#!/usr/bin/perl
use strict; use warnings; use 5.014;

open my $A, "<", "A" or die;
open my $B, "<", "B" or die;

sorted_merge($A, $B);
# memory_merge($A, $B);

sub sorted_merge {
    my @handle = @_;
    my @info;

    for my $fh (@handle) {
        my %h;
        @h{qw/key avg n/} = parse_line(scalar readline($fh));
        push @info, \%h;
    }

    while (1) {
        # smallest key
        my ($next) = sort(grep defined($_), map $$_{key}, @info);
        last unless $next;

        my $sum = 0;
        my $n = 0;
        for my $i (0..$#handle) {
            next unless $info[$i]{key} and $info[$i]{key} eq $next;

            $sum += $info[$i]{avg} * $info[$i]{n};
            $n   += $info[$i]{n};
            @{$info[$i]}{qw/key avg n/} = parse_line(scalar readline($handle[$i]));
        }

        next unless $n;
        print_line($next, $sum/$n, $n);
    }
}

sub memory_merge {
    my @handle = @_;
    my %data;

    for my $fh (@handle) {
        while (defined(my $line = <$fh>)) {
            my ($key, $avg, $n) = parse_line($line);

            if ($data{$key}) {
                $data{$key}{sum} += $avg * $n;
                $data{$key}{n}   += $n;
            }
            else {
                $data{$key} = {
                    sum => $avg * $n,
                    n   => $n,
                };
            }
        }
    }

    for my $key (sort keys(%data)) {
        print_line($key, $data{$key}{sum}/$data{$key}{n}, $data{$key}{n});
    }
}


sub print_line {
    my ($key, $avg, $n) = @_;
    my @cols = split /\s+/, $key;
    push @cols, $avg, $n;
    say join "\t", @cols;
}

sub parse_line {
    my $line = shift;
    return unless $line;
    my @col = split /\s+/, $line;
    # Format the key so that they sort correctly as strings.
    # Choose padding sizes carefully.
    my $key = sprintf "%-5s %4d %-10s %-10s", @col[0..3];
    my $avg = $col[4];
    my $n   = $col[5];
    return ($key, $avg, $n);
}