aMember (site.php): User can choose access start date during signup

site.php

<?php

/**
 * @title User can choose access start date during signup
 *
 * Add new Product option with type Date and Label "Start Date"
 * http://www.amember.com/docs/Product_Options
 * then put the following code to
 * @path  application/configs/site.php
 */

Am_Di::getInstance()->hook->add(Am_Event::CALCULATE_START_DATE, function(Am_Event $e) {
    if ($e->getIsFirst()) {

        /** @var InvoiceItem $item */
        $item = $e->getItem();
        foreach($item->getOptions() as $key => $opt) {
            if (
                $key == 'Start Date'
                && !empty($opt['value'])
            ) {
                $e->setReturn($opt['value']);
            }
        }

    }
});