use strict;
use warnings;
use Getopt::Long;
use Algorithm::Cron;

my $file;
my $howmany;
my $crontab;
my $help;
my @lines;

my $helptext = "USAGE:\n $0 [ [-f filename | -c STRING] -n N]\n\n".
			" $0 -f filename\n".
			" $0 -f filename -n 2\n".
			" crontab -l | $0 \n".
			" crontab -l | $0 -n 2\n".
			" cat filename | $0\n".
			" cat filename | $0 -n 3\n".
			" $0 -c 'crontab entry'\n".
			" $0 -c 'crontab entry' -n 5\n".
			" $0  (paste some content followed by CTRL-D or CTRL-Z on a newline)\n".
			" $0  -n 4 (paste some content followed by CTRL-D or CTRL-Z on a newline)\n".
			" $0 -h (print this help)\n";
			
GetOptions ("f|file=s" => \$file,
            "n=i"   => \$howmany,
			"c|crontab=s"	=> \$crontab,
            "h|help"  => \$help)  
	or die( $helptext );

print $helptext and exit if $help;	

if ( $crontab )	{ @lines = $crontab }
elsif ( $file and -e -f -r $file){
	open my $fh, '<', $file or die;
	@lines = <$fh>;
}
else{ @lines = <> }

foreach my $line ( 
			sort { 
				Algorithm::Cron->new( base => 'local',
				crontab => join' ',(split /\s+|\t/,$a)[0..4])->next_time(time)
				<=>
				Algorithm::Cron->new( base => 'local',
				crontab => join' ',(split /\s+|\t/,$b)[0..4])->next_time(time)
			} 
			grep { /^(\d|\*)/ } @lines 
){
	my @parts = split /\s+|\t/,$line;
	my $now = time;
	my $repeat = $howmany;
	print scalar localtime ( Algorithm::Cron->new( base => 'local',
							crontab => join' ', @parts[0..4])->next_time($now)
	);
	print " => ( @parts[0..4] )",($crontab ? "" : " => @parts[5..$#parts]"),"\n";
	if ( --$repeat ){
		while( $repeat > 0){
			$now = Algorithm::Cron->new( base => 'local',
						crontab => join' ', @parts[0..4])->next_time( $now );
			print scalar localtime ( Algorithm::Cron->new( base => 'local',
							crontab => join' ', @parts[0..4])->next_time($now)
			);
			print "\n";
			$repeat--;		
		}
	}
}