class store
{
	function sale_item($inventory_id, $item_cost, $user_id)
	{
		
	}

	function buy_item($item_id, $store_id, $user_id)
	{
		
	}

	function item_info($item_id, $data_info = false)
	{
		
	}

}

class player
{
	function init_user_stats ()
	{
	
	}

	function level_up($xp, $current_level, $user_id)
	{
	
	}

	function update_stats($user_id, $stats_array)
	{
	
	}
}

class inventory
{
	function in_inventory($user_id, $item_id)
	{
	
	}

	function give_item($item_id, $user_id)
	{
	
	}

	function take_item($inventory_id, $user_id)
	{

	}

	function transfer_item ($source_user, $target_id, $inventory_id)
	{

	}
}