Payment Choices based on Shipping

Hi all
I have searched through the forum for a solution but can't find anything. Help please.

I have a situation where If a customer selects 'store pickup' option in shipping
then goes to payment, I want to be able to have one payment method eg. 'Pay on Pickup'.

I have setup the shipping and payment options but can't see how I can limit the payment options to this one option.
or
Not have the 'Pay on Pickup' show for customers that select any other shipping method.(probably closer to what i'm trying to say)

Any Ideas or a nudge in the right direction would be most appreciated.

Thanks

Assuming you "have" a payment method called "Pay on Pickup", you could restrict it to only be available/active when the "store pickup" shipping method is selected by setting this within the class constructor of the pay-on-pickup module:

 $this->enabled = (($_SESSION['shipping']['title'] = 'storepickup') ? true : false);

Haven't checked for sure, but I suspect the 'storepickup' reference might need to be 'storepickup_storepickup'

Note: for clarity and to avoid issues between the Catalog and Admin, often times it is helpful to build a function to manage this test ...

Then, add a matching function for the Admin where it returns true ... this allows the same function call to run on both the Catalog side and allow the Admin ... Modules ... Payments ... to run on the Admin ...

You might peek at how the Shipping Modules manage this type of function ... peek at:
/includes/modules/shipping/item.php

      // disable only when entire cart is free shipping
      if (zen_get_shipping_enabled($this->code)) {
        $this->enabled = ((MODULE_SHIPPING_ITEM_STATUS == 'True') ? true : false);
      }

Find the function zen_get_shipping_enabled in the Catalog and the function zen_get_shipping_enabled in the Admin and notice how they differ ...

You are building something similar to manage the $this->enabled for the Payment modules ...

What can I say... but THANK YOU.

It worked Brilliantly DrByte and thanks Ajeh for your advice.