package main

import (
	"fmt"
	"log"
	"os"
	"os/exec"
	"strconv"
	"strings"
)

func main() {
	if len(os.Args) <= 1 {
		fmt.Printf("Usage: %s [+|-]", os.Args[0])
		return
	}
	brightness()
}

func brightness() {
	cmd := fmt.Sprintf("xrandr --verbose | grep %s -A 5 | grep Brightness | cut -f 2 -d ' '", display())
	brightness, err := exec.Command("sh", "-c", cmd).Output()
	if err != nil {
		log.Fatal(err)
	}
	f, err := strconv.ParseFloat(strings.TrimSpace(string(brightness)), 64)
	if err != nil {
		log.Fatal(err)
	}
	switch {
	case os.Args[1] == "+" && f < 1:
		f += .25
	case os.Args[1] == "-" && f > 0:
		f -= .25
	}
	exe := fmt.Sprintf("xrandr --output %s --brightness %s", display(), strconv.FormatFloat(f, 'f', 2, 64))
	exec.Command("sh", "-c", exe).Output()
}

func display() string {
	cmd, err := exec.Command("xdotool", "getmouselocation", "--shell").CombinedOutput()
	if err != nil {
		log.Fatal(err)
	}
	lines := strings.SplitAfter(string(cmd), "\n")
	i, err := strconv.Atoi(strings.TrimSpace(lines[0][len(lines)-3:]))
	if err != nil {
		log.Fatal(err)
	}
	switch {
	case i < 1920:
		return "HDMI-1"
	case i < 4480:
		return "DP-1"
	default:
		return "DP-2"
	}
}