java - Regex accept max of alpha and alphanumeric with extra % (without limit) -

i dit lot of search in regex posts didn't find solution i'm looking for.

i have fellow regex ([a-za-z]{6}[a-za-z0-9]{2}([a-za-z0-9]{3})?)? accept these cases :

now, i'm looking modify regex accept optional char % anywhere number of occurence keeping number max of alpha , alphanumeric in current regex.

examples:

empty sting -> correct
aabb -> wrong (need 6 alpha + 2 alphanumeric when there no %)
aabb% -> correct
aa33% -> wrong (need 6 alpha before numeric)
aa%33 -> correct ( % working wilcard , avoid max number)
a%3 -> correct
aa%33% -> correct
%aa33% -> correct
%aa3% -> correct
aaaaaa33 -> correct
aabbccxx -> correct
aabbcc44xxx -> correct
aabbcc44xxxe -> wrong (length of alpha not respected)
%aabbcc44xxxe -> wrong (length of alpha not respected)
%aab%bcc4%4x%xx% -> correct (because % should ignored in length, length of alpha , alphanumeric respected here)

is possible ?

the regex below should close enough.

^(?:(?=.*%)(?![a-z]{1,5}[0-9])(?:%?[a-z]){0,6}(?:(?:%?[a-z0-9]){1,2})?(?:(?:%?[a-z]){1,3})?%?)$|^(?:[a-z]{6}(?:[a-z0-9]{2})(?:[a-z]{3})?)$|^$

note how pipes (| = or) separate 3 regexes.
1 %, without % , blanks.

also, character classes use uppercase a-z.
allow lowercases, either let regex ignore case, or replace a-za-z.

you can test here

shorter alternative:

^(?=.*%)(?![a-z]{1,5}[0-9])(?!(?:.*?[0-9]){3})(?:%?[a-z0-9]){1,11}%?$|^(?:[a-z]{6}[a-z0-9]{2}(?:[a-z]{3})?)$|^$

Brent