<?php
/**
 * Show a message at the cart/checkout displaying
 * how much to go for free shipping.
 */
function wpd_free_shipping_notice() {
	if ( ! is_cart() && ! is_checkout() ) { // Remove partial if you don't want to show it on cart/checkout
		return;
	}

	$packages = WC()->cart->get_shipping_packages();
	$package = reset( $packages );
	$zone = wc_get_shipping_zone( $package );

	$cart_total = WC()->cart->get_displayed_subtotal();
	if ( WC()->cart->display_prices_including_tax() ) {
		$cart_total = round( $cart_total - ( WC()->cart->get_discount_total() + WC()->cart->get_discount_tax() ), wc_get_price_decimals() );
	} else {
		$cart_total = round( $cart_total - WC()->cart->get_discount_total(), wc_get_price_decimals() );
	}
	
	foreach ( $zone->get_shipping_methods( true ) as $k => $method ) {
		$min_amount = $method->get_option( 'min_amount' );

		if ( $method->id == 'free_shipping' && ! empty( $min_amount ) && $cart_total < $min_amount ) {
			$remaining = $min_amount - $cart_total;
			wc_add_notice( sprintf( 'Ještě zbývá %s do dopravy zdarma.', wc_price( $remaining ) ) );
		}
	}

} add_action( 'wp', 'wpd_free_shipping_notice' );