#!/usr/bin/perl -w

# name of script:  eddy4.pl
# Time-stamp: <Tuesday, 20 November 2007, 10:59 MST -- cbuerkle>


($a, $intv) = @ARGV;
open (INFILE, $a) or die "Could not open the file:  $a ($!)\n";

$out = "covresults_" . $intv . ".txt";

open (OUTFILE, ">$out") or die "Could not open the outfile. ($!)\n";

$intv = $intv * 60 * 4 ; # $intv is in minutes
$cntr=1;
print OUTFILE "hr, temp, Cov\n";

while (defined ($text = <INFILE>)) {
    chomp $text;
    (undef,undef,$HRMN,undef,undef,undef,$uzIn,undef,undef,undef,$CO2_in,
     undef,undef,$temp,undef) = split(/[,\s+]/,$text);
    
    unless($CO2_in == 99999 || $CO2_in == -99999 ||
	   $uzIn == 99999 || $uzIn == -99999 ||
	   $temp == 99999 || $temp == -99999){
	push(@CO2, $CO2_in);
	push(@wind, $uzIn);
	push(@temp, $temp);	

	if(!($cntr % $intv)){
	    $co2mean = &calcMean(@CO2);
	    $windmean = &calcMean(@wind);
	    $tempmean = &calcMean(@temp);
	    $thecov = &cov(\@CO2, $co2mean, \@wind, $windmean);
	    print OUTFILE "$HRMN,$tempmean,$thecov\n";
	    @CO2 = ();
	    @temp = ();
	    @wind = ();
	}
	$cntr++;
    }
}

close (INFILE)  || die "Could not close the file:  $a";
close (OUTFILE);

sub calcMean {
    my $tmp = 0;
    # @_ is the passed array;
    foreach my $i (@_) {
	$tmp  = $tmp + $i;
    }
    return $tmp / @_ ; #  @_ (here, a list in a scalar context) is equal to ($#_ + 1)
}

sub cov {
# call as &cov(\@CO2, $co2mean, \@wind, $windmean)
    my($xref, $xmean, $yref, $ymean) = @_;
    my $result  = 0;
#    for (my $i = 0; $i < @$xref; $i++){
    foreach my $i (0..(@$xref-1)){
	$result += ($xref->[$i] - $xmean) * ($yref->[$i] - $ymean)
    }
    return $result / (@$xref - 1);
}