How to check player item ammount

Hello there, i am making rpg server that use emerald as its currency but i have no idea how to check ammount of emeralds in player inventory so i can make scorehud addons. Pls help

 

PHP:

/** @var pocketmine\Player $player*/
$count = 0;
foreach($player->getInventory()->getContents() as $item)
{
      if($item->getId() === Item::EMERALD)
             $count += $item->getCount()
}

$player->sendMessage("§aYou have §l{$count} §r§aEmeralds !");

To make the thing show in scoreboard, in your addon instead of sending a message you could set your value to the $count variable