checkdigitcalculator/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"regexp"
	"strconv"
	"strings"

	"github.com/pterm/pterm"
	"github.com/schollz/progressbar/v3"
)

func main() {
	// Set Welcome Header
	pterm.DefaultHeader.WithBackgroundStyle(pterm.NewStyle(pterm.BgCyan)).WithTextStyle(pterm.NewStyle(pterm.FgCyan)).Println("Welcome to Checkdigit Calculator")

	// Check what directory the commandline is on when the program is launched.
	directory, err := os.Getwd()
	Error(err)

	// Get name of file to be processed.
	args := os.Args[1:]

	var input string

	if len(args) > 0 {
		input = args[0]
	} else {
		pterm.Printf(pterm.Cyan("What is the name of the file in this directory?: "))
		reader := bufio.NewReader(os.Stdin)
		input, err = reader.ReadString('\n')
		Error(err)
	}

	// Create upcs array and push all upc strings into it
	input = strings.TrimSpace(input)
	file, err := os.Open(input)
	Error(err)
	var upcs []string
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		upcs = append(upcs, scanner.Text())
	}
	err = file.Close()
	Error(err)
	if scanner.Err() != nil {
		fmt.Println(scanner.Err())
	}

	// Create gtins array that will eventually be returned
	var gtins []string

	// Using regex compile so the program stays fast
	regex, err := regexp.Compile("[^0-9]")
	Error(err)

	checkBar := progressbar.NewOptions(len(upcs),
		progressbar.OptionEnableColorCodes(true),
		progressbar.OptionSetDescription("[cyan][1/2][reset] Calculating Check Digits..."),
		progressbar.OptionSetTheme(progressbar.Theme{
			Saucer:        "[green]=[reset]",
			SaucerHead:    "[green]>[reset]",
			SaucerPadding: " ",
			BarStart:      "[",
			BarEnd:        "]",
		}))

	for _, upc := range upcs {

		upcLength := len(upc)

		// Check Digit Formula
		// Take all the digits in odd positions, add them and multiply by three
		// Take all the digits in even positions (except for the last one) and add to the number you got above
		// Divide that number by 10 and take the remainder
		// If the remainder is not 0, subtract it from 10
		//
		// 12/8/2023: New git updates from https://www.gs1.org/services/how-calculate-check-digit-manually

		oddNumber := 0
		evenNumber := 0
		var remainder int

		checkForNonNumber := regex.MatchString(upc)

		if checkForNonNumber {
			gtins = append(gtins, upc)
			continue
		}

		if upcLength < 8 {
			gtins = append(gtins, "Cannot process upcs less than 8 digits")
			continue
		}

		if upcLength > 17 {
			gtins = append(gtins, "Invalid barcode")
			continue
		}

		if upcLength%2 == 0 {
			for i, num := range upc {
				if i%2 != 0 {
					convertedOddNumber, err := strconv.Atoi(string(num))
					Error(err)
					convertedOddNumber = convertedOddNumber * 3
					oddNumber += convertedOddNumber
				} else {
					if upcLength-1 > i {
						convertedEvenNumber, err := strconv.Atoi(string(num))
						Error(err)
						evenNumber += convertedEvenNumber
					}
				}
			}
		} else {
			for i, num := range upc {
				if i%2 == 0 {
					convertedOddNumber, err := strconv.Atoi(string(num))
					Error(err)
					convertedOddNumber = convertedOddNumber * 3
					oddNumber += convertedOddNumber
				} else {
					if upcLength-1 > i {
						convertedEvenNumber, err := strconv.Atoi(string(num))
						Error(err)
						evenNumber += convertedEvenNumber
					}
				}
			}
		}

		remainder = (oddNumber + evenNumber) % 10
		if remainder != 0 {
			remainder = 10 - remainder
		}
		remainderString := strconv.Itoa(remainder)

		gtins = append(gtins, upc+remainderString)
		checkBar.Add(1)
	}

	answerBar := progressbar.NewOptions(len(gtins),
		progressbar.OptionEnableColorCodes(true),
		progressbar.OptionSetDescription("[cyan][2/2][reset] Writing answers into file..."),
		progressbar.OptionClearOnFinish(),
		progressbar.OptionSetTheme(progressbar.Theme{
			Saucer:        "[green]=[reset]",
			SaucerHead:    "[green]>[reset]",
			SaucerPadding: " ",
			BarStart:      "[",
			BarEnd:        "]",
		}))

	// Check if answer.txt already exists and if so, delete it
	if _, err := os.Stat(directory + "/answer.txt"); err == nil {
		e := os.Remove(directory + "/answer.txt")
		Error(e)
	}

	// Create new answer.txt
	answerFile, err := os.Create(directory + "/answer.txt")
	Error(err)

	defer answerFile.Close()

	// Fill the answers.txt file
	for _, gtin := range gtins {
		_, err := answerFile.WriteString(gtin + "\n")
		Error(err)
		answerBar.Add(1)
	}

	// Print Success message and exit
	pterm.Printf("\n")
	pterm.Success.Println("The answer.txt file has been successfully generated with check digits.")
	os.Exit(0)
}