from binascii import hexlify, unhexlify
import sys

B58_DIGITS = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"


class InvalidBase58Error(Exception):
    """Raised on generic invalid base58 data, such as bad characters.
    Checksum failures raise Base58ChecksumError specifically.
    """


def decode_base58(s):
    """Decode a base58-encoding string, returning bytes"""
    if not s:
        return b""

    # Convert the string to an integer
    n = 0
    for c in s:
        n *= 58
        if c not in B58_DIGITS:
            raise InvalidBase58Error(f"Character {c!r} is not a valid base58 character")
        digit = B58_DIGITS.index(c)
        n += digit

    # Convert the integer to bytes
    h = f"{n:x}"
    if len(h) % 2:
        h = "0" + h
    res = unhexlify(h.encode("utf8"))

    # Add padding back.
    pad = 0
    for c in s[:-1]:
        if c == B58_DIGITS[0]:
            pad += 1
        else:
            break
    return b"\x00" * pad + res


def encode_base58(b):
    """Encode bytes to a base58-encoded string"""

    # Convert big-endian bytes to integer
    n = int("0x0" + hexlify(b).decode("utf8"), 16)

    # Divide that integer into bas58
    res = []
    while n > 0:
        n, r = divmod(n, 58)
        res.append(B58_DIGITS[r])
    res = "".join(res[::-1])

    # Encode leading zeros as base58 zeros
    czero = b"\x00"
    if sys.version > "3":
        # In Python3 indexing a bytes returns numbers, not characters.
        czero = 0
    pad = 0
    for c in b:
        if c == czero:
            pad += 1
        else:
            break
    return B58_DIGITS[0] * pad + res