#!/bin/sh -- # A comment mentioning perl, to prevent perl from looping. Indented to work with bash.
eval 'exec perl -S $0 ${1+"$@"}'
        if 0;

$n = '0';

$List[$n++] = 'A';
$List[$n++] = 'B';
$List[$n++] = 'C';
$List[$n++] = 'D';
$List[$n++] = 'E';
$List[$n++] = 'F';
$List[$n++] = 'G';
$List[$n++] = 'H';
$List[$n++] = 'I';
$List[$n++] = 'J';
$List[$n++] = 'K';
$List[$n++] = 'L';
$List[$n++] = 'M';
$List[$n++] = 'N';
$List[$n++] = 'O';
$List[$n++] = 'P';
$List[$n++] = 'Q';
$List[$n++] = 'R';
$List[$n++] = 'S';
$List[$n++] = 'T';
$List[$n++] = 'U';
$List[$n++] = 'V';
$List[$n++] = 'W';
$List[$n++] = 'X';
$List[$n++] = 'Y';
$List[$n++] = 'Z';

select(STDERR); $| = 1;
select(STDOUT); $| = 1;

if ( $ARGV[0] eq '' ) {
	print STDERR "\nPlease enter a seed number: ";
	chop($seed = <STDIN>);
} else {
	if ( $ARGV[1] ne '' ) {
		$seed = join(' ', @ARGV);
	} else {
		$seed = $ARGV[0];
	}
}
print STDERR "\n";

if ( $seed =~ /^\d+$/ ) {
	srand($seed);
} else {
	chop($x = `echo "$seed" | sum | awk '{print \$1}' 2>/dev/null`);
	chop($y = $seed);
	$y = $seed if $y eq '';
	chop($y = `echo "$y"    | sum | awk '{print \$1}' 2>/dev/null`);
#print "X: $x\n";
#print "Y: $y\n";
	if ( $x =~ /^\d+$/ && $y =~ /^\d+$/ ) {
		$z = $x * $y;
#print "Z: $z\n";
		print STDERR "(using seed $z)\n\n";
		srand($z);
	} else {
		print STDERR "(not using seed $x * $y)\n\n";
		srand($seed);
	}
}

for ($i = 0; $i < $n; $i ++ ) {
	$Hit{$i} = '';
}

for ($i = 0; $i < $n; $i ++ ) {
	$Code[$i] = '-1';
	while ( $Code[$i] < 0 )  {
		$try = int(rand($n));
		if ( $Hit{$try} eq '' ) {
			$Hit{$try} = 1;
			$Code[$i] = $try;
		}
	}
	print STDOUT "$List[$i]  ->  $List[$Code[$i]]\n";
	$a = $List[$i];
	$b = $List[$Code[$i]];
	$Map{$a} = $b;
	$MapInv{$b} = $a;
	$a =~ tr/A-Z/a-z/;
	$b =~ tr/A-Z/a-z/;
	$Map{$a} = $b;
	$MapInv{$b} = $a;
}

print STDERR "\n";

print STDERR "Message? (encode/decode/quit) e/d/q ";
chop($reply = <STDIN>);

if ( $reply =~ /^e/i ) {
	$mode = 'encode';
} elsif ( $reply =~ /^d/i ) {
	$mode = 'decode';
} else {
	exit 0;
}

print STDERR "Enter message (end with \".\" on a line by itself)\n";

$msg = '';
while (<STDIN>) {
	last if /^\.$/;
	$msg .= $_;
}

print STDERR "\n";

$output = '';

foreach $char (split(//, $msg)) {
	if ( $mode eq 'encode' && $Map{$char})  {
		$output .= $Map{$char};
	} elsif ( $mode eq 'decode' && $MapInv{$char})  {
		$output .= $MapInv{$char};
	} else {
		$output .= $char;
	}
}

print STDERR "-------------------------------------------------\n";
print STDOUT $output;

exit 0;