# subroutine name: process_template
# Input: template filename, reference to hash {tag_name=>tag_value}
# Processes <!--$tag_name--> tags and <!--%% "perl commands" %%--> tags 
# inside template file. <!--$tag_name--> tags are replaced with corresponding values.
# Returns: string (result of tempate file processing).
# Global variables used:
#	%template_subst - hash for templates substitutions
#	%templates_cache - caching hash for small templates (<5000 bytes)
#	$templates_dir - filesystem path to templates dir (without trailing slash)
#   $admin - admin works with script (disable template substitution feature)
sub process_template {
	local ($templatefile, $namespace) = @_;
	my $template_content;
	if ($template_subst{$templatefile} ne "" && !$admin) {
		# replace filename, if this name found in template substitution hash
		$templatefile=$template_subst{$templatefile};
	}
	if ($templatefile=~m/^[\w\.\-\~]+$/s) {
		if (defined $templates_cache{$templatefile}) {
			$template_content = $templates_cache{$templatefile};
		} else {
			my $fn="$templates_dir/$templatefile";
			$| = 1;
			# Open template and read in
			open(TEMPLATE,"<$fn") or die("Error in subroutine process_template: can't open $fn. Reason: $!");
			{
				local($/) = undef;
				$template_content = <TEMPLATE>;
			}
			close(TEMPLATE);
			# cache template (useful for repeating template use within one CGI process)
			$template_content =~ s/^<!--(|[^\$\%].*?)-->//s; #remove infoheader
			$templates_cache{$templatefile}=$template_content if (length($template_content)<5000);
		}
		#$template_content =~ s/<!--\$([A-Za-z\-_\.\d]+)-->/$namespace->{$1}/gs;
		#$template_content =~ s/<\!--\%\%(.+?)\%\%-->/&evaluate($1)/egs;
		return &process_text($template_content, $namespace);
	} else {
		die("Error in subroutine process_template: template filename '$templatefile' may contain only alpha-numerical and '.', '-', '~', '_' characters.");
	}
}