_required:
+            abort(400, title="Comparisons Completed",
+                message="More comparisons aren't available, since you've finished your comparisons for this assignment. Good job!")
 
         # check if user has a comparison they have not completed yet
         new_pair = False
@@ -98,8 +103,6 @@ def get(self, course_uuid, assignment_uuid):
             except UnknownPairGeneratorException:
                 abort(500, title="Comparisons Unavailable", message="Generating scored pairs failed, this really shouldn't happen.")
 
-        comparison_count = assignment.completed_comparison_count_for_user(current_user.id)
-
         return {
             'comparison': marshal(comparison, dataformat.get_comparison(restrict_user)),
             'new_pair': new_pair,
diff --git a/compair/tests/api/test_comparisons.py b/compair/tests/api/test_comparisons.py
index 585b7b7f8..b07f1d85d 100644
--- a/compair/tests/api/test_comparisons.py
+++ b/compair/tests/api/test_comparisons.py
@@ -84,7 +84,7 @@ def test_submit_comparison_access_control(self):
             # expected_comparisons = rv.json
             comparison_submit = self._build_comparison_submit(WinningAnswer.answer1.value)
 
-        # test deny access to unenroled users
+        # test deny access to unenrolled users
         with self.login(self.data.get_unauthorized_student().username):
             rv = self.client.post(
                 self.base_url,
@@ -229,14 +229,17 @@ def test_get_and_submit_comparison(self, mocked_update_assignment_grades_run, mo
 
         users = [self.data.get_authorized_student(), self.data.get_authorized_instructor(), self.data.get_authorized_ta()]
         for user in users:
-            max_comparisons = 0
+            max_comparisons = self.assignment.number_of_comparisons
             other_student_answers = 0
             valid_answer_uuids = set()
             for answer in self.data.get_student_answers():
                 if answer.assignment.id == self.assignment.id and answer.user_id != user.id:
                     other_student_answers += 1
                     valid_answer_uuids.add(answer.uuid)
-            max_comparisons = int(other_student_answers * (other_student_answers - 1) / 2)
+
+            # instructors and tas can compare every possible pair
+            if user.id in [self.data.get_authorized_instructor().id, self.data.get_authorized_ta().id]:
+                max_comparisons = int(other_student_answers * (other_student_answers - 1) / 2)
 
             if user.id == self.data.get_authorized_student().id:
                 for comparison_example in self.data.comparisons_examples:
@@ -350,6 +353,12 @@ def test_get_and_submit_comparison(self, mocked_update_assignment_grades_run, mo
                 # all answers has been compared by the user, errors out when trying to get another pair
                 rv = self.client.get(self.base_url)
                 self.assert400(rv)
+                if user.id == self.data.get_authorized_student().id:
+                    self.assertEqual("Comparisons Completed", rv.json['title'])
+                    self.assertEqual("More comparisons aren't available, since you've finished your comparisons for this assignment. Good job!", rv.json['message'])
+                else:
+                    self.assertEqual("Comparisons Unavailable", rv.json['title'])
+                    self.assertEqual("You have compared all the currently available answer pairs. Please check back later for more answers.", rv.json['message'])
 
     def _validate_comparison_submit(self, comparison_submit, actual_comparison, expected_comparison):
         self.assertEqual(