#!/usr/bin/perl

=head1 USAGE

  ./x1.pl mkbin <filename>  ... create binary text representation
  ./x1.pl encode <filename> ... encode 0 as even digit and 1 as odd digit
  ./x1.pl decode <filename> ... encode even digit as 0 and odd digit as 1

=head1 EXAMPLE

  ./x1.pl mkbin x1.pl >@bin
  ./x1.pl encode @bin >@enc
  ./x1.pl decode @enc >@dec
  echo "@bin and @dec should be equal"
  diff @bin @dec

=cut

use strict;

my $opcode= shift(@ARGV);
my $file= shift(@ARGV);

if ($opcode eq 'mkbin') { mkbin($file); }
elsif ($opcode =~ /enc.*/) { x1_encode($file); }
elsif ($opcode =~ /dec.*/) { x1_decode($file); }
else { system ('perldoc', $0) }
exit (0);

sub read_file
{
  my $fnm= shift;

  my @st= stat($fnm);
  die "can't find $fnm" unless (@st);
  open (FI, '<:raw', $fnm) or die "can't read $fnm";
  print STDERR "reading $fnm\n";
  my $data;
  sysread (FI, $data, $st[7]);
  close (FI);

  $data;
}

sub mkbin
{
  my $fnm= shift;

  my @data= split('', read_file($fnm));
  my $bin;
  foreach my $c (@data)
  {
    my $v= my $h= ord($c);
    my @bin;
    for (my $i= 7; $i >= 0; $i--)
    {
      $bin[$i]= $h % 2;
      $h= int ($h/2);
    }
    $bin .= join ('', @bin);

    # print "c=[$c] v=[$v] bin=[$bin]\n";
  }

  print $bin, "\n";
}

sub x1_encode
{
  my $fnm= shift;

  my @data= split('', read_file($fnm));
  my $res;
  foreach my $c (@data)
  {
    if ($c =~ m#[\r\n\t ]#) { $res .= $c; next; }
    next unless ($c eq '0' || $c eq '1');
    my $v= 2*int(rand(5)) + (($c eq '1') ? 1 : 0);
    $res .= $v;

    # print "c=[$c] v=[$v]\n";
  }

  print $res;
}

sub x1_decode
{
  my $fnm= shift;

  my @data= split('', read_file($fnm));
  my $res;
  foreach my $c (@data)
  {
    if ($c =~ m#[\r\n\t ]#) { $res .= $c; next; }
    next unless ($c =~ /[0-9]/);
    my $v= (($c =~ /^[13579]$/) ? 1 : 0);
    $res .= $v;

    # print "c=[$c] v=[$v]\n";
  }

  print $res;
}