package imgedit

import (
	"image"
	"image/color"

	"github.com/disintegration/imaging"
)

func makeBoxShadow(maskImg image.Image, shadowColor color.Color, sigma float64, shadowMargin, offsetY int) image.Image {
	w, h := maskImg.Bounds().Dx(), maskImg.Bounds().Dy()
	cr, cg, cb, _ := shadowColor.RGBA()
	cr8, cg8, cb8 := uint8(cr>>8), uint8(cg>>8), uint8(cb>>8)

	// New box image
	backing := image.NewNRGBA(image.Rect(0, 0, w+shadowMargin*2, h+shadowMargin*2+offsetY))
	newImg := image.NewNRGBA(image.Rect(0, 0, w+shadowMargin*2, h+shadowMargin*2+offsetY))
	for x := 0; x < w+shadowMargin*2; x++ {
		for y := 0; y < h+shadowMargin*2; y++ {
			var c = color.NRGBA{R: 255, G: 255, B: 255, A: 0}
			if x >= shadowMargin-4 && y >= shadowMargin-4 && x <= w+shadowMargin+4 && y <= h+shadowMargin+4 {
				_, _, _, a := maskImg.At(x-shadowMargin, y-shadowMargin).RGBA()
				c = color.NRGBA{R: cr8, G: cg8, B: cb8, A: uint8(a >> 8)}
			}
			backing.SetNRGBA(x, y, color.NRGBA{R: 255, G: 255, B: 255, A: 0})
			newImg.SetNRGBA(x, y+offsetY, c)
		}
	}

	// Blur
	blurredImage := imaging.Blur(newImg, sigma)
	backing = imaging.OverlayCenter(backing, blurredImage, 0.6)

	return backing
}