Allow reference for time-based activity endpoints

app/controllers/api/groups_controller.rb

 
   # GET /api/groups/1/current_activities
   def current_activities
-    @activities = @group.current_activities
+    reference = try_parse_datetime params[:reference]
+    @activities = @group.current_activities reference
+
     render 'api/activities/index'
   end
 
   # GET /api/groups/1/upcoming_activities
   def upcoming_activities
-    @activities = @group.upcoming_activities
+    reference = try_parse_datetime params[:reference]
+    @activities = @group.upcoming_activities reference
+
     render 'api/activities/index'
   end
 
   # GET /api/groups/1/previous_activities
   def previous_activities
-    @activities = @group.previous_activities
+    reference = try_parse_datetime params[:reference]
+    @activities = @group.previous_activities reference
+
     render 'api/activities/index'
   end
 
   def set_group
     @group = Group.find(params[:id])
   end
+
+  # @return [DateTime] the parsed input.
+  def try_parse_datetime(input = nil)
+    return unless input
+    begin
+      DateTime.parse input
+    rescue ArgumentError
+      nil
+    end
+  end
 end

app/models/group.rb

 
   # @return [Array<Activity>]
   #   all Activities that have started, and not yet ended.
-  def current_activities(reference = Time.zone.now)
+  def current_activities(reference = nil)
+    reference ||= Time.zone.now
     activities
       .where('start < ?', reference)
       .where('end > ?', reference)
 
   # @return [Array<Activity>]
   #   at most 3 activities that ended recently.
-  def previous_activities(reference = Time.zone.now)
+  def previous_activities(reference = nil)
+    reference ||= Time.zone.now
     activities
       .where('end < ?', reference)
       .order(end: :desc)
 
   # @return [Array<Activity>]
   #   all Activities starting within the next 48 hours.
-  def upcoming_activities(reference = Time.zone.now)
+  def upcoming_activities(reference = nil)
+    reference ||= Time.zone.now
     activities
       .where('start > ?', reference)
       .where('start < ?', reference.days_since(2))