public static function decide(MongoCollection $coll)
 {
     $searchCityStates = ProcessSearch::processSubletLocations();
     SubletListings::init($coll);
     $subletCityStates = SubletListings::processLocations();
     // Get demand of each searched city.
     $demand = self::getDemand($searchCityStates, $subletCityStates);
     $recommendation = self::getRecommendation($demand);
     return ['searches' => $searchCityStates, 'sublets' => $subletCityStates, 'demand' => $demand, 'recommendation' => $recommendation];
 }
 public static function init(MongoCollection $coll)
 {
     self::$coll = $coll;
 }