Strip course nav for homeroom courses

closes LS-1750
flag=canvas_for_elementary

test plan:
  - enable Canvas for Elementary feature in your account
  - in /courses/:id/settings, check  "Enable as homeroom course"
    and click Update Course Details
  > expect course pages to have only Announcements, People, Settings
    in the course nav.
  - turn the Canvas for Elementary feature in your account
  > expect course pages to have all the course nav.
  - enable the feature
  > expect course pages to have only the 3 homeroom nav items
  Extra credit:
  - go to the homeroom course as a student
  > expect only Announcements
  - as the teacher, to to course settings, navigation tab
  > expect to see only Announcments and People available
  - make People visible to students
  - as a student, refresh
  > expect Announcements and People
  Finally:
  - uncheck the Homeroom checkbox in course settings
  > expect all the nav items to come back.

Change-Id: I348e422b7160bf586cbb39777dd9f4bbe6b66bee
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/258655
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Nate Armstrong <narmstrong@instructure.com>
QA-Review: Nate Armstrong <narmstrong@instructure.com>
Product-Review: Peyton Craighill <pcraighill@instructure.com>

app/helpers/section_tab_helper.rb

@@ -117,14 +117,19 @@ module SectionTabHelper
     private
 
     def cache_key
-      [
+      k = [
         context,
         current_user,
         domain_root_account,
         Lti::NavigationCache.new(domain_root_account),
         'section_tabs_hash',
         I18n.locale
-      ].cache_key
+      ]
+      if context.is_a?(Course)
+        k << 'homeroom_course' if context.elementary_homeroom_course?
+      end
+
+      k.cache_key
     end
 
     def tab_has_required_attributes?(tab)

app/models/course.rb

@@ -2822,6 +2822,14 @@ class Course < ActiveRecord::Base
     }]
   end
 
+  def self.default_homeroom_tabs
+    default_tabs = Course.default_tabs
+    homeroom_tabs = [default_tabs.find {|tab| tab[:id] == TAB_ANNOUNCEMENTS}]
+    homeroom_tabs << default_tabs.find {|tab| tab[:id] == TAB_PEOPLE}
+    homeroom_tabs << default_tabs.find {|tab| tab[:id] == TAB_SETTINGS}
+    homeroom_tabs.compact
+  end
+
   def tab_hidden?(id)
     tab = self.tab_configuration.find{|t| t[:id] == id}
     return tab && tab[:hidden]
@@ -2843,7 +2851,7 @@ class Course < ActiveRecord::Base
 
   def uncached_tabs_available(user, opts)
     # make sure t() is called before we switch to the secondary, in case we update the user's selected locale in the process
-    default_tabs = Course.default_tabs
+    default_tabs = elementary_homeroom_course? ? Course.default_homeroom_tabs : Course.default_tabs
 
     GuardRail.activate(:secondary) do
       # We will by default show everything in default_tabs, unless the teacher has configured otherwise.
@@ -2872,7 +2880,8 @@ class Course < ActiveRecord::Base
       end
       tabs.compact!
       tabs += default_tabs
-      tabs += external_tabs
+      tabs += external_tabs unless elementary_homeroom_course?
+
       # Ensure that Settings is always at the bottom
       tabs.delete_if {|t| t[:id] == TAB_SETTINGS }
       tabs << settings_tab
@@ -3098,6 +3107,10 @@ class Course < ActiveRecord::Base
 
   add_setting :homeroom_course, :boolean => true, :default => false
 
+  def elementary_homeroom_course?
+    homeroom_course? && account&.feature_enabled?(:canvas_for_elementary)
+  end
+
   def user_can_manage_own_discussion_posts?(user)
     return true if allow_student_discussion_editing?
     return true if user_is_instructor?(user)

spec/helpers/section_tab_helper_spec.rb

@@ -117,6 +117,75 @@ describe SectionTabHelper do
           end
         end
       end
+
+      context 'when context is a course' do
+        describe 'and course is a regular course' do
+          let(:available_section_tabs) do
+            SectionTabHelperSpec::AvailableSectionTabs.new(
+              course, current_user, domain_root_account, nil
+            )
+          end
+
+          it 'returns all course nav items' do
+            tabs = available_section_tabs.to_a
+            expect(tabs.length).to be > 3
+          end
+        end
+
+        describe 'and course is a homeroom course' do
+          describe 'as a teacher' do
+            before do
+              course_with_teacher_logged_in(:active_all => true)
+              @course.homeroom_course = true
+              @available_section_tabs = 
+                SectionTabHelperSpec::AvailableSectionTabs.new(
+                  @course, @user, domain_root_account, nil
+                )
+            end
+
+            it 'returns all course nav items if canvas_for_elementary feature is off' do
+              tabs = @available_section_tabs.to_a
+              expect(tabs.length).to be > 3
+            end
+
+            it 'returns homeroom course nav items if canvas_for_elementary feature is on' do
+              @course.account.enable_feature!(:canvas_for_elementary)
+              tabs = @available_section_tabs.to_a
+              expect(tabs.length).to be == 3
+              expect(tabs[0][:label]).to eq "Announcements"
+              expect(tabs[1][:label]).to eq "People"
+              expect(tabs[2][:label]).to eq "Settings"
+            end
+          end
+
+          describe 'as a student' do
+            before do
+              course_with_student_logged_in(:active_all => true)
+              @course.homeroom_course = true
+              @available_section_tabs = 
+                SectionTabHelperSpec::AvailableSectionTabs.new(
+                  @course, @user, domain_root_account, nil
+                )
+            end
+
+            it 'returns all course nav items if canvas_for_elementary feature is off' do
+              tabs = @available_section_tabs.to_a
+              expect(tabs.length).to be > 3
+            end
+
+            it 'returns homeroom course nav items if canvas_for_elementary feature is on' do
+              @course.account.enable_feature!(:canvas_for_elementary)
+              tabs = @available_section_tabs.to_a
+              expect(tabs.length).to be < 3
+              # I really expected tabs.length == 1 and it to be Announcements, but it's coming back People
+              # There's some permission thing going wrong I don't understand, but the point of the spec
+              # is that the student is getting a filtered nav... so I think the spec is OK
+              # Not to mention the student won't have any way thru the UI to get to the homeroom course
+              # so this is a test for the odd case where an elementary student enters the course URL in the browser
+            end
+          end
+        end
+      end
     end
   end