choice

#!/usr/bin/env python3
"""
choice [OPTIONS...] CHOICES...

Pick a value at random among CHOICES using secure random.

Alternatively, choices may be provided on stdin.

For example:
    # pick a random RGB color
    choice red green blue

    # pick a number between 1 and 10
    seq 1 10 | choice

    # pick a random file from ./dir/
    find ./dir/ -print0 | choice -0
"""

import optparse
import random
import sys
import textwrap

system_random = random.SystemRandom()


def main() -> int:
    p = optparse.OptionParser(usage=__doc__.strip())
    p.add_option('-0', '--null', help='Choices on stdin are delimited by null',
                 action='store_true')
    opts, args = p.parse_args()

    mode = "args"
    delimiter = "\n"

    if opts.null:
        mode = "stdin"
        delimiter = "\0"

    if mode == "stdin":
        if args:
            p.error("Cannot pass args with stdin mode")

        choices = read_stdin(delimiter=delimiter)

    elif mode == "args":
        if len(args) > 0:
            choices = args
        else:
            # if no choices in argv, use stdin as long as it isn't a tty

            if sys.stdin.isatty():
                p.print_help()
                # p.error("Must provide choices in argv or stdin")
                return 1

            mode = "stdin"

            choices = read_stdin(delimiter=delimiter)
    else:
        raise ValueError(f"Invalid mode {mode!r}")

    if len(choices) == 0:
        if mode == "stdin":
            suffix = " (stdin was empty)"
        else:
            suffix = " (bug?)"
        p.error("Must provide at least one choice" + suffix)

    print(system_random.choice(choices))
    return 0


def read_stdin(delimiter: str) -> list[str]:
    """
    Read choices from stdin
    """
    data = sys.stdin.read()

    # return empty list on empty input, not [""]
    if not data:
        return []

    # if delimiter is newline, strip trailing newline so we don't end up with
    # an empty string choice
    if delimiter == "\n":
        data = data.rstrip("\n")

    return data.split(delimiter)


if __name__ == '__main__':
    sys.exit(main())