#!/usr/bin/python3

import sys
import struct


def main():
    # Produce a file with 45899235*repeats of zero bytes

    if len(sys.argv) <= 1:
        print('Usage zero_bz2.py filename [repeats]')
        return

    filename = sys.argv[1]

    repeats = 2**10
    if len(sys.argv) > 2:
        repeats = int(sys.argv[2])

    header = b'\x42\x5a\x68\x39'
    block = b'\x31\x41\x59\x26\x53\x59\x0e\x09\xe2\xdf\x01\x5f\x8e\x40\x00\xc0\x00\x00\x08\x20\x00\x30\x80\x4d\x46\x42\xa0\x25\xa9\x0a\x80\x97'

    block_crc = int.from_bytes(block[6:10], 'big')
    footer_magic = b'\x17\x72\x45\x38\x50\x90'

    def compute_stream_crc(block_crc, repeats):
        stream_crc = 0
        for _ in range(repeats):
            stream_crc = block_crc ^ ((stream_crc << 1) | (stream_crc >> 31))
        return stream_crc & 0xffffffff

    stream_crc = compute_stream_crc(block_crc, repeats)

    with open(filename, 'wb') as f:
        f.write(header)
        for _ in range(repeats):
            f.write(block)
        f.write(footer_magic)
        f.write(stream_crc.to_bytes(4, byteorder='big'))


if __name__ == '__main__':
    main()