Battle Caster feat

[Dastir]

I am trying to code the Battle Caster feat from COmplete Arcane and am not quite sure how to proceed.

I know how to detect iof a class has the ability to ignore spell failure from a specific class of armor, and I know how to adjust that for a specific class. The question I have is this:

How do I detect, regardless of class, the highest level of armor the character can wear and still ignore spell failure, and how can I, again regardless of class, increase that? I understand logically how to do it

[pseudocode]
if (hero has CastArmor.Heavy) then
   done
elseif (hero has CastArmor.Medium) then
   assign CastArmor.Heavy
elseif (hero has CastArmor.Light) then
   assign CastArmor.Medium
endif
[/pseudocode]

The thing I don't get is how to detect and assing these tags no matter what class they have. All the examples use childfound[classid]

thanks!