#!/usr/bin/env bash

#
# maybe(1) -- Like true(1) or false(1); exit with either success or failure
# randomly. Good for basic testing, but doesn't use precise probabilities, just
# fractions of RANDOM's limit. Exits with 2 on usage errors so you can tell the
# difference.
#
# -h gives help, -v gives you stdout specifying success or failure.
#
# Author: Tom Ryder <tom@sanctum.geek.nz>
# Copyright: 2016
# License: Public domain
#
self=maybe

# Print usage information
usage() {
    printf '%s: usage: %s [-hv] [-d DENOMINATOR]\n' \
        "$self" "$self"
}

# Flag for whether to print diagnostics to stdout or not
declare -i verbose
verbose=0

# Denominator of the probability fraction, e.g. 3 is a probability of 1/3;
# defaults to 2
declare -i denom
denom=2

# Process options
while getopts 'hvd:' opt ; do
    case $opt in

        # -h: Print help
        h)
            usage
            exit 0
            ;;

        # -v: Print diagnostics to stdout
        v)
            verbose=1
            ;;

        # -d: Set the denominator of the probability fraction
        d)
            denom=$OPTARG
            ;;
        
        # Unknown option
        \?)
            usage >&2
            exit 2
            ;;
    esac
done
shift "$((OPTIND-1))"

# If there are any non-option arguments or our denominator isn't a positive
# integer, we're being abused and we won't put up with it
if (($#)) || ! ((denom > 0)) ; then
    usage >&2
    exit 2
fi

# If verbose, report the probability of the test
((verbose)) && printf '%s: Testing with probability 1/%u ... \n' \
    "$self" "$denom"

# Perform the test and print/exit appropriately
if ((RANDOM < 32767/denom)) ; then
    ((verbose)) && printf '%s: %s\n' \
        "$self" 'Success!'
    exit 0
else
    ((verbose)) && printf '%s: %s\n' \
        "$self" 'Failure!'
    exit 1
fi