Add filter for merchant order reference

[remcotolsma]

Awaiting response from customer in https://secure.helpscout.net/conversation/2282196531/25812?folderId=1425710.

<?php

add_filter(
	'pronamic_pay_adyen_merchant_order_reference',
	function( $merchant_order_reference, $payment ) {
		// Check if payment source is Gravity Forms.
		if ( 'gravityformsideal' !== $payment->get_source() ) {
			return $merchant_order_reference;
		}

		// Check if Gravity Forms API is available.
		if ( ! method_exists( 'GFAPI', 'get_entry' ) ) {
			return $merchant_order_reference;
		}

		// Check if Gravity Forms entry exists.
		$entry = GFAPI::get_entry( $payment->get_source_id() );

		if ( false === $entry ) {
			return $merchant_order_reference;
		}

		// Format merchant order reference.
		$merchant_order_reference = strtr(
			$merchant_order_reference,
			[
				'{gf_form_id}'  => $entry['form_id'],
				'{gf_entry_id}' => $entry['id'],
			]
		);

		return $merchant_order_reference;
	},
	10,
	2
);

[rvdsteege]

I've tested this with the merchant order reference setting set to GF form #{gf_form_id} + entry #{gf_entry_id}, but this resulted in GF form #2 + entry #278242912 for Gravity Forms entry ID 2782. It appears the payment ID (42912) is appended by Payment::format_string() as the setting does not contain {order_id} nor {payment_id}.

In case of Gravity Forms, the user could also set the order ID setting in the payment feed of the form. This setting supports all Gravity Forms merge tags. The value of GF form #{form_id} + entry #{entry_id} there will result in the expected merchant order reference Gravity Forms form #2 + entry #2783. We don't need the filter for this case.

The user provided the below sample code, which I think this will result in the payment ID being appended to the contract ID. I'm not sure how we can improve this — in the Payment::format_string() method?

$merchant_order_reference = rgar( $entry, strval( self::CONTRACT_ID_FIELD ) );

[rvdsteege]

Resolved the issue with forced adding of a dynamic part (payment ID). I think this PR can now be merged.