Add item if space

#define ITEMID 25
#define AMOUNT 5
#define ITEM_MYSTERY_TICKET 9999

class Test_NPC: public CreatureScript
{
public:
    Test_NPC() : CreatureScript("Test_NPC") { }

    bool OnGossipHello(Player * player, Creature * creature)
    {
        player->ADD_GOSSIP_ITEM(3, "test", GOSSIP_SENDER_MAIN, GOSSIP_ACTION_INFO_DEF+1);
        player->ADD_GOSSIP_ITEM(1, "Nevermind", GOSSIP_SENDER_MAIN, GOSSIP_ACTION_INFO_DEF+2);
        player->SEND_GOSSIP_MENU(DEFAULT_GOSSIP_MESSAGE, creature->GetGUID());
        return true;
    }

    bool OnGossipSelect(Player * player, Creature * creature, uint32 sender, uint32 uiAction)
    {
        player->PlayerTalkClass->ClearMenus();
        switch(uiAction)
        {
        case GOSSIP_ACTION_INFO_DEF+1:
            {
                if (player->GetItemCount(ITEM_MYSTERY_TICKET) >= 2)
                {
                    if(!ModifyItemAmount(player, ITEMID, AMOUNT)) // ModifyItemAmount gives the player the items if he has space. If no space, returns false.
                        player->GetSession()->SendNotification("You do not have enough space!");
                    else
                        ModifyItemAmount(player, ITEM_MYSTERY_TICKET, -2); // ModifyItemAmount can also remove items from inventory if you provide negative amount.
                }
                else
                    player->GetSession()->SendNotification("You do not have enough space!");
            } break;
        case GOSSIP_ACTION_INFO_DEF+2:
            {
                player->CLOSE_GOSSIP_MENU();
            } break;
        }
    }

    // Custom function:
    bool ModifyItemAmount(Player * player, uint32 itemEntry, uint32 amount)
    {
        if (amount < 0)
        {
            player->DestroyItemCount(itemEntry, -amount, true, false);
            return true;
        }
        if (amount == 0)
            amount = 1;

        uint32 noSpaceForCount = 0;

        ItemPosCountVec dest;
        uint8 msg = player->CanStoreNewItem(NULL_BAG, NULL_SLOT, dest, itemEntry, amount, &noSpaceForCount);

        if (msg != EQUIP_ERR_OK)
            amount -= noSpaceForCount;

        if (amount == 0 || dest.empty())
            return false;

        Item* item = player->StoreNewItem(dest, itemEntry, true, Item::GenerateItemRandomPropertyId(60000));
        return true;
    }
};

void AddSC_Test_NPC()
{
    new Test_NPC();
}