Richmond CC extensions to Ninja forms

functions.py

<?php
add_shortcode( 'ninja_forms_paypal', 'ninja_forms_paypal_shortcode' );

function ninja_forms_paypal_shortcode( $atts ){
        global $ninja_forms_processing;
        extract( shortcode_atts(
            array(
              'ref' => null,
              'amount_field' => null,
              'currency' => 'GBP',
              'business' => null
            ), $atts )
        );
        if ( is_object ( $ninja_forms_processing ) ) {
            $html = '<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top"><input name="cmd" type="hidden" value="_xclick" />';
            if ( !empty( $ref ) ) {
                $ref_with_values = preg_replace_callback("/\\{([0-9]+)\\}/", function($m) {
                    global $ninja_forms_processing;
                    return $ninja_forms_processing->get_field_value( $m[1] );
                }, $ref);
                $html .= '<input name="item_name" type="hidden" value="' . $ref_with_values . '" />';
            }
            if ( !empty( $amount ) ) {
                $html .= '<input name="amount" type="hidden" value="' . $amount . '" />';
            }
            if ( !empty( $amount_field ) ) {
                $amount = $ninja_forms_processing->get_field_value( $amount_field );
                $html .= '<input name="amount" type="hidden" value="' . $amount . '" />';
            }
            if ( !empty( $currency ) ) {
                $html .= '<input name="currency_code" type="hidden" value="' . $currency . '" />';
            }
            if ( !empty( $business ) ) {
                $html .= '<input name="business" type="hidden" value="' . $business . '" />';
            }
            $html .= '<input alt="PayPal – The safer, easier way to pay online." name="submit" src="https://www.paypalobjects.com/en_GB/i/btn/btn_paynowCC_LG.gif" type="image" /><img src="https://www.paypalobjects.com/en_GB/i/scr/pixel.gif" alt="" width="1" height="1" border="0" /></form>';
            return $html;
        } else {
            return '';
        }
}
?>