#!/usr/bin/env perl

use strict;
use warnings;
use v5.22;

if (@ARGV !=1) {
    die "Usage: $0 [input-filename]";
}

my $input_filename = $ARGV[0];
open my $filehandle, '<', $input_filename or
    die "Could not open input file $input_filename: $!";

chomp( my @input = ( <$filehandle> ) );

# Part 1
my ($horizontal, $depth);

foreach (@input) {
    my ($direction, $distance) = split;
    $horizontal += $distance if ($direction eq 'forward');
    $depth      += $distance if ($direction eq 'down');
    $depth      -= $distance if ($direction eq 'up');
}

say $horizontal * $depth;

# Part 2
($horizontal, $depth) = (0, 0);
my $aim = 0;

foreach (@input) {
    my ($direction, $distance) = split;
    if ($direction eq 'forward') {
        $horizontal += $distance;
        $depth      += $aim * $distance;
    }
    $aim      += $distance if ($direction eq 'down');
    $aim      -= $distance if ($direction eq 'up');
}

say $horizontal * $depth;