package labels

import (
	"fmt"
	"image"
	"image/color"
	"image/draw"
	"regexp"

	"github.com/skip2/go-qrcode"
	"golang.org/x/image/font"
	"golang.org/x/image/font/basicfont"
	"golang.org/x/image/math/fixed"
)

const (
	LabelWidth  = 384 // pixels at 203 DPI ≈ 48mm usable
	LabelHeight = 120 // pixels ≈ 15mm
	QRSize      = 96  // pixels
	QROffsetX   = 8
	QROffsetY   = 12
	TextOffsetX = 112
	BaseURL     = "http://mac-mini.mg:8080/hw/"
)

// hwIDPattern validates the HW-XXXXX format (T-04-07 mitigation).
var hwIDPattern = regexp.MustCompile(`^HW-\d{5}$`)

// LabelData holds the fields needed to render a standard item label.
type LabelData struct {
	HWID     string // e.g. "HW-00001"
	Name     string // item name from NetBox
	SpecLine string // key spec summary, e.g. "Intel NUC i5 2019"
}

// RenderStandard produces a 384x120 label bitmap (black on white) for a standard item.
// Layout: QR code left (96x96 at x=8,y=12), text right (HW ID bold top, name middle, spec bottom).
// Returns an error if HWID does not match HW-\d{5} (T-04-07 mitigation).
func RenderStandard(d LabelData) (image.Image, error) {
	if !hwIDPattern.MatchString(d.HWID) {
		return nil, fmt.Errorf("labels: invalid HWID %q: must match HW-NNNNN", d.HWID)
	}
	if d.Name == "" {
		d.Name = "Unknown Item"
	}

	img := image.NewNRGBA(image.Rect(0, 0, LabelWidth, LabelHeight))
	// Fill white background
	draw.Draw(img, img.Bounds(), image.NewUniform(color.NRGBA{R: 255, G: 255, B: 255, A: 255}), image.Point{}, draw.Src)

	// QR code
	qr, err := qrcode.New(BaseURL+d.HWID, qrcode.Low)
	if err != nil {
		return nil, fmt.Errorf("labels: QR generation failed: %w", err)
	}
	qr.DisableBorder = true
	qrImg := qr.Image(QRSize)
	qrDst := image.Rect(QROffsetX, QROffsetY, QROffsetX+QRSize, QROffsetY+QRSize)
	draw.Draw(img, qrDst, qrImg, image.Point{}, draw.Over)

	// Text: HW ID (y=26), Name (y=60), SpecLine (y=92)
	drawText(img, TextOffsetX, 26, d.HWID)
	drawText(img, TextOffsetX, 60, truncate(d.Name, 30))
	drawText(img, TextOffsetX, 92, truncate(d.SpecLine, 30))

	return img, nil
}

// drawText renders text onto a draw.Image at (x, y) using basicfont.Face7x13.
func drawText(img draw.Image, x, y int, text string) {
	d := &font.Drawer{
		Dst:  img,
		Src:  image.NewUniform(color.Black),
		Face: basicfont.Face7x13,
		Dot:  fixed.Point26_6{X: fixed.I(x), Y: fixed.I(y)},
	}
	d.DrawString(text)
}

// truncate caps s at max runes, appending "…" if truncated.
func truncate(s string, max int) string {
	runes := []rune(s)
	if len(runes) <= max {
		return s
	}
	return string(runes[:max-1]) + "…"
}