Rails - Mar 2006 - Error Checking and Processing

Does anyone have any ideas on the best way to perform error checking and 
processing for a particular problem:

- A customer fills in an order form with their credit card details and 
hits submit.

The controller has to do the following work:

 - Try to find an existing customer matched by email
    - if the customer exists, update their details in the database
    - if the customer is new save a new record
    - validation errors could occur here
 - Copy the data from the cart session variable to an Order object
 - Save the order to the orders table
 - Send the credit card details to PayPal for processing
    - parse success/fail and save any errors to forward to the user
 - If anything failed, redirect back to the form filling in the form 
details and showing all error messages.

Now some things I''m not too clear on in Rails land:
 - How to I parse the response from PayPal for error messages (using 
SOAP and the PayPayl Rails plugin)?
 - How do I redirect back to the form and send the data to fill in?  (I 
can redirect to the form, but there are no values filled in)
 - What is the best way to structure these steps in code (order, etc) 
and the best way to handle the success/fail, rollback, errors, etc?

It may be obvious, but my brain is a bit mushed from staring at this 
problem too long, any help appreciated.

Cheers,
Dan

Dan Harper wrote:
> Now some things I''m not too clear on in Rails land:
> - How to I parse the response from PayPal for error messages (using 
> SOAP and the PayPayl Rails plugin)?
> - How do I redirect back to the form and send the data to fill in?  (I 
> can redirect to the form, but there are no values filled in)
I figured out the blank values problem (sorta), but the others are still 
a mystery.

Any ideas?
> - What is the best way to structure these steps in code (order, etc) 
> and the best way to handle the success/fail, rollback, errors, etc?

Dan Harper wrote:
> Dan Harper wrote:
> 
>> Now some things I''m not too clear on in Rails land:
>> - How to I parse the response from PayPal for error messages (using 
>> SOAP and the PayPayl Rails plugin)?
>> - How do I redirect back to the form and send the data to fill in?  (I 
>> can redirect to the form, but there are no values filled in)
> 
I don''t know anything about SOAP, but the latter problem sounds like
it''s simply the
result of redirects being a new request... save the form data in the flash and
pull it
back out after the redirect.

b