package main

import (
	"fmt"
	"log"
	"regexp"
	"strings"
	"unicode"
)

const lettersInTheAlphabet = 26
const startUpperCase = 65
const endUpperCase = 65 + lettersInTheAlphabet
const startLowerCase = 97
const endLowerCase = 97 + lettersInTheAlphabet

var key string

type keyLetter struct {
	upperCase string
	position  int32
}

func getKeyWord() {
	var input string
	fmt.Println("Please enter a key word:")
	_, err := fmt.Scanln(&input)
	if err != nil {
		log.Fatalln(err)
	}
	reg, err := regexp.Compile("[^a-zA-Z]+")
	if err != nil {
		log.Fatalln(err)
	}
	processedString := reg.ReplaceAllString(input, "")
	key = strings.ToUpper(processedString)
}

func initKeyWord() []keyLetter {
	var keyWord []keyLetter
	for _, letter := range key {
		keyWord = append(keyWord, keyLetter{
			upperCase: string(letter),
			position:  letter - 'A',
		})
	}
	fmt.Println(keyWord)
	return keyWord
}

func encryptMessage(keyWord []keyLetter, message string) string {
	encrypted := ""
	index := 0
	for _, letter := range message {
		if letter == 32 {
			encrypted += " "
		} else {
			keyWordIndex := index % len(keyWord)
			newLetter := letter + keyWord[keyWordIndex].position
			if (unicode.IsLower(letter) && newLetter >= endLowerCase) ||
				(unicode.IsUpper(letter) && newLetter >= endUpperCase) {
				newLetter -= lettersInTheAlphabet
			}
			encrypted += string(newLetter)
			index += 1
		}
	}
	return encrypted
}

func main() {
	message := "Make It Happen"
	fmt.Println(message)
	getKeyWord()
	keyWord := initKeyWord()
	fmt.Println(encryptMessage(keyWord, message))
}