GP eCommerce Fields: Sync Tax Field Rate with WooCommerce Tax Rate

gpef-sync-tax-rate-with-wc.php

<?php
/**
 * Note: See https://gravitywiz.com/documentation/how-do-i-install-a-snippet/ for details on how to install snippets.
 *
 * The following snippet will the specified tax field to use the rate from a specified WooCommerce tax class.
 *
 * Instructions:
 *   * Set $form_id
 *   * Set $tax_field_id
 *   * Set $wc_tax_rate_id
 */
$form_id = 17; /* Set me */

add_filter( 'gform_pre_render_' . $form_id, 'gwiz_link_tax_field_to_wc_tax' );
function gwiz_link_tax_field_to_wc_tax( $form ) {
	$tax_field_id = 4; /* Set me */
	$wc_tax_rate_id = 1; /* Set me */

	$tax_instance   = new WC_Tax;
	$tax_rate       = $tax_instance->_get_tax_rate( $wc_tax_rate_id );

	foreach ( $form['fields'] as &$field ) {
		if ( $field->type !== 'tax' || $field->id !== $tax_field_id ) {
			continue;
		}

		$field->taxAmount = rgar( $tax_rate, 'tax_rate', $field->taxAmount );
	}

	return $form;
}