package fb

import (
	"bufio"
	"fmt"
	"image"
	"image/color"
	"io"
	"os"
	"path/filepath"
)

/* old version that worked some time for some reason
func Resolution() (w int, h int) {
	resFile, err := os.Open("/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 Resolution() (w int, h int) {
	matches, err := filepath.Glob("sys/class/drm/*/modes")
	if err != nil {
		panic(err)
	}

	for _, match := range matches {
		f, err := os.Open(match)
		if err != nil {
			panic(err)
		}
		r := bufio.NewReader(f)
		s, err := r.ReadString('\n')
		if err != nil {
			switch err {
			case io.EOF:
				continue
			default:
				panic(err)
			}
		}
		fmt.Sscanf(s, "%dx%d", &w, &h)
	}
	return
}

var devfb *os.File
var width, height = Resolution()

func init() {
	var err error
	devfb, err = os.OpenFile("/dev/fb0", 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
	}
	_, err = devfb.Seek(0, 0)
	if err != nil {
		return err
	}
	return nil
}