WooCommerce Shipping Additional Days - Stand Alone

<?php

function mytheme_get_max_shipping_classes_additional_time( $shipping_classes_ids = array() ) {
    if ( ! is_array( $shipping_classes_ids ) ) {
        return 0;
    }

    $shipping_classes_ids = array_filter( $shipping_classes_ids, function( $id ) {
        return ! is_nan( intval( $id ) );
    } );

    if ( empty( $shipping_classes_ids ) ) {
        return 0;
    }

    $shipping_class = get_terms( array(
        'taxonomy'      => 'product_shipping_class',
        'hide_empty'    => true,
        'include'       => (array) $shipping_classes_ids,
        'number'        => 1,
        'order'         => 'DESC',
        'orderby'       => 'meta_value_num',
        'meta_key'      => WCSAD_SHIPPING_CLASS_ADDITIONAL_TIME,
    ) );

    if ( is_wp_error( $shipping_class ) || empty( $shipping_class ) ) {
        return 0;
    }

    return get_shipping_class_additional_time( $shipping_class[0]->term_id );
}


function mytheme_woocommerce_correios_shipping_additional_time( $package ) {
    if ( empty( $package['contents'] ) ) {
        return 0;
    }

    $shipping_classes_ids = array();
    $product_additional_days = array();

    foreach ( $package['contents'] as $product_data ) {
        $shipping_classes_ids[] = $product_data['data']->get_shipping_class_id();
        $product_additional_days = get_products_additional_time( $product_data['product_id'] );
    }


    $shipping_classes_ids = array_unique( array_values( array_filter( $shipping_classes_ids ) ) );
    $max_additional_time = mytheme_get_max_shipping_classes_additional_time( $shipping_classes_ids );

    return max( $max_additional_time, $product_additional_days );
}

function mytheme_get_additional_days() {
    $packages = WC_Cart::get_shipping_packages();

    $additional_days = 0;
    foreach ( $packages as $package ) {
        $package_additional_days = mytheme_woocommerce_correios_shipping_additional_time( $package );

        $additional_days = max( $additional_days, $package_additional_days );
    }

    return $additional_days;
}