package sprite

import (
	"fmt"
	"io"
)

// WriteSVG encodes g as an SVG where each horizontal run of same-colored
// pixels becomes one <rect>. shape-rendering="crispEdges" keeps the pixel
// look at any zoom. scale only affects the document width/height; the
// viewBox stays in pixel units.
func WriteSVG(w io.Writer, g PixelGrid, scale int) error {
	if scale < 1 {
		scale = 1
	}
	gw, gh := g.Bounds()
	_, err := fmt.Fprintf(w,
		`<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="%d" viewBox="0 0 %d %d" shape-rendering="crispEdges">`+"\n",
		gw*scale, gh*scale, gw, gh)
	if err != nil {
		return err
	}
	for y := 0; y < gh; y++ {
		for x := 0; x < gw; {
			c := g.At(x, y)
			run := 1
			for x+run < gw && g.At(x+run, y) == c {
				run++
			}
			if c.A > 0 {
				opacity := ""
				if c.A < 255 {
					opacity = fmt.Sprintf(` fill-opacity="%.3f"`, float64(c.A)/255)
				}
				_, err = fmt.Fprintf(w, `<rect x="%d" y="%d" width="%d" height="1" fill="#%02x%02x%02x"%s/>`+"\n",
					x, y, run, c.R, c.G, c.B, opacity)
				if err != nil {
					return err
				}
			}
			x += run
		}
	}
	_, err = io.WriteString(w, "</svg>\n")
	return err
}