add custom_time_zone parameter to lti launches

test plan:
* create a external tool with a custom field keys like:

custom_time_zone=$Person.address.timezone
custom_time_zone2=$Canvas.user.timezone
custom_offset=$Canvas.user.timezone.offset

* confirm that the tool launch parameters includes the
custom keys substituted with the current set time zone
or time zone offset (which derives from the user,
or the root account)

fixes #CNVS-6281

Change-Id: I9bf44f7ba10b2c7f68cae65496caba30ff601f15
Reviewed-on: https://gerrit.instructure.com/21621
QA-Review: Clare Strong <clare@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>

lib/basic_lti/variable_substitutor.rb

@@ -65,6 +65,21 @@ class VariableSubstitutor
     @launch.tool.include_name? ? @launch.user.first_name : nil
   end
 
+  # $Person.address.timezone
+  def sub_Person_address_timezone
+    Time.zone || nil
+  end
+
+  # $Canvas.user.timezone
+  def sub_Canvas_user_timezone
+    Time.zone || nil
+  end
+
+  # $Canvas.user.timezone.offset
+  def sub_Canvas_user_timezone_offset
+    Time.zone ? Time.zone.formatted_offset : nil
+  end
+
   # returns the same LIS Role values as the default 'roles' parameter,
   # but for concluded enrollments
   # $Canvas.membership.concludedRoles

spec/integration/external_tools_spec.rb

@@ -68,6 +68,38 @@ describe "External Tools" do
       doc.at_css('form#tool_form input#lis_outcome_service_url').should be_nil
     end
 
+    it "should include time zone in LTI paramaters if included in custom fields" do
+      @tool.custom_fields = {
+        "custom_time_zone" => "$Person.address.timezone",
+        "custom_user_time_zone" => "$Canvas.user.timezone",
+        "custom_user_offset" => "$Canvas.user.timezone.offset"
+      }
+      @tool.save!
+      student_in_course(:course => @course, :active_all => true)
+      user_session(@user)
+
+      account = @course.root_account
+      account.default_time_zone = 'Alaska'
+      account.save!
+
+      get "/courses/#{@course.id}/assignments/#{@assignment.id}"
+      response.should be_success
+      doc = Nokogiri::HTML.parse(response.body)
+      doc.at_css('form#tool_form input#custom_time_zone')['value'].should == "(GMT-09:00) Alaska"
+      doc.at_css('form#tool_form input#custom_user_time_zone')['value'].should == "(GMT-09:00) Alaska"
+      doc.at_css('form#tool_form input#custom_user_offset')['value'].should == "-09:00"
+
+      @user.time_zone = "Hawaii"
+      @user.save!
+
+      get "/courses/#{@course.id}/assignments/#{@assignment.id}"
+      response.should be_success
+      doc = Nokogiri::HTML.parse(response.body)
+      doc.at_css('form#tool_form input#custom_time_zone')['value'].should == "(GMT-10:00) Hawaii"
+      doc.at_css('form#tool_form input#custom_user_time_zone')['value'].should == "(GMT-10:00) Hawaii"
+      doc.at_css('form#tool_form input#custom_user_offset')['value'].should == "-10:00"
+    end
+
     it "should redirect if the tool can't be configured" do
       @tag.update_attribute(:url, "http://example.net")