From 53eee12a7a9787baa6b9c1700a8cae54222dee56 Mon Sep 17 00:00:00 2001
From: Tim Hunt <T.J.Hunt@open.ac.uk>
Date: Thu, 20 Aug 2015 19:12:02 +0100
Subject: [PATCH] MDL-51147 qtype_match: stats should cope even if Q edited
 badly

The numbers become pretty meaningless, but we need to avoid fatal
errors.
---
 question/type/match/question.php            | 23 +++++++----
 question/type/match/tests/question_test.php | 44 +++++++++++++++++++++
 2 files changed, 60 insertions(+), 7 deletions(-)

diff --git a/question/type/match/question.php b/question/type/match/question.php
index 671047405c8..28c20a22a0a 100644
--- a/question/type/match/question.php
+++ b/question/type/match/question.php
@@ -134,25 +134,34 @@ class qtype_match_question extends question_graded_automatically_with_countback
     }
 
     public function classify_response(array $response) {
-        $selectedchoices = array();
+        $selectedchoicekeys = array();
         foreach ($this->stemorder as $key => $stemid) {
             if (array_key_exists($this->field($key), $response) && $response[$this->field($key)]) {
-                $selectedchoices[$stemid] = $this->choiceorder[$response[$this->field($key)]];
+                $selectedchoicekeys[$stemid] = $this->choiceorder[$response[$this->field($key)]];
             } else {
-                $selectedchoices[$stemid] = 0;
+                $selectedchoicekeys[$stemid] = 0;
             }
         }
 
         $parts = array();
         foreach ($this->stems as $stemid => $stem) {
-            if (empty($selectedchoices[$stemid])) {
+            if ($this->right[$stemid] == 0 || !isset($selectedchoicekeys[$stemid])) {
+                // Choice for a deleted subquestion, ignore. (See apply_attempt_state.)
+                continue;
+            }
+            $selectedchoicekey = $selectedchoicekeys[$stemid];
+            if (empty($selectedchoicekey)) {
                 $parts[$stemid] = question_classified_response::no_response();
                 continue;
             }
-            $choice = $this->choices[$selectedchoices[$stemid]];
+            $choice = $this->choices[$selectedchoicekey];
+            if ($choice == get_string('deletedchoice', 'qtype_match')) {
+                // Deleted choice, ignore. (See apply_attempt_state.)
+                continue;
+            }
             $parts[$stemid] = new question_classified_response(
-                    $selectedchoices[$stemid], $choice,
-                    ($selectedchoices[$stemid] == $this->right[$stemid]) / count($this->stems));
+                    $selectedchoicekey, $choice,
+                    ($selectedchoicekey == $this->right[$stemid]) / count($this->stems));
         }
         return $parts;
     }
diff --git a/question/type/match/tests/question_test.php b/question/type/match/tests/question_test.php
index be6a5a7dac6..4e83431d2c3 100644
--- a/question/type/match/tests/question_test.php
+++ b/question/type/match/tests/question_test.php
@@ -181,6 +181,50 @@ class qtype_match_question_test extends advanced_testcase {
                 ), $match->classify_response($response));
     }
 
+    public function test_classify_response_choice_deleted_after_attempt() {
+        $match = test_question_maker::make_a_matching_question();
+        $firststep = new question_attempt_step();
+
+        $match->start_attempt($firststep, 1);
+        $response = $match->prepare_simulated_post_data(array(
+                'Dog' => 'Amphibian', 'Frog' => 'Insect', 'Toad' => '', 'Cat' => 'Mammal'));
+
+        $match = test_question_maker::make_a_matching_question();
+        unset($match->stems[4]);
+        unset($match->stemsformat[4]);
+        unset($match->right[4]);
+        $match->apply_attempt_state($firststep);
+
+        $this->assertEquals(array(
+                1 => new question_classified_response(2, 'Amphibian', 0),
+                2 => new question_classified_response(3, 'Insect', 0),
+                3 => question_classified_response::no_response(),
+        ), $match->classify_response($response));
+    }
+
+    public function test_classify_response_choice_added_after_attempt() {
+        $match = test_question_maker::make_a_matching_question();
+        $firststep = new question_attempt_step();
+
+        $match->start_attempt($firststep, 1);
+        $response = $match->prepare_simulated_post_data(array(
+                'Dog' => 'Amphibian', 'Frog' => 'Insect', 'Toad' => '', 'Cat' => 'Mammal'));
+
+        $match = test_question_maker::make_a_matching_question();
+        $match->stems[5] = "Snake";
+        $match->stemsformat[5] = FORMAT_HTML;
+        $match->choices[5] = "Reptile";
+        $match->right[5] = 5;
+        $match->apply_attempt_state($firststep);
+
+        $this->assertEquals(array(
+                1 => new question_classified_response(2, 'Amphibian', 0),
+                2 => new question_classified_response(3, 'Insect', 0),
+                3 => question_classified_response::no_response(),
+                4 => new question_classified_response(1, 'Mammal', 0.20),
+        ), $match->classify_response($response));
+    }
+
     public function test_prepare_simulated_post_data() {
         $m = test_question_maker::make_a_matching_question();
         $m->start_attempt(new question_attempt_step(), 1);