Highlight gaps in exercise working time

app/controllers/exercises_controller.rb

@@ -326,6 +326,16 @@ class ExercisesController < ApplicationController
 
   def statistics
     if(@external_user)
+      @submissions = Submission.where("user_id = ?  AND exercise_id = ?", @external_user.id, @exercise.id).order("created_at")
+      @submissions_and_interventions = (@submissions + UserExerciseIntervention.where("user_id = ?  AND exercise_id = ?", @external_user.id, @exercise.id)).sort_by { |a| a.created_at }
+      deltas = @submissions.map.with_index do |item, index|
+        delta = item.created_at - @submissions[index - 1].created_at if index > 0
+        if delta == nil or delta > 10 * 60 then 0 else delta end
+      end
+      @working_times_until = []
+      @submissions_and_interventions.each_with_index do |submission, index|
+        @working_times_until.push((Time.at(deltas[1..index].inject(:+)).utc.strftime("%H:%M:%S") if index > 0))
+      end
       render 'exercises/external_users/statistics'
     else
       user_statistics = {}