#!/usr/local/bin/perl5
# -*- perl -*-
#
# CMSC443 Project 2
# Michael A. Gurski 
# Simple rotor project
#

# make sure filename is supplied
die "Usage: rotor <inputfile>\n" if ($#ARGV < 0);


# set up the rotors & their wiring...make sure 2 wires don't end at same
# spot
@Rotor1 =  ( Q, W, E, R, T, Y, U, I, O, P, A, S, D,
	     F, G, H, J, K, L, Z, X, C, V, B, N, M);
@Rotor1N = ( 3, 1, 9,24, 0,19, 2,24,18, 5,23,21, 8,
	    22,24, 2,25, 5,21,17,25,21,25, 2,20,24);
@Rotor2 =  ( Z, A, Q, X, S, W, C, D, E, V, F, R, B,
	     G, T, N, H, Y, M, J, U, K, I, L, O, P);
@Rotor2N = (21, 8,22,24, 2,25, 5,21,17,25,21,25, 2,
	    20,24, 3, 1, 9,24, 0,19, 2,24,18, 5,23);
# optional plugboard...
#@Plugboard = (18, 1,25,12, 3, 5, 9,11,24,17,22,20, 2,
#               7,15, 6,16, 8,19,13,21, 4, 0,23,14,10);

# reflector to make this self-inverting
@Reflector = ( 3, 2, 1, 0, 7, 6, 5, 4,11,10, 9, 8,15,
	      14,13,12,19,18,17,16,23,22,21,20,25,24);


# get the key from the user
print STDERR "Enter key:\n";
$key = <STDIN>;

# eat EOL
chomp $key;

# convert to upper case
$key =~ tr/a-z_/A-Z+/;

# ensure key is 2 characters
die "key must be of length 2!\n" if (length($key) != 2);

# ensure key is alphabetic
die "key must be alphabetic characters!\n"
    if (($key =~ /\W+/) || ($key =~ /\d+/));

# split key into 2 characters
($i1,$i2) = $key =~ /(\w)(\w)/;

# set up initial offsets
$off1 = 0;
$off2 = 0;

# "rotate" rotor 1 to initial position
while($Rotor1[0] ne "$i1") {
    $tmp = shift(@Rotor1);
    push(@Rotor1,$tmp);
    $tmp = shift(@Rotor1N);
    push(@Rotor1N,$tmp);
}
# "rotate" rotor 2 to initial position
while($Rotor2[0] ne "$i2") {
    $tmp = shift(@Rotor2);
    push(@Rotor2,$tmp);
    $tmp = shift(@Rotor2N);
    push(@Rotor2N,$tmp);
}

# open the input file
open(FILE,"$ARGV[0]");

# read line by line
while ($FILE = <FILE>) {

    # ignore end of line...
    chomp $FILE;

    # convert line to uppercase
    $FILE =~ tr/a-z/A-Z/;

    # split line into array of individual characters
    @FILE = split("",$FILE);

    # loop through array of plaintext characters
    while(@FILE) {

	# remove first character in array
	$Char = shift(@FILE);

	# encrypt it only if it's alphabetic
	if (($Char =~ /\w/) && ($Char =~ /\D/) && ("$Char" ne "_")) {

	    # index into first rotor
	    $R1ind = ord($Char) - ord("A");

	    # index into second rotor based on wiring of 1st
	    $R2ind = ($R1ind + $Rotor1N[$R1ind]) % 26;

	    # index into reflector based on wiring of 2nd rotor
	    $RefInd = ($R2ind + $Rotor2N[$R2ind]) % 26;

	    # the hard part...finding the reverse entries...

	    # find the left side of rotor 2 that's connected to the
	    # reflector's current index
	    for($i=0;$i<26;$i++) {
		if(($i+$Rotor2N[$i])%26 == $Reflector[$RefInd]) {
		    $R2ind = $i;
		    last;
		}
	    }
	    # find the left side of rotor 1 that's connected to
	    # rotor 2's current index
	    for($i=0;$i<26;$i++) {
		if(($i+$Rotor1N[$i])%26 == $R2ind) {
		    $R1ind = $i;
		    last;
		}
	    }

	    # convert index to encrypted character
	    $Char = pack("C",$R1ind+ord("A"));
	}

	# output ciphertext or non-alpha text
	print "$Char";

	# rotate rotor 1 by 1
	$off1 = ($off1 + 1) % 26;
	$tmp = shift(@Rotor1);
	push(@Rotor1,$tmp);
	$tmp = shift(@Rotor1N);
	push(@Rotor1N,$tmp);

	# rotate rotor 2 by 1 if rotor 1 has made a full rev
	if(($off1 + $origOff1) % 26 == 0) {
	    $tmp = shift(@Rotor2);
	    push(@Rotor2,$tmp);
	    $tmp = shift(@Rotor2N);
	    push(@Rotor2N,$tmp);
	}
	
    }

    # print end of line
    print "\n";
}

# EOF