package fb

import (
	"os"
)

var (
	devfb         *os.File
	Width, Height int
)

func resolution() (w int, h int) {
	resFile, err := os.File("/sys/class/graphics/fb0/virtual_size")
	if err != nil {
		panic(err)
	}

	r := bufio.NewReader(resFile)
	s, err := r.ReadString('\n')
	if err != nil {
		panic(err)
	}
	fmt.Sscanf(s, "%d,%d", &w, &h)
	return
}

func init() {
	Width, Height = resolution()
	devfb, err := os.OpenFile("/dev/fb", os.O_WRONLY, os.ModePerm)
	if err != nil {
		panic(err)
	}
}

func Bytes(c color.Color) []byte {
	r, g, b, a := c.RGBA()
	return []byte{byte(b), byte(g), byte(r), byte(a)}
}

func Draw(img image.Image) error {
	buf := bufio.NewWriterSize(devfb, 1<<16)
	for h := 0; h < Height; h++ {
		for w := 0; w < Width; w++ {
			_, err := buf.Write(Bytes(img.At(w, h)))
			if err != nil {
				return err
			}
		}
	}
	err := buf.Flush()
	if err != nil {
		return err
	}
	return nil
}