use 5.010;
use strict;
use warnings;

our $start_time = time;

#Embedded perl HTML template compiler object class
package HTML::template;

#Preloads new template object: 
#@_ = class, embedded perl/html input source
sub new
{	
	my ($class, $input) = @_;
	$input //= $_;

	#Slurp the source template
	open my $fh, "<", $input or die "$! \"$input\"";
	local $/;
	my $slurp = <$fh>;
	close $fh;

	#Extract perl script from the template
	my $content = \$slurp;
	my $position = 0;
	my $script = "sub {\n\# line 1 \"$input\"\n";

	#Scan html comment tags
	while ( $slurp =~ /<!--(?<cmd>.*?)-->/gso )
	{
		#Insert text block
		$script .= "print substr(\${\$content},$position,$-[0]-$position);\n";
		#Translate line numbers
		my $line = ( substr($slurp,0,$position) =~ tr/\n// ) + 1;
		#Insert perl block using fixed line number
		$script .= "\# line $line\n$+{cmd}\n";
		#Advance to next block
		$position = $+[0];
	}	
	#Insert the last text block
	$script .= "print substr(\${\$content},$position);}";

	#Precompile script
	my $compiled = eval($script) or die;

	#Define template object list
	bless [$content, $compiled], $class;
}

#Execute the template object
##@_ = class, html output target
sub run
{
	my ($self, $output) = @_;
	my ($content, $compiled) = @{$self};
	$output //= $_;
	#Redirect output
	local (*STDOUT);
	open(STDOUT, ">", $output);
	#Excute precompiled script
	$compiled->();
}

#Sample program utilizing HTML::template
my $sample_input = <<'END';
Numbers generated at <!--print $start_time;--><br>
<!--for(my $x = 1; $x < 5; $x++) {-->Number=<!--print $x;--><br>
<!--}-->Time used <!--print time - $start_time;--> seconds.<br>
END

my $template = HTML::template->new(\$sample_input);
my $sample_output = '';
$template->run(\$sample_output);
print $sample_output;

#Output from sample_template
Numbers generated at 1265498059<br>
Number=1<br>
Number=2<br>
Number=3<br>
Number=4<br>
Time used 0 seconds.<br>