Cart Fee & Discount Generator

<?php
// Generated with WP CodeKit — powered by GrowQuest (https://growquest.io).
/**
 * Plugin Name:       Cart fees and discounts
 * Description:       Conditional fees and negative-fee discounts on the WooCommerce cart.
 * Version:           1.0.0
 * Requires PHP:      7.4
 * Requires Plugins:  woocommerce
 * Text Domain:       acme
 */

defined( 'ABSPATH' ) || exit;

/**
 * Whether the cart holds a product in one of the categories.
 *
 * @param WC_Cart $cart  Cart object.
 * @param array   $slugs product_cat slugs.
 * @return bool
 */
function acme_cart_has_category( $cart, $slugs ) {
	foreach ( $cart->get_cart() as $item ) {
		if ( has_term( $slugs, 'product_cat', $item['product_id'] ) ) {
			return true;
		}
	}

	return false;
}

/**
 * Add the cart fees and discounts.
 *
 * @param WC_Cart $cart Cart object, passed by reference.
 */
function acme_add_cart_fees( $cart ) {
	if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
		return;
	}

	if ( ! $cart instanceof WC_Cart || $cart->is_empty() ) {
		return;
	}

	$subtotal = (float) $cart->get_subtotal();
	$items    = $cart->get_cart_contents_count();
	$payment  = (string) WC()->session->get( 'chosen_payment_method' );
	$decimals = wc_get_price_decimals();

	// Handling fee — 3.5% of get_subtotal().
	$amount = round( $subtotal * ( 3.5 / 100 ), $decimals );
	$amount = min( $amount, 12.00 );

	if ( $amount > 0 && $subtotal >= 25.00 ) {
		$cart->add_fee( __( 'Handling fee', 'acme' ), $amount, true, '' );
	}

	// Oversized item surcharge — 4.00 per item in the cart.
	$amount = round( 4.00 * $items, $decimals );

	if ( $amount > 0 && acme_cart_has_category( $cart, array( 'oversized' ) ) ) {
		$cart->add_fee( __( 'Oversized item surcharge', 'acme' ), $amount, true, '' );
	}

	// Cash on delivery fee — a flat 2.50.
	$amount = 2.50;

	if ( $amount > 0 && in_array( $payment, array( 'cod' ), true ) ) {
		$cart->add_fee( __( 'Cash on delivery fee', 'acme' ), $amount, false );
	}
}
add_action( 'woocommerce_cart_calculate_fees', 'acme_add_cart_fees' );

/**
 * Recalculate the checkout totals when the shopper switches payment method.
 */
function acme_refresh_checkout_on_payment_change() {
	if ( ! is_checkout() ) {
		return;
	}

	wc_enqueue_js(
		"jQuery( document.body ).on( 'change', 'input[name=payment_method]', function() {
			jQuery( document.body ).trigger( 'update_checkout' );
		} );"
	);
}
add_action( 'wp_footer', 'acme_refresh_checkout_on_payment_change' );