#!/usr/bin/perl -T

use strict;
use warnings;
use utf8;
use open qw(:std :utf8);
use Encode qw(encode decode);
use POSIX qw(strftime);

# runs thru my gps altitude data files, and spits out monthly averages.
# meant to be run from a cron job such like:
# min	hour	mday	month	wday	command
# 01	00	1	*	*	~/projects/gps/gen_month_avg

@ARGV = map { decode("UTF-8", $_) } @ARGV;

my $num = 0;
my $asum = 0;
my $esum = 0;

my $date = time;
my $datey = $date - 86400;	# a day ago, in seconds (60 * 60 * 24).
my $ydatey = strftime "%Y", localtime($datey);
my $mdatey = strftime "%Y%m", localtime($datey);

my $in_dat_f = "/import/home/ghz/projects/gps/data/$ydatey/gps_alt.day.avg.$mdatey";
my $out_dat_f = "/import/home/ghz/projects/gps/data/gps_alt_monthly_averages";

open(IN, "<", $in_dat_f) or die "omg! can't open input file: $in_dat_f";

unless (open(OUT, ">>", $out_dat_f)) {
	close(IN);
	die "omg! can't open output file: $out_dat_f";
}

while (<IN>) {
	chomp;
	my ($x, $y, $a, $z, $b) = split;
	$num++;
	$asum+=$y;
	$esum+=$z;
}

printf OUT "%s\t%.1f m\t%.1f m\n", $mdatey, $asum / $num, $esum / $num;
close(IN);
close(OUT);