/**
  * Calculate the average date length it took to solve tickets within date period
  * @param $from
  * @param $to
  * @return int
  */
 public function intervalPerformance($from, $to, $cat_id = false)
 {
     if ($cat_id) {
         $tickets = Ticket::where('category_id', $cat_id)->whereBetween('completed_at', array($from, $to))->get();
     } else {
         $tickets = Ticket::whereBetween('completed_at', array($from, $to))->get();
     }
     if (empty($tickets->first())) {
         return false;
     }
     $performance_count = 0;
     $counter = 0;
     foreach ($tickets as $ticket) {
         $performance_count += $this->ticketPerformance($ticket);
         $counter++;
     }
     $performance_average = $performance_count / $counter;
     return $performance_average;
 }