Format and validate postal codes for Poland in WooCommerce

functions.php

<?php
/* This will "normalize" the postcode entered by the customer, if the country seleced is Poland.
 * Normalize meaning that it doesn't matter if they entered the post code as xx-xxx or xxxxx the 
 * function will be able to format it correctly. Once a "normalized" postcode is generated, the 
 * function will add a hyphen (-) in between the 2nd and 3rd numbers in the post code.
 * This will always generate a xx-xxx formatted postcode.
 */
add_filter( 'woocommerce_format_postcode', 'sd_add_poland_post_code_format', 10, 2 );
function sd_add_poland_post_code_format( $postcode, $country ){
	$postcode = wc_normalize_postcode( $postcode );
	switch ( $country ) {
		case 'PL' :
			$postcode = trim( substr_replace( $postcode, '-', 2, 0 ) );
			break;
	}
	return $postcode;
}

/* This will validate the postcode entered by the customer and returned by the function above if the
 * country selected is Poland. This function checks to see if the post code is formatted as two characters
 * between 0-9, a hyphen, then three characters between 0-9.
 * If this check passes, the function will return 'true', otherwise it will return 'false'.
 */

add_filter( 'woocommerce_validate_postcode', 'sd_validate_poland_post_code', 10, 3 );
function sd_validate_poland_post_code( $valid, $postcode, $country ){
	switch ( $country ) {
		case 'PL':
			$valid = (bool) preg_match( '/^([0-9]{2})(-[0-9]{3})?$/i', $postcode );
			break;
	}
	return $valid;
}