package img

import (
	"image"
	"image/draw"
	"image/png"
	"os"

	"github.com/anthonynsimon/bild/adjust"
)

const (
	StyleDark = 0.70
)

func Overlay(inputFile, overlayFile string, style float64) (err error) {
	thumb, err := os.Open(inputFile)
	if err != nil {
		return err
	}

	overlay, err := os.Open(overlayFile)
	if err != nil {
		return err
	}

	img0, err := png.Decode(thumb)
	if err != nil {
		return err
	}
	defer thumb.Close()

	img1, err := png.Decode(overlay)
	if err != nil {
		return err
	}
	defer overlay.Close()

	b0 := img0.Bounds()
	b1 := img1.Bounds()

	img0 = adjust.Brightness(img0, style)

	offset := image.Pt(b0.Dx()/2-b1.Dx()/2, b0.Dy()/2-b1.Dy()/2)

	m := image.NewRGBA(b0)
	draw.Draw(m, b0, img0, image.Point{}, draw.Src)
	draw.Draw(m, img1.Bounds().Add(offset), img1, image.Point{}, draw.Over)

	imgw, err := os.Create(inputFile)
	if err != nil {
		return err
	}

	png.Encode(imgw, m)
	defer imgw.Close()

	return nil
}