img2pdf/main.go

package main

import (
	"bytes"
	"errors"
	"fmt"
	"image"
	"image/color"
	_ "image/gif"
	_ "image/jpeg"
	"image/png"
	"os"
	"path/filepath"
	"strings"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/canvas"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/dialog"
	"fyne.io/fyne/v2/layout"
	"fyne.io/fyne/v2/storage"
	"fyne.io/fyne/v2/theme"
	"fyne.io/fyne/v2/widget"
	"github.com/jung-kurt/gofpdf"
)

var (
	CreamMain  = color.NRGBA{0xE6, 0xE1, 0xD6, 0xFF}
	CreamInset = color.NRGBA{0xE3, 0xDD, 0xCF, 0xFF}
	InkPrimary = color.NRGBA{0x1E, 0x1F, 0x22, 0xFF}
	InkSoft    = color.NRGBA{0x2A, 0x2B, 0x2F, 0xFF}
)

const dropPrompt = "Drag and drop files to\nbatch convert to PDF."

func main() {
	a := app.New()
	w := a.NewWindow("img2pdf")

	w.Resize(fyne.NewSize(420, 380))
	w.SetFixedSize(true)

	// Root background
	bg := canvas.NewRectangle(CreamMain)

	// Drop area
	dropBg := canvas.NewRectangle(CreamInset)
	dropBg.CornerRadius = 10

	dropBorder := canvas.NewRectangle(color.Transparent)
	dropBorder.StrokeColor = InkPrimary
	dropBorder.StrokeWidth = 2
	dropBorder.CornerRadius = 10

	folderIcon := widget.NewIcon(theme.FolderIcon())

	dropText := canvas.NewText(dropPrompt, InkPrimary)
	dropText.TextSize = 11
	dropText.Alignment = fyne.TextAlignCenter

	dropContent := container.NewVBox(
		folderIcon,
		dropText,
	)

	dropArea := container.NewStack(
		dropBorder,
		container.NewPadded(
			dropBg,
			container.NewCenter(dropContent),
		),
	)

	// Output bar
	pathBg := canvas.NewRectangle(CreamInset)
	pathBg.CornerRadius = 5
	pathEntry := widget.NewEntry()
	pathEntry.SetText(defaultOutputPath())

	browseBtn := widget.NewButton("Browse", func() {
		saveDialog := dialog.NewFileSave(func(uc fyne.URIWriteCloser, err error) {
			if err != nil {
				dialog.ShowError(err, w)
				return
			}
			if uc == nil {
				return
			}
			path := uc.URI().Path()
			_ = uc.Close()
			pathEntry.SetText(ensurePDFExtension(path))
		}, w)
		saveDialog.SetFileName(filepath.Base(pathEntry.Text))
		saveDialog.SetFilter(storage.NewExtensionFileFilter([]string{".pdf"}))
		saveDialog.Show()
	})
	browseBtn.Importance = widget.LowImportance

	pathBar := container.NewStack(
		pathBg,
		container.NewPadded(
			container.NewBorder(nil, nil, nil, browseBtn, pathEntry),
		),
	)

	// Layout stack
	content := container.NewVBox(
		layout.NewSpacer(),
		dropArea,
		layout.NewSpacer(),
		pathBar,
	)

	padded := container.NewPadded(content)
	root := container.NewStack(bg, padded)

	w.SetContent(root)

	updateStatus := func(text string) {
		fyne.CurrentApp().Driver().RunOnMain(func() {
			dropText.Text = text
			dropText.Refresh()
		})
	}

	w.SetOnDropped(func(_ fyne.Position, uris []fyne.URI) {
		paths := uriPaths(uris)
		if len(paths) == 0 {
			dialog.ShowInformation("No Files", "Drop one or more image files.", w)
			return
		}

		outputPath := expandUser(pathEntry.Text)
		if outputPath == "" {
			outputPath = defaultOutputPath()
			pathEntry.SetText(outputPath)
		}

