I just hit a bit of a problem with Typo filters, and I’m not sure what the best way out is.

The problem first showed up with the sparkline filter. This filter turns a block like <typo:sparkline data="10 20 30 40 50"/> into an <img/> tag that points to a Sparkline generator on the current website. Things were going great with this until I realized that the filters don’t know anything about “the current website.” Even though my filters are technically Rails controllers (there’s a reason for this, I just haven’t fully implemented it yet–it’s next on the list once this problem is fixed), the actual filter method is a class method, not an instance method, and anyway most of the time, the filtering code is called from outside of a controller context. Basically, when the filter code gets called, it doesn’t know which website it’s getting called for.

And that sucks. Even ignoring complex things like the sparkline code, this makes it impossible for filters to produce URL references to elsewhere in the current Typo site. That means filters can’t do locally-hosted images, or WikiWord-style links, or AJAX. And that’s going to be a problem.

As I see it, I have two options:

1. Re-spin the filter API so that it’s all controller helpers and components. This way they’ll always be able to use url_for. It’s a big conceptual change, but the code will be cleaner, and I doubt I’ll actually have to change more then 50 lines of code, not counting unit tests.
2. Cache the base URL for the site somewhere and hand-code URLs myself. This is easy, but ugly.

Since I’m trying to avoid ugly, it looks like I’m going to be taking option #1. That’ll probably push the first filter release out to this weekend, but it’ll be better code.

As a side note, my Rails Book finally showed up yesterday, so I have printed documentation to work with finally. PDFs are nice for skimming and searching, but they’re a pain to read cover-to-cover.