public static function increaseInventory($id, $variation = '', $qty = 1)
 {
     Cart66Common::log("Increasing Inventory: line " . __LINE__);
     // Build varation ikey string component
     if (!empty($variation)) {
         $variation = self::scrubVaritationsForIkey(str_replace(', ', '~', $variation));
     }
     $p = new Cart66Product($id);
     $is_gravity_form = false;
     $valid_options = array();
     if ($p->isGravityProduct()) {
         $valid_options = Cart66GravityReader::getFormValuesArray($p->gravity_form_id);
         $is_gravity_form = true;
     } else {
         if (strlen($p->options_1) > 1) {
             $valid_options[] = explode(',', str_replace(' ', '', $p->options_1));
         }
         if (strlen($p->options_2) > 1) {
             $valid_options[] = explode(',', str_replace(' ', '', $p->options_2));
         }
     }
     $newVariation = '';
     $options = explode(',', $variation);
     foreach ($options as $option) {
         if ($p->validate_option($valid_options, $option, $is_gravity_form)) {
             $newVariation .= $option;
         }
     }
     $ikey = $p->getInventoryKey($newVariation);
     $count = $p->getInventoryCount($ikey);
     $newCount = $count + $qty;
     $p->setInventoryLevel($ikey, $newCount);
 }