Add NIF/CIF to WooCommerce (only as example)

woocommerce-vat.php

<?php

/*
 * Only used for example purposes, for also incluidng VAT validation and calculation
 * I recommend using the plugin https://wordpress.org/plugins/wc-apg-nifcifnie-field/
*/

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

/*
 * Add VAT field to 
 * My Account - Edit Form - Billing fields
 * Checkout - Edit Form - Billing Fields
 * 
 * https://gist.github.com/Miq3l/4870eecc80bb6a1f537c575e848ef2b5 
 * Source:  https://docs.woothemes.com/document/tutorial-customising-checkout-fields-using-actions-and-filters
*/
function add_vat_to_billing_fields($billing_fields){

	$billing_fields['billing_vat'] = array(
		'type' => 'text',
		'label' =>  __('NIF/CIF',  'woocommerce' ),
		'class' => array('form-row-wide'),
		'required' => false,
        'clear' => true, 
        'priority' => 31
	);
	
	return $billing_fields;
}
add_filter('woocommerce_billing_fields' , 'add_vat_to_billing_fields');


/*
 * Add VAT when printing billing address on:
 * (1) My account
 * (2) Checkout - Order Received (printed after having completed checkout and in other parts where this function is used)
 */

// (1) My Account
add_filter( 'woocommerce_my_account_my_address_formatted_address', 'custom_my_account_my_address_formatted_address', 10, 3 );
function custom_my_account_my_address_formatted_address( $fields, $customer_id, $type ) {

	if ( $type == 'billing' ) {
		$fields['vat'] = get_user_meta( $customer_id, 'billing_vat', true );
	}

	return $fields;
}

// (2) Checkout
add_filter( 'woocommerce_order_formatted_billing_address', 'custom_add_vat_formatted_billing_address', 10, 2 );
function custom_add_vat_formatted_billing_address( $fields, $order ) {
	$fields['vat'] = $order->billing_vat;

	return $fields;
}


// Creating merger VAT variables for printing formatting
add_filter( 'woocommerce_formatted_address_replacements', 'custom_formatted_address_replacements', 10, 2 );
function custom_formatted_address_replacements( $address, $args ) {
	$address['{vat}'] = '';
	$address['{vat_upper}']= '';

	if ( ! empty( $args['vat'] ) ) {
		$address['{vat}'] = $args['vat'];
		$address['{vat_upper}'] = strtoupper($args['vat']);
	}
	return $address;
}


//Defining the Spanish formatting to print the address, including VAT.
add_filter( 'woocommerce_localisation_address_formats', 'custom_localisation_address_format' );
function custom_localisation_address_format( $formats ) {
	$formats['ES'] = "{name}\n{company}\n{vat_upper}\n{address_1}\n{address_2}\n{postcode} {city}\n{state}\n{country}";

	return $formats;
}


/*
 * Add VAT form meta field on Wordpress Admin -> User Profile -> Billing
 */

add_filter( 'woocommerce_customer_meta_fields', 'custom_customer_meta_fields' );
function custom_customer_meta_fields( $fields ) {
	$fields['billing']['fields']['billing_vat'] = array(
		'label'       => __( 'NIF/CIF', 'woocommerce' )
	);

	return $fields;
}


/*
 * Add VAT form meta field on Wordpress Admin -> Order -> Billing Edit Form
 */

add_filter( 'woocommerce_admin_billing_fields', 'custom_admin_billing_fields' );
function custom_admin_billing_fields( $fields ) {
	$fields['vat'] = array(
		'label' => __( 'NIF/CIF', 'woocommerce' ),
		'show'  => true
	);
	
	return $fields;
}


/*
 * Copy VAT user meta field stored, to the order when creating a new order and selecting a client (ajax request)
 * Or when using the pencil on the Order Edit Page "Usar la dirección de facturación" (ajax request)
 * Both cases, selecting a new order and a client or copying billing data from stored client data use the same filter.
 * 
 * On Wordpress Admin -> Order -> New Order or Order Edit Page (same page)
 */

add_filter( 'woocommerce_ajax_get_customer_details', 'custom_found_customer_details' );
function custom_found_customer_details( $customer_data ) {
    
	$customer_data['billing']['vat'] = get_user_meta( $_POST['user_id'], 'billing_vat', true );

	return $customer_data;
}