		updateStatus("Converting images...")
		go func() {
			err := convertImagesToPDF(paths, outputPath)
			if err != nil {
				updateStatus(dropPrompt)
				fyne.CurrentApp().Driver().RunOnMain(func() {
					dialog.ShowError(err, w)
				})
				return
			}
			updateStatus(dropPrompt)
			fyne.CurrentApp().Driver().RunOnMain(func() {
				dialog.ShowInformation("Done", fmt.Sprintf("Saved PDF to:\n%s", outputPath), w)
			})
		}()
	})

	w.ShowAndRun()
}

func defaultOutputPath() string {
	home, err := os.UserHomeDir()
	if err != nil || home == "" {
		return "magazine.pdf"
	}
	return filepath.Join(home, "Documents", "img2pdf", "magazine.pdf")
}

func ensurePDFExtension(path string) string {
	if strings.EqualFold(filepath.Ext(path), ".pdf") {
		return path
	}
	return path + ".pdf"
}

func expandUser(path string) string {
	path = strings.TrimSpace(path)
	if path == "" {
		return ""
	}
	if path == "~" {
		home, err := os.UserHomeDir()
		if err == nil {
			return home
		}
		return path
	}
	if strings.HasPrefix(path, "~"+string(os.PathSeparator)) {
		home, err := os.UserHomeDir()
		if err == nil {
			return filepath.Join(home, path[2:])
		}
	}
	return path
}

func uriPaths(uris []fyne.URI) []string {
	paths := make([]string, 0, len(uris))
	for _, uri := range uris {
		if uri == nil || uri.Scheme() != "file" {
			continue
		}
		path := uri.Path()
		if path == "" {
			continue
		}
		paths = append(paths, path)
	}
	return paths
}

func convertImagesToPDF(paths []string, outputPath string) error {
	if len(paths) == 0 {
		return errors.New("no image files provided")
	}
	outputPath = ensurePDFExtension(expandUser(outputPath))
	if outputPath == "" {
		return errors.New("output path is empty")
	}
	if err := os.MkdirAll(filepath.Dir(outputPath), 0o755); err != nil {
		return fmt.Errorf("create output folder: %w", err)
	}

	pdf := gofpdf.New("P", "pt", "A4", "")
	pdf.SetMargins(0, 0, 0)
	pdf.SetAutoPageBreak(false, 0)

	for i, path := range paths {
		img, err := loadImage(path)
		if err != nil {
			return fmt.Errorf("decode %s: %w", filepath.Base(path), err)
		}

		bounds := img.Bounds()
		if bounds.Dx() == 0 || bounds.Dy() == 0 {
			return fmt.Errorf("image has no size: %s", filepath.Base(path))
		}

		buf := &bytes.Buffer{}
		if err := png.Encode(buf, img); err != nil {
			return fmt.Errorf("encode %s: %w", filepath.Base(path), err)
		}

		name := fmt.Sprintf("img-%d", i)
		opts := gofpdf.ImageOptions{ImageType: "PNG", ReadDpi: true}
		if _, err := pdf.RegisterImageOptionsReader(name, opts, buf); err != nil {
			return fmt.Errorf("register %s: %w", filepath.Base(path), err)
		}

		pageSize := gofpdf.SizeType{Wd: float64(bounds.Dx()), Ht: float64(bounds.Dy())}
		pdf.AddPageFormat("P", pageSize)
		pdf.ImageOptions(name, 0, 0, pageSize.Wd, pageSize.Ht, false, opts, 0, "")
	}

	if err := pdf.OutputFileAndClose(outputPath); err != nil {
		return fmt.Errorf("write pdf: %w", err)
	}
	return nil
}

func loadImage(path string) (image.Image, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	img, _, err := image.Decode(file)
	if err != nil {
		return nil, err
	}
	return img, nil
}