#!/usr/bin/perl
use strict;
use warnings;
use Getopt::Std;

my %opt;
get_args(\%opt);

my $desired = load_date_file($opt{d});
open(my $fh, '<', $opt{i}) or die "Unable to open '$opt{i}' for reading: $!";
while (<$fh>) {
    chomp;
    my ($id, $date, $val) = split ' ', $_, 3;
    next if ! defined $date || ! exists $desired->{$date};
    $desired->{$date}{sum} += $val;
    $desired->{$date}{cnt}++;
}

for my $date (sort keys %desired) {
    my $sum = $desired->{$date}{sum} || 0;
    my $cnt = $desired->{$date} || 0;
    my $avg = $cnt ? sprintf('%.2f', $sum / $cnt) : 0;
    print join(',', $date, $sum, $cnt, $avg), "\n";
}

sub load_date_file {
    my ($file) = @_;
    my %desired;
    open(my $fh, '<', $file) or die "Unable to open '$file' for reading: $!";
    while (<$fh>) {
        chomp;
        if (! /^\d{4}$/) {
            warn "'$_' is not in MMYY format - skipping\n";
            next;
        }
        $desired{$_} = undef;
    }
    return \%desired;
}

sub get_args {
    my ($opt) = @_;
    my $Usage = qq{Usage: $0 -d <date_file> -i <input_file>
        -h : This help message

        -d : The (d)ate file

        -i : The (i)nput file
    } . "\n";
    getopts('hd:i:', $opt) or die $Usage;
    die $Usage if $opt->{h} || ! defined $opt->{d} || ! defined $opt->{i};
}