pocketmine\tile\Furnace::onUpdate PHP Method

    public function onUpdate()
    {
        if ($this->closed === true) {
            return false;
        }
        $this->timings->startTiming();
        $ret = false;
        $fuel = $this->inventory->getFuel();
        $raw = $this->inventory->getSmelting();
        $product = $this->inventory->getResult();
        $smelt = $this->server->getCraftingManager()->matchFurnaceRecipe($raw);
        $canSmelt = ($smelt instanceof FurnaceRecipe and $raw->getCount() > 0 and ($smelt->getResult()->equals($product) and $product->getCount() < $product->getMaxStackSize() or $product->getId() === Item::AIR));
        if ($this->namedtag["BurnTime"] <= 0 and $canSmelt and $fuel->getFuelTime() !== null and $fuel->getCount() > 0) {
            $this->checkFuel($fuel);
        }
        if ($this->namedtag["BurnTime"] > 0) {
            $this->namedtag->BurnTime = new ShortTag("BurnTime", $this->namedtag["BurnTime"] - 1);
            $this->namedtag->BurnTicks = new ShortTag("BurnTicks", ceil($this->namedtag["BurnTime"] / $this->namedtag["MaxTime"] * 200));
            if ($smelt instanceof FurnaceRecipe and $canSmelt) {
                $this->namedtag->CookTime = new ShortTag("CookTime", $this->namedtag["CookTime"] + 1);
                if ($this->namedtag["CookTime"] >= 200) {
                    //10 seconds
                    $product = Item::get($smelt->getResult()->getId(), $smelt->getResult()->getDamage(), $product->getCount() + 1);
                    $this->server->getPluginManager()->callEvent($ev = new FurnaceSmeltEvent($this, $raw, $product));
                    if (!$ev->isCancelled()) {
                        $this->inventory->setResult($ev->getResult());
                        $raw->setCount($raw->getCount() - 1);
                        if ($raw->getCount() === 0) {
                            $raw = Item::get(Item::AIR, 0, 0);
                        }
                        $this->inventory->setSmelting($raw);
                    }
                    $this->namedtag->CookTime = new ShortTag("CookTime", $this->namedtag["CookTime"] - 200);
                }
            } elseif ($this->namedtag["BurnTime"] <= 0) {
                $this->namedtag->BurnTime = new ShortTag("BurnTime", 0);
                $this->namedtag->CookTime = new ShortTag("CookTime", 0);
                $this->namedtag->BurnTicks = new ShortTag("BurnTicks", 0);
            } else {
                $this->namedtag->CookTime = new ShortTag("CookTime", 0);
            }
            $ret = true;
        } else {
            if ($this->getBlock()->getId() === Item::BURNING_FURNACE) {
                $this->getLevel()->setBlock($this, Block::get(Item::FURNACE, $this->getBlock()->getDamage()), true);
            }
            $this->namedtag->BurnTime = new ShortTag("BurnTime", 0);
            $this->namedtag->CookTime = new ShortTag("CookTime", 0);
            $this->namedtag->BurnTicks = new ShortTag("BurnTicks", 0);
        }
        foreach ($this->getInventory()->getViewers() as $player) {
            $windowId = $player->getWindowId($this->getInventory());
            if ($windowId > 0) {
                $pk = new ContainerSetDataPacket();
                $pk->windowid = $windowId;
                $pk->property = 0;
                //Smelting
                $pk->value = floor($this->namedtag["CookTime"]);
                $player->dataPacket($pk);
                $pk = new ContainerSetDataPacket();
                $pk->windowid = $windowId;
                $pk->property = 1;
                //Fire icon
                $pk->value = $this->namedtag["BurnTicks"];
                $player->dataPacket($pk);
            }
        }
        $this->lastUpdate = microtime(true);
        $this->timings->stopTiming();
        return $ret;
    }