replace_existing_booking.php

<?php
/**
 * Replace existing booking in cart with new one
 * 
 * When a customer adds a new booking for a specific bookable product, 
 * any existing booking for the same product is automatically removed.
 * This ensures cross-resource blocking works correctly since it triggers on payment.
 */

// Define the bookable product ID (update after creating the product)
define('SINGLE_CART_BOOKING_PRODUCT_ID', 123); // Replace with actual product ID

function replace_existing_booking_in_cart($passed, $product_id, $quantity) {
    // Only apply to the specified bookable product
    if ($product_id != SINGLE_CART_BOOKING_PRODUCT_ID) {
        return $passed;
    }

    if (!WC()->cart) {
        return $passed;
    }

    // Find and remove any existing bookings for this product from cart
    $removed = false;
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {
        if ($cart_item['product_id'] == SINGLE_CART_BOOKING_PRODUCT_ID) {
            WC()->cart->remove_cart_item($cart_item_key);
            $removed = true;
        }
    }

    // Notify customer that their previous booking was replaced
    if ($removed) {
        wc_add_notice(
            __('Your previous booking has been replaced with the new selection.', 'woocommerce'),
            'notice'
        );
    }

    return $passed;
}

add_filter('woocommerce_add_to_cart_validation', 'replace_existing_booking_in_cart', 10, 3);