#!/usr/bin/perl
#
# Copyright (c) 2007, Gregory Fleischer (gfleischer@gmail.com)
# 
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#   
#   1. Redistributions of source code must retain the above copyright
#      notice, this list of conditions and the following disclaimer.
#   2. Redistributions in binary form must reproduce the above copyright
#      notice, this list of conditions and the following disclaimer in
#      the documentation and/or other materials provided with the
#      distribution.
#   3. The names of the authors may not be used to endorse or promote
#      products derived from this software without specific prior
#      written permission.
#   
# THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
# 

my @special_chars = qw[! @ $ % ^ & * ( ) { } \ | + = - _ , . / ? : ; ];
my @chars = ('a'..'z', 'A'..'Z', '0'..'9');

my @args = ();

my $special = 0;
foreach my $arg (@ARGV) {
    if ($arg=~/^--?special$/) {
	$special = 1;
    } elsif ($arg=~/^--?s(?:pecial)?=(.+)$/) {
	$special = 1;
	@special_chars=split(//, $1);
    } elsif ($arg=~/^--?c(?:harset)?=(alpha|alnum|digit|lower|upper)$/) {
	if ("alpha" eq $1) {
	    @chars= ('a'..'z','A'..'Z');
	} elsif ("alnum" eq $1) {
	    @chars = ('a'..'z', 'A'..'Z', '0'..'9');
	} elsif ("lower" eq $1) {
	    @chars = ('a'..'z');
	} elsif ("upper" eq $1) {
	    @chars = ('A'..'Z');
	} elsif ("digit" eq $1) {
	    @chars = ('0'..'9');
	} else {
	    die "unexpected charset: $1";
	}
    } elsif ($arg=~/^--?h(elp)?$/) {
	&help();
	exit(0);
    } elsif ($arg=~/^\d+$/) {
	push(@args, $arg);
    } else {
	print "invalid option: $arg\n";
	&help();
	exit(0);
    }
}

my $wanted = shift(@args) || 8;
if ($wanted !~ /^\d+$/) {
    die "bad number of chars wanted: $wanted";
}
open(FH, '<', '/dev/urandom') or die "failed to open /dev/urandom: $!";

if ($special) {
    push(@chars, @special_chars);
}

my ($random, $this);
my $needed = $wanted;
while ((read(FH, $this, 1)) > 0) {
    my $i = ord($this) % ($#chars + 1);
    $random .= $chars[$i];
    if (0 == --$needed) {
	last;
    }
}
if ($needed != 0) {
    die "entropy failed us!";
}

print "$random\n";

exit(0);

sub help {
    print "generate desired number of random characters (default 8)\n";
    print "usage: $0 [options] [count]\n";
    print " --chars=<charset>    character set: alpha|alnum|digit (default alnum)\n";
    print " --special            include special characters:\n";
    print "                      @special_chars\n";
    print " --special=<list>     list of special characters\n";
    print "\n";
}
# eof