#!/usr/bin/perl
use strict;
use warnings;

my @months = ( qw/Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec/); 

# source file directory
my $srcdir = '../source';

# source file name
my $srcfile = $srcdir . '/vol.dat';

my $desdir = '../target';

my $desfile = $desdir . '/total_volume.csv';

# Open source file.
open my $read, '<', $srcfile or die "Can't open the DAT file $!\n";

open my $write, '>', $desfile or die "Can't open the CSV file. $!\n";

print $write "Date,Total_Volume\n";

my ( $year, $month, $day ) = ( localtime( time() - 2592000 ) )[ 5, 4, 3 ];

$year += 1900;

my $startdate = "$day-".$months[$month]."-$year";

while (<$read>) {
    if ( /^$startdate/ .. /\x4/ ) {
        chomp;
        my (@items) = split /,/;
        printf $write "%s,%d\n", $items[0], $items[1] + $items[2];
    }
}

# probably not necessary but not a bad idea
close $read  or die "Couldn't close the DAT file: $!\n"; 
close $write or die "Couldn't close the CSV file: $!\n";