Writing a PAS plugin is not that complicated. You can look at existing PAS plugins and learn from them (anyone with a good example for starters?)
The pain part with PAS plugins is the debugging process, in particular when your plugin has to implement a lot of interfaces. Debugging drives you nuts when a particular HTTP request calls a PAS plugin and its functionality a myriade of times (due to all page resources).
Some tips:
- instead of loading a related page through the browser, try to limit calls to one request (e.g. using wget or curl)
- add enough logger calls to each function for introspecting incoming and outgoing data
- pdb is your friend