package platepdf

import (
	"bytes"
	"encoding/base64"
	"fmt"

	"printer.backend/internal/model"
)

const renderDPI = 300

// BuildCompositeSVG assembles a plate-sized SVG by embedding each item as a PNG
// rendered by rsvg-convert (identical to the standalone item file).
func BuildCompositeSVG(plate model.Plate, spec model.ItemSpec, itemSVG []byte, preview model.LayoutPreview) ([]byte, error) {
	slotSVGs := make([][]byte, len(preview.Positions))
	for i := range preview.Positions {
		slotSVGs[i] = itemSVG
	}
	return BuildCompositeSVGSlots(plate, spec, slotSVGs, preview)
}

// BuildCompositeSVGSlots places one rendered item PNG per layout position.
// len(slotSVGs) must equal len(preview.Positions).
func BuildCompositeSVGSlots(plate model.Plate, spec model.ItemSpec, slotSVGs [][]byte, preview model.LayoutPreview) ([]byte, error) {
	if len(slotSVGs) != len(preview.Positions) {
		return nil, fmt.Errorf("slot svg count %d does not match positions %d", len(slotSVGs), len(preview.Positions))
	}

	canvasW := preview.CanvasWidthMM
	canvasH := preview.CanvasHeightMM
	if canvasW <= 0 || canvasH <= 0 {
		canvasW = spec.CanvasWidthMM()
		canvasH = spec.CanvasHeightMM()
	}

	slotPNGs := make([]string, len(slotSVGs))
	for i, svg := range slotSVGs {
		itemPNG, err := svgToPNGViaRsvg(svg, renderDPI)
		if err != nil {
			return nil, fmt.Errorf("render item slot %d: %w", i, err)
		}
		slotPNGs[i] = base64.StdEncoding.EncodeToString(itemPNG)
	}

	var b bytes.Buffer
	fmt.Fprintf(&b, `<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 %.4f %.4f" width="%.4fmm" height="%.4fmm">
  <rect width="%.4f" height="%.4f" fill="#ffffff"/>
  <rect x="%.4f" y="%.4f" width="%.4f" height="%.4f" fill="none" stroke="#cccccc" stroke-width="0.2"/>
`,
		plate.WidthMM, plate.HeightMM, plate.WidthMM, plate.HeightMM,
		plate.WidthMM, plate.HeightMM,
		preview.PrintableXMM, preview.PrintableYMM, preview.PrintableWMM, preview.PrintableHMM,
	)

	for i, pos := range preview.Positions {
		fmt.Fprintf(&b,
			`<image x="%.4f" y="%.4f" width="%.4f" height="%.4f" href="data:image/png;base64,%s"/>`,
			pos.XMM, pos.YMM, canvasW, canvasH, slotPNGs[i],
		)
	}

	b.WriteString("\n</svg>")
	return b.Bytes(), nil
}