use warnings;
use strict;

use MCE::Loop;
use MCE::Candy;

## Select input and output files
my $input_file  = 'InputFile.OH1';
my $output_file = 'OutputFile.csv';

open my $ofh, ">", $output_file
   or die "cannot open '$output_file' for writing: $!\n";

## Creates a header at the beginning of the file
my $header = "HEC1_ID,Q100_Base,TTP,Area\n";
print $ofh $header;

## Extracts data from input in parallel.
MCE::Loop::init {
   use_slurpio => 1, chunk_size => '20k', max_workers => 4,
   gather => MCE::Candy::out_iter_fh($ofh),
};

mce_loop_f {
   my ( $output, $mce, $chunk_ref, $chunk_id ) = ( '', @_ );

   open my $ifh, "<", $chunk_ref;
   while (<$ifh>) {
     s{
      ^             # at the beginning of the line
      \+            # followed by literal plus
      (?:\s+(\S+))  # column one
      (?:\s+(\S+))  # column two
      (?:\s+(\S+))  # column three
      (?:\s+\S+){3} # skip three columns
      \s+(\S+)$     # catch the last one, too
     }{$1,$2,$3,$4}x
      and do { $output .= $_ };
   }
   close $ifh;

   MCE->gather( $chunk_id, $output );

} $input_file;

close $ofh;