Disable a shipping option or payment option during checkout

This message was sent from: Suggestions and Proposals
http://forums.oscommerce.com/viewtopic.php?p=184746#184746
----------------------------------------------------------------

I have written a couple of shipping and payment modules to fit my needs and I have a proposal for the core team - a way to disable a shipping option or payment option during the checkout process with a message why the option is not enabled. 

I would like to "disable" some shipping and/or payment options depending on order value and order weight, etc. I found that it's easy to disable a shipping option in a shipping module by setting the 'error' field of the qoutes array in the function quote:

$this->quotes['error'] = MODULE_SHIPPING_PACKET_TOO_VALUABLE 

The file "checkout_shipping.php" is then displaying the message and the option is not able to select (i.e the radio box is not even printed). 

I had the same idea when implementing my payment module. This time I am setting the 'error' field of returning array in function selection:

'error' => MODULE_PAYMENT_COD_2_TEXT_MAX_VALUE

The message is displayed fine but the things is that it is still possible to select the payment option (due to that the radio box is printed). So I changed the logic in "checkout_payment.php" according to this (please note the if statement tagged with Fred):

[code]  $selection = $payment_modules->selection();

...

  $radio_buttons = 0;
  for ($i=0, $n=sizeof($selection); $i<$n; $i++) {
?>
...
<?php
    if (!isset($selection[$i]['error'])) { //Fred - added to be able to disable a payment module
      if (sizeof($selection) > 1) {
        echo tep_draw_radio_field('payment', $selection[$i]['id']);
      } else {
        echo tep_draw_hidden_field('payment', $selection[$i]['id']);
      }
    } //Fred - added to be able to disable a payment module
?>
...
?>[/code]

I know I can set $this->enabled = false in the update_status function, the only issue with this is that the payment option is not displayed and the user may not know why the option isn't there. 

What I am asking for is the some logic in both shipping and payment stage. 

/Fred