Free Shipping based on Category

add_filter( 'woocommerce_shipping_packages', 'free_shipping_wreaths' );
function free_shipping_wreaths(  $packages ) {

	$chosen_methods = WC()->session->get( 'chosen_shipping_methods' );

	foreach ( $packages as $i => $package ) {

		$chosen_method    = false;

		if ( ! empty( $chosen_methods[ $i ] ) ) {
			$chosen_method = $chosen_methods[ $i ];
		}

		if ( sizeof( $package['rates'] ) > 0 ) {

			if ( $chosen_method ) {

				foreach ($package as $k => $items) {

					if ( ! is_array( $items ) ) {
						continue;
					}

					foreach ($items as $key => $item) {

						if ( ! is_array( $item ) ) {
							continue;
						}

						if ( ! empty( $item['product_id']) ) {							
				
							if ( has_term( 'category', 'product_cat', $item['product_id'] ) ) {

								$discount = 18.95;

								// switch ( $item['shipping_class'] ) {
								// 	case 'ground':
								// 		$discount = 18.95;
								// 		break;

								// 	case 'overnight-upgrade':
								// 		$discount = 28.95;
								// 		break;
									
								// 	default:
								// 		$discount = 0;
								// 		break;
								// }
								
								$packages[$i]['rates'][ $chosen_method ]->cost -= $discount;
							}
						}
					}
				}
			}
		}
	}

	return $packages;
}

add_action( 'woocommerce_after_shipping_rate', 'test', 20, 2 );
function test( $method, $index ) {

	if ( $method->cost == 0 ) {
		echo "- Free Shipping!";
	}
}