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

my $inc;
if ($ARGV[0] eq 'inc') {
    $inc = 1;
}
elsif ($ARGV[0] eq 'dec') {
    $inc = -1;
}
else {
    die "unknown arg '$ARGV[0]'";
}

my @levels = (
    1,
    2,
    4,
    8,
    16,
    31,
    63,
    125,
    250,
    500,
    1000,
);
chomp(my $current = `xbacklight -getf`);
$current = int($current * 10);
my $idx;
for my $i (0..$#levels) {
    my $level = $levels[$i];
    $idx = $i;
    last if $level >= $current;
}
my $new_idx = $idx + $inc;
if ($new_idx >= 0 && $new_idx <= $#levels) {
    my $new_level = $levels[$new_idx] * 0.1;
    system("xbacklight -set $new_level");
}