filters: add comparison operators

[Omkar-Ugal]

Summary

• Add support for >, <, >=, and <= operators
• Implement numeric and size comparisons

[jedevc]

I don't love that this package needs to include these helpers - ideally, downstream, in the cli, we'd be able to define custom handlers for comparison.

Here's my idea for that - let me know if this seems reasonable:

• Update the Adaptor, so that it includes a Compare(any) function (returns -1 for less-than, 0 for equal, and +1 for larger than, similar to cmp.Compare. It should also return a boolean, which should be false if the comparison was invalid, e.g. you can't do running>stopped).
  • While you're there, maybe actually change Value to return any. But keep a String method, since we should use that for regexp comparisons.
• Then, in selector.Match, use the Adaptor.Compare to compare against the value for all normal comparisons. If the comparison is invalid, it doesn't match. If it turns out that the equal comparison is invalid - then just callback to comparing Adaptor.String. You should also fallback Compare < and > comparisons of int/float/etc by using cmp.Compare directly.
• Finally, in the cli, is the place to actually put the custom comparators for sizes + dates + such. Probably into the custom internal/types package.

Because of this, it's a bit more complicated, but means that the actual comparisons are correctly implemented in the CLI. I want to avoid CLI-specific abstractions and helpers from leaking into this more generic package.

[Omkar-Ugal]

Hey @jedevc, just wanted to make sure I'm on the right track.

From your review, my understanding is that selector.Match should call Adaptor.Compare, and this package shouldn't contain helpers like parseSize anymore.

The only thing I'm unsure about is Compare(any). Since the parser passes comparison values as strings (like "50"), should Adaptor.Compare handle parsing them before comparing, or were you thinking of a different approach?

Just wanted to check before I continue.