#!/usr/bin/env pypy3

# pylint: disable=superfluous-parens
# superfluous-parens: Parentheses are good for clarity and portability

"""Rapidly generates psuedo-random numbers between 0 and 2^64-1."""

import os
import signal
import sys
import time


VALUE = 0


def random():
    # pylint: disable=global-statement
    # global-statement: We need something with a global lifetime
    """Return a random number."""
    global VALUE
    # define M (((WIDE_TYPE)1) << 64)
    # define A ((WIDE_TYPE)18136136422342313421ULL)
    # define C ((WIDE_TYPE)1ULL)
    coeff_a = 18136136422342313421
    coeff_c = 1
    coeff_m = 2**64
    VALUE = (coeff_a * VALUE + coeff_c) % coeff_m
    return VALUE


def usage(retval):
    """Output a usage message."""
    sys.stderr.write("Usage: %s --bytes n --seed s\n" % sys.argv[0])
    sys.exit(retval)


def sigpipe_handler(signum, frame):
    """Exit on SIGPIPE."""
    del signum
    del frame

    sys.exit(0)


def gen_blocks(number_of_bytes, blocksize):
    """Generate a series of random blocks."""
    list_ = []
    for _dummy in range(0, number_of_bytes, 8):
        value = random()
        for bitno in range(0, 64, 8):
            sampled_value = (value >> bitno) & 0xFF
            list_.append(sampled_value)
            if list_[blocksize:]:
                yield list_
                list_ = []
    if list_:
        yield list_


def main():
    """Start the ball rolling."""
    signal.signal(signal.SIGPIPE, sigpipe_handler)

    seed = -1
    global VALUE
    number_of_bytes = 1

    while sys.argv[1:]:
        if sys.argv[1] == "--bytes":
            number_of_bytes = int(sys.argv[2])
            del sys.argv[1]
        elif sys.argv[1] == "--seed":
            seed = int(sys.argv[2])
            del sys.argv[1]
        elif sys.argv[1] in ("--help", "-h"):
            usage(0)
        else:
            sys.stderr.write("Illegal argument: %s\n" % sys.argv[1])
            usage(1)
        del sys.argv[1]

    all_good = True

    if (number_of_bytes // 8) * 8 != number_of_bytes:
        print(f"{sys.argv[0]}: --bytes must be a multiple of 8", file=sys.stderr)
        all_good = False

    if not all_good:
        print(f"{sys.argv[0]}: One or more items in preflight check failed\n", file=sys.stderr)
        sys.exit(1)

    blocksize = 2**18

    if seed >= 0:
        VALUE = seed
    else:
        VALUE = int(time.time())

    for block in gen_blocks(number_of_bytes, blocksize):
        os.write(1, bytes(block))


if __name__ == "__main__":
    main()