use strict; use warnings;
use Date::Calendar::Profiles qw( $Profiles );
use Date::Calendar;

sub to_date {
		my ($d,$m,$y) = split /\//, shift;
		return [$y,$m,$d];
}

sub from_date {
		my $date = shift;
		$date =~ s/(\d{4})(\d{2})(\d{2})/$3\/$2\/$1/;
		return $date;
}

my $calendar  = Date::Calendar->new( $Profiles->{'DE-SN'} );

# first read in the whole file and
# record start and end dates for each employee
my %dates;

# simplified data reading, pls stick to Text::CSV
while (<DATA>) {
		next if /^empl/;
		chomp;
		my( $employee_id,$start_date,$end_date,$total_days) = split /,/;
		$dates{$employee_id}{$start_date}{'end'} = $end_date;
		$dates{$employee_id}{$start_date}{'days'} = $total_days;
}

# now we have all the data
# and can process it
for my $employid (sort keys %dates) {
		my $data = $dates{$employid}; 
		for my $startdate (keys %{$data}) {
				my $enddate = $$data{$startdate}{'end'};
				next if $enddate eq 'invalid'; # redundant, see below
				# find next businessday
				my $next = from_date( $calendar->add_delta_workdays(to_date($enddate),1) );
				# do we have a record for the next business day ?
				if( exists $$data{$next} ) {
						# merge two records
						$$data{$startdate}{'end'} = $$data{$next}{'end'};
						$$data{$startdate}{'days'} += $$data{$next}{'days'};
						$$data{$next}{'end'} = 'invalid'; # mark redundant
				}
		}
}

for my $employid (sort keys %dates) {
		my $data = $dates{$employid}; 
		for my $startdate  (keys %{$data}) {
				my $enddate = $$data{$startdate}{'end'};
				next if $enddate eq 'invalid';			
				print "$employid,$startdate,$enddate,";
				print $$data{$startdate}{'days'},"\n";
		}
}
__DATA__
employid, start, stop, total
1234,01/04/2013,05/04/2013,5
1234,08/04/2013,12/04/2013,5
1234,18/04/2013,18/04/2013,1
1234,22/04/2013,22/04/2013,1
1234,23/04/2013,23/04/2013,1
5678,01/01/2013,01/01/2013,1