#!/usr/bin/perl -w

use strict;

if( $#ARGV != 0 )
{
   die "$0 <line count>\n";
}
my $line_count = $ARGV[0];

my $pi = atan2(0, -1);
my @buffer = ();
for(my $i = 0; $i < 20; $i++)
{
   push @buffer, (("X" x 79) . "\n");
}

my $char = 0;
my $zone = 0;
for(; $line_count > 0; $line_count--)
{
   # Generate extra rows when buffered rows fall below some threshold.
   # Note that the newly appended rows are not sufficient to hold
   # generated stars, so every new star may overlap a bit with
   # previously generated star.
   if( $#buffer < 50 )
   {
      # Fill buffer with extra rows
      for(my $i = 0; $i < 20; $i++)
      {
         push @buffer, (("X" x 79) . "\n");
      }

      # Generate star
      my $cx = rand(40) - 20 + ($zone ? 20 : 79 - 20);
      my $size0 = 1 + rand(2);
      my $size1 = 12 - $size0 + rand(8);
      my $phase = rand(2 * $pi);

      for(my $ta = 0; $ta < 10 * $pi; $ta += 0.1)
      {
         my $r = $size0 + $size1 + $size1 * 0.5 * sin($ta + $phase);
         for(my $tr = 0; $tr < $r; $tr += 0.1)
         {
            my $x = $cx + $tr * cos($ta / 5);
            my $y = $#buffer - 20 + $tr * sin($ta / 5) * 0.5;
            $y = int($y + 0.5);
            $x = int($x + 0.5);
            if( $x >= 0 && $x < length($buffer[$y]) )
            {
               substr($buffer[int($y + 0.5)], int($x + 0.5), 1) = ' ';
            }
         }
      }
      $zone ^= 1;
   }

   # Output text following template
   my $template = shift @buffer;
   foreach my $c (unpack 'C*', $template)
   {
      $c = chr($c);
      if( $c =~ /\s/s )
      {
         print $c;
      }
      else
      {
         print chr($char + ord('a'));
         $char = ($char + 1) % 26;
      }
   }
}