replacing letters in text (pseudo-code)

Question

I'm making a script to create a username. It should be four letters long; traditionally we've used 3 letters of the last name + 1 of the first name.
If it was already used we manually thought of an alternative.

So if my name is Fred Flinstones we should try FLIF. If this doesnt work; we loop through the name: FLIA, FLIB, FLIC ... FLIZ, FLAA, FLAB, FLAC, ... FLZZ, FAAA, FAAB, ...

The easiest way is to loop through last letters; then make another set of loops through second last letter and loop through last letters; then a set of loops through third last, second last, last; and fourth+third+second+last. This makes a lot of do while loops nested in eachother + unreadable for other humans + a lot of typing.
I could use a counter per letter but that also doesn't seem elegant I could try with one counter and then using mod 26 to see how many letters need replacement (but that seems very complex).

Is there some elegant/efficient ways to do this?

Bonus points for first trying to keep the string as 'logically correct' as possible (f.e. keeping the last letter an F for Fred or skipping letters FLIF; FLNF, FLSF, FLTF, ...) .

Answer 1

Not sure if this is what you mean, but if you structure your username-script in the following way (I used PHP as language), you can extend it by adding options with higher fuzz factors while keeping the code readable:

echo findName('FLINTSTONE', 'FRED');

function findName($last, $first) {
    for ($fuzzFactor = 0; ; $fuzzFactor++) {
        $candidates = fuzzNames($last, $first, $fuzzFactor);

        if (empty($candidates)) {
            // exhausted
            return "sorry, I'm out of options!";
        }

        foreach ($candidates as $candidate) {
            if (isUnique($candidate)) {
                return $candidate;
            }
        }
    }
}

function fuzzNames($last, $first, $fuzzFactor) {
    switch ($fuzzFactor) {
        case 0:
            // no fuzz, return first choice
            return array(substr($last, 0, 3) . $first[0]);
        case 1:
            // replace the third letter of the last name
            // by the fourth/fifth/.../last letter (FLNF, FLTF, ... , FLEF)
            $candidates = array();
            for ($i = 3; $i < strlen($last); $i++) {
                $candidates[] = substr($last, 0, 2) . $last[$i] . $first[0];
            }
            return $candidates;
        case 2:
            // replace the second and third letter of the last name
            // by their follow-ups (FINF, FITF, ... , FNEF)
            $candidates = array();
            for ($i = 2; $i < strlen($last) - 1; $i++) {
                for ($j = $i + 1; $j < strlen($last); $j++) {
                    $candidates[] = $last[0] . $last[$i] . $last[$j] . $first[0];
                }
            }
            return $candidates;
        default:
            return array();
    }
}