#!/usr/local/bin/perl --
# use strict;

if ($#ARGV < 0) {
	&display_usage;
	exit(0);
}

my $datafile = $ARGV[0] || $0 . '.txt';
my ($height, $width, $bcharlist, @board) = &read_data($datafile);
my @borderchars = split('', $bcharlist);

&display_board($width, $height, 0, @board);

my $changes = $height * $width;
my $passes = 0;
while ($changes > 0) {
	$changes = 0;
	$passes++;
	for (my $y = 0; $y < $height; $y++) {
		for (my $x = 0; $x <= $#{$board[$y]}; $x++) {
			next	if (&is_border($board[$y][$x]));
			my $sum = &count_neighbors($x, $y, 
						$width, $height, \@board);
			if ($sum >= 3) {
				$changes++;
				$board[$y][$x] = $borderchars[0];
			}
		}
	}
}

&display_board($width, $height, $passes, @board);

sub read_data {
	my ($filename) = @_;
	my $h = 0, $w = 0, $charlist = '#';
	my (@board);
	open(DATAFILE, $filename) or die("Can't open $filename : $!\n");
		while (my $line = <DATAFILE>) {
			chomp($line);
			next		unless (length($line));
			next		if ($line =~ m/^#/); 

			my @parts = split(/\s*[:=]\s*/, $line, 2);
			$w = $parts[1]	if ($parts[0] =~ m/width|x/i);
			$h = $parts[1]	if ($parts[0] =~ m/height|y/i);
			$charlist = $parts[1]
				if ($parts[0] =~ m/border|wall|char/i);
			if ($parts[0] =~ m/board|screen/i) {
				for (my $i = 0; $i < $w; $i++) {
					$line = <DATAFILE>;
					chomp($line);
					@{$board[$i]} = split('', $line);
				}
			}
		}
	close(DATAFILE);
	return($h, $w, $charlist, @board);
}
sub display_board {
	my ($i, $j, $pass, @screen) = @_;
	printf("Pass : %d\nHeight : %d, Width : %d\nBoard : \n",
		$pass, $j, $i);
	for (my $y = 0; $y < $j; $y++) 
		{ print(join('', @{$screen[$y]}, "\n")); }
	print("\n");
}
sub is_border {
	my ($character) = @_;
	return(scalar(grep(/$character/, @borderchars)));
}
sub count_neighbors {
	local ($i, $j, $w, $h, *screen) = @_;
	my $ncount = 0;
	if ($j > 0)
		{ $ncount++	if (&is_border($screen[$j - 1][$i])); }
	if ($j < ($h - 1))
		{ $ncount++	if (&is_border($screen[$j + 1][$i])); }
	if ($i > 0)
		{ $ncount++	if (&is_border($screen[$j][$i - 1])); }
	if ($i < $w)
		{ $ncount++	if (&is_border($screen[$j][$i + 1])); }
	return($ncount);
}
sub display_usage {
	while (<DATA>) {
		s/\$0/$0/;
		print $_	unless (m/^__DATA__$/);
	}
}
__END__
__DATA__
Program execution:
	$0 filename

where filename is the name of the data file to use.

Datafile format:
<line> : <parameter1><seperator><parameter1_value>
<line> : <parameter2<seperator>parameter2_value>
<line> : <parameter2><seperator>
<line> : <dataline>

<seperator> : <space>*['='|':']<space>*
<parameter1> : ['height'|'width'|'x'|'y']
<parameter1_value> : <number>
<parameter2> : ['border'|'wall'|'char']
<parameter2_value> : <string1>
<dataline> : <string2>

<number> : <digit>+
<string1> : <non_whitespace>+
<string2> : <character>

<digit> : (equivalent to perl regex /\d/)
<space> : (equivalent to perl regex /\s/)
<non_whitespace> : (equivalent to perl regex /\S/)
<character> : (matched by perl regex /./)

Sample file:
x:4
y= 3
wall=#
screen=
## #
#  #
# ##