__all__ = ['encode', 'decode']

ALPHABET = '23456789abcdefghijkmnpqrstuvwxyz'

ALPHABET_INVERSE = [
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1,  0,  1,  2,  3,  4,  5,  6,  7, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, -1, 19, 20, -1,
    21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
]


def encode(input: int, pad_to_length: int) -> str:
    digits = []
    while input:
        digits.append(ALPHABET[input & 31])
        input >>= 5
    while len(digits) < pad_to_length:
        digits.append(ALPHABET[0])
    return ''.join(digits[::-1])


def decode(input: str) -> int | None:
    out = 0
    for c in input:
        try:
            n = ALPHABET_INVERSE[ord(c)]
        except IndexError:
            return None
        if n == -1:
            return None
        out = (out << 5) | n
    return out