package layout

import (
	"printer.backend/internal/model"
)

// Pack computes the maximum grid of items that fit on the plate.
// Cells use the full item SVG canvas (product + bleed, margin, crop marks); spacing is between canvases.
func Pack(plate model.Plate, spec model.ItemSpec, spacingMM float64) model.LayoutPreview {
	pw := plate.PrintableWidth()
	ph := plate.PrintableHeight()
	footW := spec.ViewportWidth()
	footH := spec.ViewportHeight()
	canvasW := spec.CanvasWidthMM()
	canvasH := spec.CanvasHeightMM()
	trim := spec.TrimOffsetMM()
	cw := canvasW + spacingMM
	ch := canvasH + spacingMM

	cols, rows := gridCount(pw, ph, cw, ch)
	count := cols * rows

	ox := plate.MarginLeft
	oy := plate.MarginTop

	positions := make([]model.LayoutPosition, 0, count)
	for row := 0; row < rows; row++ {
		for col := 0; col < cols; col++ {
			positions = append(positions, model.LayoutPosition{
				XMM: ox + float64(col)*cw,
				YMM: oy + float64(row)*ch,
			})
		}
	}

	return model.LayoutPreview{
		PlateWidthMM:   plate.WidthMM,
		PlateHeightMM:  plate.HeightMM,
		PrintableXMM:   ox,
		PrintableYMM:   oy,
		PrintableWMM:   pw,
		PrintableHMM:   ph,
		CellWidthMM:    cw,
		CellHeightMM:   ch,
		FootprintWMM:   footW,
		FootprintHMM:   footH,
		TrimOffsetMM:   trim,
		CanvasWidthMM:  canvasW,
		CanvasHeightMM: canvasH,
		Columns:        cols,
		Rows:           rows,
		Count:          count,
		Positions:      positions,
	}
}

func gridCount(printableW, printableH, cellW, cellH float64) (cols, rows int) {
	if printableW <= 0 || printableH <= 0 || cellW <= 0 || cellH <= 0 {
		return 0, 0
	}
	cols = int(printableW / cellW)
	rows = int(printableH / cellH)
	if cols < 0 {
		cols = 0
	}
	if rows < 0 {
		rows = 0
	}
	return cols, rows
}