Commerce v1 Developer Custom Tax Rate Providers

Before diving into custom tax rate providers, make sure that you've read (and understood) how taxes work in Commerce.

With a Custom Tax Rate provider it's possible to set tax rates based on your own business/tax regulation logic. While Tax Rules should be used for the basic logic ("use this tax rate provider for customers from Europe"), the tax rate provider can access any order/address data to return the tax rate (percentage) that needs to be applied to an order.

High-level Overview

To create a custom tax provider, you need to create an implementation of the abstract modmore\Commerce\Taxes\RateProvider class. That class can be found in core/components/commerce/src/Taxes/RateProvider.php.

There are 2 primary class methods to implement:

  • public function getModelFields(\comTaxRule $rule): to return an array of Form Fields that make up the rate provider options. They all need a name of rate_provider_options[KEY], and check for a previously saved value in $rule->get('rate_provider_options').
  • public function determine(): to determine and return an array of comTaxRate objects. This method is only called when the tax rules determined that your rate provider needs to be run, but it may run multiple times for multiple products. You can access $this->order and $this->getOption() to make your determination.

Determining the comTaxRate

Here's an example, part of the Manual tax rate provider, that shows a simple way of determining and returning a tax rate:

<?php

namespace modmore\Commerce\Taxes;

use modmore\Commerce\Admin\Widgets\Form\NumberField;
use modmore\Commerce\Admin\Widgets\Form\TextField;

class Manual extends RateProvider {

    public function getModelFields(\comTaxRule $rule)
    {
        $fields = [];
        // ...
        return $fields
    }

    /**
     * @return \comTaxRate[]
     */
    public function determine()
    {
        $percentage = (float)$this->getOption('rate', 0.00);
        $key = $this->getOption('key', 'TAX-' . $percentage);
        $name = $this->getOption('name', $percentage . '% VAT');
        $taxRate = $this->getTaxRateObject($key, $name, $percentage);
        return [$taxRate];
    }

    public function getTaxRateObject($key, $name, $percentage)
    {
        /** @var \comTaxRate $taxRate */
        $taxRate = $this->adapter->getObject('comTaxRate', array(
            'key' => $key,
            'rate_provider' => __CLASS__,
            'percentage' => $percentage,
        ));

        if (!$taxRate) {
            $taxRate = $this->adapter->newObject('comTaxRate', array(
                'key' => $key,
                'rate_provider' => __CLASS__,
                'name' => $name,
                'percentage' => $percentage,
            ));
            $taxRate->save();
        }
        return $taxRate;
    }
}

Note: Make sure you return an array of comTaxRate objects - not the single object. Even if it's just one rate, it needs to be an array.

Within your rate provider, use $this->order->getBillingAddress() and $this->order->getExpectedAddress() to get the address for the customer. The expected address is filled by modules such as AutoFillGeoIP, and UserProfileAddress. That address is not yet confirmed by the customer, but can be used to show an initial calculation.

The percentage set on the tax rate object can have up to 4 decimals. Setting it to 20.123 will charge a 20.123% tax rate. The order items handle the calculation for both inclusive and exclusive tax rates, so you just have to provide the percentage.