import re


def normalize_for_username(value):
    """Turkce karakterleri ASCII'ye cevirip username-safe hale getirir."""
    tr_map = str.maketrans({
        'c': 'c',
        'C': 'c',
        'g': 'g',
        'G': 'g',
        'i': 'i',
        'I': 'i',
        'o': 'o',
        'O': 'o',
        's': 's',
        'S': 's',
        'u': 'u',
        'U': 'u',
        'ç': 'c',
        'Ç': 'c',
        'ğ': 'g',
        'Ğ': 'g',
        'ı': 'i',
        'İ': 'i',
        'ö': 'o',
        'Ö': 'o',
        'ş': 's',
        'Ş': 's',
        'ü': 'u',
        'Ü': 'u',
    })
    value = value.translate(tr_map).lower()
    return re.sub(r'[^a-z0-9]+', '', value)


def build_unique_username(first_name, last_name, birth_date, used_usernames, _force_suffix=None):
    """
    ad.soyadYY formatinda username uretir, cakisma olursa sonek ekler.
    _force_suffix: verilirse bare base denenmez, bu sayidan itibaren baslar
                   (regeneration ping-pong onlemek icin kullanilir).
    """
    first = normalize_for_username(first_name or '')
    last = normalize_for_username(last_name or '')
    yy = str(birth_date.year)[-2:]
    base = f"{first}.{last}{yy}" if first and last else f"user{yy}"

    if _force_suffix is not None:
        # Yeniden uretim: bare base'i hic deneme, rastgele bir sonek ile basla
        counter = _force_suffix
        candidate = f"{base}{counter}"
    else:
        candidate = base
        counter = 1

    while candidate in used_usernames:
        counter += 1
        candidate = f"{base}{counter}"

    used_usernames.add(candidate)
    return candidate