#!/usr/bin/env python

import argparse
import sys

LONG_KEY = (
    0x6c, 0x1b, 0x99, 0x5f, 0xb9, 0xcd, 0x5f, 0x13,
    0xcb, 0x04, 0x20, 0x0e, 0x5e, 0x1c, 0xa1, 0x0e,
)
OTHER_LONG_KEY = (
    0x67, 0xa8, 0xd6, 0x26, 0xb6, 0xdd, 0x45, 0x1b,
    0x32, 0x7e, 0x22, 0x13, 0x15, 0xc2, 0x94, 0x37,
)


class Byte:
    def __init__(self, v: int):
        self.v = v & 0xff

    def __add__(self, v: int):
        return Byte(self.v + v)

    def __iadd__(self, v: "Byte"):
        self.v = (self.v + v) & 0xff
        return self

    def __sub__(self, v: int):
        return Byte(self.v - v)

    def __isub__(self, v: "Byte"):
        self.v = (self.v - v) & 0xff
        return self

    def __mod__(self, v: int):
        return Byte(self.v % v)

    def __imod__(self, v: int):
        self.v %= v
        return self

    def __xor__(self, v: int):
        return Byte(self.v ^ v)

    def __ixor__(self, v: int):
        self.v = (self.v ^ v) & 0xff
        return self

    def __and__(self, v: int):
        return Byte(self.v & v)

    def __iand__(self, v: int):
        self.v = (self.v & v) & 0xff
        return self

    def __eq__(self, other):
        if isinstance(other, Byte):
            return self.v == other.v
        elif isinstance(other, int):
            return self.v == (other & 0xff)
        raise ValueError(f"Object {other:r} of invalid type {type(other)}")


def decode_line(line: bytes, method: int) -> str:
    line = line.rstrip(b"\r\n")
    key = LONG_KEY
    seed = len(line) % len(LONG_KEY)
    dline = bytearray(len(line))
    for i, c in enumerate(line):
        b = Byte(c)
        if dline[i - 2:i] == b'//':
            key = OTHER_LONG_KEY
        if method == 1:
            if b == ord(b'\t'):
                b = Byte(0x9f)

            b -= 0x20
            b ^= key[seed]
            b &= 0x7f
            b += 0x20

            seed += 7
            seed %= len(key)

            if b == 0x9f:
                b = Byte(ord(b'\t'))
        else:
            if b == ord(b'\t'):
                b = Byte(0x80)

            b -= 0x20
            if (b & 0x80) == 0:
                b ^= key[seed] & 0x7f
            b += 0x20

            seed += 7
            seed %= len(key)

            if b == 0x80:
                b = Byte(ord(b'\t'))
        dline[i] = b.v
    return dline.decode(errors="replace")


def main():
    parser = argparse.ArgumentParser(allow_abbrev=False, description="Decode a Carmageddon encoded file")
    parser.add_argument("file", metavar="FILE", nargs="?", help="input file (default=stdin)")
    parser.add_argument("--method", choices=[1, 2], type=int, default=2, help="decryption method to use")
    args = parser.parse_args()

    istream = open(args.file, "rb") if args.file else sys.stdin.buffer

    for line in istream.readlines():
        if line[0] == ord(b'@'):
            dline = decode_line(line[1:], args.method)
            print(dline)
        else:
            print(line.decode())


if __name__ == "__main__":
    raise SystemExit(main())