b64d

#!/usr/bin/python3

import sys
import re

from base64 import b64decode
from base64 import urlsafe_b64decode

USAGE = """
USAGE
    b64 < text.b64
    b64 text.b64

DESCRIPTION
    Decode base64 encoded UTF-8 text with optional padding that's either url or
    normal base64. Also continue decoding recursively for things that are
    encoded multiple times.
"""

b64u_chars = re.compile("[-_]")


def decode(data):
    _decode = b64decode
    if b64u_chars.search(data) is not None:
        _decode = urlsafe_b64decode

    while True:
        padding = "=" * (4 - (len(data) % 4))

        try:
            data = _decode(data + padding).decode(encoding="utf-8")
        except:
            return data


def main():
    match len(sys.argv):
        case 1:
            infile = sys.stdin
        case 2:
            infile = open(sys.argv[1], encoding="UTF-8")
        case _:
            print(usage, file=sys.stderr)
            sys.exit(1)

    try:
        print(decode(infile.read()))
    finally:
        infile.close()


if __name__ == "__main__":
    main()