code: private function extractInput()
      {
          $params = $this->request->getParams();
          $period = $params[self::REQ_PERIOD] ?? '';
          if (empty($period)) {
              $period = $this->hlpPeriod->getPeriodCurrent(null, 0, HPeriod::TYPE_MONTH);
          } else {
              $period = $this->hlpPeriod->normalizePeriod($period, HPeriod::TYPE_MONTH);
          }
          $dsBegin = $this->hlpPeriod->getPeriodFirstDate($period);
          $treeType = $params[self::REQ_TREE_TYPE] ?? '';
          if ($treeType != OptionTreeType::VAL_PLAIN) {
              $treeType = OptionTreeType::VAL_COMPRESS; // 'compressed' by default
          }
          return [$dsBegin, $treeType];
      }
docs: Extract and validate input parameters.
  
  @return array [$dsBegin, $treeType]