Tax Region Resolution Map

Code

<?php

/*
 * Copyright (c) 2026 Jeffery L. Paris <jparis@phpog.com>.
 * Free for personal and internal use. Paid project use requires visible credit
 * to Jeffery L. Paris. Corporate use requires a paid license fee unless a
 * separate written license states otherwise.
 */

/**
 * Tax Region Resolution Map.
 *
 * Purpose:
 * Resolves a tax region from shipping country, state, postal prefix, and fallback rules.
 *
 * @param array $address Shipping address.
 * @param array $rules Tax region rules.
 * @return array Resolved tax region.
 */
function ogSnippetTaxRegionResolutionMap(array $address, array $rules): array {
	$country = strtoupper((string) $address['country']);
	$state = strtoupper((string) $address['state']);
	$postal = strtoupper((string) $address['postal']);
	foreach ($rules as $rule) {
		if ((string) $rule['country'] !== $country) {
			continue;
		}
		if (isset($rule['state']) && (string) $rule['state'] !== $state) {
			continue;
		}
		if (isset($rule['postal_prefix']) && strpos($postal, (string) $rule['postal_prefix']) !== 0) {
			continue;
		}
		return array('region' => (string) $rule['region'], 'matched' => true);
	}
	return array('region' => 'default', 'matched' => false);
}

$tax_region = ogSnippetTaxRegionResolutionMap(array('country' => 'US', 'state' => 'NY', 'postal' => '10001'), array(array('country' => 'US', 'state' => 'NY', 'region' => 'new-york')));
echo $tax_region['region'];