Magento2, Customized quote subtotal in cart page

Question

Through observing the event checkout_cart_product_add_after, I was able to customize the price of the item in the cart, now I need to have an observer for customizing its subtotal calculation. What event/events need to be observed?

Is it possible to customize the calculation like $cart->setQuote()->getSubtotal() in observer and save the quote?

And basically, can it be done through observer or plugin is the solution?

Edit:

Here is my current event:

<event name="sales_quote_collect_totals_before">
        <observer name="customuitemprice" instance="vendor\code\Observer\BindUpdateItem"/>
    </event>

Observer:

class BindUpdateItem implements ObserverInterface
{
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $quote = $observer->getQuote();
        foreach ($quote->getAllItems() as $item)
        {
            $product = $item->getProduct();
            ?How change the subtotal?

        }
        return $this;
    }
}

Answer 1

You can change the price using custom price method like:

$newPrice = '';
$item->setCustomPrice($newPrice);
$item->setOriginalCustomPrice($newPrice);
$item->getProduct()->setIsSuperMode(true);
$item->save();

and update all totals that you have:

$quote->collectTotals()

It is not a good idea to update only subTotals or grand totals because you will have a lot of problem with the final price calculation

Answer 2

I managed to changed the sub total for any item, here is the code:

$item->setCustomRowTotalPrice($item->getCustomPrice() * $item->getQty());
$item->setRowTotal($item->getCustomPrice() * $item->getQty());
$item->setBaseRowTotal($item->getCustomPrice() * $item->getQty());

This should be ok. This code couldn't work properly if you are running the function

calcRowTotal()

which calculate again the sub total for each item in the cart again overwriting your change.

Let me know if you have luck.