grayscale_one.go

package main

import (
	"flag"
	"fmt"
	"os"
	"path/filepath"
)

func pathExists(path string) bool {
	if _, err := os.Stat(path); os.IsNotExist(err) {
		return false
	}
	return true
}

func main() {
	fmt.Println("Usage: ./grayscale-cbz --dest=/path/to/dest <FILE>")
	dest := flag.String("dest", "/tmp/", "Destination directory for grayscale images")

	flag.Parse()

	// check if flags valid
	cbz := flag.Args()[0]
	if !pathExists(cbz) {
		fmt.Printf("path to file '%s' doesn't exist\n", cbz)
		os.Exit(1)
	}

	// check if cbz is valid
	ext := filepath.Ext(cbz)
	if ext != ".cbz" {
		fmt.Printf("invalid file extension: '%s'\n", ext)
		os.Exit(1)
	}

	// check if dest exists (if no create or exit with error)
	if !pathExists(*dest) {
		fmt.Printf("destination folder '%s' doesn't exist. Creating...", *dest)
		err := os.MkdirAll(*dest, os.ModePerm)
		if err != nil {
			fmt.Printf("error creating directory: %s", err.Error())
			os.Exit(1)
		}
		fmt.Println("done!")
	}
}