package itemimage

import (
	"bytes"
	"fmt"
	"image"
	"image/jpeg"
	"math"

	"golang.org/x/image/draw"
	_ "golang.org/x/image/webp"

	"printer.backend/internal/svgtemplate"
)

// EmbedDPI matches plate PDF rasterization; embedded pixels need not exceed this resolution.
const EmbedDPI = 300

const jpegEmbedQuality = 88

// prepareRaster decodes and downscales image data so the resulting SVG stays small enough for rsvg-convert.
func prepareRaster(data []byte, d svgtemplate.Data) ([]byte, string, error) {
	img, _, err := image.Decode(bytes.NewReader(data))
	if err != nil {
		return nil, "", fmt.Errorf("decode image: %w", err)
	}

	maxW := mmToPx(d.OuterWidth)
	maxH := mmToPx(d.OuterHeight)
	if maxW < 1 {
		maxW = 1
	}
	if maxH < 1 {
		maxH = 1
	}

	covered := scaleCover(img, maxW, maxH)
	rgba := image.NewNRGBA(image.Rect(0, 0, maxW, maxH))
	draw.CatmullRom.Scale(rgba, rgba.Bounds(), covered, covered.Bounds(), draw.Over, nil)

	var buf bytes.Buffer
	if err := jpeg.Encode(&buf, rgba, &jpeg.Options{Quality: jpegEmbedQuality}); err != nil {
		return nil, "", fmt.Errorf("encode jpeg: %w", err)
	}
	return buf.Bytes(), "image/jpeg", nil
}

func mmToPx(mm float64) int {
	return int(math.Ceil(mm / 25.4 * EmbedDPI))
}

// scaleCover returns an image scaled to cover dw×dh (center crop), for preserveAspectRatio slice.
func scaleCover(src image.Image, dw, dh int) image.Image {
	sb := src.Bounds()
	sw, sh := sb.Dx(), sb.Dy()
	if sw <= 0 || sh <= 0 {
		return image.NewNRGBA(image.Rect(0, 0, dw, dh))
	}

	scale := math.Max(float64(dw)/float64(sw), float64(dh)/float64(sh))
	nw := int(math.Ceil(float64(sw) * scale))
	nh := int(math.Ceil(float64(sh) * scale))

	scaled := image.NewNRGBA(image.Rect(0, 0, nw, nh))
	draw.CatmullRom.Scale(scaled, scaled.Bounds(), src, sb, draw.Over, nil)

	x0 := (nw - dw) / 2
	y0 := (nh - dh) / 2
	if x0 < 0 {
		x0 = 0
	}
	if y0 < 0 {
		y0 = 0
	}
	if nw < dw {
		dw = nw
	}
	if nh < dh {
		dh = nh
	}
	cropped := image.NewNRGBA(image.Rect(0, 0, dw, dh))
	draw.Draw(cropped, cropped.Bounds(), scaled, image.Point{x0, y0}, draw.Src)
	return cropped
}