PHP class or functions to manipulate PDF metadata?

Hi group, I am looking for an easy way to manipulate (read, write) the metadata (title, subject, keywords, author) in PDF files through PHP. Most PHP/PDF solutions I have found so far (through Google) are aimed at constructing PDFs from text and graphics, with lots of fancy features, but most of them omit metadata functions altogether. I would also prefer something extremely lightweight that I could just include_once() into my script, i.e. not a module or external program. I am currently using pdfinfo from xpdf-utils, but it has to go. My use case is I want to build a database with the metadata of a bunch (many hundreds, perhaps thousands) of PDF files in a directory on the server for easy search, statistics and retrieval. I also want users to be able to make edits to any PDF's metadata from the web. If it can be at all avoided, I would rather not have to invent the wheel myself here. I have looked at the Adobe PDF specification a bit and it looks quite... challenging. Or should I say daunting. Any and all suggestions are welcome. Thank you in advance.