How to get a document number that should contains product context name

Hi All,

one of my customers requirement is as follows

If he wants to create a document in XYZ product context, then while creating it, in number field if he manually enters 3434  then after creation of document, it should appear like ABC\1234\XYZ3434.

Where ABC\123 is static name which will be same for all documents and XYZ is the product context.

Can anyone suggest me how to achieve this ?

Regards,

Krishna Chaithanya