Where to override the tax in Magento 2?

Question

I need the tax to be added from external source. But I have hard time to find when should I alter the tax. Any idea?

Answer 1

A good starting point would be to create a class preference for Magento\Tax\Model\Sales\Total\Quote\Tax:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager:etc/config.xsd">
    <preference for="Magento\Tax\Model\Sales\Total\Quote\Tax" type="Taxjar\SalesTax\Model\Tax\Sales\Total\Quote\Tax" />
</config>

https://github.com/taxjar/taxjar-magento2-extension/blob/develop/etc/di.xml#L20

You'd then extend the Tax class and override the collect method:

https://github.com/taxjar/taxjar-magento2-extension/blob/develop/Model/Tax/Sales/Total/Quote/Tax.php#L107

In TaxJar's extension, we pass in the tax by line item by overriding the mapItem method inherited from CommonTaxCollector:

https://github.com/taxjar/taxjar-magento2-extension/blob/ba687328ce1cb91030617a74394b318649fc50f3/Model/Tax/Sales/Total/Quote/Tax.php#L256

There's certainly a lot more to this if you want to do it the right way. I recommend studying TaxJar's source code and looking at the relevant classes in Magento 2 to see how it's done.

Answer 2

I rewrite the Tax classname and it works for me.

    <preference for="Magento\Tax\Model\Sales\Total\Quote\Tax" type="BA\Vertex\Rewrite\Magento\Tax\Model\Sales\Total\Quote\Tax"/>

Rewrite class

 public function collect(
    \Magento\Quote\Model\Quote $quote,
    \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment,
    \Magento\Quote\Model\Quote\Address\Total $total
) {
    
    $this->clearValues($total);
    if (!$shippingAssignment->getItems()) {
        return $this;
    }

    $x= $quote->getItems();
    if (isset($x)) {
        foreach ($x as $item) {
            $g = $item;
            $y = $item->getSku();
            $y = $item->getProductId();
        }
    }
    
    $baseTaxDetails = $this->getQuoteTaxDetails($shippingAssignment, $total, true);
    $taxDetails = $this->getQuoteTaxDetails($shippingAssignment, $total, false);

    //Populate address and items with tax calculation results
    $itemsByType = $this->organizeItemTaxDetailsByType($taxDetails, $baseTaxDetails);
    if (isset($itemsByType[self::ITEM_TYPE_PRODUCT])) {
        $this->processProductItems($shippingAssignment, $itemsByType[self::ITEM_TYPE_PRODUCT], $total);
    }

    if (isset($itemsByType[self::ITEM_TYPE_SHIPPING])) {
        $shippingTaxDetails = $itemsByType[self::ITEM_TYPE_SHIPPING][self::ITEM_CODE_SHIPPING][self::KEY_ITEM];
        $baseShippingTaxDetails =
            $itemsByType[self::ITEM_TYPE_SHIPPING][self::ITEM_CODE_SHIPPING][self::KEY_BASE_ITEM];
        $this->processShippingTaxInfo($shippingAssignment, $total, $shippingTaxDetails, $baseShippingTaxDetails);
    }

    //Process taxable items that are not product or shipping
    $this->processExtraTaxables($total, $itemsByType);

   $total->setTaxAmount(2000);
   $total->setGrandTotal($total->getBaseGrandTotal()+2000);
   
    //Save applied taxes for each item and the quote in aggregation
    $this->processAppliedTaxes($total, $shippingAssignment, $itemsByType);

    if ($this->includeExtraTax()) {
        $total->addTotalAmount('extra_tax', $total->getExtraTaxAmount());
        $total->addBaseTotalAmount('extra_tax', $total->getBaseExtraTaxAmount());
    }

    return $this;
}