qr_labels/main.go

package main

import (
	"fmt"
	"io"
	"log/slog"
	"os"

	"codeberg.org/go-pdf/fpdf"
	"github.com/yeqown/go-qrcode/v2"
	"github.com/yeqown/go-qrcode/writer/standard"
)

var textTopPadding = 0.0      // typically none is required
var qrTopPadding = 5.0        // below the baseline of the text, remember the descenders like 'y', 'q'
var requiredCellPadding = 3.0 // half on each side, effectively

func main() {
	f, _ := os.Create("hello.pdf")
	err := generatePage(f, PageOptions{
		qrURL:   "https://nanocat.net/dom/sdfih/dsifj/sidhof/sdifho/sdfiuoh/safiuho",
		qrLabel: "Á[Hjqy]|",
		qrSize:  54,

		font:      "Helvetica",
		fontStyle: "B",
		fontSize:  34.0,
		rows:      4,
		cols:      3,
		borders:   true,
	})
	if err != nil {
		slog.Error("could not generate pdf", "error", err)
		os.Exit(1)
	}

}

type PageOptions struct {
	qrURL     string
	qrLabel   string
	qrSize    float64
	font      string
	fontStyle string
	fontSize  float64
	rows      int
	cols      int
	borders   bool
}

func generatePage(w io.Writer, po PageOptions) error {

	fontSizeMM := po.fontSize / 72 * 25.4

	qrc, err := qrcode.New(po.qrURL)

	if err != nil {
		return fmt.Errorf("could not generate QRCode: %v", err)
	}

	b := newBWC()
	qrBytes := standard.NewWithWriter(&b,
		// standard.WithQRWidth(uint8(qrSize)),
		standard.WithBorderWidth(0),
		standard.WithBuiltinImageEncoder(standard.PNG_FORMAT),
		// standard.WithCircleShape(),
		// standard.WithFgGradient(&standard.LinearGradient{
		// 	Stops: []standard.ColorStop{{
		// 		T: 0.0,
		// 		Color: color.RGBA{
		// 			R: 255,
		// 			G: 0,
		// 			B: 0,
		// 			A: 0,
		// 		},
		// 	}, {
		// 		T: 1.0,
		// 		Color: color.RGBA{
		// 			R: 0,
		// 			G: 255,
		// 			B: 0,
		// 			A: 0,
		// 		},
		// 	}},
		// 	Angle: 45,
		// }),
	)

	// save file
	if err = qrc.Save(qrBytes); err != nil {
		fmt.Printf("could not save image: %v", err)
	}
	// dim := qrc.Dimension()

	pdf := fpdf.New("P", "mm", "A4", "")
	pdf.SetMargins(0, 0, 0)
	pageWidth, pageHeight := pdf.GetPageSize()

	// register the qr
	pdf.RegisterImageOptionsReader("qr", fpdf.ImageOptions{
		ImageType:             "png",
		ReadDpi:               false,
		AllowNegativePosition: false,
	}, b)

	pdf.AddPage()
	pdf.SetFont(po.font, po.fontStyle, float64(po.fontSize))

	textWidth := pdf.GetStringWidth(po.qrLabel)

	colWidth := pageWidth / float64(po.cols)
	rowHeight := pageHeight / float64(po.rows)

	cellHeight := textTopPadding + fontSizeMM + qrTopPadding + po.qrSize
	cellWidth := po.qrSize

	if cellHeight > rowHeight-requiredCellPadding {
		slog.Warn("qr is too big for row", "cell_height", cellHeight, "row_height", rowHeight)
		return fmt.Errorf("qr is too big for row size")
	}

	//	slog.Info("check width", "cell_width", cellWidth, "col_width", colWidth)

	if cellWidth > colWidth-requiredCellPadding {
		slog.Warn("qr is too big for column", "cell_width", cellWidth, "col_width", colWidth)
		return fmt.Errorf("qr is too big for col size")
	}

	if textWidth > colWidth {
		slog.Warn("text probably too wide")
		return fmt.Errorf("text is too wide for col size")
	}

	for rowIdx := range po.rows {
		for colIdx := range po.cols {
			topLeftX := colWidth * float64(colIdx)
			topLeftY := rowHeight * float64(rowIdx)

			// draw box
			if po.borders {
				pdf.SetDashPattern([]float64{1, 1}, 0)
				pdf.Rect(topLeftX, topLeftY, colWidth, rowHeight, "D")
				pdf.SetDashPattern([]float64{}, 0)
			}

			// label at the top
			pdf.Text(
				topLeftX+colWidth/2-textWidth/2,
				topLeftY+fontSizeMM+textTopPadding,
				po.qrLabel, // +fmt.Sprintf("%d/%d", rowIdx, colIdx)
			)

			// qr at the bottom
			pdf.ImageOptions("qr",
				topLeftX+colWidth/2-po.qrSize/2,
				topLeftY+textTopPadding+fontSizeMM+qrTopPadding,
				po.qrSize, po.qrSize,
				false,
				fpdf.ImageOptions{AllowNegativePosition: true}, 0, "")
		}
	}

	err = pdf.Output(w)
	if err != nil {
		return fmt.Errorf("could not output PDF: %w", err)
	}
	return nil
}