Build EDI x12 Class in PHP

I am looking to outsource the development of a PHP class that can work in PHP 5.2.17 as a self-contained "Black Box" class for EDI file development (ANSI x12). The successful candidate would have already written EDI file creation output before in PHP, and also embraces true object oriented development so that this class can be fitted into other projects without a lot of plumbing required. This will be used to produce HIPAA compliant 835 file output and its structures would be fed by JSON or XML data structures, resulting in a final EDI file as the output. It would be ideal if the developer already has built EDI file class libraries before, and we are only interested in working with developers who have done EDI work and can demonstrate their experience in this. If you are a general "body shop", don't bother. We only want to deal directly with the developer doing the work.