How to create employee ID auto numbering system

public static str getNewPersonnelNumber()
{
    int maxLenght = 4;
    str tempEmployeeID;
    str newNumber;
    int newIndex;
    str companyIdx;
    HCMWorker localWorker;
    str ret;
    str 2 companyIdFilter;

    //Pickup the first digit as company name
    companyIdx = String::trimToLength(curext(), 1);
    companyIdx = strUpr(companyIdx);
    companyIdFilter = companyIdx + '*';
    select firstOnly localWorker
        order by localWorker.PersonnelNumber desc
        where localWorker.PersonnelNumber like companyIdFilter;
    tempEmployeeID = localWorker.PersonnelNumber;
    newNumber = String::replaceAll(tempEmployeeID, companyIdx, "");
    newIndex = str2int(newNumber);
    newIndex = newIndex + 1;
    newNumber = String::fillString(maxLenght - strLen(int2str(newIndex)), '0') + int2str(newIndex);
    newNumber = companyIdx + newNumber;
    ret  = newNumber;

    return ret;
}