a naive webp-to-jpeg converter

webp2jpeg.go

package main

import (
	"flag"
	"fmt"
	"image"
	"image/jpeg"
	"log"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"sync"

	_ "golang.org/x/image/webp"
)

func main() {
	srcDirPath := ""
	dryRun := false
	flag.StringVar(&srcDirPath, "src", "", "source directory path")
	flag.BoolVar(&dryRun, "dry-run", false, "whether dry-run or not")
	flag.Parse()
	if srcDirPath == "" {
		log.Fatal("empty source directory path given")
	}

	if v, err := filepath.Abs(srcDirPath); err != nil {
		log.Fatal(err)
	} else {
		srcDirPath = v
	}

	destDirPath := filepath.Join(srcDirPath, "converted")
	if err := os.Mkdir(destDirPath, 0755); err != nil && !os.IsExist(err) {
		log.Fatal(err)
	}

	files, err := os.ReadDir(srcDirPath)
	if err != nil {
		log.Fatal(err)
	}

	concurrency := make(chan struct{}, runtime.GOMAXPROCS(0))
	defer close(concurrency)

	var wg sync.WaitGroup

	for _, file := range files {
		if file.IsDir() || !file.Type().IsRegular() {
			continue
		}

		srcFileName := file.Name()
		srcFilePath := filepath.Join(srcDirPath, srcFileName)

		destFileName := fmt.Sprintf("%s.jpg", strings.TrimSuffix(srcFileName, filepath.Ext(srcFileName)))
		destFilePath := filepath.Join(destDirPath, destFileName)

		log.Printf("%s -> %s", srcFilePath, destFilePath)
		if dryRun {
			continue
		}

		concurrency <- struct{}{}
		wg.Go(func() {
			if err := convert(srcFilePath, destFilePath); err != nil {
				log.Print(err)
			}
			<-concurrency
		})
	}

	wg.Wait()
}

func convert(srcFilePath, destFilePath string) error {
	srcFp, err := os.Open(srcFilePath)
	if err != nil {
		return err
	}
	defer srcFp.Close()

	img, format, err := image.Decode(srcFp)
	if err != nil {
		return err
	}
	if format != "webp" {
		return fmt.Errorf("unexpected file format: %s", format)
	}

	destFp, err := os.OpenFile(destFilePath, os.O_RDWR|os.O_CREATE, 0644)
	if err != nil {
		return err
	}
	defer destFp.Close()

	if err := jpeg.Encode(destFp, img, &jpeg.Options{Quality: jpeg.DefaultQuality}); err != nil {
		return err
	}

	return nil
}