#!/usr/bin/perl -w
# encode_template.pl - Don Yang (uguu.org)
#
# Encode ASCII art template to run-length encoding.  Accepts these characters:
# @ = eye
# + = toggle eye
# X = other non-whitespace
#
# 07/06/10

use strict;
my $newline = ord('!');
my $toggle_eye_code = ord('*');
my $toggle_eye_output = $toggle_eye_code + 1;
my $eye_min = $newline + 2;
my $eye_max = $toggle_eye_code - 1;
my $space_min = $eye_max + 3;
my $space_max = ord('\\') - 1;
my $char_min = $space_max + 2;
my $char_max = ord('~');
my $eye_range = $eye_max - $eye_min + 1;
my $space_range = $space_max - $space_min + 1;
my $char_range = $char_max - $char_min + 1;

sub encode_run($$$$)
{
   my ($index, $text, $range, $condition) = @_;

   my $length = 1;
   for(++$$index;
       $$index < length($$text) && $length < $range && eval($condition);
       ++$$index)
   {
      $length++;
   }
   return $length;
}

sub encode_text()
{
   my $text = join '', <>;

   for(my $i = 0; $i < length($text);)
   {
      my $c = substr($text, $i, 1);
      if( $c eq "\n" )
      {
         # Newline
         print chr($newline);
         $i++;
      }
      elsif( $c eq '`' )
      {
         # Toggle eye
         print chr($toggle_eye_code);
         $i++;
      }
      elsif( $c eq ' ' )
      {
         # Space
         my $length = encode_run(\$i, \$text, $space_range,
                                 q{substr($$text, $$index, 1) eq ' '});
         print chr($space_min + $length - 1);
      }
      elsif( $c eq '@' )
      {
         # Eye
         my $length = encode_run(\$i, \$text, $eye_range,
                                 q{substr($$text, $$index, 1) eq '@'});
         print chr($eye_min + $length - 1);
      }
      else
      {
         # Non-space
         my $length = encode_run(\$i, \$text, $char_range,
                                 q{substr($$text, $$index, 1) !~ /[@`\s]/});
         print chr($char_min + $length - 1);
      }
   }
   print "\n";
}

encode_text();