gradebook: better sorting for total columns

fixes CNVS-9300

Test plan:
  * make a course with 2 assignments:
    * one has 10 points possible
    * one has 100 points possible
  * give a student 10/10 on the first assignment (no score on the
    second)
  * give another student 20/100 on the second assignment
  * sort by total grade
  * it should sort by percent
  * switch the total grade to display as points
  * it should sort by points

Change-Id: Ie0651fcefb3c0880a017c438b40aa169158f34ba
Reviewed-on: https://gerrit.instructure.com/36664
Reviewed-by: Cameron Sutter <csutter@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>

app/coffeescripts/gradebook2/Gradebook.coffee

@@ -1057,13 +1057,11 @@ define [
             data.sortCol.field
 
           @sortRowsBy (a, b) =>
-            [b, a] = [a, b] if not data.sortAsc
+            [b, a] = [a, b] unless data.sortAsc
             @localeSort(a[sortProp], b[sortProp])
         else
-          @sortRowsBy (a, b) ->
-            aScore = a[data.sortCol.field]?.score
-            bScore = b[data.sortCol.field]?.score
-            numberCompare(aScore, bScore, descending: !data.sortAsc)
+          @sortRowsBy (a, b) =>
+            @gradeSort(a, b, data.sortCol.field, data.sortAsc)
 
       @grid.onKeyDown.subscribe ->
         # TODO: start editing automatically when a number or letter is typed
@@ -1108,6 +1106,28 @@ define [
         window.I18n.locale,
         sensitivity: 'accent', numeric: true
 
+    gradeSort: (a, b, field, asc) =>
+      scoreForSorting = (obj) =>
+        percent = (obj) ->
+          if obj[field].possible > 0
+            obj[field].score / obj[field].possible
+          else
+            null
+
+        switch
+          when field == "total_grade"
+            if @options.show_total_grade_as_points
+              obj[field].score
+            else
+              percent(obj)
+          when field.match /^assignment_group/
+            percent(obj)
+          else
+            # TODO: support assignment grading types
+            obj[field].score
+
+      numberCompare(scoreForSorting(a), scoreForSorting(b), descending: !asc)
+
     # show warnings for bad grading setups
     setAssignmentWarnings: =>
       if @weightedGroups()

spec/coffeescripts/gradebook2/GradebookSpec.coffee

@@ -0,0 +1,35 @@
+define ['compiled/gradebook2/Gradebook'], (Gradebook) ->
+
+  module "Gradebook2"
+
+  test "gradeSort - total_grade", ->
+    gradeSort = (showTotalGradeAsPoints, a, b, field, asc) ->
+      asc = true unless asc?
+
+      Gradebook.prototype.gradeSort.call options:
+        show_total_grade_as_points: showTotalGradeAsPoints
+      , a, b, field, asc
+
+    ok gradeSort(false
+    , {total_grade: {score: 10, possible: 20}}
+    , {total_grade: {score: 5, possible: 10}}
+    , 'total_grade') == 0
+    , "total_grade sorts by percent (normally)"
+
+    ok gradeSort(true
+    , {total_grade: {score: 10, possible: 20}}
+    , {total_grade: {score: 5, possible: 10}}
+    , 'total_grade') > 0
+    , "total_grade sorts by score when if show_total_grade_as_points"
+
+    ok gradeSort(true
+    , {assignment_group_1: {score: 10, possible: 20}}
+    , {assignment_group_1: {score: 5, possible: 10}}
+    , 'assignment_group_1') == 0
+    , "assignment groups are always sorted by percent"
+
+    ok gradeSort(false
+    , {assignment1: {score: 5, possible: 10}}
+    , {assignment1: {score: 10, possible: 20}}
+    , 'assignment1') < 0
+    , "other fields are sorted by score"