#!/usr/bin/env bash
set -euo pipefail

direction="${1:-up}"
state_dir="${XDG_RUNTIME_DIR:-/tmp}"
if [ ! -w "$state_dir" ]; then
  state_dir="${XDG_CACHE_HOME:-$HOME/.cache}"
  mkdir -p "$state_dir"
fi
if [ ! -w "$state_dir" ]; then
  state_dir="/tmp"
fi
state_file="$state_dir/polybar-display-brightness.state"

export DISPLAY="${DISPLAY:-:0}"
if [ -z "${XAUTHORITY:-}" ] && [ -r "$HOME/.Xauthority" ]; then
  export XAUTHORITY="$HOME/.Xauthority"
fi

output="$(
  xrandr --query 2>/dev/null |
    awk '/ connected primary/ { print $1; exit } / connected/ && !out { out = $1 } END { if (out) print out }'
)"

[ -n "$output" ] || exit 0

brightness="$(cat "$state_file" 2>/dev/null || printf '1.0')"

case "$direction" in
  up)
    brightness="$(awk -v v="$brightness" 'BEGIN { v += 0.05; if (v > 1.00) v = 1.00; printf "%.2f", v }')"
    ;;
  down)
    brightness="$(awk -v v="$brightness" 'BEGIN { v -= 0.05; if (v < 0.30) v = 0.30; printf "%.2f", v }')"
    ;;
esac

printf '%s\n' "$brightness" >"$state_file"
xrandr --output "$output" --brightness "$brightness"