package thumbnail

import (
	"bytes"
	"image"
	"image/color"
	"image/png"
)

func Blend(a, b color.Color) color.Color {
	switch a.(type) {
	case color.RGBA:
		return BlendRGBA(a.(color.RGBA), b.(color.RGBA)) // FIXME there's syntax for this

	case color.YCbCr:
		return BlendYCbCr(a.(color.YCbCr), b.(color.YCbCr))

	default:
		return a // ??? unknown color format
	}
}

func BlendYCbCr(a, b color.YCbCr) color.YCbCr {
	return color.YCbCr{
		Y:  uint8((int(a.Y) + int(b.Y)) / 2),
		Cb: uint8((int(a.Cb) + int(b.Cb)) / 2),
		Cr: uint8((int(a.Cr) + int(b.Cr)) / 2),
	}
}

func BlendRGBA(a, b color.RGBA) color.RGBA {
	return color.RGBA{
		R: uint8((int(a.R) + int(b.R)) / 2),
		G: uint8((int(a.G) + int(b.G)) / 2),
		B: uint8((int(a.B) + int(b.B)) / 2),
		A: uint8((int(a.A) + int(b.A)) / 2),
	}
}

func (this *Thumbnailer) RenderScaledImage(src image.Image) ([]byte, error) {
	srcW := src.Bounds().Max.X
	srcH := src.Bounds().Max.Y
	destW := 0
	destH := 0

	if srcW > srcH {
		destW = this.Width
		destH = this.Height * srcH / srcW
	} else {
		destW = this.Width * srcW / srcH
		destH = this.Height
	}

	offsetX := (this.Width - destW) / 2
	offsetY := (this.Height - destH) / 2

	scaleW := float64(srcW) / float64(destW)
	scaleH := float64(srcH) / float64(destH)

	dest := image.NewRGBA(image.Rectangle{Max: image.Point{X: this.Width, Y: this.Height}})

	for y := 0; y < destH; y += 1 {
		for x := 0; x < destW; x += 1 {

			/*
				// NN
				mapx := int(float64(x) * scaleW)
				mapy := int(float64(y) * scaleH)
				dest.Set(x+offsetX, y+offsetY, src.At(mapx, mapy))
			*/

			// Bilinear
			c00 := src.At(int(float64(x)*scaleW), int(float64(y)*scaleH))
			c01 := src.At(int((float64(x)+0.5)*scaleW), int(float64(y)*scaleH))
			c10 := src.At(int(float64(x)*scaleW), int((float64(y)+0.5)*scaleH))
			c11 := src.At(int((float64(x)+0.5)*scaleW), int((float64(y)+0.5)*scaleH))
			cBlend := Blend(Blend(c00, c01), Blend(c10, c11))
			dest.Set(x+offsetX, y+offsetY, cBlend)

		}
	}

	var b bytes.Buffer

	err := png.Encode(&b, dest)
	if err != nil {
		return nil, err
	}

	return b.Bytes(), nil
}