#!/usr/bin/env bash
#
# This is a shell "application", but doesn't have to be one, so
# leaving the shebang in place.
set -euo pipefail

dir=$(find /sys/devices/ -name intel_backlight | head -1)
if [[ -z "$dir" ]]; then
    echo "intel_backlight not found"
    exit 1
fi

max=$(cat "$dir/max_brightness")
now=$(cat "$dir/brightness")
step=$((max * 5 / 100))
min=100

clamp() {
    if [[ $1 -gt $max ]]; then
        echo "$max"
    elif [[ $1 -lt $min ]]; then
        echo "$min"
    else
        echo "$1"
    fi
}

info() {
    perc="$(echo "$1*100/$max" | bc -l)"
    printf "%s of %s (%.2f%%)\n" "$1" "$max" "$perc"
}

new=
case "${1:-}" in
up)
    new=$(clamp $((now + step)) ) ;;
down)
    new=$(clamp $((now - step)) ) ;;
esac

if [[ -n "$new" ]]; then
    echo "$new" | sudo tee "$dir/brightness" > /dev/null
    info "$new"
else
    info "$now"
fi