/**
 * Created by Ashish Patel
 * Copyright © 2017 ashish.me
 * ashishsushilpatel@gmail.com
 */

/**
 * Problem:
 * One of the simplest and most widely known ciphers is a Caesar cipher, also known as a shift cipher.
 * In a shift cipher the meanings of the letters are shifted by some set amount.
 * A common modern use is the ROT13 cipher, where the values of the letters are shifted by 13 places. Thus 'A' ↔ 'N', 'B' ↔ 'O' and so on.
 * Write a function which takes a ROT13 encoded string as input and returns a decoded string.
 * All letters will be uppercase. Do not transform any non-alphabetic character (i.e. spaces, punctuation), but do pass them on.
 */

function rot13(str) {
    // Use regex \w to remove any word character from string. Word character to alphanumeric characters
    const regex = /\W/g;

    const decodedString = str.split("").map(item => {
        const codeOfItem = item.charCodeAt();
        if (regex.test(item)) {
            return item.charCodeAt();
        } if (codeOfItem > 77) {
            return codeOfItem - 13;
        } if (codeOfItem < 78) {
            return codeOfItem + 13;
        }
    });

    // Spread operator allows you to pass array or string where array literals are expected
    return String.fromCharCode(...decodedString);
}

// Change the inputs below to test
console.log(rot13("SERR CVMMN!"));